Performance carb woes

[herbilious]

Hi, I just bought this carb (https://www.amazon.com/gp/product/B07JWFTKHN/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 ) in hopes of improving performance further. I already have an expansion chamber and high compression head, so this seemed like the next best upgrade. After installing it, the bike would run super lean, it had a high idle even when the screw was all the way out, and it would take a long time before it would return to idle from revving. It had a worse low end than the stock carb did but didn't seem too terrible in the mid to high end, but I didn't feel a performance boost. (I checked for air leaks and I'm pretty sure it's not that). I upped the jet to 80, and that solved the high idle and long return times but it didn't end my issues. On any larger jets I tried (80, 85) the bike would be about the same as the stock carb at the low end, but my top speed would be like 10 mph less than before, and the engine would stop accelerating way earlier along with having a lot less mid power and torque. I'm pretty sure this is a lack of fuel, but I have no larger jets. I checked my fuel line and it's straight, always pointing down into the carb, and I removed the out of tank fuel filter to see if it was the problem but it wasn't. Any ideas?

 

[FNTPuck]

That's a dellorto clone so should be a pretty easy to tune carb. Sounds like a vacuum leak to me. Check the plastic insert inside the carb intake flange for cracks. I can pretty much promise you that an 80 jet on that carb will not be lean but crazy rich.

Hanging idle is usually from air leaking in at the carb/intake flange. The 80 main is way too big for a small carb that size, so when it falls on its face it is from being rich, not lean. If I had to guess, I would start with a 70 jet and work down from there AFTER verifying no air leaks (let it idle and spray carb cleaner around the carb and intake flange for RPM changes. Do it on a cold engine for less chance of igniting anything on the exhaust.). If none are found around the carb/intake area, pull the magneto side cover and check the crank seal to see if it pushed out and is leaking from there since that can be a vacuum leak too.

 

[herbilious]

That's a dellorto clone so should be a pretty easy to tune carb. Sounds like a vacuum leak to me. Check the plastic insert inside the carb intake flange for cracks. I can pretty much promise you that an 80 jet on that carb will not be lean but crazy rich.

Hanging idle is usually from air leaking in at the carb/intake flange. The 80 main is way too big for a small carb that size, so when it falls on its face it is from being rich, not lean. If I had to guess, I would start with a 70 jet and work down from there AFTER verifying no air leaks (let it idle and spray carb cleaner around the carb and intake flange for RPM changes. Do it on a cold engine for less chance of igniting anything on the exhaust.). If none are found around the carb/intake area, pull the magneto side cover and check the crank seal to see if it pushed out and is leaking from there since that can be a vacuum leak too.

There are no cracks, but I noticed the plastic bit between the clamp doesnt go onto the intake all the way. Theres a bit of a gap. Could this be causing the issue?

 

[gary55]

There are no cracks, but I noticed the plastic bit between the clamp doesnt go onto the intake all the way. Theres a bit of a gap. Could this be causing the issue?View attachment 87928

why won't it go all the way on? Is it a simple matter of trimming it so it will?

 

[herbilious]

why won't it go all the way on? Is it a simple matter of trimming it so it will?

The air filter would not be able to clear the frame without dremeling part of the intake off. It will not go further because the bend in the intake prevents it.

Yes, Iv read about this issue online. Rubber O Ring will do or some plumbers tape. Overtightening does work short term but results in premature failure.

Thank you, I will try to find an O-ring that fits.