misfire mystery

maylar · Jun 26, 2016

texasSlick said:
maylar said:

Awesome. I'm gonna check mine as well.

Click to expand...

Be sure to do it with engine hot. From your original post, it seems that is when the leak is pronounced.

Slick

Bingo!

Went for a ride yesterday, and when I returned home with the engine good and hot I sprayed carb cleaner around the head gasket and intake manifold on the left side. No effect at the head gasket, but spraying the intake at the phenolic gasket caused the engine to stutter. I swear I've done this a dozen times before, but maybe not when it was really hot. Eureka!

Last time I had it apart I swapped the intakes and the problem went away for a while. I figured I'd finally got a good seal, problem solved. But it returned again and (according to my brother's memory) swapped sides. So the culprit seems to be one of the manifolds. I've inspected them for hairline cracks before and flattened them on a glass plate but obviously something's amiss.

Now to find the proper manifolds and get a new set of gaskets. Maybe I'll goop some RTV around that joint and see if I can get a temporary seal.

Thanks to the forum for the insights.

eskasteve · Jun 27, 2016

RTV is fuel soluble. Not a good idea.

batrider · Jun 27, 2016

eskasteve said:
RTV is fuel soluble. Not a good idea.

What do you recommend?

eskasteve · Jun 27, 2016

Hylomar sealant has always worked for me even when all others have failed. If it's not available in your area good old fashion non-hardening Permatex should work.

Tornado · Apr 22, 2020

maylar said:
Bingo!

Went for a ride yesterday, and when I returned home with the engine good and hot I sprayed carb cleaner around the head gasket and intake manifold on the left side. No effect at the head gasket, but spraying the intake at the phenolic gasket caused the engine to stutter. I swear I've done this a dozen times before, but maybe not when it was really hot. Eureka!

Last time I had it apart I swapped the intakes and the problem went away for a while. I figured I'd finally got a good seal, problem solved. But it returned again and (according to my brother's memory) swapped sides. So the culprit seems to be one of the manifolds. I've inspected them for hairline cracks before and flattened them on a glass plate but obviously something's amiss.

Now to find the proper manifolds and get a new set of gaskets. Maybe I'll goop some RTV around that joint and see if I can get a temporary seal.

Thanks to the forum for the insights.

I know this is an old thread but I'm having similar issues on my 850 MKII. Bit of a mis on the left bank....popping/missing at idle when cold. Jerky power output while riding along at steady speeds, various throttle openings.

From your findings, seems headgasket had some small leak, but then you also found manifold leaks, right? What was ultimate solution?
Cheers.

maylar · Apr 22, 2020

Tornado said:
I know this is an old thread but I'm having similar issues on my 850 MKII. Bit of a mis on the left bank....popping/missing at idle when cold. Jerky power output while riding along at steady speeds, various throttle openings.

From your findings, seems headgasket had some small leak, but then you also found manifold leaks, right? What was ultimate solution?
Cheers.

Intake manifold leak at the head. New phenolic gaskets and a smear of sealer on them seems to have done the trick. Though now I'm using a Trispark, so the idle drifting has gone away completely.

misfire mystery

maylar

eskasteve

batrider

eskasteve

Tornado

maylar

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