Help: My Lifan 150 is being an *******.

[EnFlaNEd]

My Lifan 150 will only run on full choke. It idle speed hunts ie it randomly revs faster and slower. It hisses (backfires) out of the carburettor a lot, this usually results in the engine stalling. It dies as soon as the choke is off and on the rare occasion I manage to keep it running with the choke off I have to give it a lot of throttle and it will surge cutout surge bunny hop etc all over the shop, I just end up doing mono bunny hops until it stalls. After trying to run it with out the choke off it will not start again at all for some time, regardless of putting the choke back on.

Things I have tried so far

-Valve clearance, .08in .1ex mm
-plug gap 0.7mm
-silicone gasket the inlet manifold joints
-replaced carburetor with "mikuni" clone
-cleaned out the carburetor.
-Fresh fuel.
-New coil
-checked timing
-Re-torqued head.

I have tried spraying start ya bastard around various locations trying to find an air leak but its just not consistant, I cant rule out that its just feeding back though the carb. Soapy water bubbles but only on the head gasket near the exhaust but kind looked like it was just boiling from the heat.

I have run out of ideas. Please help. I am a bit of a noob at bikes so my appologies if this is a common problem/question.

 

[zwebx]

Check float level height, New cdi or only coil?

Inspect intake manifold gasket for straightness on a tile or something you know is flat.

 

[my67xr]

get an new Pilot Jet for it, a #20 will help it, but may need a #22.5, they are $5 each from DHZ

are you running a lightly oiled foam filter ?

have you set the idle mixtures yet ?

 

[my67xr]

what size carby is on it ?
is the plug new? and is it a genuine NGK C7HSA ?
have you checked the earths? especially for the frame ,and the ignition coil

 

[EnFlaNEd]

I only replaced the coil, as the lead on the old coil had melted from the exhaust.

Im pretty sure the carb is one of these.

NEW Mikuni 30mm Racing Carburetor KIT 140cc 150cc Lifan | eBay

I replaced it a couple of years ago but the bike has probably done less than 1hr work since then.

It has a lightly oiled k&n filter but I have been trying to get it running with no air filter attached.

I wound both the the verticle screw under neath on the manifold side in and the one on the side clockwise a fair way as that was the only way I could get it to idle at all.

It has never really run 100%, mostly idle problems, it has always stalled so easily and it has always chugged out of the carburettor. But the last time I used it, it still ran quite well.

Ill have to check the plug, I dont think its that old. I gave it a clean as it was fouled up a bit. Ill report back after Ive seen what it is, I just cant remember.

 

[EnFlaNEd]

Well don't I feel like an idiot. Went to have a look at the plug and thought I would give the carb another look over and low and behold, the pilot jet was totally blocked :hache:

So now it runs and idles! I need to do an oil change before taking it for a ride tomorrow but it does seem like it starves if I quickly snap full throttle. The needle is on the second from bottom notch so Ill move it to the lowest tomorrow and see how that goes. If its still leaning out at open throttle does that mean next size up main jet?

Cheers for all the suggestions my67xr. Oh and it does have the plug you mentioned

 

[EnFlaNEd]

and on trying to find some info for the carb I ended up getting it from east50s, not ebay as I thought. So really I cant remember what it is other than its a mikuni and has japan written on it. Maybe the standard pitpro150xr carb?

 

[my67xr]

so are you in SA ? if so take the Pilot jet to Show and Go motorcycles on brighton rd, somerton park, they'll have a bigger one there, about $12

moving the clip on the needle wont help the hesitation, that controls the amount of fuel let into the carby between 1/2 and 34/ throttle
a bigger Pilot Jet will definately help, get at least a #20 for it.

to set the mixture, run the bike for 5 mins to warm it up
then turn the screw in that is central to the carby body about 3/4 turn.
this will raise the idle speed.
now adjust the mixture screw underneath in or out, you want to find the point where the engine runs that the highest/smoothest rpms
adjust it 1/4 turn at a time, then let it run for a bit and settle.
then adjust it another 1/4 turn.
once you have it pretty close adjust it a 1/8 turn at a time to fine tune it.
let it settle for 10 seconds or so, then you can turn the central idle speed screw back out to give it a good idle speed.
somewhere between 1000-1200 rpms.

then take it for a ride and see how it goes then


most pitbike carbys need the filter fitted when running/riding tuning etc, otherwise they will run quite rich

 

[EnFlaNEd]

Awesome thanks for the info man! Yeah I'm in SA

 

[my67xr]

what area are you from?
i could drill it out to a #20 for you if you want ?

 

[EnFlaNEd]

what area are you from?
i could drill it out to a #20 for you if you want ?

Im up towards inglewood, bit past TTG. Do you know size bit it needs? I have a collection of tiny drill bits from my motorised pushy tuning days

 

[my67xr]

it's a .35mm or .4mm bit from memory, use them in a pin drill

ring MR Motorcycles at St Agnes, they might have jets, or know where to get them from out your way

they use Mikuni VM28 Pilot Jets

 

[EnFlaNEd]

Thanks for in the info.

I changed the oil and stuck the air filter back on today and took it for a decent ride. Seems pretty good now once it had warmed up. Didn't bog down at all really.