jdsleds.com -> Technical Information -> Troubleshooting

INTRODUCTION

This particular discussion is geared toward 00 series and JDX sleds with CCW engines, but much of it is applicable to all. This represents a distillation of many posts from many individuals of this group over the past couple of years.

So you just got yourself a vintage John Deere snowmobile, welcome to the group!
Now you are wondering what to do next. You have found this web site, so you have a good start.
The first thing you need to decide, is what your goals are. Full restoration, partial restoration, fix it up a bit, or toggle it up and cut every corner you can.

However much time and money you think it will take to accomplish your goal, forget that, it will be a whole bunch more. If you are serious about this, the first thing you need to get is a genuine JD Shop Manual, this will save you a lot of time and trouble. You can get one for your sled from Deere: SM 2100 covers JDX / 00 sleds. http://techpubs.deere.com/deere/Default.aspx
or watch ebay, they show up there from time to time.

Your new ride has most likely been sitting for a long while. It is around three decades old, and it no doubt needs a bit of attention to put it into running condition.
Your sled needs 3 things to run: 1) ignition 2) fuel / air 3) compression.

Lets look at them one at a time.

IGNITION

No doubt you have already pulled the starter rope to see if the engine is free. If it is stuck, it needs to be disassembled to find the reason why. Keeping in mind that you most likely have no idea what all has happened to this engine over the past 30 years, you need to keep yourself open to most any possibility.

Take the plugs out and put a couple of teaspoons of 2-stroke oil down the cylinders before you continue ( it won't hurt ) reconnect the plug wires to the plugs, and lay them on top of the motor, making sure they are touching metal . Turn the ignition switch on, and check the kill switch position. Now pull the motor over while watching the plugs. You should see nice bright spark on both. If you do, you are set. If you have weak , intermittent, or nonexistent spark on one or both plugs, you are about to become better acquainted with 2 stroke ignition systems. If you have no spark at all, there is one trick to try: near the pull starter is a plastic electrical plug, unplug it. This takes the ignition switch and kill switch out of the loop, if you now have spark when you pull it over, you have a bad switch or wiring to deal with.

Before you tear things all apart, look at those plug wires and caps. Are they any good? New solid core wires and new caps could be in order. While not original, I really like the genuine NGK caps. They go on and off easily, yet snap on positively. Forget the cheap "sparky" caps. Oh yeah, the plug wires screw into the caps and the coils, with the exception of the CDI systems, the wires are not removable from the coils on those. Take a look at the screw inside the coil, is it burnt down to a nub?
If it is, a new coil may be in order.

If you have a '72-'74 sled, you have a point ignition system, after that Deere used cdi ignition. The points are the next thing we need to look at.

You very likely have corrosion on the contact point surfaces, which is preventing them from making good electrical contact.

Remove the pull starter housing, then the cup and flywheel cover under it. You will see two "windows" in the wheel, rotate the wheel until you can see the points through them.. Take a nail file or similar thin object, wrap a bit of fine abrasive paper around it and work it back and forth in the point contacts ( 400 grit ). Blow out any residue with compressed air, reassemble, and check for spark again. If after several attempts you are still not getting spark, you will have to remove the flywheel so you can remove the points to get a good look at their condition. If the points are worn, you may have to file a ridge off them to make them smooth and get good contact between them.

To remove the flywheel, first you will have to remove the fan tower ( fan cover ).
The ring gear on the flywheel will not come through the opening in the tower.
There are four bolts to remove from the backing plate, and the electrical connector plug must be detached from the fan tower.

Then the large nut on the end of the crankshaft must be removed. An impact wrench makes short work of this, otherwise you must hold the flywheel from turning ( I prefer holding the flywheel by the ring gear ). Then a steering wheel or harmonic balancer puller can be installed to pull the flywheel off by the three tapped holes near the center. Do not use a 2 or 3 arm puller, they are for pulling sprockets and hubs, you will likely bend the ring gear. This is a tapered fit, it is either on or off.

Wind the puller up until it is tight, then give the puller main bolt head a sharp rap with a heavy hammer, you are not trying to drive the crank out the other side of the crankcase, so just a sharp rap. Wind up the puller and try again. If it still is stuck tight, a bit of heat may be required to get things moving. Don't feed flame inside the wheel, warm the key way area of the wheel with a torch and rap again. It might be a good idea to pack the windows shut with a flame proof material. Don't get the wheel so hot that you cook all the coils and wiring inside.

Once the flywheel is off, you can remove the points, and recondition or replace them.
It is not always easy to get the correct points. Your flywheel may say Nippondenso or Kokusan on it, this helps confirm what you have. You may consider sending your supplier a digital photo of your stator assembly to help in the selection.

It is possible that you may have a bad generating coil. The two coils at the top are your ignition generating coils ( 2 singles or 1 double ) The coil at the bottom is your lighting coil. The ignition coils are mounted to the side of the fan tower just above the pull starter. All these coils can be tested for continuity, opens or grounds, and resistance.


FUEL SYSTEM

CARBS

The 00 series and JDX sleds used Bendix or Walbro carbs with the exception of the 295S which used twin Mikunis.

The Walbros used were "pumper" carbs. This means they have the fuel pump built into them. The fuel tank that was used with the Walbro had two fittings, a supply fitting and a return fitting. Rebuild kits for Walbro carbs are available from most parts suppliers.

Bendix carbs were "float" carbs. They require a separate fuel pump. The fuel tank used with these carbs has only a supply fitting.
Parts for Bendix carbs seem to be nonexistent.

Most likely your carb will have to be disassembled, cleaned and rebuilt. Don't fight it, it seems a high percentage of 2 stroke running problems are related to dirty carbs, or carbs needing repair.

FUEL TANK

A temporary tank may be best for your initial engine testing. A jug such as bleach or antifreeze comes in can work. Rinse and drill a couple of holes in the cap for your fuel lines. With fresh premix added, secure the jug beside the engine, ahead of the footwell. Keep the lines away from the exhaust , and keep fire safety in mind.

The metal fuel tanks these sleds used have a tendency to rust , and generally have a good coating of crud in the bottom.
To clean the tank, remove it, remove the gauge and fuel pickup fitting, drain, and spray a can of oven cleaner into it.
Let it sit for an hour or so, ( or days, whatever it takes to loosen the residue ) then toss in a handful of nuts and bolts and agitate. When it looks good, drain out the crud, flush with hot water, shake out the nuts and bolts, and blow dry. If it has no holes rusted in it, it should be good to go.

On a '72 400 tank I cleaned that had been sitting half full of fuel for 20 years, it took two treatments of EZ-OFF to get the tar-like fuel residue out, then several days of acid soak to get the rust cleaned out. A phosphoric acid used as a dairy equipment cleaner was used, check farm stores such as Fleet Farm, or Tractor Supply.
When the rust has been removed, drain the acid and flush the tank with a little diesel fuel. If you flush an acid treated tank with water then dry, it will oxidize ( rust ) almost instantly! Drain the diesel and coat the inside of the tank with some light oil, or 2 stroke oil to prevent rusting if you are not going to be putting it in service right away.

Replace the fuel lines. I prefer the clear lines, they allow you to see if you have fuel flow. Deere originally used one clear, one green, to prevent connection mix-ups.
Poly will work, but a TYGON line willl last far longer. A check valve should be installed on the end of the pickup line to prevent the fuel from running back to the tank every time you shut down the engine. I got mine from Central Snowmobile. Install a fuel filter between the tank and the carb. Clamps at all connection are advised. A cheap clamp is a small double wrapped zip tie.

Don't forget the pulse line. This is the line between the carb and crankcase on Walbros, and the fuel pump and crankcase on others. This line must be as short as practical, and a fairly stiff line works better. Braided rubber fuel line will work, but can de-laminate and suck shut internally. A thick wall poly or TYGON line may be best.


COMPRESSION / ENGINE CONDITION


The mechanical condition of your engine is the other important consideration.

It seems that few sleds ever got run enough to wear out the CCW engines. Most can be returned to good running condition. How much effort and $$ it takes will depend on the conditions the sled was stored in, and how well the engine was treated in the past.

How long has your engine been sitting? Time is not kind to 2 strokes. Just an example: In UL aircraft applications, Rotax recommends crankshaft seal replacement, every year or every 150 hours of operation. Rotax recomends crankshaft replacement every 5 years or 300 hours of operation. Micro pitting of crank pins due to humidity and the limited amount of oil film on internal parts, combined with extended periods of storage, cause increased incidence of crank failures beyond those parameters. So if you have a sled that has been sitting in a barn for the last 20 years, how much can you expect?

If your engine is stuck, you really need to disassemble it to find out why. Dumping penetrating oil in it and hoping for the best is for old tractors and Briggs and Strattons.

There are a couple of kinds of seizures. If the engine simply overheats, the piston expands faster than the cylinder, your clearances go away, and it will bog down and stop. Then you may discover that it has seized. However, after it cools off, it may turn over and start and run. It may smoke a bit, and not have much power. An engine in this state can probably be salvaged . The piston can be polished up, and the jug honed and treated with muratic acid to remove the aluminum from the steel cylinder liner. The clearances will be more than they were before, but you aren't out much more than your time at this point if it doesn't turn out satisfactorly.

The other kind of seizure is when someone forgot to put the oil in the pre-mix. This is a lack of lubrication seizure, and your engine is pretty much toast at that point. You may need jugs, pistons, and rods, along with your new or rebuilt crankshaft. $$

A compression test will confirm another common failure, "the meltdown". This is when you have combustion chamber temps in excess of the melting temp of aluminum. A lean fuel mixture condition due to improper carb tuning, or air being admitted into the engine due to a seal or gasket leak, will cause high exhaust gas temps, which may melt a hole in the piston, typically near the exhaust port. Thus, the lack of compression, a thumb over the plug hole may diagnose that. Otherwise, you should see over 100 lbs of compression on a cylinder in decent condition.

Another diagnostic test you might consider is a case pressure test. Especially if you are returning a seized motor to service. It is important that you find the cause of the original seizure to prevent another. This test will check the condition of your seals and gaskets. Performing this test on an un-rebuilt engine will tell you less. The results are only good for that moment. Once you start running an old engine, the seals could fail fairly quickly, even though a pressure test earlier had shown them to be OK. Directions and photos of how to perform this test is in another FAQ courtesy of <Harleysportster>

In any case, if you have an engine which has sat without running for many years, it may be prudent to tear the engine down to inspect it, lightly hone the cylinders, and replace the crankshaft seals. <JDFANPA> has related that he has seen the time when an early compression test indicated good compression. But after running the engine a bit, the rings collect the rust in the cylinders, which causes the rings to become stuck in the pistons, resulting in low compression.

You will hear a lot about crankshaft seals on this list. Leaking seals can cause several different problems. An engine that doesn't idle despite all attempts at carb adjustment, may well need seals. If you have oily crud around the crankshaft behind the clutch, you may have leaking seals. The gas evaporates, leaving the oil behind. Some bad seals show up on a high power run across a lake when the engine violently seizes. With the engine running, starting fluid sprayed at the seal should cause an increase in rpm if the seal is bad. This is problematic on the mag end, as access is limited, and you have arcing points under the flywheel. Sounds like it has been done though.

The '72 engines seem to require the case to be split to replace the seals because of a retainer installed outboard of the seal. On the '73 on up engines, it appears that at least the PTO end seal can be pried out and replaced ( after clutch removal ). The service manual doesn't say if the mag end seal can be replaced in the same manner or not. At any rate, it would require the removal of the fan tower and stator plate to gain access to the seal.

On sleds that have sat, it is a good idea to inspect the carb air box for mouse nests and acorns. Same holds for the muffler. There have been cases where engines didn't run right because the exhaust was restricted.

Also, the couplers between the exhaust manifold and the muffler, need to be free to wiggle. If they are rusted solid, the engine vibration will be transmitted through the muffler into the tunnel. The muffler may break, and nuts and bolts in the sled may be hard to keep tight.

Good luck, and have fun! Anyone with money can ride a new sled, only a dedicated enthusiast can ride a vintage one!