A couple carb adjustment questions

Joast

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I am trying to adjust my new Bofeng carb on my Schwinn with a 66/80, but I am not quite sure if it needs much tuning. Below is a plug pic after full throttle.
It seems to be four stroking just a bit at mid and high rpm, but not near as bad as with my original carb. Top speed is now just a little over 28 mph on gps with a 44-tooth rear sprocket. The only non-stock part is an expansion chamber exhaust pipe. The air filter foam is out for now.
I had a couple of questions:
1. Does the idle adjustment screw setting affect how rich or lean the mixture is when the throttle is partially or fully open?

My elevation level here is about 500 feet, and the throttle needle is still set in the middle position.
I still have the stock jet in --a 70 I think.
2) Does the needle setting and jet size sound about right looking at the plug?
I also have a 68 and 65 jet if needed.
Thanks for any info. John
 

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DieselTech

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I am trying to adjust my new Bofeng carb on my Schwinn with a 66/80, but I am not quite sure if it needs much tuning. Below is a plug pic after full throttle.
It seems to be four stroking just a bit at mid and high rpm, but not near as bad as with my original carb. Top speed is now just a little over 28 mph on gps with a 44-tooth rear sprocket. The only non-stock part is an expansion chamber exhaust pipe. The air filter foam is out for now.
I had a couple of questions:
1. Does the idle adjustment screw setting affect how rich or lean the mixture is when the throttle is partially or fully open?

My elevation level here is about 500 feet, and the throttle needle is still set in the middle position.
I still have the stock jet in --a 70 I think.
2) Does the needle setting and jet size sound about right looking at the plug?
I also have a 68 and 65 jet I needed.
Thanks for any info. John
I'm thinking leave the 70 jet, install new foam in the air filter & drop needle setting by 1 or raise your e-clip by 1.
 

Joast

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Thanks for the suggestions. So raising the clip a notch would lean the mixture slightly?
Is that affected one way or another by further adjustment to the idle speed screw? John
 

Chainlube

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Thanks for the suggestions. So raising the clip a notch would lean the mixture slightly?
Is that affected one way or another by further adjustment to the idle speed screw? John
It doesn't affect the idle screw. The needle clip position only affects off idle to a bit less that 3/4 throttle then it's all jet after that.
When you took the picture of the plug, was that after a sustained full throttle, like more than 3 minutes?
 

Joast

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When you took the picture of the plug, was that after a sustained full throttle, like more than 3 minutes?
No. It was just a shorter burst-- maybe 1 minute or even a little less (then I hit the kill switch). I don't run it wide open too long.
The plug was not brand new--I used it probably 30 miles or so with my old carb. It was alot darker then.
 

Chainlube

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No. It was just a shorter burst-- maybe 1 minute or even a little less (then I hit the kill switch). I don't run it wide open too long.
The plug was not brand new--I used it probably 30 miles or so with my old carb. It was alot darker then.
It looks good for the way you ride. Carry on.
 
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