Idle and low throttle issues after installing NIBBI PE19FL on 80/100cc 2-stroke bicycle engine

[lumpenbike]

Hello everyone,
I have a standard Chinese 2-stroke 80/100cc bicycle engine. I recently installed a NIBBI PE19FL carburetor with a tuned air filter and fresh fuel mix (1:45 oil ratio).

The issue:
-The engine cannot hold idle unless I slightly open the throttle.

-At low throttle it hesitates and “four-strokes”.

-At ~50% throttle and up it suddenly runs great.

-When I snap the throttle closed, the engine stalls.

-Sometimes I get backfire through the carb.

-Air screw is ~2.5–3 turns out. Turning it in makes the engine richer and it dies → so idle seems too rich.

-I tried pilot jets #35 and #30, neither makes a meaningful difference.

Do you have any idea what is causing these problems? Is it the setting, the carburetor is too big, or something else?
Thanks in advance.

 

[Venice Motor Bikes]

Backfiring usually means you don't have enough fuel.
Theres a youtube video where the guy modifies one of these carbs by drilling it for better low speed performance

Also... too much oil in the mix will cause a lean condition... try 32:1 instead

 

[Wevil Kenevil]

Hello everyone,
I have a standard Chinese 2-stroke 80/100cc bicycle engine. I recently installed a NIBBI PE19FL carburetor with a tuned air filter and fresh fuel mix (1:45 oil ratio).

The issue:
-The engine cannot hold idle unless I slightly open the throttle.

-At low throttle it hesitates and “four-strokes”.

-At ~50% throttle and up it suddenly runs great.

-When I snap the throttle closed, the engine stalls.

-Sometimes I get backfire through the carb.

-Air screw is ~2.5–3 turns out. Turning it in makes the engine richer and it dies → so idle seems too rich.

-I tried pilot jets #35 and #30, neither makes a meaningful difference.

Do you have any idea what is causing these problems? Is it the setting, the carburetor is too big, or something else?
Thanks in advance.

You say tuned air filter? tuned to the carb? And aren't you supposed to start nibi carbs at 1 1/2 to 1 3/4 turns out on both the idle and low jet screws?

 

[lumpenbike]

You say tuned air filter? tuned to the carb? And aren't you supposed to start nibi carbs at 1 1/2 to 1 3/4 turns out on both the idle and low jet screws?

I've tried all sorts of positions on the air and idle screw. The only way I can get it to hold any idle is with the idle screw all the way in. The air screw makes almost no difference in all positions. I'm already suspecting a bad crankshaft oil seal, but that doesn't explain why it's worse when the engine warms up.

 

[Wevil Kenevil]

Re jet the carb and do a thorough air leak check. Check the top of the float bowl to make sure that it is flat and sealable because a lot of them aren't even though they look like it so deck the top of the bowl and check your reed valve. And start in the middle of the carburetor throttle pin with the c-clip.... It sounds pre oil seal to me. I don't think your oil seals would affect your carburetor it would affect the compression but I don't think it would affect the carburetor.