Common Problems, Simple Fixes: Veteran Savvy Allows for Easier Diagnosis

When I was a teenager, I remember giving my dad a ride in my Chevy Monte Carlo. We weren’t even into our second mile when he said, “How long has it been making that growling noise when you start to turn the wheel to the left?”

Being a dumb kid, I of course replied, “Uhhhh… what noise?” Quite frankly, when it was just me and my friends in the car, the only noises we could usually hear were Journey, Foreigner or R.E.M. tunes being blasted out of the speakers.

“I think you have a wheel bearing going out,” he said, before adding scornfully, “You don’t hear that, or even feel a vibration in the steering wheel?” Well, as a new driver, I didn’t know what feeling he was talking about because I’d never experienced such car issues before.

Flash forward about 30 years. I was in the passenger seat of my then-teenage son’s Ford Taurus when I looked to him and said, “How long has your car been making that noise when you turn to the right?”

Of course he replied, “What noise?!” Time and experience had now made me the grumpy old… er… wise sage!

It’s been said that “you don’t know what you don’t know until you know it.” That is true with many things in life, including snowmobile ownership. Many veteran, mechanically minded snowmobilers will hear or feel a certain symptom and will know from past experience exactly where to start looking for a solution.

But our sport is always adding new riders – just like when me and later my son were each new drivers – who may not be as tuned into common problems and their solutions as longtime riders because they haven’t encountered the issues yet.

For them, and also as a review for veteran riders, we’re going to share a few circumstances we’ve encountered out on the trails in recent years when riding with relative newcomers.

Belt Deflection

QUESTION: “When stopped with the engine running, my sled squeals and will occasionally creep forward unless I hold the brake. What’s going on?”

ANSWER: The problem is very likely related to your sled’s belt deflection.

In simple terms, belt deflection is the amount of flex in your sled’s drive belt when the sled is at rest. A drive belt that is too tight can be grabbed by the spinning but wide-open primary clutch when the sled is idling, allowing the sled to crawl forward or at the very least squeal against the belt.

Conversely, a drive belt that is too loose or effectively “too long” – often caused when a higher-mile belt narrows or stretches – will cause a sled to feel sluggish upon clutch engagement. Initial, out-of-the-hole acceleration will feel like a vehicle with a manual transmission starting in second gear.

The most accurate way to check belt deflection is to push against the belt with a finger midway between the two clutches and measure how far the belt moves/flexes and then compare it to the spec for your sled. Pressure and the amount of expected deflection varies by make and model, as does the procedure for adjusting belt deflection. But it usually involves an adjustment in the secondary clutch.     

Rattle And Hum

QUESTION: “My sled has suddenly developed excess vibration that I can feel through the seat and the handlebar. It wasn’t there on my last ride. What could it be?”

ANSWER: There are several things that can cause a sudden increase in vibration that the rider feels when motoring down the trail. It could be coming from the belt or clutches, from the driveshaft or rear suspension, or it might be related to the track.

Depending on your riding conditions, one of the simplest (and least expensive) possibilities is that a chunk of ice has fallen off of your heat exchanger and has gotten lodged somewhere against the whirring track or driveshaft. Pull over, grab your sled’s rear bumper and lift the sled’s rear end off the ground and then slam it down a couple of times to try to shake loose whatever could be trapped. Tipping the sled on its side to inspect will also work. Another option is lifting the rear of the sled and spinning the track to break loose a frozen clump, or if nothing else you should be able to hear the grinding restriction. Be careful with this tact, though, as that frozen clod might come shooting out the back! 

If that didn’t take care of it, look at the clutches and drive belt next. Inspect the belt to see if (1) any cogs are missing; (2) any cords are coming loose on the edges; or (3) the belt generally looks like it’s degrading or coming apart. The problem could also be related to a misbalancing of something within the clutches. Such a problem would be rare, though, unless you recently had your clutches serviced and they weren’t put together correctly.

If that all checks out, return to the rear suspension and the driveline. Your problem could be related to damage to the drive shaft or drivers (do you remember smacking anything hard?) or maybe the bearings in one or more of your bogie wheels are seizing up or wearing out. Inspect the track for missing lugs or chunks. Basically, just check anything in the drive trail that spins or rotates.

Running Engine Backfire

QUESTION: “When I’m trail riding, my two-stroke engine will occasionally backfire. What would cause this?”

ANSWER: In broad terms, a backfire occurs due to an incorrect mixture of fuel and air, and/or an ignition problem, where the spark is either weak or mis-timed.

Specific to traditional two-stroke engines, many times a backfire is a symptom of an engine that is running too lean due to a restriction in the fuel flow. On a carbureted sled, cleaning the jets is a common first step. On more modern sleds, a clogged injector could be the problem. It could also trace back to a clogged fuel filter or weak fuel pump, or could even be a reflection of poor fuel quality on your last fill-up.

The issue could instead be related to airflow. A sled with a crack in a carb/intake boot, reed cage boot or airbox can suck in air and lean out the mixture. Even a crack in the exhaust system can suck in air. Conversely, a restriction in airflow could also cause misfiring.

The third leg on the stool is the ignition system. A fouled or even incorrectly gapped spark plug, weak coil or incorrect ignition timing could be the cause of the problem.

Dead-Engine Backfire

QUESTION: “My sled runs great but often backfires right after I shut it off, which can startle folks in my riding party and really scares people at the fuel pumps. Is there anything I can do about this?”

ANSWER: This has been a common problem for some select snowmobile engines over the years.

Like some running engine backfires, a dead-engine backfire is a result of a fuel/air mixture not being burned in the cylinder but instead igniting within the exhaust system.

The most common solution may involve a change in your riding habits and, more specifically, your stopping habits. If a sled has been run hard and is then abruptly shut off, extra fuel and air can be fed to the cylinders after the spark has been cut. That mixture works its way to the exhaust where it ignites and gives you the head-turning “bang” after the engine is no longer running.

Try letting the engine RPM come all the way down to idle speed before punching the kill switch and see if that makes a difference.