OK, it's a nice day and I decide to work on my '78 and '80 NC50's. They've been sitting for about 6 months while we played with our new toys - CT 90's and CT 110's. Anyway back to the problem. The '78 had a cracked carb bowl that I temporarily JB welded until I found a new one. I got a new bowl but since it wasn't leaking I never replaced it. Well today I decided to replace it and that's where the trouble started.
When I took off the old bowl I decided to clean the main and idle jets and check the float. I pulled out the jets (mine are removable) cleaned them with carb cleaner, put them back in and put everything back together. Now when I start the NC, it idles for a few seconds then starts increasing RPM's until it's racing at full throttle. The throttle piston moves up and down correctly but has no effect on the engine speed. It acts like it has a vacuum leak, like it's pulling air from somewhere other than through the throttle body, but if I put my hand over the intake it'll die so that can't be the case. Also, when I put my hand over the intake, it causes gas to come out of the carb into my hand.
I tried putting the old bowl back on thinking that was the problem, but the same thing happened. I've had the carb on and off probably 50 times looking for a problem and can't see anything obvious. I was even going to change carbs but the other two I have do not have the same size throttle cable screw.
Only thing I can think of is that maybe the rubber
o-ring on the main jet is deteriorated and is allowing fuel/air to bypass the throttle needle - it is a bit loose. The other two carbs do not have removable jets or I would try one of those. Anyway before I go any further I thought I'd ask if anyone has seen this problem. Thanks
Posted on Sep 27, 2005, 4:33 PM from IP address 69.230.193.119
