Bike dies at WOT.

cobrapowered1

cobrapowered1

New Member
Just got a new NT carb. I have a RAW 66cc engine with expansion pipe, match ports on exaust and intake, velocity stack , performance ufo type filter and boost bottle. The issue is that it runs best with needle clip at the richest setting but engine will die at WOT. If I back off a bit (3/4 throttle) it comes back to life. The plug is quite white on the lean side. Can the jet be too small for the slightly larger diameter carb ( vs old nt ) allowing more air and less fuel with my engine setup ? I live in North Carolina and I am a bit up in elevation and thought I'd have to deal with running rich but in this case I feel like I am starving for fuel at top end ??? Feedback anyone. Thanks.
 
Yes. No air leaks. Manifold gasket fresh and snug and carb to intake manifold I wrapped with electric tape as a unit. Held it together with a hose clamp of course.
 

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This was just discussed on another thread... The tip of the primer button was actually touching the float inside the carb & keeping it from filling the float bowl completely.
He cut 1/16" fron the tip of the primer button & it solved the problem!!!
 
and bent the tabs ofc lol

but my prob was a result of my carb being canted slightly, with the primer pin on the low side. I dunno if this would be your problem - yet checking the float level is a good idea as yours has about the same symptoms...

I hope it's as easy as that :D
 
Checked inside float bowl and all is good. Removed the e-tube to blow out it out along with the main jet, even seperated main jet from e-tube to make sure all was clean. Assembled carb and ran it. Same S**t. The clip is at the richest setting and even put a small washer in between e-tube and threading point on the carb to off set it even richer and I still get a light plug. I also die at WOT. It just backs off totally and kicks back in if I go 3/4 throttle. I'm thinking drilling out main jet to next size up . Feed Back from anyone.?
 
It races like **** on the leanest setting and continues to taper off ( still racing ) coming down every notch. The richest is best. When I shimmed the e-tube with a small washer it did not run as well. I think I found the problem. Magneto side oil seal seams to be leaking. Not very easy to determine given the fact that The copper header pieces leak a bit of oil on start up til the exaust heats up, then it burns it. With the cover removed there is not a great trail of oil around the casing but there is a little bit. On the outside, the lower mating area was clearly soaked with oil. On the other side of engine, Oil seal has clearly bubbled up hot on the outer part of seal but no trace of oil. Compresion may be compromised. I may have gotten to happy with higher RPM experimenting with the expansion chamber and header length to early. It was really crankin' out. Sounded like real moped at high RPM's. I have topped it at 37.7 (flat ground) on the Schwinn speedometer properly calibrated with wheel size with a 44 tooth stock sprocket with the older NT carb. The bike is quite light and I way a buck 65 ( 165 at 5-10). I have no internal modifications yet but know for sure this bike can take us past the 40 mark. I live in the mountains and it is all hills and few straights. I am setting up this particular bike for climbing at a good speed and maintaining power without blowing up. I may consider dropping some teeth on a maybe 40 or 41 toother later after I clean up the casting materials of the ports up a bit and trim piston skirt after slightly widening intake and exaust ports . No hack saw chopping on the sleeves for the transfer ports. They will be cleaned up and shinned up a bit using long dremel shank. There is always the option on not full gassing it if it is revving high enough before the little big bang.

Having a blast with these things. These bikes sure set my soul free when riding. People break necks ( check u out ) and ask questions at every light. Thanks guys for support. Nice bike builds on your website Venice Boy. Mike G.
 
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Thanks Bike Joe. I will try changing jet size modifying jet off the older NT carb when I receive the pin vise and micro bit set I am waiting on. Still curious about getting it running soon but if you read the thread before this one I wrote what issues are really at hand. I may have to replace seals on engine it seems. I will still experiment with jetting and carefully monitor engine plug and performance if I do get it running in the right zone. Heck, the motors are not impossible to replace. We are having fun here bulding a little race motor that doesn't require a fortune to customize. Good fun. Love passing 50 cc scooters out here. There's a hand full of them. Gives me a big Colgate smile ! These guys are like WTF ! LOL.
 
Hey Cobra, I have a very similar setup to yours and had the exact same problem after fitting my velocity stack and UFO style filter. I have a skyhawk 66cc with new style NT carb,jack shaft, boost bottle, billet high comp head and expansion chamber.
After some running around to various places trying to get different jets yesterday I became impatient and decided to just try drilling out my jet. I used a 1mm ( 0.03937") drill bit and just wound it through slowly with my fingers using a kind of back and forth twizzling motion. Just took her for a spin then with the e-clip on the second from bottom notch and it is running absolutely spot on perfect! Slightly rich just off idle but otherwise running awesomely. Ive picked up a lot of accelaration and the weird jolty spot I had around 45kmh is complete gone. Hopefully now I'll be able to beat my PB speed of 62kmh.
Hopefully this is of some help to you mate.
 
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