2002 Trail Touring: good on stand, bad on snow

[JakeVIII]

I bought this 2002 Polaris Trail Touring off a friend who moved away. He bought it as a parts sled for his 550 fan, and I bought it from him as a fixer upper to learn how to work on snowmobiles.

I have rebuilt the chaincase, replaced the throttle cable, replaced the gaskets on the top end and have rebuilt the carbs. New spark plugs are also in there.
It moves...kinda.
I believe I have the throttle and idle adjusted pretty well. It idles, and once it warms up it idles around 2000 rpm.

On the stand, the sled will go wide open and seemingly through the full range of rpms. The belt moves, the primary clutch tightens, the secondary rotates. Sorta rewarding since this is my first kick at the snowmobile game.
Problem is, when I go to drive the sled, it will only move forward in a sweet spot at the 4200 rpm range - it'll go along at about 10-15 mph as long as I keep the throttle in the sweet spot. Attempting to open the throttle more than that results in the sled bogging down to a solid 3000 rpm. If I open the throttle fully when the sled is on the ground, it will just chug at 3000 rpm and the sled won't move.
It reverses, and the same stuff happens in reverse.

So I feel like I'm like 80% of the way to having a fully functioning bargain basement sled.

It actually starts pretty well, too. The issue is that it has absolutely no power and it will only move in a super narrow rpm band.

Any thoughts? Please bear in mind that almost nothing can really be overlooked- I wouldn't say I know what I'm doing with snowmobiles.

Other wildcard issues (which could matter for the key issue above?):
-fuel lines should be changed out
-sled only idles with kill switch unplugged
-spark only occurs when starting if throttle is slightly open, unless kill switch is unplugged
-belt deflection is about 1 inch, I really do think I have it set right- the plate on the secondary is set to 4 for a new belt
- I overlooked doing the crankcase seal
- I haven't touched the air screw on the carb to adjust idle
- carbs were synched with a 7/32 drill bit

 

[retiredpop]

What size of jets are you running at what altitude? Sounds like your mains are too big. Do you have a jetting chart?
Belt deflection should be set for 1 1/4 inches.
Your kill switch is shorted out.

 

[JakeVIII]

I'm running 300s at 625 ft. The rebuild kit came with 290s and 300s, and since the ones I pulled out were 300s, I put clean 300s in.
I also dropped the needle clip from 4/5 to 3/5 right in the middle- not sure if that matters here.
I don't have a jetting chart, but I will see what I can find.

 

[JakeVIII]

This jetting chart is for a 2002 550 F/C classic, but it makes sense they should be pretty similar. I'm dealing with -30 F in Yellowknife, so at 0-2000 ft it looks likes 300 could be right.
The pistons were oversized to 1.25 by some previous owner, any idea how that could change jetting?

 

[whoisthatguy]

Generally you jet for the lowest altitude that you will be riding WFO with the throttle. In my 2004 manual, for 2000 to 4000 feet at -30F to -10F, use 280PTO /270 MAG with the needle clip in the #3 position from the top. So 300's are fat. And the mains in their charts are also always fat. They come delivered with 260 PTO/ 250 MAG which you can probable get away with because you will not likely be riding it WFO. They should idle at 1600 RPM. Carburetor air screw is 1.0 turns out.
You can buy used kill switches off of EBAY, but wait until you solve your biggest problem because you can turn it off with the ignition key.
The older sleds have all kinds of electrical issues. You can start by eliminating a possibly defective bright headlight switch by taking apart the left side handlebar controls and unplugging all of the wires. A bad one causes RPM problems.
If that doesn't fix it, when you have is running and you have the hood open, then give it some gas and see whether the headlight dims. If it does, then you need a new stator. Buy new aftermarket stators off of EBAY for 25% what Polaris will gouge you for one.
Next, after replacing the stator and testing it out, if that doesn't work you buy a new coil off of EBAY. You can quickly plug that in and test it, without actually mounting it to the air box.
Next, after testing out your coil, if that doesn't work you buy a new voltage regulator off of EBAY since the new and used price is about the same. It should be located over the left foot well.
Next, after testing out the voltage regulator, if that doesn't work you buy a good used CDI box. They are all used so you buy one out of a running sled with as low as mileage as you can find.
If it still does not run, you are running out of options. You might try buying a fuel pump rebuilding kit off of EBAY, and do that. Especially if it does not start with the first pull if you just ran it the previous day.
The fuel leader inside of the tank may be cracked and with a low fuel level, you might be sucking air. If you have it on a trailer and the front is tilted down, it takes at least 3 gallons to run the engine on that incline. The fuel tank leader has to be gas compatible plastic hose. Once you buy on off of EBAY, you will have to straighten it out before installing it, by stretching, mild heating and running a straight coat hanger wire down the middle of it to get it to set straight.

 

[whoisthatguy]

Clutch engagement RPM is 3800 RPM. So your primary clutch may be rusted up on the center slide which you can sand down with 2000 grit sandpaper, or your weights have too much play and not pushing inward on the outside pressure plate. Verify 10-62 or 10-60 weights and tight bushings inside of those weights. You complain of the action at 3000 RPM, when the primary clutch is not even supposed to be engaging. I would move this primary clutch inspection up to the very top of the list that I provided above.

 

[JakeVIII]

Wow, thank you for the help! I am going to start working down this list.

 

[retiredpop]

A good point about the primary clutch needing to be looked at. If you don't have a clutch puller you can remove the 6 bolts holding on the cover. Loosen them evenly so it doesn't get jammed to one side. There will be some spring pressure pushing against it so hold the cover once it is almost off. The primary spring is probably broken by the sound of it which would cause the symptoms described by you. Here is the proper specs for you as found in Polaris owners manuals spec sheets.

 

[JakeVIII]

Ok, cool. I was thinking it could be clutch as well, but I just don't have the experience to make that call with so many other things to look at.
With your advice, I'll definitely do that one first.
Thanks for the specs! I didn't realize all models were all in one big file.

 

[JakeVIII]

For the new spring, the specs say 120/310. It makes sense to get the same part, but is it more complicated than that?

 

[retiredpop]

I've always run the stock recommendation on clutching and been happy with the performance so yeah just replace it with the same.

 

[stephengivensjr]

I have melted down several engines in this manner with bad crankcase seals. The pressure leak stops the engine from building rpms and doesnt show up on a compression test. That would be my guess.

 

[JakeVIII]

Yeah, a guy I work with used to work in a small engine shop. He said to check the carb boots based off what I told him. The carb boots look like they need work for sure, what from your observation the crankcase seals almost certainly need to be done. It seems like both issues are similar and if both are in effect it would sewer an engine's power for sure

 

[BeartoothBaron]

Definitely replace the carb boots if they look bad. At that age, new crank seals would be a good idea (although hopefully they were done with the pistons). Unfortunately - unless this engine is different than I'm thinking - the crank seals can't be replaced without opening the crankcase. I've had carb boots go bad on my old 600, and it caused some noticeable issues, but not as bad as this before I found it. With a project like this, it's usually a process of looking for things that don't check out and knocking them out one by one. The things mentioned that can cause air leaks and therefore a lean-out are most critical. It's up to you as to how proactive you want to be; it's pretty easy to blow through several hundred dollars and a couple weekends chasing down every little thing.

The clutching has also been mentioned, and that will often cause what you might think is an engine problem. These tuned pipe two-strokes make relatively little power outside their peak power window, and the clutch is a pretty carefully designed system to get into that range and stay there, unless you're idling or just puttering around. New springs would be a good idea. You can replace the spring on the primary and check for broken or worn pieces there (look for anything stuck or loose). You need a heavy-duty snap ring pliers to get the secondary apart, and it's not fool-proof to put back together, but not difficult with instructions.

 

[JakeVIII]

So this is actually still going on. I started rebuilding the engine, then I learned what ring gaps are after I sealed the crank case.
The ring end gap on the 73.25 mm pistons is, best as I can tell from my feeler gauge, 0.025 inches/0.625 mm. Based off the bore, the gap could be about 0.014 inches/0.355 mm. Polaris spec seems to be something like 0.18"/0.452 mm.

Barring any disability on my end to push a piston on to a ring about an inch down a hole and have it level, it looks like the gap is fully twice (or 1.5) what it should be on both cylinders. This is, given my inexperience, completely possible.

What can I do about this?
Does anyone happen to know what the acceptable upper limit is for this machine?

 

[retiredpop]

This is for the 2002 Indy Trail RMK not the touring but the engine specs should be the same. Clutching and jetting of course is different.

 

[JakeVIII]

Thank you, it's right there! After reading more into how to check gaps, it looks like I'm right on the edge at 0.55mm- good for now.

Where do you find these pdfs? Is this something I should go to Polaris for? Creative googling hasn't really helped me find spec sheets.

 

[retiredpop]

I found some manuals at Box.com It's been a while but I think you have to create an account and then it should show some manuals. Hopefully the link opens the manual page for you.
Other manuals I have stumbled upon by doing a search so I download them to my computer. Of course you could most likely go to Polaris and buy it.

 

[whoisthatguy]

The three most frequent problems with installing brand new pistons and brand new rings that came with those pistons is 1. installing the piston with the arrow on the top pointing towards the front of the engine, and 2. installing the dark faced ring in the lower slot and the shiny faced ring in the upper slot, and 3. installing the flat side of the ring facing DOWN and the beveled side of the ring facing UP. If the piston and ring set came from a reputable manufacturer, then you don't likely have to examine the ring gaps that are not easily measured without a method to compress those rings so that they are flush with the face of the piston. When you install the piston, you should know right away whether there is no gap at the end of the rings because of the difficulty in getting the piston into the cylinder. Oil the cylinder walls up before installing pistons.

 

[JakeVIII]

The three most frequent problems with installing brand new pistons and brand new rings that came with those pistons is 1. installing the piston with the arrow on the top pointing towards the front of the engine, and 2. installing the dark faced ring in the lower slot and the shiny faced ring in the upper slot, and 3. installing the flat side of the ring facing DOWN and the beveled side of the ring facing UP. If the piston and ring set came from a reputable manufacturer, then you don't likely have to examine the ring gaps that are not easily measured without a method to compress those rings so that they are flush with the face of the piston. When you install the piston, you should know right away whether there is no gap at the end of the rings because of the difficulty in getting the piston into the cylinder. Oil the cylinder walls up before installing pistons.

Thanks! This seems like really great advice, I will make sure I do all these things.