engine races full throttle all the time

[BrokenBONEZ]

I just bought and installed a 48cc engine on my bike. I finished the intallation at work and took it home last night with everything seemingly working good. But when I went to show my kids, the engine only raced full throttle. I can move the throttle on the handlebar and hear things moving inside the carb but it makes no difference. I can move the idle screw from one extreme to the other with no difference. just full tilt.

I watched youtube videos on how to adjust these with the throttle cable so I did exactly what they said but it changed nothing. I put duct tape around the expansion slots on the carburetor mounting flange to seal any air leaks but it made no difference.

any ideas why this would be?

 

[Venice Motor Bikes]

Sounds like you might have installed the carb slider upside down, or a possible air leak somewhere.

Also... if you tighten the top cap of the carb too tight, it can warp the carb body & cause the slider to stick at full throttle.

 

[Slogger]

Assuming an NT (standard CG) carb, the throttle slide has a slit up one side, the carb body has a little nub in the side that has to run in the slide slit.
All this sounds almost R Rated.. hahaha
It always jams up if this isn't assembled right. When its right it just freely drops down the throat with no sticking.
The top cap has to be snug but not too tight as Venice Motor Bikes pointed out above.
I just get it finger tight then give it a hair more with the pliers to keep it from loosening up from the vibes.
The spring above the slide is the throttle return spring, it has to be in there or it won't close. (Idle)
Good luck to ya.

 

[crassius]

if carb is closing, then it is getting air from someplace else

take off carb and watch to see that slide goes all the way down - if so, it is an air leak causing it

note that steel intakes often have a bit of chrome at the end that needs to be filed down for proper fit of carb

 

[BrokenBONEZ]

Assuming an NT (standard CG) carb, the throttle slide has a slit up one side, the carb body has a little nub in the side that has to run in the slide slit.
All this sounds almost R Rated.. hahaha
It always jams up if this isn't assembled right. When its right it just freely drops down the throat with no sticking.
The top cap has to be snug but not too tight as Venice Motor Bikes pointed out above.
I just get it finger tight then give it a hair more with the pliers to keep it from loosening up from the vibes.
The spring above the slide is the throttle return spring, it has to be in there or it won't close. (Idle)
Good luck to ya.

Thanks for all the replies. I'll take the throttle body thing off tonight. I know I assembled it correctly because I was watching the video on how to do it as I was doing it. Maybe something stuck open. I did have a hard time getting the wire over the throttle slide. A co-worker suggested removing the air filter assembly and just trying to move the throttle to see if it ever closes. I may have over-tightened that nut on the top too. Lots of things to look for. At least this makes me more confident it can be resolved fairly easily.

thanks again

 

[Slogger]

One other thing that can cause it to be sticky- the cable can't be tied down to the frame with too sharp of bends, or it might have even gotten kinked.
If all else fails cut all the tie wraps that might have it in a bind and try it.
Good luck!

 

[BrokenBONEZ]

Thank you guys! I figured it out. There was interference in the plastic kill switch housing that wasn't allowing the throttle to move all the way forward to the idle position. So the throttle was actually limited in it's range from about 75% open to 100% open. When I loosened the bolts holding the two housing halves together, I heard the throttle snap forward and I looked and sure enough, the slider in the carb had moved down all of the way. I tightened the bolts again and the throttle was hard to turn. once it reached a certain point it would not pivot forward again.

So I took my dremel and removed some of the white nylon that holds the cable to the throttle and some of the plastic in the kill switch housing. Now it moves through its entire range of motion and the bike is running great.

Newbie problem.