2008 Kawisaki KFX 50

[jrbard]

Hello, I really need some help. I recently installed the 100cc big bore kit on the little 50. Im having problems now. Machine runs. Problem is on 3/4 to half throttle. It stumbles when it gets there. Idle is fine. If I slowly take the throttle to 3/4 it is fine, but will eventually start to stumble. The stock main jet was an 85. The stock pilot was a 40. I have gone all the way up to a 120 on the main and nothing changes. I have tried changing the pilot also. I have gone as high as 55. I have also lifted and lowered the needle. I do have an aftermarket cdi which has no rev limit. It also has an aftermarket coil. It also has a k&n air filter. Which I tried removing and reinstalling the stock. No change. I am running the stock exhaust. The head has been ported both intake and exhaust side. I have removed the egr system on the motor as the head did not have it on it. I am beginning to believe that the problem may not be carburetor related. I did not have this problem with the 50cc kit. When I pull the plug out to inspect, It is black in color, but the electrode and arm are whitish. I have checked it at all spectrums of the throttle. Any help or direction that someone could point me in would greatly help. Thank you

[LT80]

My first thought is the stock pipe.

[jrbard]

My first thought is the stock pipe.

Any way to be certain of this. Im gonna get a couple new plugs and try to find out exactly where it is running lean or rich. Pain in the butt just to go faster. lol

[jrbard]

Is it possible that the stock carburetor is unable to keep up with the air requirements of the new 100cc kit.

[LT80]

My thoughts remain the same.
IMO, Any reputable sales person that would sell a 100cc kit for a 50cc mini should know that it needs a carb and a pipe to make it run.
Course, anyone looking to make such a monster change would have/should have studied up and know that they would need a carb and pipe to go with the motor mods.

[mcclelland32]

Is it possible that the stock carburetor is unable to keep up with the air requirements of the new 100cc kit.


Stock carb will work but with that auto choke it is a POS. If you want to keep the stock carb size get a keihin PB19 carb (manual choke) off of ebay for less than $50. Your BBK is not actually a 100cc. It is a 90cc kit, not sure why they call them that but it is not 100cc. The stock carb is the same carb used on the KFX90. 19mm carb but I.D. is 16mm. Stock exhaust will work just fine with the BBK. If you want a monster. This is what worked for my kids quad: Naraku part # NK100.52 (says 100cc but it is 90cc), NCY trans kit part # 1200-1171, Keihin PE20mm carb, Uni filter # 4182ST, naraku 50 to 150 carb conversion tapered flange (http://enviromoto.ecrater.com/p/5507609/naraku-50-to-150cc-carb-conversion-tapered), GY6 150cc OEM intake (correct fit for PE20mm carb to intake manifold, GY6 150cc and 50cc have the same intake manifold bolt pattern, tapered flange helps the transition from the intake to the head, need to plug the vacuum port on the intake). Naraku racing cam part# NK500.02R, Throttle cable for the PE20mm carb, 17t JT front sprocket part # JTF259.17, ooracing 4 pin D/C CDI (wire it as a KFX90 CDI to work). Had PBI make a smaller sprocket but do not remember the teeth count.

Set-up works amazing! Compression will be high so I would use another base or head gasket to help reduce the compression.