Coolster Challenger 250cc lost performance??

[dniksich]

I posted another topic when I had the weak/no spark question which is fixed and I thought would've helped performance but it hasn't Just took it for a ride and it starts right up and runs good but for some reason top speed used to be close to 50mph now is only 28? Can't feel any slippage in the clutch/belt but the engine just doesn't rev like it should. Hit's a certain RPM and just stops climbing. Took the carb apart and cleaned it up including the main jet. Anyone have any ideas on what could be the problem?

 

[BrownStainRacing]

I posted another topic when I had the weak/no spark question which is fixed and I thought would've helped performance but it hasn't Just took it for a ride and it starts right up and runs good but for some reason top speed used to be close to 50mph now is only 28? Can't feel any slippage in the clutch/belt but the engine just doesn't rev like it should. Hit's a certain RPM and just stops climbing. Took the carb apart and cleaned it up including the main jet. Anyone have any ideas on what could be the problem?

Post pics.

Sounds like the cvt needs some attention.

I'm working on a buggy with a water cooled 250cc, I think it's a gnx or something like that.

To me, it's a over complicated, over weight, over priced, over rated, under powered..... TURD.

But the customer is always right.

 

[dniksich]

Don't have pics right now but it's this one in this link. I had the cover off and when I had it running the cvt appears to be working fine. Pulled the clutch bell off also and sanded the pads/sandblasted the contact area on the bell. I see from the specs, it's rated hp is at 7000 rpm and I know it's not hitting anywhere near that. RPM just seems to top out quick and not go any higher.

I worked on it last year for the guy that gave it to me and he said it ran great then all of a sudden one day he took it out and it lost power big time. I first thought it wasn't getting full throttle but it is.

 

[BaconBitRacing]

If I'm being honest, and I could be wrong, I think the previous owner was lying about 50mph top speed. It happens all the time.

Hopefully someone has a better answer than I.

 

[BrownStainRacing]

Don't have pics right now but it's this one in this link. I had the cover off and when I had it running the cvt appears to be working fine. Pulled the clutch bell off also and sanded the pads/sandblasted the contact area on the bell. I see from the specs, it's rated hp is at 7000 rpm and I know it's not hitting anywhere near that. RPM just seems to top out quick and not go any higher.

I worked on it last year for the guy that gave it to me and he said it ran great then all of a sudden one day he took it out and it lost power big time. I first thought it wasn't getting full throttle but it is.

The variator weights will get a flat spot and cause cvt problems, also the compression spring on the driven will weaken over time.
I see it alot on old gy6 150's.

Pull the variator apart and inspect the rollers.

With a power loss like that, I say the cvt is shifting to high too fast and the high revving engine jus don't have enough grunt to pull that high gear at that low of rpm.

You could put a tach on it and see where the clutch starts to grap the drum. This is the clutch stall rpm engagement.

That high revving 250 needs 3000-3500 stall to allow it to reach that 7k.
They have a real narrow powerband, and don't make enough torque under 3k to be able to hit that high rpm.

 

[dniksich]

I'm gonna pull it apart and check it. Makes sense what you said.

Rollers look good. Don't see anything obviously wrong. Here's a few pics.

 

[BrownStainRacing]

I'm gonna pull it apart and check it. Makes sense what you said.

Rollers look good. Don't see anything obviously wrong. Here's a few pics.

I agree, those rollers look good.

They look like lighter weight then stock.
Do you have a gram scale to weigh them??? For future upgrades, so you know what you have now, and won't have to tear it back down later to find out.

Lighter rollers will delay the shift, which is good .

How's the compression spring and driven pulley seem??? Moves freely and springs back???.

They can be dangerous when removing that big nut.

That looks like the same 250 I'm working on, with the straight up and down cylinder.

 

[dniksich]

I don't have a scale that measures grams. Maybe I'll pick one up since that's a good idea you said to weigh them. As far as the driven pulley, there must be a problem cause I can't get it to budge. I tried standing on it and it seems frozen in place. I believe it overheated because the bell was blue from heat before I sandblasted it. Maybe this froze it up?

I have a press and can try to bust it loose.

 

[BrownStainRacing]

I don't have a scale that measures grams. Maybe I'll pick one up since that's a good idea you said to weigh them. As far as the driven pulley, there must be a problem cause I can't get it to budge. I tried standing on it and it seems frozen in place. I believe it overheated because the bell was blue from heat before I sandblasted it. Maybe this froze it up?

I have a press and can try to bust it loose.

It might be froze.

You should be able to pull the 1st sheave out and it youn clockwise while the other sheave does not move.

I see if I can get a pic, of old gy6 driven, they the same operation, but the 250 is jus bigger.

 

[BrownStainRacing]

I don't have a scale that measures grams. Maybe I'll pick one up since that's a good idea you said to weigh them. As far as the driven pulley, there must be a problem cause I can't get it to budge. I tried standing on it and it seems frozen in place. I believe it overheated because the bell was blue from heat before I sandblasted it. Maybe this froze it up?

I have a press and can try to bust it loose.

Sorry bud, I forgot that pic yesterday.

You can put it back together without the cover on and start it up to see if both are opening and closing.

Jus make sure you have it in neutral and rear tires off the ground.

 

[dniksich]

No problem on the pic. I think the clutch is locked up. Can't get it to move. I don't know if the overheating affected it but I noticed some fine cracks on the belt surface? I'm gonna get a new one and at least not have to worry about it. I'll let you know how that goes. Hopefully I can post that it's fixed. Thanks

 

[BrownStainRacing]

No problem on the pic. I think the clutch is locked up. Can't get it to move. I don't know if the overheating affected it but I noticed some fine cracks on the belt surface? I'm gonna get a new one and at least not have to worry about it. I'll let you know how that goes. Hopefully I can post that it's fixed. Thanks