Well new to this site, so please bare with me!? I have recently got my hands on a Kolpin 90cc two stoke atv. It’s been through a few hands it sounds like. Decent shape besides the power issue. I’ve had my share of snowmobiles and dirt bikes over the years and this one is making me crazy. I’m a diesel/ car mechanic for about thirty years now and am banging my head on this one. It has enough power to get my 13 year old daughter around but only for about 10 min. Then total loss of power. Starts and idols fine. Carbs been replaced by myself with a new one. It’s been impossible to get help from any one on this. My research figured out it’s basically a Polaris predator 90cc. Engine wise anyway! But trying to get help from the local dealer wasn’t going anywhere. I understand I guess, but myself like helping others when I’m asked questions about the stuff I work on. Compression is good, 125 psi , carb, gas , oil pump all good. It’s got a gear box for the reverse and forward gears. Basically an automatic with the cvt system it just simply can’t get out of its own way. Even with a 100 pound kid on it. This thing should be able to scare the pants of her but it just seems to just disappoint. Getting any answers has proven almost impossible, sold by Gander mountain 15 years ago but I’m finding out these things came and went in just a few years. It’s my understanding that Polaris bought the rights to these back in 06-07. I’m not even sure who really made this thing other then being Chinese. Sorry for the long intro just trying to get everything I kinda know out there. Almost seems like something after getting hot is binding and bogging down the engine. I’ll admit as simple as I thought it should be has proven me wrong. Any help or questions leading to help me stop this madness would be greatly appreciated Before I let my daughter down even more and make me even more frustrated.

 

I'm guessing a plugged pipe. Did you service the clutchs?

 

I haven’t touched the clutches yet. I just got a dvd for the Polaris predator from the same year range. From what I can see, the motors are the same. So I’m going to dig into it this weekend. It doesn’t act like a snowmobile clutch when it’s week or the belt is burnt up. Although it’s a cvt from what I can see. Not sure what to look for other then maybe something obvious. I’ve been told from a couple different places that have some knowledge on these Chinese ATVs That I could have a flat spot in the crank from sitting a long time. Wich from the guy I got it from said it ran like that fur him when it was given to him, plus possibly a few more owners before. Been told possibly trans gesrs out of alignment causing a binding when hot. Honestly it doesn’t have a lot of power even cold. Gets my daughter around for about 10 with limited power, I get on it, bearly gets me across the yard. Every once in awhile you get some signs of life at first. Unfortunately I’ve gotten a few opinions and probably thinking to much and forgetting the basics. Thought about the pipe but it seems like it flowing decent. It’s also got an AMS gear box for the forward and reverse. Reverse engagement you get like you should. Forward gear has a noise like gears clashing then slams into it. Not always but usually, but even when it’s engaging normally it still lacks power. Reves up pretty good, slams into gear. Something is holding it back. The clutches or the gear box definitely have something going on. I did loosen up the exhaust to try and give it some breathing room. Like drilling wholes it a plugged cat converter on a car. Didn’t seem to help. And you can tell others have taken things apart. Like the gear box and possibly the clutches. But not really having anyone that owned it before to ask . I’m not sure. Got it fir free figuring, like most things that sit around awhile. It would be a simple carb gummed up. Wrong on that one. Rebuilt the original mikuni carb twice just to make sure I got all the passages clear , no help. Bought a cheap brand new knockoff carb. Same exact one. Didn’t change a thing

 

No I haven’t got into the clutches yet. I just a dvd for the same year or years for the Polaris predator 90cc. The engine is the same. Looks identical to the one in the atv I have. But from my looking on the internet, looks like most of the manufacturers started making cheaper ATVs around the same time. Anyway I did loosen up the exhaust at the head , with the idea that I would give it some more breathing room if it is clogged. But no difference. I’ve gotten a few ideas from a dealer I found in Wisconsin that sold these Chinese ATVs around the same time. Was told possibly the crank getting a flat spot if it sat for a long time. Transmission gears out of alignment causing a bind when hot. But honestly it doesn’t have the power I think it would even cold. Just worse after about 10 min of riding it. Then it doesn’t really recover unless it sits fir a few hours. I guess I was thinking it would act like a snowmobile if the clutches were bad. Slipping and the engine over reving. And going no where.

 

Well now sure if my reply is getting posted. I can’t see it

 

I’ll try again, I haven’t got into the clutches yet. Guess I figured if something was wrong with them, it would act like a snowmobile would. Slipping belt and going nowhere. Except the engine red lining. This thing just bogges down. Exhaust I loosened at the head hopefully giving it some breathing room if it was clogging. No change. I did have a guy who used to sell these Chinese ATVs, tell me the crank might have a flat spot from sitting long periods of time. Even suggested the trans gears might be out of alignment? Should be simpler than all those things. But nevertheless it’s been handed off a few times before I got it, with the same problem

 

Cant see a flat spot on crank causing your issues. Clogged or carboned up exhaust...yes. Clogged carb yes....poor or weak spark yes.....what does the plug look like? These are set up to have complete airbox in tact, if part of airbox is missing they will run lean.

 

I thought the crank having a flat spot seemed unlikely too. Actually I just got done starting over with the basics to make sure I didn’t miss something simple. And your spot on with the exhaust being clogged. When I loosened up the exhaust the first time I was trying many things that day. Plus my daughter was helping me so I really wasn’t paying as much attention to what I was doing and trying to show her and explain what we were trying to do. Loosened it up more. Runs like it should. Totally different machine. Should have known better, but I had too many suggestions to look at. So thank you for reminding me about the exhaust!!! Keep it simple works more often than not !!!

 

You had 1 suggestion that mattered.. Your welcome.. LOL
Now get into the clutch's for maintenance. They do not act like the snowmobile clutch's like you mention. Make sure the rollers have no flat spots.
Flat spot in crank... Stupidest thing I've heard. I needed a good laugh.
Hope the kid has a ball!!