problem idling

[Pro70]

Probbaly a noob question.....but i just installed my new 138cc lifan motor...and got it running....but when its idling and u revv it a little bit.....it will hold the revs high for about 5-10secs and then go bak to idle?????
Any ideas what this could be????

Cheers guys

 

[Sidney]

Throttle cable is getting stuck on something.

 

[jwe97015]

choke could b up or your air fuel mixture screw could b out a bit??

 

[motoluver]

Sounds lean to me.

 

[Pro70]

Ok ill check tomorrow what the mixture is like. But why does it running lean make it hold revvs???

 

[jwe97015]

just does happens 2 my mates 125 every now and then adjust thr screw seems good

 

[Sidney]

If that isn't your problem make sure the rubber thing is pushed all the way onto your throttle.

Its a cone type thing where the cable connects to your throttle, if its not on your throttle can get stuck open.

 

[DHZ73]

Ok ill check tomorrow what the mixture is like. But why does it running lean make it hold revvs???

I would believe the rpm hangs up due to the lack of gas goin into the engine, the same way it reacts when we're running out of gas.
There is still gas after throttle is close, but just insufficient, resulting in the hang up. After idling for few seconds, the rpm settles down when gas start to build up.

 

[jthump110]

ur idle is set way too high, also ur mixture, is set off badly.

 

[Cactus Jack]

ur idle is set way too high, also ur mixture, is set off badly.

You've hit the nail clean on the head ...... that's precisely what's wrong with it ....... I've already told him that ...... I installed the engine and carb in a rush (both were brand new ...... I only had a few hours to remove his old 70 motor and fit the new one plus ran into problems) but we ran out of time to start it and tune it as his fuel line didn't fit the carb and he had to go out urgently ....... the fuel mixture screw is out too far and needs to be screwed in (it's flush with the outside of the screw thread - miles out) ...... it's running rich and he has turned the idle up to compensate in order to stop it from stalling ......... as a result it's taking its time to idle down . People could help him by checking to see how many turns out from right in the mixture screws are on their "30" mm Mikuni carbs .... I'd tune it for him only I live well over 100 K's away from where he lives .........

Since the mixture screws on those carbs are a PITA to get at with the carb on the engine ..... we would have needed a fair bit more time to get it dialed in .........

 

[motoluver]

My "30mm" is set at two turns out.

 

[Cactus Jack]

My "30mm" is set at two turns out.

Thanks for that dude - that should get him close enough !!!!! The carb was new in a kit from DHZ and had never been on an engine ......