Performance Carb Jetting

Sully10101

New Member
Joined
Jul 20, 2018
Messages
24
I bought an HP Performance carburetor for my 2-stroke motorized bicycle to replace my NT carburetor. As of right now, my NT carb blows the performance carb out of the water. I'm guessing a jet issue? It cranks right up but, lacks power, torque and top speed. Anybody have ideas about what jets I can try or even a range of them? Would it be the Main jet AND the Pilot jet since it has no power from the get go? I'm also at sea level because I know that elevation plays a role in jetting air to gas ratio.
 


crassius

Well-Known Member
Joined
Jul 23, 2012
Messages
4,575
NT-style usually works best on these if other big mods have not been done to motor
 

rwaterman00

Member
Joined
Jul 7, 2018
Messages
71
I would take off the air filter to start with( that air filter pictured above is a piece of crap and most likely is restricting flow )( put a piece of ladies nylons over the intake and secure with a ladies hair tie). is it running lean? does it 4 stroke when you ride? if its not 4 stroking at all its too lean. I use a set of finger drills for drilling jets to the proper size. if its too rich I decide what drill bit is the same size as it currently is and then solder the jet shut and redrill it one size smaller or the opposite if its lean. if it is not responsive from the start that's your pilot jet and or needle settings most likely. I would start by setting it up running as rich as your carb will allow from factory in respect to needle settings and see how that works. move the needle leaner till you are 4 stroking only when letting off the throttle. if it still is lean after adjusting the needle drill out that jet one size. I like my bike to run a tad rich . its better for the motor and will have more power then when running lean. if its a tad rich as your motor gets hot it will run better .
 
Last edited:

Sully10101

New Member
Joined
Jul 20, 2018
Messages
24
Greatest formation rwaterman00! Crassius' answer also make sense. I was just trying to get the performance carb to work since I already bought it. The first one I bought was a knock off so I wasn't surprised when I didn't get the performance I was expecting but, the second one I bought from bikeberry so I was trying to get it tuned up to run with my bike.
 

gary55

Well-Known Member
Joined
Nov 27, 2012
Messages
3,947
The Bikeberry one is a knock off as well. If you want a real one you can get them from Dellorto Direct, but they are pricey. I think the biggest in the SHA line is 16/16. I have one and it works great. It should for nearly 100 bucks. These guys are right though it's hard to beat the Stock NT unless your trying to soup up the beast. Their are a few companies making the Dellorto clones and all I have seen needed to be jetted down more than the NT.
 

crassius

Well-Known Member
Joined
Jul 23, 2012
Messages
4,575
typically, a performance carb will perform better if you motor is modded such that it flows more air than the NT can handle - for the standard amount of air flow, what is it that you would expect the performance carb to do - once you have a 15:1 mix for the flow you have, changing that ratio just drops you off peak
 

rwaterman00

Member
Joined
Jul 7, 2018
Messages
71
do you have the improved 40mm intake size ? if so try to port match your intake manifold to match your jug intake( depending what intake yoyu have the hole on the intake is significantly smaller the the motor opening . use a Dremel (you can get one at harbor freight for 20 dollars) and there are videos on how to do it on youtube. this will allow for more flow into the motor and along w adjusting your carb properly may improve performance. lol its rarely as easy as strapping on a new carb and seeing some magical results. a bigger carb wont help if the intake cant have more air pushed through the opening.
 

gary55

Well-Known Member
Joined
Nov 27, 2012
Messages
3,947
I think he means cast vs. steel, and at the carb. end. Most of the 40mm intakes are now cast and only 14.5 mm ID while the older 40mm steel and 32mm steel are 16mm ID and the 32mm cast are 13.6mm ID.
 
Top