New rebuild runaway issue

[mitchconley]

just rebuilt my 05 to a 416 and im having some issues with it. It tends to just "runaway" after about 20 minutes of riding when it gets to full operating temp. I talked to a mechanic at my local shop and he said it was most likely from the cylinder warping when it warmed up because it wasnt properly torqued down. So i had them machine the cylinder to be truely flat again and got it back from them today, just to have the same problem. Not sure where else to turn on this one. ive checked all of the intake boots and other misc vaccuum hoses but im stumped. any new leads would be appreciated.

[dxcody]

what do you mean by runaway?

[Stickman400]

x2 Never heard that term used to describe how an engine is running.

[theduke300]

When you say runaway do you mean the bike revs sky high on its own?

[dxcody]

Originally posted by theduke300
When you say runaway do you mean the bike revs sky high on its own?

That was what i was thinking.

Dunno though. Maybe like a high idle?

[theduke300]

I thought that too. Ive just always heard runaway when a motor just revs up and is basically outta control til you kill it. Dont really know a cause though...

[on the rocks]

this is typically caused by air getting in through some where it shouldn't be. a good place to check in the head and base gaskets. just any where air could be sneeking in to the combustion chamber.

[xcracer416]

ive had this problem and it was my carb.

the linkage that rides against my throttle arm was binding once the carb got hot. i like to have never figured it out, it would keep the engine reved up sometimes bouncing off the rev limiter. it happened to me the first time during a race. it was nerve racking in the woods on a 460 stroker.

the only way to tell if that is what it is, is to be prepared to take your airbox or boot off and look at the carb slide to see if it is open.

the 450r carb can do the same thing also, basically the same linkage design

[dxcody]

The first thing that comes to mind is, CRUSH GASKETS!.

Did you replace them? And Did you make sure to pick the old ones out??

[JOHNDOE83]

Crush gaskets wouldnt make it rev at unwanted times.

If you did a 416 and didnt rejet anything your deffinetly running to lean, running to lean is like opening up the throttle and introducing more air rather then fuel.

Have you changed the jets since you bored it out?

[xcracer416]

Originally posted by JOHNDOE83
Crush gaskets wouldnt make it rev at unwanted times.

If you did a 416 and didnt rejet anything your deffinetly running to lean, running to lean is like opening up the throttle and introducing more air rather then fuel.

Have you changed the jets since you bored it out?

i agree with what you are saying on the jetting. i dont really belive it could be the jetting. the reason i say that is, running lean because of lack of fuel would cause a bog or dead spot. it wouldnt make it jusst rev up for no reason. for it to rev up it would need both fuel and air. that being said the jetting would have to be running primarily on the pilot circut it it reved up on idle. the needle would need to be raised for it to rev really higher than normal. thats why the idle adjustment works with the slide, therefore bringing the needle up to let more fuel and air to both come into play. if the slide does not come up the vinturi (sp), how a carb brings fuel in, will not be as strong as it should to let enough fuel in for a high rev.

if you put in to much air and not enough fuel it will not idle up. thats just a simple fact. now if the choke was stuck i could maybe possibly think vacuum leak, but im going to bet carb problem.


my .02 cents

[buddy willard]

cracked head maybe. after it gets warmed up crack opens up. still could be in the carb,linkage,or cable.

[TheAwesomehonda]

I think it's about time for the thread starter to respond :huh :huh

[JOHNDOE83]

Originally posted by xcracer416
i agree with what you are saying on the jetting. i dont really belive it could be the jetting. the reason i say that is, running lean because of lack of fuel would cause a bog or dead spot. it wouldnt make it jusst rev up for no reason. for it to rev up it would need both fuel and air. that being said the jetting would have to be running primarily on the pilot circut it it reved up on idle. the needle would need to be raised for it to rev really higher than normal. thats why the idle adjustment works with the slide, therefore bringing the needle up to let more fuel and air to both come into play. if the slide does not come up the vinturi (sp), how a carb brings fuel in, will not be as strong as it should to let enough fuel in for a high rev.

if you put in to much air and not enough fuel it will not idle up. thats just a simple fact. now if the choke was stuck i could maybe possibly think vacuum leak, but im going to bet carb problem.


my .02 cents

Thats not the exact direction I was going with the jetting, but it sounds good.

[mitchconley]

sorry im just getting back, kinda forgot i posted this to be honest. Im thinking its the carb too. Yes i rejetted, i believe its 158 main and 42 piolot. I mean runaway by just revving up really high when it shouldnt. not necesarrily all the way through the roof, but very high idle. there was a leak between the cylinder and the crankcase, some oil was leaking out but that has been fixed and it is still doing it. I had the carb apart and was inspecting the slide and the needle, but im still not sure what would cause it to do that when it gets hot.

[JOHNDOE83]

One way to find out if its to lean is to slightly turn the choke on and see if it kinda stops or gets better, if you removed your airbox lid put it back on and see if it helps.

If either method makes it better your to lean somewhere.

158 is way to small in my opinion but then again Ive never jetted anything in your state....lol.

keep in mind that slipon manufacturers reccomend a 155 main jet just for a slipon and you now have a bigger bore.

Your issue seems to not be main jet related but may be playing a factor in a heat related issue causing you to randomly lean out at low RPM...... it is a possibility.

I would get random high reving when my throttle cable wasnt laying right under the tank also.

[mitchconley]

finally found the issue, there was a tiny little nick on an o-ring between the carb boot and the cylinder. after heating up the connection was expanding just enough to let a little extra air in. i replaced the o-ring and beat the hell out of the machine yesterday and she was great to me all day