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Discussion Starter #1
Greetings friends, I recently bought a 96 Indy 500, it's fricken awesome for the most part. Just one slight issue. Occasionally the sled will bog while throttling up. The circumstances and things I've noticed while riding are listed below. Hopefully someone can make sense of it and point me in the right direction.

1. Bogging only occurs from idle as I apply power. Does not matter if I stomp the gas or apply power gradually.

2. It virtually never bogs on packed trails. 90% of the time it's in powder, unpacked snow, or going up a hill. It bogs every time the track is put under more load / resistance than a packed trail has. Again, this is if I'm at a stop or underway slowly from a stop and need a lot of power to get moving. If I'm already moving along at say 20mph, or if I'm coasting down and apply power again, I can do whatever I want and it WILL NOT bog.

3. Once it bogs, I can hold the throttle all the way open and it will stay right at 3500-4000rpm, no more.

4. Usually feathering the throttle will let me start moving, once I break about 10mph and Rpms get up to 4500+ I no longer have any issues and sled takes off like a rocket.

5. This may not be important but I'll add it just in case. The sled likes to idle between 2900 and 3500rpm. As I sit there the idle will stop down to 2900 and stabilize. What I noticed is that the second I apply power the primary clutch engages the belt.

My gut is telling me the primary clutch is the culprit. My guess is it's engaging too soon, before the motor has a chance to generate horsepower and it's bogging down.

The input you fine fellows and gals is so very much appreciated, so let me know what you guys think. Thanks all! Merry Chrismas!
 

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Where's the belt riding in the secondary?

If it's been a while since the primary spring has been replaced, it may be a good idea to do that. A weak spring will definitely engage at lower RPM.

I would replace both springs and check for wear in both clutches. You may have worn parts that's contributing to the problem, too.
 

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Discussion Starter #3
Top of the belt is riding hair above the rim of the secondary. Initial inspection, the primary looks good. I'll buy a new spring Monday and clean everything when I disassemble the primary. Then go from there. Correct me if I'm wrong but a clutch that engages too early will big the engine correct?
 

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Discussion Starter #5
Not sure if it will change anything, but the symptoms experienced above started all of a sudden, not really gradually. When I test drove the sled the night I bought it, the test drive was in about 8-12 inches of powder. The following day is when I started having bogging issues, and they just got worse from there. I'm omw to the store now for the new spring, we'll see what happens
 

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Over time the center bushing aquires a build up of belt grime.
Blowing it out frequently and using a dry lube will help.
I have seen owners use white grease on the primary as a temporary (for several years) fix.
Over time it takes a toll on other parts as well.
The symptoms are exactly as you have described.
 

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Discussion Starter #7
The spring seemed to help, though I haven't had a chance to test it. While the clutch is out tomorrow I'll clean it good. Hopefully tomorrow I get to ride.
 

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Discussion Starter #8
*haven't had a chance to test in under heavy load* one of these days I'll learn to proof read. Lol
 

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Discussion Starter #9
***Resolved***

I replaced the original gold spring with an SPI red spring. It has the same amount of tension, but is about an inch longer. Clutch now engages between 4500-4600rpm as apposed to the original 4100-4200rpm. It's been a week now of fairly consistant riding in a variety of conditions, no bogging, plenty of power.
 

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Discussion Starter #10
***UNRESOLVED*** lol

So all was good, and now it's not good. In short, stopped in some powder, tried to get going again and the engine bogged. It held 5000rpm until I hit the packed trail, then burped the throttle and took off without problems. Same issue again. Trying to get out of a ditch. Bogged on the hill until I got out of the powder and onto the road, then took off again.

Intially, changing the spring to a slightly longer spring fixed the issue (as stated earlier in the thread). I just did a compression test. Both cylinders have 91psi. Seems a little low but my father in laws 1989 Indy trail also has 90psi and that thing rips.

As usual where to go from here?
 

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I've had the EXACT same problem driving me nuts on my 1996 Polaris Indy 500. Some days it would be ok, others it just wouldn't get going at all. Just as you described, once I get it up over ~20mph, it takes off like a rocket. Feathering the throttle helps, giving it more throttle just seems to bog it down even worse, and the plugs get fouled/flooded. I took it to a shop at the end of last season and they said the carburetor was gummed up. They cleaned it and I didn't get a chance to ride it again until this year. It seems like it's a little better now, but the problem is definitely still there. If I stop off the side of a groomed trail in some powder it barely wants to move when I try to get going again. Sometimes I have to get off the sled and walk along side it, feathering the throttle, until I get it back on packed snow. I have a hard time believing that it could be a carb/engine power problem. It starts easy, idles smooth as silk, and once it gets above that ~20mph threshold it's got a ton of power.

So, I also suspected a possible early clutching problem. I'm replacing the primary clutch this weekend with a used/calibrated clutch from a local salvage shop. The spring in it feels pretty strong. I have to put nearly all of my weight on it to compress the sheaves. But now after reading the above it sounds like that didn't work for Planem1. So if that doesn't take care of it for me either then I guess I'll have to look at the secondary clutch, but at that point I feel like I'll just be throwing parts at the problem. The only way I can think of to observe the clutch action to see if that's really the root cause of the problem would be to remove the hood and belt guard and then take it for a test ride. Not exactly ideal, but I don't think just raising the track and testing it without a load would do me any good.

I'm never in deep enough snow to plug the exhaust. If it's not the clutches then I'm at a loss as to what else it could be. Would really be interested to hear if Planem1 found a fix.
 

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I know, silly stupid question, but gotta ask.

Is the hole in the tub plugged? i.e., is it getting snow inside the belt area?

Is the belt the one specified for the machine (OEM)? Could the belt be a harder belt than OEM?

How tight is the track?

Check your drive axel bearings lately?
 

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Are the carbs clean and set properly? Disregard if you've already addressed it, but I'd be looking at the carbs, especially considering you mentioned the idle being off. I was tinkering with the carbs on my sled recently - figured out later I was significantly off factory settings the whole time - and it really screwed with the low-speed performance. Just when I thought I'd got the idle right, it made it really hard to get going from low speed or a stop. Maybe yours is in that kinda-sorta range. I finally reset everything to factory settings and it's working almost perfectly. My only other stab in the dark is maybe the secondary spring is shot and letting the clutch up-shift too quickly when it doesn't have enough resistance to bring the helix into the picture. Is your peak RPM where it should be? So many questions...
 

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I would agree! I would think your idle should be about 1000 lower!
Also you mentioned the belt rides just out of the secondary, but is the center to center right?
I personally get my motor to driven as far apart as I can without squealing or creeping.
 

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Discussion Starter #17
After doing multiple compression tests with different gauges, both hot and cold engines, I found compress to be between 70psi-90psi. I ended up taking the head off the engine and found some scoring on the cylinders. The cylinder heads are completely black except along the rims. Not sure if this is the cause of my bogging, but I know compression is supposed to be 120psi, and the scoring needs to be addressed. One I finish the rebuild I'll add if the bogging was eliminated.
 

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Black on the head and on the piston crowns is normal for a two stroke. There should be small washed areas where the intake ports allow the fuel/air mix into the cylinder that are visible on the piston crown. Something about the size of a thumbnail on each intake would indicate an adequate air/fuel mix (not too lean.)

I doubt that the carbon is the reason for the bogging, but a lean condition could be. I would consider splitting the case and replacing both crank seals just to make sure you don't have an issue, and take a good look at the carb boot adapters when you have it apart. Cracks in the adapters can lead to a lean condition and can cause overheating and possibly scoring of the cylinder walls.
 

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Discussion Starter #19
Good things to know Dan, thanks. The scoring on both cylinders btw is on the back of the cylinder, same spot on both. By Back I mean if you are looking at the cylinders from the front of the sled. Scoring is not visible from the drivers seat, and Jed on the same side as the carbs.
 

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Pretty sure I fixed mine. I went to replace the spring in my secondary clutch, but once I removed the clutch I could see that the Helix was bashed and corroded. So that could've been causing two problems: it might have been sticking open once I got up to speed, so the next time I took off from a stop it was like taking off in high-gear. -OR- When I was taking off, it wasn't allowing the secondary sheaves to open as the primary clutch tried to engage, so it wasn't giving out any belt slack for the primary to take up.

I recall once when it was bogging down and struggling to accelerate, I hit a big bump in the trail and then it instantly took off. That must've been knocking the stuck secondary sheave off of a corroded/bent spot on the helix.
 

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