Hi.
Im new to the forum, hope you guys can help med with some problems.

I have this chinese quad with a 157qmj, it run very well, with a max. of 40km/h, but its too slow.
What can be wrong? The carb is cleand, its not leaky and as I said, it run very well.
For a 150cc it should run at least 55km/h
Could it be a worn drive belt or the variator sliders?

Kristoffer

 

You could try a new belt. If it's slipping now, it's on it's way out. Next check the throttle linkage that it is actually opening all the way. My Arctic Cat gas models have a screw on the thumb throttle to slow them down (governor). Then a new spark plug and clean the air filter. Try running wide open with the old spark plug, then turn off the ignition at wot, pull the plug. If the porcelain has a nice tan color, thats about it. However, if it's got a whitish tint, you can try going up a size or 2 on the main jet. Likewise, if it's black, try going down a size or 2 with the main jet. Be very careful not to get it too lean! A good source for jets is JETS R US. You will have to do a search.Lastly , here is a chart comparing Keihin,Mikuni and Dynojet. Sorry, I don't know how fast a 150 should run, but with a good tune, it should run better. I got my Arctic Cat 400 from 50 mph to 57 mph with just a K&N and a Dynojet Stage 1 kit in the carburetor.

 

The belt cover haven't been of yet, so I will giv it a try. The plug is a bit grey, but it's the original main jet and as said, the carb is cleaned totally. The air filter is cleaned and throttle linkage is opening all the way.

 

Hold on a minute, I would have thought 40kph from a 150 quad is about right. Anyone else on here got an un-modified four stroke 150, if so what is the max speed?

 

I have 4 150cc, one of them is identical with the one who drive 40km/h. That runs 50km/h another one goes 58km/h. They are all standard and with Gy6 motor.
I also have a 100cc Unilli, with a Yamaha Jog motor, it goes 56km/h.
In Denmark, a normal 50cc scooter is Limited to 35km/h. When you remove the restrictions it goes about 50-55km/h.
So i dont think 40km/h is enough

 

I know some of the EU ATV's have a "restrictor" in the intake side. Have you checked for that?

 

No i have not. I will tale a look, but i didn't think there was a resticktor in atv's.

 

Speed also depends on the size of the person riding it. Those machines are meant for kids and smaller riders.