85 125m driving me nuts...

[kb0nly]

Working on this trike for a friend and its driving me nuts. It starts and runs smooth as can be great idle and no problem there but it just randomly revs up on its own. Not even touching the thing it will just decide to rev. Also if you tap the throttle it revs smooth but hangs a few seconds returning to idle.

New plug, New fuel lines and filter, New carb, New cables, there is no reason for it. Took off air tube to airbox and verified slide is down and it drops down. Checked needle its not floating. Brand new carb that wasn't exposed to any crap but I did open it up just to be sure. It burns a little oil after sitting a day or two figure a leakdown of oil from valve or gasket when sitting but not a big deal.

Only thing I can figure after hours of tweaking is its an air leak. And the only place I could think of would be the intake tube gasket to the head and insulator at the carb. Other than those two gaskets any other suggestions?

About to light it on fire and walk away.

[86T3]

is your throttle cable routed properly and not sticking? If it isn't routed right sometimes they tighten up when you turn the handle bars, which makes it rev up.

[kb0nly]

New cable routed correctly... As I said it revs up without anyone even touching it. In other words it was idling nicely and I was about ten feet away and it starts reving up all on its own. I even disconnected the throttle cable from the handlebar control the cable is slack the slide is down I can look in from the back of the carb when it revs and the slide is still down. so thinking air leak but only place that could be is on intake pipe.

[kb0nly]

Fixed...

Stopped by the local NAPA and got some gasket material, tore off the carb and made gaskets for both ends of the intake pipe and put it back on, cracked right off idles great and revs and drops smooth as can be now. So i was just a darn air leak.

[Jon Boy]

my 125 does this also, not sure why though. haven't found any air leaks. it has always had a lope to it since i got it, but it has gotten less and less over the last couple years. it's not a high rev type of lope, more like a high idle, then it'll drop to the point where it just about wants to die. to me it's almost as if the choke is going in and out if you get my meaning. it would be nice to get it figured out.

[kb0nly]

The old carb on this one did that, after i replaced the carb i got the random self revving which makes sense now because they gaskets failed after replacing the carburetor.

It runs smoother than silk now.

[tri again]

I had a trail 90 doing the same thing.

The 'w' clip that holds the main needle down inside the slide had flipped over
so the main needle would settle wherever it wanted.

idle perfect and die.
idle perfect and rev up?

lower the idle and it would die, raise the idle and it would slowly
rev up too high after a minute or so.

[Jason125m]

For future reference, if you ever have a high rev problem, take carb cleaner, wd 40, or anything, and spray it around between the motor and the carb... if any change in idle you have an airleak.

[kb0nly]

Oh i know all about spraying around for air leaks, but i tried that an no changes whatsoever.

I think it was only showing up on days when it was cold and it would leak, but as the engine warmed up the problem went away as everything expanded. Thats why it was so intermittent. One day it was doing the revving problem and i went to grab my propane torch, i usually crack that just barely open to get a trickle of propane to find air leaks, vacuum line leaks, etc. But by the time i grabbed my torch it had just started to behave as the head was warming up and sealing. So rather than trying to troubleshoot it further i just made a couple new gaskets and put them in, fixed it right up. I knew it was likely a leak but figured eh it cant hurt to ask as other 125 owners have probably already fought this before me and will know the gremlins they get.

Generally 200's and 250's are the only things i get to tinker on, sometimes i see a 185 but rarely, now for some reason a lot of the 110's and 125's are showing up again. I have dug two 110's out of the trash already this year!