Post by Detasman on Dec 11, 2004 16:57:46 GMT -5
I've got an NP Passport with the 89cc engine. I've made some simple intake & exhaust mods (see my earlier post on this) which have improved performance somewhat, but it was becoming apparent that the limiting factor was now fuel flow. Also, the increased air flow, combined with the larger than originally intended piston, had led to a slightly lean running engine. I considered rejetting the carburetor but opted to adjust the main fuel needle before taking this more invasive measure.
Prior to adjusting the needle I was topping out at about 42mph. I can now get an easy 47mph with higher speeds possible. NOTE: my bike has only 200 miles on the clock. I'm sure my performance will improve even further as the engine fully breaks-in. I did not notice any ill effects on the bike's ability to hold idle or on making a smooth transition from fully closed throttle to fully open. I did note a slight increase in the time it takes to return to idle but nothing to be concerned about. Also, the bike is no longer running lean.
Refer to the Fox50 manual at www.kidatvs.com/50cc.html for instructions on adjusting the main fuel needle. The c-clip was originally adjusted to the 3rd slot from the blunt end of the needle. I moved it to the 4th slot (one slot closer to the pointed end). There are 5 slots in total.
I don't recommend adjusting your main fuel needle unless you've made other modifications as I have, or if you've determined that your engine is running lean. The Fox50 manual also specifies a procedure for determining the lean/rich condition of your air/fuel mix. By the way, I would never want to go any faster on this bike. It was becoming very light.
Here are a few tips if you decide to try this. Again, refer to the Fox50 manual for instructions. Pull the slide assembly straight up out of the top of the carburetor until the entire thing, including the needle, is free. The needle protrudes from the bottom of the slide by about 3/4". You don't want to bend the needle. Once you've removed the throttle cable from the slide assembly, take it to a workbench and have a towel ready to catch the w-shaped retaining clip when you eject it from the slide. You can do this by simply pushing the needle up through the slide. Removing and reinstalling the c-clip onto the needle is a little hard on the fingers but it can be done without too much effort. When reinstalling the w-shaped retaining clip I used a long socket that fit just inside the slide to push the clip down evenly into place. This was the hardest part of the job until I realized a socket was the thing to use. It made the job a snap. When reinserting the slide assembly back into the carburetor make sure it seats completely and that the cap can be reinstalled without compressing the long spring on the throttle cable. You'll need to readjust your mixture and idle screws after making this change.
Good luck.
Prior to adjusting the needle I was topping out at about 42mph. I can now get an easy 47mph with higher speeds possible. NOTE: my bike has only 200 miles on the clock. I'm sure my performance will improve even further as the engine fully breaks-in. I did not notice any ill effects on the bike's ability to hold idle or on making a smooth transition from fully closed throttle to fully open. I did note a slight increase in the time it takes to return to idle but nothing to be concerned about. Also, the bike is no longer running lean.
Refer to the Fox50 manual at www.kidatvs.com/50cc.html for instructions on adjusting the main fuel needle. The c-clip was originally adjusted to the 3rd slot from the blunt end of the needle. I moved it to the 4th slot (one slot closer to the pointed end). There are 5 slots in total.
I don't recommend adjusting your main fuel needle unless you've made other modifications as I have, or if you've determined that your engine is running lean. The Fox50 manual also specifies a procedure for determining the lean/rich condition of your air/fuel mix. By the way, I would never want to go any faster on this bike. It was becoming very light.
Here are a few tips if you decide to try this. Again, refer to the Fox50 manual for instructions. Pull the slide assembly straight up out of the top of the carburetor until the entire thing, including the needle, is free. The needle protrudes from the bottom of the slide by about 3/4". You don't want to bend the needle. Once you've removed the throttle cable from the slide assembly, take it to a workbench and have a towel ready to catch the w-shaped retaining clip when you eject it from the slide. You can do this by simply pushing the needle up through the slide. Removing and reinstalling the c-clip onto the needle is a little hard on the fingers but it can be done without too much effort. When reinstalling the w-shaped retaining clip I used a long socket that fit just inside the slide to push the clip down evenly into place. This was the hardest part of the job until I realized a socket was the thing to use. It made the job a snap. When reinserting the slide assembly back into the carburetor make sure it seats completely and that the cap can be reinstalled without compressing the long spring on the throttle cable. You'll need to readjust your mixture and idle screws after making this change.
Good luck.
