How can you tell if your running rich or lean?

Dawelny97

New Member
Jan 7, 2020
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Hey all, I have a 53cc 4 stroke huasheng that I got installed. It wouldn't clear my frame with the outer part of the air filter box, so I left the inner part of the airfilter box on (just the side with the bolts exposed) and ziptied the foam on. It works well, but I would assume its running lean since it now has more air flow. When I tried to start it for the first time, it did not want to start at all. Choke or not. It would start if I gave it half throttle when pulling it, but then immediately die. Weirdly enough, turning the fuel screw 3/4 of the way out from seated allows it to start first pull and idle normally. Isn't this leaner? When I tried to make it richer, around 2 turns out, it would stall and die and white smoke would come out of the carb. Is this normal? So I put I put the fuel screw back on 3/4th of the way out and rode it for around 20 miles or so. I take the plug out and this is what it looks like. Am I running rich? lean? I've tried looking at the forums for answer and I couldn't figure this situation out.
IMG_2240.jpg IMG_2239.jpg
 

FOG

Well-Known Member
Mar 3, 2019
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Plug looks good and what you're thinking is a fuel screw is probably an air screw so it's the other way around. Out is more air. Leaner. In is less air. Richer.

Ride On!
 

Dawelny97

New Member
Jan 7, 2020
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On the huasheng carb? But the screw to adjust the air/fuel ratio is closer to the engine than the air intake side of the carb, doesn't that mean its a fuel screw? Im sorry, im new to these small engines and the concept of carburetors. Oh also by the way, when I took the spark plug out it wasn't a plug chop. Its the same plug ive been using since I first got the engine. That doesn't affect the info the plug can give you right?
 

FOG

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Mar 3, 2019
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I'm no expert on Chinese carbs, that's for sure, but, in general, in the idle circuit your fuel comes from a pilot jet. In Japanese carbs that pilot can be tuned with different sizes just like a main jet. Dunno about Chinese.

The fine tune is the tapered air screw. The air typically gets fed from a separate passageway you'll find in the mouth of the carb. Where the designer/engineer put the screw doesn't matter.
 

Dawelny97

New Member
Jan 7, 2020
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I'm no expert on Chinese carbs, that's for sure, but, in general, in the idle circuit your fuel comes from a pilot jet. In Japanese carbs that pilot can be tuned with different sizes just like a main jet. Dunno about Chinese.

The fine tune is the tapered air screw. The air typically gets fed from a separate passageway you'll find in the mouth of the carb. Where the designer/engineer put the screw doesn't matter.
That makes sense. So I made it richer by turning it only 3/4 of the way out which is why it can run now. I read somewhere tho that if you have less than 1 turn or more than 3 on the screw that you need to change the pilot jet. Is this true? Also do you know the correct setting for the screw on the 4 stroke huasheng?
 

FOG

Well-Known Member
Mar 3, 2019
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I read somewhere tho that if you have less than 1 turn or more than 3 on the screw that you need to change the pilot jet. Is this true? Also do you know the correct setting for the screw on the 4 stroke huasheng?
Probably some truth to that but I wouldn't worry about it. I've got 5K miles on a Vintage 360 Yamaha at 7/8 of a turn out and really, the correct setting is where it idles and starts the best.