Lifan 125 revving extremely high, always

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M

morphus

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Help my Lifan 125 has extreem high revs. Its the carby as this happened to the last motor I tried it on but I don't know what. I have tried adjusting the needle setting, idle screw and fuel mixture srew but it does not seem to help. Slide is put in right and I have full throttle movement. Idle screw is right out and it does not stop high reving. High revs are completly consistant with no ups and downs. I can rev engine higher with throttle but it does not come down. Any advice welcome. Ps all seals are ok.
Matt
 
have you checked for air leaks mate? all gaskets are in good order? and everythings nice and tight?
 
all gaskets good

Hi Lenny. All gaskets are good. Its revs its head off and it does not seem to respond. Carby is brand new! I know bikes but this one has me beat. Do these things have some sort of rev limiter as well? I have stater to cdi to coil. Is there a basic start point that carby's can be tuned to? ie 2.5 turns on fuel mix and so on? How can it rev real high when carby slide is returned to idle?
 
sound like the float aint in it check where your float sit or check your cable dose not have a kink in it to
 
needle could be lost in float as well they have a liltle c clip on them
 
too short of throttle cable
muddy/dirty throttle cable
throttle assembly muddy/dirty or even damaged

slide needle floating around.. it should have a flat washer that sits over it then the slide spring holds that down when assembled..

if you have an air blower on a compressor, with the engine NOT running pop your air cleaner off and blow air thru the holes in the back of the carb.. fuel should blow out everywhere but that is normal.
make sure you are running a fuel filter and then try starting the bike again..
failing those there is nothing else that can do what your describing..

the carb should run and idle no matter where the needle is sitting, but mixture screw needs to be wound out approx 1.5 turns..maybe more on the final tune..
 
Thanks for reply, carby is new,never used. Cable is new, never used. With the idle screw right out it revs high. I have full throttle available to use and it still screams at about 3/4 revs. I will ispect inside carby when reving to see what needle is doing, perhaps coming out and getting stuck? I don't know, I'm nearly ready to give up! I've owned heaps of bikes before, pulled them down, serviced, replace rings pistons but this pit bike is bizarre! Q. why are pit bikes fraught with mechanical faults? This is the 4th pit bike I've owned

Matt
 
Lifan 125 revving High(still)

I have tried everything! How does an engine rev its head off when carby slide is fully down? All seals good. Carby new. Cable new. Cable not stuck. All screws adjusted correctly. Arrgh!
 
So if you have the airfilter off off you can see the slide totally bottoming out and no gap for air to get through? If this is true then if you start it up with the aircleaner off and cover the carb inlet with your hand and it wont affect its revs. I think you've overlooked something, its getting air from somewhere, but that sounds like it'll have to have a massive air leak to run as you've described. The fact that the idle screw is making no effect would suggest the slide isnt bottoming out(cable too short or carb slide installed 180' out or you have mistaken mixture screw for idle screw). If when the slide was installed if the needle wasn't lined up with the main jet it would hold the slide open at about 3/4 throttle. Or disconnect the cable from your throttle, to eliminate the cable length as an issue. Never assume just because a chinese carb is new that its assembled correctly, last one i pulled apart had an upside down float straight from the factory
 
Last edited:
High Revs on startup

Thanks for reply. Carby has slide completly lowered, needle is correctly inserted. Engine will die when hand is placed over opening. I agree it must be drawing air in somewhere. I know what fuel/mix and idle srews are and where located. Could it be a seal in the actual motor, like a 2 stroke? I have taken to a shop as I am completly out of ideas. Will post the answer when fixed!

Matt
 
Lifan 125 revving High(still)

I have tried all and have finally taken it to a mechanic who's the grand age of 18! I'm dying to know what it is. Will post for anyone to refer to for themselves in the future.
 
if ever you are looking for an air leak, start the bike up and spray some carby cleaner over the joins where it meets the manifold, manifold to head, fuel bowl , carby top cap etc etc
if there's a leak it will run differently to the way it was, eg smoother or rougher depending on the problem

sounds like the leak is between the cab and head somehere

craig
 
carby is the fault

Hi all
I had the mechanic ring and he says its as simple as the wrong carby for bike. It is a 22'' mikuni carb off ebay that was advertised as the correct carby for a 125 Lifan, which I'm sure it is. I have not seen the mechanic personally but what do other think? Could this be it for all the presenting probs? I have my doubts.
 
22 inch mikuni is huge, lolz. Seriously though anything from 22 to 26 mm will work well on a 125 IF jetted right. That being said, if its chinese its more likely that the carbs a dud than it being the wrong size, unfortuantley because cheap chinese carbs are just that cheap, there isnt much quality control going on at the factory
 
cheap carby

Ok so a further talk to the mech revealed that the carby was poorly matched to the manifold althogh he was unsure if this resulted in air leak. He will do spray for leaks test. The fact that it does die when hand is placed over shows that air is not being sucked in another way. It seems that carby is in some way faulty, just not sure how. Like you say, poor manufacture. Yes 22 mm!
 
latest on carby

Ok so latest for those still following, carby is for some reason dodgy. mechanice put on another smaller carb and it purrs. What could be possibly wrong with this carby? I'v had a look and compared with another carby the exact same and it all looks good? Well there is the answer to the hardest to fix prob I've ever had, carby was stuffed even though new and never used
 
Could be lots of things, i had a carb i pulled apart atleast a dozen times that just ran like a pig whenever i cracked the throttle, by the end the inside of it was so clean you'd think i'd polished it. Finally realised the o ring that went around the main jet wasn't sealing at all even though it looked perfect, so whenever you tried to rev over 1/4 throttle it was rich as all hell.
 
got the same problem with mine was just wondering if I should get a brand new carb when I start the bike and not pulling the throttle it just high revs all the time
 
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