Carb Jetting, Racing style carb.

[skywalker73]

Hello, I just purchased on of those cheap "racing style" carbs that came with several jets ranging from 65-80. I installed the carb, and it seemed to run slower than the stock carb. I took the jet out, and it did not have any markings as to what size it is. I have a 66cc engine with a 6cc, CNC head. Anyone running a similar setup, and what jet size do you use.

 

[MotorBicycleRacing]

Stock jet is a 70 which is too rich.
best bet is the 66

 

[skywalker73]

The seller just contacted me and stated the stock jet in the Carb I just bought was a 78. It just seems lean to me. What altitude are you at MotorBicycleRacing?

 

[MotorBicycleRacing]

The seller just contacted me and stated the stock jet in the Carb I just bought was a 78. It just seems lean to me. What altitude are you at MotorBicycleRacing?

Who is the seller?

The jet is a 70, I measure them with jet drill bits.
I am in Socal at sea level.

 

[skywalker73]

Who is the seller?
JNMotors?

The jet is a 70, I measure them with jet drill bits.
I am in Socal at sea level.

The seller was Bicycle_motor_works. I am on the East Coast, a bit above sea level around 300ft.
I installed the carb, the higher compression head and the bike seemed slower than the stock head and NT carb. There shouldn't be any vacuum leaks. It just smelled lean to me, and didn't smoke as much.
I will check and see what the jet was in the stock carb.

 

[MotorBicycleRacing]

It is a 70 jet but just put the 65 in.

Your bike is running slower because it's too rich as in the 70 jet hole is larger than a 65.

What pipe do you have on your bike?

 

[skywalker73]

It is a 70 jet but just put the 65 in.

Your bike is running slower because it's too rich as in the 70 jet hole is larger than a 65.

What pipe do you have on your bike?

I was running it with the stock pipe, but I just installed one of those Speed Demon pipes with the little expansion chamber and the muffler on the tip. I have not run it since I switched the pipe.
I will put that smaller jet it and give it a run. Do you think that pipe will have much effect on the jetting? The little expansion chamber doesn't look like it will do much.

I built this this bike last year, and have a couple hundred miles on it. It ran pretty good stock, I probably should have just left it alone! Lol

 

[skywalker73]

 

[skywalker73]

I installed the 65 jet. It runs a lot better. The pipe sounds pretty good too! I checked the plug and it looks a little fat. I have a 60 jet, so I will try it. I really like that carb, it is much smoother than the NT and the choke works much better. Thanks for your help.