Pre Season Prep
We are the fortunate ones who get winter for nine months of the year. If you like winter sports this is what echoes through your head as we endure the long hot summer days watching the wildfire weeds engulf your snowmachine. I have put together some tips here to help kick the summer blues and to keep your sled ready for the snow season ahead.
Under The Hood
In a testosterone filled sport everybody wants to know about the power, we even have major auto manufactures asking if "that thing got a hemi" no… but it does have a ROTAX and to me that is even better. Knowing what is under the hood is not enough you need to know how to care and maintain the heart of your snowmachine. Before you get going there are questions that need to be answered, did it run OK when you put it away, did you store it properly and has anything happened to your sled while in storage? If it had running issues when it was put away get an appointment with Compeau's to address it before the season is here, if not did a family of voles move into your airbox and use your wiring for insulation? If you answered no to the above then the prep should be relatively simple. Fuel…is it old, varnished or maybe even contaminated. If there is any doubt drain and replace with fresh. If the fuel varnished you should also clean the carbs and fuel system. Spark plugs are a simple item to replace and should be at the start of every new season. Another simple but very important adjustment is the throttle and oil injection cables. If not looked at you could run the motor lean on oil and these cables do stretch so proper alignment is crucial. Lastly you should check the cooling system, is the antifreeze level and condition OK for those -60 winters. If you have a fan cooled the belt should be inspected and adjusted.
Driveline
Most of the wear items in the driveline are made of rubber and should be checked for wear. Remove the drive belt and look for burn marks or weather cracking. Proper alignment of the belt is necessary and if you go through belts it is a good idea to have Compeau's realign the motor. The track is also part of the driveline and needs to be aligned. Check for fraying on the edges, torn lugs or any weathering. While you are down there you should also check the hyfax (slides) if they show wear it is best to replace before you wear into the aluminum runners. The last item to check is the chaincase…back under the hood you will find the chaincase and it needs to be properly tensioned and it is a good idea to replace the oil before winter gets underway.
Suspension & Steering
This portion of the check is more visual. Crawl inside and out looking for loose nuts or bolts. Unusual wear is not that hard to spot and if you see a hole that a bolt goes through that looks like an egg would fit perfect you probably have some loose hardware. A mechanic told me once to touch everything…meaning put a wrench on it if its tight move to the next one and so on. Not bad advice when you have a lot of moving parts like a suspension. The steering portion should also be checked for loose hardware along with the proper alignment of the skis. Don't forget to lift up those skis and make sure you have plenty of carbide on the runners. Skis usually do not wear but in low snow conditions this also can be a wear item and should be looked at while inspecting the runners.
Electrical & Test Run
The electrical needs to be done last as most snowmachines do not have a battery. If your model is equipped with a battery now is the time to reinstall it…remember last season at the end you took it out, set it on a shelf, charged it once a month? Yeah right, most just parked the sled under the cotton wood trees and hoped it would fire in the fall and felt let down when the battery was dead. Well if you catch the dead battery before the first freeze you might have a chance to give life back into it and follow the proper filling and charging method. For those of us without a battery go into your pre-ride check and if all is OK give the rope a hearty pull. Once you have the machine running check all the lights and gauges.
Before You Ride
This article was intended to help you get things ready but nothing will help as much as getting it in and having a qualified mechanic give it a pre season tune up. The mechanics do this for a living and might catch items that you had overlooked. This is a general overview of what is needed and you should always follow your operator's manual and have a trained professional do your service intervals or repairs.
Rodney Vesper
Compeau’s Inc
JETTING
Introduction
Jetting is a common topic that you will hear thrown around by many snowmobilers. The focus on jetting is beginning to take a back seat to new technology. Even with the modern advancements in fuel delivery systems this topic still remains one that most have an opinion on and usually base it on misinformation. I hope with this article some of the mystery is cleared up about what really is going on in the carburetor and fuel system.
Basics
To start this off what is jetting? Jetting is referring to the passages in the carburetor. These are calibrated passages that have removable inserts and outserts that change the diameter of the passageway. By changing the diameter we can vary the amount of fuel delivered at that given throttle opening. All motors will have a minimum that they need to run. When you give the motor too little fuel it is called a lean condition and to the other side it is called a rich condition when there is too much fuel. The complication of this mixture begins when we change the conditions we ride in. Alaska offers a wide array of conditions with elevation changes, vast temperature changes, types of fuel offered and engine RPMs will all have an effect.
Under pressure
As you know living on Earth we are always under pressure. Atmospheric pressure or barometric pressure is what I am talking about. This is really the base where most jetting is done. Factories like Ski-Doo calibrate their snowmobiles to sea level and compensate with different methods as these base calculations change. The base or sea level we need to keep in mind is 14.7 pounds. This is the weight of the air above one square inch at sea level. As we change elevation this amount of pressure decreases as most of the air molecules are held closer to Earth with gravity. This is where the expression “thin air” comes from. As we go up the air molecules are not as dense, changing the jetting. We know that we are calibrated for 14.7 parts of air to 1 part of fuel so when we climb through the Alaska Range we know that without changing our jets we will be running in a rich condition.
Hot vs. Cold
Keeping on track with the air molecule discussion, we also know that as things heat up the air will get moving causing it to thin and as it cools the molecules slow down and become denser. This will also be very crucial for an ideal mixture rate. As the temperature rises we will need to decrease the size of jet and when the temps drop we will need to increase the size of jet we are using.
Fuel
Let me start this segment by saying that I am not a chemist. I do however understand the basics here. All motors have base requirements and they are usually stated in octane rating. This min octane rating is usually very easy to buy at the pump and more often than not people will buy a higher grade of fuel in hopes that their machine will run better. On a two stroke engine this is not really true. Octane is basically the rate at which the fuel will burn and by using a higher octane you slow the burn down. When you slow the burn down you might not be able to use all of the fuel supplied in the motor and you are dumping excess out the exhaust. The topic of premixing oil with fuel also, remember that when you add anything to the fuel you are taking away the amount of fuel that can pass through the jet size and you are leaning out the mixture. By adding a lot of oil you may in fact be leaning out the mixture to a level that could cause motor damage given the right circumstances.
Mixing it up
With all the basics in place we need something to mix it up. I will use a carburetor for this example. A carb has many different passageways that flow in different circuits. The passages are opened and closed by the throttle settings. As you open the throttle an internal slide rises and allows the fuel to escape in different passageways. The atmospheric pressure will push the fuel from the float bowl out the passageways and mix the raw fuel into a gas when mixed in the venturi and down into the motor. Now we can see how all the factors come into play and knowing that the amount of air molecules around a fuel charge is what really effects the jetting we can better understand how changing jets will richen or lean your motor. Ski-Doo has been using some form of a compensating calibration since 1994 on their Summit line of snowmobiles. They have expanded on this technology to what we use today on most of the Ski-Doo line up. It is called DPM (digital performance management). Without over complicating the process, the DPM will keep a constant atmospheric pressure in the float bowl no matter on outside air temp (to -10f) and up to 14,000 feet. By “tricking” the float bowl pressure to assume it is at sea level it will always be able to mix at its optimum 14.7: 1 ratio. This in turn means that you get to go out and ride all day without the often-smelly task of changing your jets like the competition. Just one more reason to ride Ski-Doo “There’s nothing like it”.
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Snowmobile Shocks
This is a brief explanation of the different types and a simple explanation of how they work. I will cover only modern types of shock absorbers, as the old emulsion types are all but extinct. These basic types and principals are found on almost all modern snowmachines and should better help you understand why the ride is better than ever in this type of recreation.
Front suspension vs. rear suspension:
Aside from the obvious differences in the front and rear suspensions the shocks remain very similar. Most front suspensions have a coil over spring that is wrapped around the shock body. This spring aids in the shock in compensating the bumps in uneven terrain. The first difference you will see here is the rear suspension normally has the rear shock alone and is assisted by two springs separately mounted in the skid frame. The center shock of the rear suspension is like the two front shocks having a coil over type spring. Although these differences are present they all react about the same in the way the shock controls the ride.
The Shock:
There is a body, which is usually made of aluminum. This type of metal is used to help dissipate heat. The body is the largest part of the shock and all the other components make up the rest. The base of the body will have an eyelet that mounts directly to the chassis or suspension arm. The second largest part will be the stem or rod. This will have the other side of the mounting point. The stem travels through a top cap that is threaded to the top of the body and helps to seal all the internal components. Inside the body at the opposite end of the shock eyelet is a shim stack. This shim stack is the heart of the shock and what most will refer to the valving of the shock. The valving is a very complicated series of flexible washers. The shock body contains oil; this oil is specific to the valving also. The term gas shock is from the fact that on the opposite side of the oil is a floating piston with a gas charge. This gas is nitrogen at high pressure. Nitrogen is used because it is an inert gas and is not as effected by heat. As the shock stem travels in and out it will move the shim stack through this oil in the body. The amount of washers, diameter and thickness of the washers will dictate the rate at which the dampening rod will move. There are two sides to the shim stack, a compression side and a rebound side. These two sides can have different shims causing different rates of travel for compression and rebound. It is here that we can make your Ski-Doo ride stiff or soft and give it a tendency to be a good bump, mountain, speed, utility or touring ride.
Modern Advancements:
With what we know about the shock, we can now evolve a little bit more and create the best of more than one riding condition. A good example is a remote oil cavity. This reservoir can be located directly to the body of the shock and transfer oil through a passageway, or it may use a hose to transfer fluid. This additional use of shock oil will also help dissipate heat in the extreme riding conditions where the terrain is very harsh. To help shape the future Bombardier (SKI-DOO) is now using a variable rate shock. This type of valving will help make the ride more usable in different types of terrain. The theory here is very simple. When we talked about the way the shock uses the valving we had said that how much oil is allowed to pass through the shim stack is the rate at which it will travel. This variable valving is done with a bypass passageway. This extra passage for oil to travel will allow a free range for the shim stack to pass over. By skipping a stage in the valving it will give certain ride characteristics that will benefit more than the one type of terrain or vehicle speed. At the time of writing this Ski-Doo is now using air assisted shocks that will again reshape how we ride.
Springs:
The topic of springs is not really what we are talking about here but they do deserve a mention. There are different types, coil over and the commonly know as torsion type are what most are using now. There is straight rate and progressive rate spring. All the responsibility of the spring is to aid the rate at which the shock travels and it is the differences in the type and diameter of the spring that controls this. The spring needs to match the type of riding, weight of rider and the shock itself.
Maintenance:
In closing we have discussed all the aspects of what a shock does, how it does it and the differences in the designs. One area that is usually skipped is the maintenance of the shocks. These suspension dampners do a lot of work through a very tough climate and conditions. The shock body is usually made of aluminum and the oil on the inside travels at great speed back and forth. All of this internal movement will cause wear and this wear will result in poor performance in your shocks. In Alaska, where ungroomed trails, ice heaves and big whoops are all in a days ride, this wear happens much faster than on smooth, groomed trails found throughout the states and Canada. You should have your shocks disassembled by a quality service center on a regular schedule. Far too often they are overlooked and do not get the attention they need. This is one area you can improve how your machine rides and how you feel after riding your machine. We all like to ride a lot of miles and some will put those miles on as quickly as possible. Rider fatigue will slow a persons riding style to as much as 30% just because you can no longer control you or the machine. So next time you go knocking at the local aftermarket door looking for cheap horsepower, remember that if you could hold on all day you might just be faster in the end!
Rodney Vesper
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Track Tension:
There is an amazing little item that comes as a standard feature with just about every snowmachine sold, and incredibly, it very seldom gets used. It's called an owners manual, and can usually be found rolling around in the rear storage compartment along with several empty 12 oz cans, busted goggles, and something that was once beef jerky. While sitting down and reading the manual front to back isn't on the top of most peoples priority list (after loading a new sled in the back of their truck) there is some important information in there. Listed below is one very simple item that many overlook, and that can have a dramatic impact on how good the machine runs, or doesn't run during its first couple hundred miles.
Especially on the newer generation mountain sleds, these hi-lug snow rippers put an unusual amount of demand on the vehicles track. Track stretch in the first 200-500 miles on any snowmachine is normal, however you may find yourself needing to tighten the track up after as little as 20 miles to avoid "driver slip". That is the noise and vibration you feel when a loose track is unable to keep it's windows snug around the front drive axle sprockets. It's most evident on a hard hole-shot, or when you drop off a hard trail and pour the power to it in soft snow.
Dig out that little manual I spoke about earlier and look for what is referred to as track deflection. Many people mistake this term with the amount of free-hang a track has with the rear suspension elevated. The deflection is the distance between the plastic runners, (or hifax), and the inside edge of the track with a specific amount of downward pressure applied to the center of the track. 1.5 inches of deflection with 15-16 lb. of downward pressure applied are somewhat common on most recent models, but you really need to see what your manual recommends for your machine.
Two things to keep in mind:
You should never adjust your track tension until after you warm up the track, (that is to run it around a half a mile or more), to give yourself a true tension measurement. (Rubber, like certain body parts shrink up in the cold)
Remember to always re-adjust your track tension after making any suspension adjustments to the front or rear of your undercarriage. For example if you suck up the front rails for additional ski pressure, you'll need to re-adjust the track to specs. Otherwise, the track may be too tight, causing drag, excessive drive belt wear, not to mention a decrease in performance.
Here's what I recommend. Next time you're out in the yard, move your owners manual from the snowmachine to your bathroom. While it may not be the most exciting toilet material you've ever sat down with you may just find the end result is a sled that runs a whole lot better.
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Springtime Riding
The chances are pretty good that spring will follow winter again this year, which means most die-hard sledheads will make tracks for the mountains. With our low snow in the interior this year, the Alaska Range has been the riding destination of choice for most of the winter, and that will continue until the white stuff is gone. Here's a few simple but often overlooked items that can make a big difference in your springtime riding plans:
If you have an externally adjustable drive clutch, (like Ski-Doo's T.R.A. clutch), make sure you dial it up to obtain the peak RPM, (without exceeding that number). 400-600 revs up at 5-6000 feet make all the difference in the world. Each "click" or increase in number on your clutch gives you 200 additional RPM on the upper end. This adjustment has the ability to get you up and over those peaks that you probably shouldn't be topping anyway. (Testosterone has for centuries overridden common sense, and nothing I can say here will change that !) It is very important though, that you make sure you turn the clickers back down when you're done in the mountains, or you will certainly over rev the motor. Overevving past the peak power number of your sled not only robs horsepower, it can really tear up your wallet. We have a spec sheet that tells where you're sled should be set for sea-level, so give a call if you're unsure.
If you live for the mountains, you should have a sled with an altitude compensator, EFI, or some sort of fuel management system. If you don't, sell it and get one that does. If that simple solution isn't in your immediate plans, than make sure you properly rejet the carbs to match the conditions for your destination. Proper jetting makes the difference between driving a crisp, responsive crotch rocket, or getting passed by a late 70's John Deer Liquifier . Again, get a spec sheet for your sled to ensure that you're not jetting to rich, or more importantly, too lean for the conditions. And jet back to stock when you get back to lower elevation, (like Fairbanks). Otherwise, that first cold ride of the winter next October will really ruin your month.
Warm temperatures, deep soft snow, and steep hill climbing can take a toll on your drive belt. Heat kills rubber, so make sure you always have a spare belt before a big outing. It's a great idea to put 20 or 30 easy miles on a new belt, and then take it off and carry it as your spare. That way, if you blow a belt hillclimbing, you're installing a properly broken-in belt, and you'll find it will have much better life than a new, stock "off the shelf" belt.
Very few riders pay attention to drive belt tension, and it really is among the most critical adjustments between the engine and the track. Check your manual and make sure it's where it should be, or you're just tossing away performance. The torque stop, which sits between the motor and the jackshaft needs to be snug, (not tight) as well, They are threaded, and take 5 seconds to check, and 15 seconds to properly adjust if loose. The special tools required for this intense procedure are four fingers, a thumb, and typical human dexterity...that's it. Keeping the torque stop where it should be will help drive belt life between servicing of your clutches.
Remember. We live on a steep planet. Be careful out there.
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&$@#%#@ Battery !
Batteries. If your boat, snowmachine and personal watercraft battery could talk, it would likely only know foul language. That's because it's used to being the lowlife-scapegoat, blame-all item that just ruined your weekend. Fact is, the battery is usually the most neglected item on your outdoor playtoy. A little regular battery maintenance can no only save you $50 -$75 a year, & it can prevent you ruining one of these all to valuable summer weekends.....How?...
First, go out and buy a trickle charger. They're cheap, they're small, and they're easy to use. Second, take it out of the box and use it once in a while.
Here's a few facts on lead-acid batteries to file away in your grey-matter:
A) Installing a new, out of the box battery, with electrolyte added, but without a proper initial charge will have a maximum charge capacity of only 80% for the rest of it's life.
B) You should charge your battery once a month for maximum protection.
C) A battery exposed to a temperature of 95 degrees F will discharge twice as fast as a battery stored at 75 F. (Remember, it can get real hot in our summers under the hood of your snowmachine or PWC)
D) If you keep your battery fully charged, the electrolyte inside it won't freeze until -75 degrees F. At 50% charged, it will freeze at just 6 degrees F.
E) Quick charging is not good for your battery. Most automotive charges are rated at 10-15 amps or more. This will quickly "burn-out" your PWC battery. Using your just-purchased trickle charger, set at a rate of 1/10th of the rated ampere-hour capacity.
F) Clean, tight battery cables are just as important on your boat or PWC as they are on your car. Check them once in a while.
G) For extended periods of non-use, remove the battery form the vehicle. If you haven't done it, make sure you trickle charge the battery in your snowmachine by at least mid summer, and then again in the fall.
A battery is kind of like a muscle; if you don't use it it'll get weak. There. I've just given you another reason to get out on the water and go play. Do it for the good of your battery !
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Mountain Riding
In Alaska, runs can be long and remote, so common replacement parts like extra belts (meaning more than one), spark plugs, gas, etc. - should be considered. A basic tool kit may not be enough. Know your machine well enough to have the right tools for the more mundane items you know could need repair. It can be a long, miserable walk out of the mountains if your machine quits.
Next, prepare your machine for Alaska sledding. A proper tune-up or engine adjustment is recommended. Depending on your intended riding altitude, some carburetor and clutching changes might be necessary. The carburetors on snowmobiles can lose as much as 3 percent of the rated HP for every 1000 feet above sea level. Even at 5000 feet, which is not all that high, there is a significant loss of horsepower. The air is thinner, so carburetor jets have to be smaller. The sled manufacturer should have recommendations on high altitude carburetor settings or they may be specified on a decal in the engine compartment.
If you have significant miles on your machine, now is a good time to replace the chain. Reducing gear ratios will allow the clutch to operate through the full speed range. The typical secondary gear ratios are in the 1.7 to 1.8:1 range. When riding in steep terrain, the normal clutch operation keeps the drive in low and second gear, where the belt rides low in the engine pulley (the drive clutch). This condition, in turn, fatigues belts and heats up clutches much quicker, a condition that leads to premature belt and clutch component failure.
To minimize this problem, secondary ratios should be changed to an approximate range of from 2.0 to 2.2:1. The gear ratio change allows the clutches to be more efficient and prevents unnecessary belt failure, It also changes the top speed of each machine, from the normal plus-8O MPH mark to the 50 to 70 MPH range. This will keep the belt from continually operating in the smaller diameters of the drive pulley, thereby increasing belt life. To determine the recommended gear ratios for mountain riding, check with your snowmobile dealer where you intend to ride.
The major sled manufacturers also have specific clutch recommendations for riding mountainous terrain. Typically, different weights and springs or adjustment of springs are recommended. Plan ahead and have your clutch cleaned and inspected for worn components since many of the movable parts are prone to wear. These include all of the bushings and rollers or buttons, clutch weights and the belt surface. A qualified technician should do any removal and repair. Upon reinstalling the clutches, alignment should be checked to the manufacturers specification. This one issue can seriously affect belt life and, to a lesser degree, clutch efficiency and component life, It involves a specific tool to align the clutches or measure the prescribed offset of the primary clutch to the secondary clutch.
While work is being performed on the clutch system, the belt should be inspected for signs of pending failure. Symptoms include loose edge cords, significant cracking between the notches, loss of undercord material and excessive glazing or polishing of sidewalls. Belt conditions most likely to affect drive performance are excessive wear and spin burns on the sidewall. The former can cause noticeable degradation in both acceleration and top speed; the latter causes excessive vibration.
As a general rule, a well-used belt should be replaced.
When replacing the belt choose the belt recommended by the dealer for that specific model Many experienced riders carry several new belts that have been broken in prior to riding in the mountains.
Make sure the basic belt fit is correct for all belts used on the machine to prevent poor clutch performance. The sled manufacturer has specific belt fit specifications or you can use accepted industry specifications available. One should check the belt deflection, belt sidewall clearance in the motor pulley and belt rideout in the jackshaft or driven pulley.
Most mountain machines have 1-to 2-inch Lugs or paddle tracks for traction in deep snow. Remember, if you add a deep-lug track, be sure to change your clutching.
For additional information on belt and clutch troubleshooting, and fine tuning for the mountains, contact Robin or Keith in our service department.
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Ocean Corrosion
Two or three springs ago, a customer brought us his aluminum inboard boat for summarization. Sounded simple enough. Replace the engine oil, grease the jet bearing and u joint, synch and link, and everything else to get it ready for a water test. Before leaving, the customer went into detail of the last trip he had made with the boat. He had limited out on silvers in Valdez the previous fall, and had the best fishing trip of his life. He told us, in fact, about 45 minutes more of the story than we actually cared to hear, including how his wife left part of her stomach lining in Prince William Sound out by Galena Bay. What he forgot to tell us, was that after leaving his boat in the slip at Valdez from mid June until late August, he came straight back to Fairbanks, and proceeded to put a blue tarp on it, before boarding a plane for three weeks in Hawaii. That explained why the boat still smelled like fish when we uncovered it. And that also explained why his repair bill, which should have been a couple hundred bucks at the most, cost about the same as his 3 week trip to the islands. New carburetor. New Starter motor. New linkage. We almost had to use a chisel to remove the components. Sad.
This type of customer is good for our bottom line, but, with that being said, I hate to see it happen. Why?.... Because it's so easily preventable. There's an incredible product on the market called Corrosion Block, and for about the price of 2 tropical rum cocktails, this customer could have saved himself a fistfull of dough.
What is corrosion anyway?... Corrosion is the gradual destruction of a metal surface caused by an electro- chemical reaction with moisture. A product like Corrosion Block penetrates corrosion cells, emulsifies the moisture, and then separates it from the metal. Basically it stops the electro-activity in it's tracks.
What you really want to do though, is use the product BEFORE you subject your boat's engine, (inboard OR outboard) to its toughest competitor....the Ocean. It's probably the best money you could ever spend for preventing damage. And as long as you have a functional index finger on at least one hand, you're more than qualified to do the job yourself. Simply spray a generous amount of the stuff on the entire engine, carb, and other parts under the hood. What you're doing, is putting an ultra thin atmospheric barrier to protect the metal from further damage. By doing this, you have, in effect, stopped corrosion from starting in the first place.
I also recommend coating your battery terminals, switches, circuit panels, and the like. I even heard stories from customers that swear it restored their faulty electronic gear after spraying it down.
I've tried several other products on the market that are suppose to be similar, but I haven't seen similar results. Either a waxy film remains that makes it almost impossible to work on the engine, or the product just doesn't give long enough protection. All the products sell for about the same...$8-$12 per can.
And don't forget to check the condition of the zinc anodes you have on your boat. If they look like they have a bad case of Leprosy, change them. Mother Nature has, in effect, kicked their butts by this point and rendered them almost useless. Zinc is cheap.... As opposed to the alternative.... (see customer above)
By the way, I've discovered that Corrosion Block also works great for my fishing reels and downriggers.. So throw the small can in your tackle box when you're done. Might just make the difference on that monster that's still lurking down there waiting for your lure
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Tips from Service Center ~ Understanding Your Jet Boat
Most boat owners like to perform at least a certain amount of their boat maintenance themselves to ensure continuing good performance and reliability.
To avoid unnecessary trips to the service center, it is useful to have a checklist which can be run through systematically, in the hope of pinpointing the problem quickly. The boat can be divided into three categories - Jet Unit, Engine and Hull.
If something is "wrong" with the boat it is usually poor acceleration and load carrying, coupled with excessive fuel consumption or engine RPM's. It could be unusual noise coming from the mechanicals, or possibly just poor top speed.
Tachometer The most important single instrument of the boat when considering performance drop-off is the engine tachometer. The great thing about jet boats is that the engine RPM's should remain the same throughout the life of the boat, regardless of age, loading, water conditions, towing, etc., unless wear is present in pump or motor. For speed calibration a GPS unit should be used (most speedo's in boats are optimistic). For fuel consumption checks a floscan fuel meter should be used. Don't forget that fuel consumption is lower and speed is higher in shallow water than in deep water because of the "ground effect" of running in shallow water.
There is no situation where the RPM's should be different from when the boat was new, and as an owner, you will know what these are. At any time, you should be able to open the throttle fully and get the same maximum reading you have been used to. Or perhaps you are finding it needs more RPM's to cruise your normal load? RPM's are a most important indicator of proper operation of the boat.
It is important at this stage to feel confident that your tachometer is reading accurately. Use a high quality digital timing light to verify tachometer.
Now we come to our checklist, and determination of which major area is the problem. The simplest way is a check on the RPM's first. They could be normal, high or low, and this will pin point the place to look:
Normal Maximum RPM = Hull Problem
If the boat is performing poorly and the maximum RPM's are normal and what you are used to, you can look to the hull and some of the external parts. These include:
Overload: There is too much weight aboard.
Balance: Either too much weight aft, which will cause the nose to be too high and make planing difficult, or if the weight is too far forward, it will cause the nose to plow, difficult steering, wetness and poor top speed.
Reverse Bucket: Is the bucket dragging in the reverse stream? Make sure the control is fully up.
Excessive Hull Drag: Is there some external hull obstruction such as rough surface, broken keel strips, or other reason impeding the smooth flow of water over the hull bottom? A visual check on the trailer should reveal if there is. Metal hulls can have a "hook" bashed into them forward of the transom which can cause the bow to plow. The planing surface forward of the transom six to nine feet should be true and flat.
High RPM = Jet Unit Problem
Higher than normal RPM's, lack of thrust, slipping clutch feel, engine racing and no go?
Blockage: The most common problem is weeds and stones blocking the intake grate. Also be aware of ski rope, fishing line and plastic bags winding around the pump shaft. Small sticks and stones can become lodged in the impeller affecting the performance dramatically, objects trapped in the impeller can cause the rotating assembly to be out of balance, causing severe vibration. Make sure the water passage through the jet is clear.
Impeller Wear: The heart of the jet is the impeller, and its condition. If you run in shallow gravel beds or across sand bars the leading edges will become dull and inefficient. Pumping sand will increase the wear-ring to impeller clearance, causing cavitation and loss of performance.
Bowl / Stator Vanes: It's not too much of a problem, but the leading edge of the fixed stator vanes can become blunt and damaged.
Air Leaks: If excessive air leaks into the intake ahead of impeller, the jet unit will "slip". Possible sources of air leaks are through a faulty gland seal, which is usually accompanied by a static water leak into the boat when standing idle.
So if the gland is worn out and leaking into the boat with the engine off, it can also suck air when accelerating on to plane, and if this happens, then the thrust is reduced dramatically. Air can also be introduced into the system via the inspection cover, so you will want to make sure the cover is tight and the O Ring is sealing. Air can also enter thru cracked intake blocks, faulty base gasket and the rear of the intake grate.
Low RPM = Engine Problem
There is generally no way the jet unit can overload the engine and bring the RPM's down (unless the main thrust bearing fails). If the RPM's are down from usual, it is almost certain to be an engine problem. A compression check will usually reveal leaking piston rings or valves, but the most common reasons for reduced engine power are:
Throttle: Check that the throttle is opening fully.
Fuel: The fuel supply must be adequate for the engine size. Racing boats frequently have a fuel pressure gauge which is, with the tachometer, probably the most important engine instrument. Sufficient fuel must be reaching the engine.
Air To The Engine: The carburetor must be getting its full quota of cool air. If the engine has to work to get adequate air, and if it is hot air, this will reduce power. Altitude also reduces power often 100 RPM / 1000 FT.
Ignition Spark: Be satisfied the ignition system is operating properly. A problem here is usually indicated by a rough running or missing engine.
Exhaust: Check for a free flowing exhaust system. Some silencers can become blocked, rubber hoses disintegrate internally, or there is excessive water injection. Such things can cause excessive back pressure and reduce power. Supertrapps often become plugged with silt or woodchips.
Provided your engine is getting its full quote of air and fuel, and is getting enough spark and at the right time, the engine will usually be ok and maximum RPM's will result. However, if the RPM's are down and you believe the tachometer, look for an engine problem.
The hull, engine and jet unit are the three main areas to look at when your performance is down.
Excessive Noise
This can often be a concern even if there is not a reduction in performance. The most common causes of noise are:
Cavitation: The jet unit is starved for water, and usually sounds like a rattle or a can of loose bolts in the back of the boat. Most likely a blocked intake grate.
Moan or Whine: The jet unit can exhibit some "turbine whine" not unlike a turbocharger noise but you will know what is usual with your boat. However, if you have a new more obvious moan / whine, especially if it is a very low frequency grumble at idle, that increases with engine RPM's, then it is likely to be a rough / worn / water damaged thrust bearing. If water has entered the bearing, it is usually as a result of a flooded bilge at some time on a warm bearing, then water can be sucked in as it cools.
Moan or Whine: The jet unit can exhibit some "turbine whine" not unlike a turbocharger noise but you will know what is usual with your boat. However, if you have a new more obvious moan / whine, especially if it is a very low frequency grumble at idle, that increases with engine RPM's, then it is likely to be a rough / worn / water damaged thrust bearing. If water has entered the bearing, it is usually as a result of a flooded bilge at some time on a warm bearing, then water can be sucked in as it cools.
Periodic Vibration: Often at specific RPM's and disappearing at other throttle openings is probably a torsional vibration emanating most likely from the universal joints on the drive shaft. Check them for worn / slack joint needle rollers, or if they have been installed incorrectly after an overhaul. Some strake and intake grate noise is normal, especially on aluminum boats; the important thing is to be aware of any unusual noises.
Some Rattle Or Noise At Idle: This is normal with American Turbine / Berkeley pump equipped with steel or bronze impeller.
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