Jet change

Kman123

Member
Joined
Apr 28, 2018
Messages
64
So I swithched from the nt carb to the hp carb on a bullet train 2 stroke motor. The bike seemed to run faster and at higher rpm with the nt carb. It is 4 stroking a little on the top end. If i put in a leaner jet will the bike get those rpms back and that little extra speed?
 


Lukesky36

Active Member
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Oct 3, 2018
Messages
464
are you full throttle and its 4 stroking at high rpm then it is the main jet. if your quarter throttle putting down the road and it 4 strokes the needle needs too be set more lean
 

Kman123

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Joined
Apr 28, 2018
Messages
64
are you full throttle and its 4 stroking at high rpm then it is the main jet. if your quarter throttle putting down the road and it 4 strokes the needle needs too be set more lean
It is four stroking at high speed. Getting there is no problem. But it seems that the nt carb got lets say 1000 more rpm than the hp carb. If I put in a leaner jet should i get higher rpm out of the hp carb?
 

GreasyChris

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Jan 3, 2019
Messages
683
If its 4 stroking then it's running rich. If you change the jet to a leaner jet the 4 stroking will go and it should rev out more. You will gain more speed because the engine is running more efficiently with the proper mixture. It's a test and tune kind of thing. When I set up my carb I take a screw driver and the jets with me while I'm riding and adjust accordingly until I find the sweet spot. Don't go to lean tho because you risk over heating.
 

Kman123

Member
Joined
Apr 28, 2018
Messages
64
If its 4 stroking then it's running rich. If you change the jet to a leaner jet the 4 stroking will go and it should rev out more. You will gain more speed because the engine is running more efficiently with the proper mixture. It's a test and tune kind of thing. When I set up my carb I take a screw driver and the jets with me while I'm riding and adjust accordingly until I find the sweet spot. Don't go to lean tho because you risk over heating.
Ok so I read that the stock jet is .70 mil so I will start with .69 and down? Thanks.
 

GreasyChris

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Jan 3, 2019
Messages
683
A leaner fuel mixture burns hotter therefore there engine runs hotter. A rich mixture burns cooler and lowers combustion temperature resulting in a cooler running engine.
 

Tyler6357

Active Member
Joined
Sep 28, 2011
Messages
729
Usually these little engines will run leaner after they are warmed up. If it's 4 stroking at top end I would try a smaller jet on the hp carb, maybe #65
 
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