Engine ramdomly started to idle high and uneven with clutch in

Evan Frucht

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Oct 23, 2017
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Hey everyone,

I know a couple things about these engines and am somewhat experienced with small engines in general. I have a probem I can't figure out.

I put my bike together about a month ago and have been feeling an increase in power since the first rides (assuming break in). I actually had to lean it out (needle adjustment) one notch recently to get it to idle properly and not die. That was after a long ride when It really warmed up. Anyways it been running very well for a little while now.

I have a custom made expansion chamber on it, bing 14mm moped carburator ( very similar in design to the stock NT but better quality and made in Germany, came off a 60's moped, #65 jet), long intake, and puch 70cc old style hi compression head, among other things. Those are the basic upgrades I've made.

I tried to take it for a ride a few minutes ago but it didn't sound right (it was running fine an hour ago.) I started it in my driveway and pulled the clutch in so I could let her warm up a few min..., this is what I usually do. But this time when I pulled the clutch in the idle was very rough and then quickly got higher and higher. Sounded like an air leak but I've checked thoroughly for those. Funny thing is that it seems to run fine normally with clutch engaged. It's only when you want to stop and idle does it start reving like crazy.

Did my clutch possiby fail? I tried adjusting it thinking it may have come out of adjustment but that's not the case. (When I tightened it slightly it wouldnt release at all.) There is play in the clutch arm when it's out, not sure if that is normal?

I've checked for air leaks in the usual places. I've opened up the carb and sprayed some cleaner through the jet, seems to not be clogged.

Any ideas?
 
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How did you check for air leaks?

It was an air leak... I didn't check thoroughly enough. After all that, HA!
Was going to update the thread.

I had an o-ring sealing the carb to the manifold I made... it got sucked into the engine and (I assume) it's somewhere in the exhaust by now probably in a few pieces.

Just replaced it and it's running good again.
 
any carb that doesn't have a slot for o-ring to sit in tight should never have an o-ring - seen a bunch sucked in and sometimes trash the motor
 
any carb that doesn't have a slot for o-ring to sit in tight should never have an o-ring - seen a bunch sucked in and sometimes trash the motor

What would you recommend I use, instead of the o-ring, to seal the carburetor to the manifold? The fit is nice and secure, but not air tight. The o-ring seems to seal it but it could get inhaled by the motor again.

The original manifold for this carburetor originally used a plastic sleeve type thing on the end.
 
my first thought is get the nt-clone with chinese chars on slide tube, never had to rejet or do anything else with those

second thought is somehow get intake that fits carb onto bike

third would be to apply a coat of solder onto intake and gently sand it down for airtight fit
 
My carb is basically like the NT but just better quality. The mounting clamp is actually much better. Easy to take off and on and when it's tightened its very secure to the manifold. But like many people report with the NT it's manifold connection is not completely airtight.

My home made manifold is probabaly not completely round causing small air leaks. It's very close though and the fit is tight. I would prefer to keep my current carb and intake since they work very well when sealed by the o-ring. I need a better alternative to the oring. I doubt solder will work I tried very hard to get the intake round initially when I made it, I don't think I could get it better with solder. I would need a lathe or something which I don't have.

I'm looking into gasket maker stuff but u don't know if that would be good
 
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My carb is basically like the NT but just better quality. The mounting clamp is actually much better. Easy to take off and on and when it's tightened its very secure to the manifold. But like many people report with the NT it's manifold connection is not completely airtight.

My home made manifold is probabaly not completely round causing small air leaks. It's very close though and the fit is tight. I would prefer to keep my current carb and intake since they work very well when sealed by the o-ring. I need a better alternative to the oring. I doubt solder will work I tried very hard to get the intake round initially when I made it, I don't think I could get it better with solder. I would need a lathe or something which I don't have.

I'm looking into gasket maker stuff but u don't know if that would be good
Personally, I'm successfully using PTFE / Teflon / plumber's tape. Just one or two turns (layers) around the manifold, and just barely overhanging the end of the manifold so that it doesn't obstruct the flow. It likes to be a PITA to position at first; but once it's on, its on.
It seals fine, even makes a great super thin head gasket (0.05mm), and it is very inexpensive.
 
Personally, I'm successfully using PTFE / Teflon / plumber's tape. Just one or two turns (layers) around the manifold, and just barely overhanging the end of the manifold so that it doesn't obstruct the flow. It likes to be a PITA to position at first; but once it's on, its on.
It seals fine, even makes a great super thin head gasket (0.05mm), and it is very inexpensive.
Yea I was just about to type just this too, I've found that often globs of rtv can be substituted with a strip of teflon tape on those nt like setups. They work on Dellorto clones too and basically any carb with an almost airtight seal on the intake. My carbs brass nipple was loose and pulled out with the gas line so it would leak very very very slowly at the connection, a teenie tiny piece of tape made that snug and stopped the leak. Screw in petcocks on gas tanks with the stupid o-ring thing do better with teflon tape too instead in threads.
 
auto parts stores sell the kind that doesn't dissolve in fuel
 
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