Lean condition lml star 125 4t

The original 2-stroke Genuine scooter and its 4-stroke manual and automatic offspring

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Guestmorais56
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Joined: Thu Oct 29, 2020 11:33 pm

Lean condition lml star 125 4t

Post by Guestmorais56 »

I can't find any leak on my lml. I check everything but can't find the leak that causing the lean condition.

Symptoms:
-hard to get engine rev from idle
-back fire while going downhill
-noticeable lost on engine breaking

The motorcycle is on running condition, but with less power.

I test every possible leak between carburettor and the engine, float level, clean carburettor, valve gap adjust, every thing.

I need help...
mjrally
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Location: Oceanside, CA

Post by mjrally »

Have you checked for leaks at the exhaust? What about at the fly side engine seal behind the flywheel? Leaky head? Have you removed any of the head components?

One way you can enrichen it is to pull the choke. It’s not a permanent solution but it will help when you need it.
Guestmorais56
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Post by Guestmorais56 »

Hi,

I check the carb again. I found one suspicious things: the slow jet can be clogged. I can't see light through the channel. But if I blow the air passes. I try to clean but unsuccessful. I try stick wire inside but locks like it narrow inside.

It is possible the slow jet is messing with fuel ratio?
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Keihin PB18 diagram
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mjrally
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Joined: Fri Feb 03, 2012 2:27 am
Location: Oceanside, CA

Post by mjrally »

Find a small electric guitar string and poke out the jets.

Have you messed with the needle height?

Last question, did you try riding and pulling out the choke? Did that make things better or worse?
Guestmorais56
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Post by Guestmorais56 »

I check float level, and set the needle height to the 3rd grove, like manufacture recommended. Before was on 2nd. The motorcycle run ok without choke, but if I applied it runs worst. I set the air fuel ration to make it more rich, so the engine wont overheat. In the past, the oil became to hot, and the clutch split.

I try many mechanics last years and no one could fixit right. The motorcycle never run perfect. It run perfect before, like two months after buying.

So this time I will try my best. I wasted too much money on this mechanics.

The motorcycle doesn't respond immediately to throttle on idle. And if I push it fast the engine stalls. So I have to use the throttle gently.
mjrally
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Location: Oceanside, CA

Post by mjrally »

Do you have the air filter installed, the snorkel and everything sealed up tight on the carburetor? Some systems require it in order to run right.

That was good you raised the clip to the third groove. Raising the clip leans out the 1/4- 3/4 throttle. You can try going to the 4th clip up and see if that helps revs.

The fact that the scooter runs worse with the choke on means its too rich. Not lean like you say.

Dont mess with the air/ fuel screw as that only affects starting, idle and the first 1/4 throttle. Put it back to where its supposed to be as you could be making it worse. Usually 1/8-1/4 turn either way from factory standards are all you need. If you need more, your carburetor has problems (could need a better clean/ leak/ problem)

Oil getting hot and clutch splitting have nothing to do with the carburetor/ jetting. Oil getting hot should be cooled by heat dissipation from the flywheel fan and the oil sump. The clutch splitting is a problem with the clutch basket/ wrong springs/ mechanical defect.
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srbbnd
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Post by srbbnd »

Drain tubes top and bottom might be clogged a bit as well.
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Guestmorais56
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Post by Guestmorais56 »

I think the clogged pilot jet was the problem. I cleaned with a guitar string, and was very hard. The engine sounds a lot nicer and the exhaust gas smell different in a good way. Throttle response is not perfect but very much better than before. I find much more easy to setup the air/fuel screw. Before I unscrew it as many turns I can and the rpm doesn't drop much (more vague).

I didn't test drive because today is very stormy. But high hopes.

I have the air filter installed and the tubes connect to the air box are ok. There is pollution regulations systems on this motorcycle, like a EGR type system and a PCV type system, all linked to the air box. One more question, there is one more vent tube on the end of the engine resting down. What is the function of this one, since there is another vent directly connect to the air box?
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