Hi Everyone,
First time posting (but have read many posts in the past that have been helpful though!). I have an old Chinese quad with a lifan 250cc engine with a semiautomatic transmission.
Not sure on model/year etc- it was bought in pieces and I have been slowly rebuilding.

I was told that the engine/transmission were both great- which until now I have trusted. I have just managed to get it to the point of giving it a trial.

On car stands it works great-starts easily with some choke and once warmed it idles well. On stands it can be placed into forward/reverse. The back wheels spin well (rear wheel drive only) and can accelerate well. It easily changes from forward/neutral/reverse whilst on car stands.

2 issues though when it is placed under load (is off car stands with someone sitting on top)

1) starts in idle and goes well once warmed up but when placed in either forwards or reverse will give a sudden thrust/jerk (gear engaged) and then stop (no spluttering etc). It does not matter if it is idling or a small amount of accelerator-the same thing happens (almost as if it wants to move but the gears are jammed).

2) once the above issue has happened it will sometimes get stuck in that gear (forward/reverse) and will not shift out unless the shifter is either wriggled repeatedly or sometimes even needs the engine turned over a few times (with it still engaged) before it can be wriggled into neutral.

I don't think its a carby problem as it doesn't seem to splutter etc. A new carby was also installed when I was rebuilding it. I'm thinking maybe a worn selector fork? This is my first quad (actually first any type of motorized bike) so I don't really know much about the engine aide of things (hence why I bought one that I thought didn't need any engine work!).

Any help would be greatly appreciated.
Cheers, Richard

 

The gearchange pedal on a "semi automatic" bike doubles as the clutch pedal once the bike is moving. I suspect your centrifugal clutch may be locked, if so, let the gearpedal off very slowly, like a car clutch pedal and see if you can get the bike moving that way. If that doesn't work, and it still locks, don't forget the problem may be anywhere in the transmission, gearbox, chain jumping sprockets if it is chain drive, or diff locking up if it is shaft drive, etc.

 

Thanks for the reply merryman.
It either seems to be engaged or non-engaged. Doesn't matter how slowly I try to change into forward/reverse it still happens.

Looks like I might be taking the transmission apart soon!