Pit Bike Idling High then low then high .exc. with choke on or off:(

[Naturalbornthriller]

I have an EVO 140cc Lifan Engine

Iv noticed it is low on oil but dont know if it could be causing this problem,
sorry im fairly new to bikes,

also nothing really changes with the air fuel mix (only one screw on the carb and its on the left hAND SIDE opposite ide from the choke.

Any help would be fantastic , thankyou for your time .
Josh

 

[Cordogs]

A close up picture of the carburettor will help mate, also a clearer description of exactly what happeneds once you kick the bike over. Eg: how long it idles/revs for, rpm range of revs and what you've checked/ done to solve the issue.

Cheers
Cordogs

 

[Naturalbornthriller]

ok ill take the pics and post them and a link to a vid of me starting it up and idling

But when i checked the oil it wasnt even touching the dipstick ( once i found this out i didnt try again for obvious reasons ) so im gonna do an oil change but i dont think that would really effect it , Would it?

 

[Cordogs]

Very important that you get that oil sorted asap before any starting/riding. No it probably wont change your idling issues but it will save you buying a new engine.

Sort that out and we'll take it from there. :thumbup:

 

[headsmess]

wheres the freaking pics? theres enough videos on the net of bikes being started and idling...we just want to see the carb.

a fair few carbs have the air screw in the best place ever designed...underneath, where you cant get to them! (without burnt fingers, short stumpy screwdrivers or right angle drives, at least)

the IDLE SPEED screw is obvious, its just about always on the side, in line with the slide. if you can only see one screw, assume its the idle screw and not the air screw.

but, in diagnosing idle issues...firstly, make sure theres no air leaks. air leaks cause more trouble at idle than at any other throttle opening, due to the ratio of air passing the slide, and air leaking in where it shouldnt. it causes lean, which causes fast idle. fixes...check for the o-rings in carb and in carb spacer. make sure the manifold isnt cracked, and the face is flat, followed by the last resort...sealants.

then... when you blip the throttle... if the engine takes some time to get back to a steady idle, ie, revs high, slowly dropping...its lean.

if it sags down then picks up speed to the steady idle...its rich.

if adjusting the air screw doesnt change things much, you usually have to go up a size or two on the pilot jet.

 

[Naturalbornthriller]

Today the idle was going up and down and u and down :S any ideas?

 

[AntNZ]

That looks like a mikuni carb, the screw on the side is the idle adjustment screw, the air/fuel mixture screw will most likely be on the bottom at the front.

 

[Naturalbornthriller]

thankyou very much buddy , do you think thats the reason for erratic idle speed? or should i just clean the pilot jet/carb /ext.

 

[Naturalbornthriller]

thankyou very much buddy , do you think thats the reason for erratic idle speed? or should i just clean the pilot jet/carb /ext.

 

[gottagetacheaperhobby]

The mikunis seem to like a size up on the pilot jet from stock, think its 18.5 just from memory.
Definitely clean the carb, do the valve timing and follow headmess's walkthrough. Hope your filter is oiled as well, if not it would be running rather lean. Dont ride or run the engine while low on oil either, your risking major damage there..

Sent from my SM-T110 using Tapatalk

 

[Naturalbornthriller]

thankyou again for advice

 

[gottagetacheaperhobby]

The fact its running lean would also account for the hot exhaust you spoke about in another thread..

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[Naturalbornthriller]

do i need to richen the mixture is that screwing in or out?
or is that in carb maintenance

 

[Naturalbornthriller]

THANK YOU ALL FOR YOUR HELP !
its running sweet as a nut , turned out on the throttle slide the air/fuel screw , made a dent in the slider making screw adjustments useless (keeping high revs) so smoothed it out , lubed it up , changed the oil , and for the first time in 14 years i could ride a bike again (first time using clutch , never stalled or flipped) IM OVER THE MOON !!! THANKYOU !!!!