1991 Polaris Indy 440 low max rpm

[Justin.s]

Hi, I recently picked up a 1991 Polaris Indy sport 440 fan, took it out for the first time and would barely hit 45mph and wot rpm would never climb past 4800 to 5000 rpm even right from a stop.
Took it home and started tearing into it, here’s a list of things that were checked.
Cleaned carbs and verified proper jets and made sure that they were synced, choke plunger has free play, sled starts up easy and idle fine.
Changed spark plug boots and plugs.
Cleaned both secondary and primary, and insured they were both moving and functioning properly, then took the sled out again to try it and still doing same thing.
Pulled belt off ( I know it’s not recommended ) and ran the sled to wot and it would pull 6300 rpm which is in spec according to the sticker under the hood, but with the belt on and sled jacked up won’t rev higher the 5000,
Took secondary apart again and added preload to the spring,
Pulled shims out of primary to achieve proper belt to sheave clearance,
Replaced primary spring with new one ( stock replacement )
Removed weight from clutch weights
Belt slack is in spec,
All Bearing from jacks shaft to rear of skid and good ,
Tried tightening and loosening track,
Took air box off to make sure there is no air restrictions
Stator and ignition coil ohms are in spec
Compression is good and both cylinders match
Plug readings are good,
I’ve played with the air screw and raised and lowered the clip on the needle, nothing I do seems to have any effect on max rpm. I’ve ran out of ideas and things to check, the only thing I can think of trying would be a primary spring with a much stiffer finishing rate,
If anyone has any ideas it would be greatly appreciated, thanks !

 

[retiredpop]

It's a shot in the dark but maybe a restriction in the pipe or the can.

 

[Justin.s]

It's a shot in the dark but maybe a restriction in the pipe or the can.

Haven’t check that yet, I’ll take a look

 

[TRS]

Mouse nest?
CDI could be bad as well.

 

[Justin.s]

Mouse nest?
CDI could be bad as well.

I was thinking cdi as well, I’m gonna swap cdi boxes with a buddy of mines and see if that works

 

[Justin.s]

Changed the cdi box and rebuilt fuel pump and still nothing

 

[BeartoothBaron]

One of the first "worth a try" items is a new, and correct belt (you may have, but I didn't see it mentioned). If it's clutching, the clutch is shifting out too quickly, which tends to come down to too much weight in the primary, or too steep a helix (weights and helix have the strongest overall influence), or light spring in the primary and/or secondary. Hopefully a stupid question, but is the secondary is assembled correctly? The spring has to be twisted so that the buttons are loaded against the helix. Also, make sure you have the correct helix. Another shot in the dark: how much do you trust the tachometer? I have an old Indy Trail, and it'd hit 50, but that's about it. 45MPH is a lot more than I'd expect from that sled if it's really not revving past 5000, especially if it's because the engine isn't pulling.

 

[Justin.s]

One of the first "worth a try" items is a new, and correct belt (you may have, but I didn't see it mentioned). If it's clutching, the clutch is shifting out too quickly, which tends to come down to too much weight in the primary, or too steep a helix (weights and helix have the strongest overall influence), or light spring in the primary and/or secondary. Hopefully a stupid question, but is the secondary is assembled correctly? The spring has to be twisted so that the buttons are loaded against the helix. Also, make sure you have the correct helix. Another shot in the dark: how much do you trust the tachometer? I have an old Indy Trail, and it'd hit 50, but that's about it. 45MPH is a lot more than I'd expect from that sled if it's really not revving past 5000, especially if it's because the engine isn't pulling

One of the first "worth a try" items is a new, and correct belt (you may have, but I didn't see it mentioned). If it's clutching, the clutch is shifting out too quickly, which tends to come down to too much weight in the primary, or too steep a helix (weights and helix have the strongest overall influence), or light spring in the primary and/or secondary. Hopefully a stupid question, but is the secondary is assembled correctly? The spring has to be twisted so that the buttons are loaded against the helix. Also, make sure you have the correct helix. Another shot in the dark: how much do you trust the tachometer? I have an old Indy Trail, and it'd hit 50, but that's about it. 45MPH is a lot more than I'd expect from that sled if it's really not revving past 5000, especially if it's because the engine isn't pulling.

Belt is the correct one I’ve tried 3 different ones now, secondary is wound properly on highest preload hole, I rode next to my buddy sled to verify that the tach wasn’t off, what rpm should the primary be engaging on these sled ?

 

[Justin.s]

Update, I lightened up my clutch weights and put a little stiffer spring in and I got the engagement up to 3000 rpm and the max rpm to 5300, so It’s narrowed down to the clutching, now I’m wondering if I go with a stiffer spring to get my desired max rpm or lighten the weights more, I’ve already got the weights down to 41 grams just not sure how much more I should go

 

[retiredpop]

Definitely seems to be clutch related. With 41 gram weights I would expect engagement to be higher than 3000. Only specs I can find are operating rpm of 6800 but even that doesn't match your underhood sticker of 6300. Anyway here is the clutching specs I found. Even high altitude specs only go down to 47.5 grams so you definitely have some issues there.
I also think there may be other issues too. Have you checked the timing with a dial gauge? It could be off.
Is your buddie's sled a fan cooled 440 as well? If possible could you swap exhaust, clutches etc with his just to isolate things.

 

[Justin.s]

Definitely seems to be clutch related. With 41 gram weights I would expect engagement to be higher than 3000. Only specs I can find are operating rpm of 6800 but even that doesn't match your underhood sticker of 6300. Anyway here is the clutching specs I found. Even high altitude specs only go down to 47.5 grams so you definitely have some issues there.
I also think there may be other issues too. Have you checked the timing with a dial gauge? It could be off.
Is your buddie's sled a fan cooled 440 as well? If possible could you swap exhaust, clutches etc with his just to isolate things.

I haven’t gone threw any timing yet I’m gonna pick up a timing light and check all
that this weekend,

 

[retiredpop]

Just to let you know a regular 4 stroke timing light won't work on a 2 stroke. Ignition firing is too fast and the 2 stroke fires both plugs every revolution which makes it even worse. Regular timing light just misfires. If you can find a timing light with a 2 stroke setting you're good to go with a timing light. That is why I mentioned using a dial gauge.

 

[Justin.s]

Just to let you know a regular 4 stroke timing light won't work on a 2 stroke. Ignition firing is too fast and the 2 stroke fires both plugs every revolution which makes it even worse. Regular timing light just misfires. If you can find a timing light with a 2 stroke setting you're good to go with a timing light. That is why I mentioned using a dial gauge.

Picked up a timing light with the 2 stroke function and verified timing is within spec

 

[retiredpop]

Have you checked crank seals for leaking by spraying starter fluid behind the primary clutch? You probably can't access seals under recoil. If idle changes that indicates a problem. One last thing would be very carboned up exhaust ports but that is not very likely.
Fresh out of any other ideas.

 

[Justin.s]

Checked crank seals, no increase in idle.

 

[polaris754]

good read , just my opinion, sounds like with the weights down to 41 and only a 300 rpm change , the engine isn't making good poowwwwaaaaaaaaaaa,, with all u have done , just a guess , top end might be pooched, do a cyl leak down test

 

[NEWDUCK]

Are your clutches in alignment? When I first built my "89 wildcat it had zero top end, wouldnt tach etc... re aligned the clutches and bingo bango. We had a runner.