Engine Won't rev

[Ryley]

OK, before anyone asks. Yes I have searched, I have read ALL of the Mikuni PDF, and still can't seem to find an answer. I have exhausted all avenues, it's either you guys can help. or it goes in the skip....and I have a very upset 7 year old

I have a 48cc Zongshen engined mini dirt bike with a 19mm Sheng Wey carb on it. The deal is, it will start easy, will run to about 1/2 throttle, then after that, it just dies out slowly (over about 20 seconds if you keep the throttle on) if you back the throttle off, it goes back to idling fine.

I have cleaned the carb, tried the e-clip in all positions, the plug will be coffee coloured or black depending where the e clip is, and I have replaced the spark plug. It still will not rev past 1/2 throttle... 2 days wasted on this and it's driving me nutso...

Hoepfully someone can point me in the right direction

 

[Sidney]

Fuel could be leaking out somewhere?

 

[daniel40]

sounds like the jetting isn't right.

 

[Ryley]

Fuel could be leaking out somewhere?

it did have a fuel leak, but thats been fixed, had a broken fuel tap on the tank, and needed a new o ring seal on the bowl.. but it still won't bloody rev

 

[Sidney]

If it's one of those chinese 2 stoke bikes. I think it's probably irrepairable man. I have a chinese pocket bike and I've tried everything but it just doesn't want to go with out something breaking.

 

[Ryley]

sounds like the jetting isn't right.

it didn't run when I got it due to a dicky CDI unit, fixed that, but just won't rev. took it to a bike shop, and was told that the chinese bikes without air box's suck in to much air.

I forgot to mention (and it's important) that if you pull the choke on, it revs the whole way, but sounds a bit flat, but it will rev with the choke on...

 

[Ryley]

If it's one of those chinese 2 stoke bikes. I think it's probably irrepairable man. I have a chinese pocket bike and I've tried everything but it just doesn't want to go with out something breaking.

It's a 4 stroke....I HATE 2 strokes.....

 

[tomahawk76]

i dont know much about engines but it could be air/fuel mixture check the air filter isnt blocked with crap. you prob already have though. does it blow any smoke when revved?

 

[Sidney]

That's exactly is what happens with my bike. When the choke is OFF it dies but when it is on it's fine

 

[daniel40]

do you mean like you rev it and it cuts out a dies? that means it could be the jetting or the carby needs tuning.

 

[Ryley]

do you mean like you rev it and it cuts out a dies? that means it could be the jetting or the carby needs tuning.

Basically. it's a flat spot that goes from 1/2 throttle to WOT.

If you turn the throttle slowly, after 1/2 way it just starts to die, and after about 20 seconds it will just die..

BUT, if I leave the choke on, it won't idle (obviously) but it will rev the whole way... I have no way of knowing what jets are supposed to be in it, as I can't find any info on the net about thses carby's

 

[daniel40]

maybe the idle is set to low or somthing? if it is the jet take the carby off take the jet out and it should have what number it is on the jet then take it to like honda or yamaha and they might have the correct part for you i could be wrong but it sounds like the jetting.

 

[Sidney]

Basically. it's a flat spot that goes from 1/2 throttle to WOT.

maybe the idle is set to low or somthing?

The idle speed would have NOTHING to do with that.

 

[Ryley]

maybe the idle is set to low or somthing? if it is the jet take the carby off take the jet out and it should have what number it is on the jet then take it to like honda or yamaha and they might have the correct part for you i could be wrong but it sounds like the jetting.

Considering the guy I got the bike off, I would seriously doubt that it has ever had the jet changed. it still had the original spark plug in it.....

I'm hoping it's something stupid that I've missed.....

 

[dirttau]

try another carby

 

[Ryley]

try another carby

Don't suppose you have one I can try ???

 

[daniel40]

thanks for telling me Sidney guy who knows everything about bikes.

 

[dirttau]

i do have a small carby here not sure if its right one for u

 

[motoluver]

sounds like your spark is braking down? Could be a faulty coil or even the spark plug?

 

[Ryley]

sounds like your spark is braking down? Could be a faulty coil or even the spark plug?

I've had 3 plugs in it now, plug makes no difference at all...

The coil sounds like it might be an option though