Spark Plugs
Thread Starter
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Intermediate
Joined: Feb 2011
Posts: 47
Likes: 0
From: Washington
Spark Plugs
Hey All,
I ride a 1990 FXSTC EVO.
My cylinders are burning differently.
Front cylinders is burning hot and had detonations. I measured the gap and it was much larger than .040 and the rear is black and sooty.
I had a lot of backfires, then I replaced the plugs
This happens after maybe 60 miles on new plugs.
Could this be a coil or plug wire issues?
I thought maybe the battery, but I would think that both plugs would be black sooty if it was a weak battery.
Any thoughts?
Thanks,
Joe
I ride a 1990 FXSTC EVO.
My cylinders are burning differently.
Front cylinders is burning hot and had detonations. I measured the gap and it was much larger than .040 and the rear is black and sooty.
I had a lot of backfires, then I replaced the plugs
This happens after maybe 60 miles on new plugs.
Could this be a coil or plug wire issues?
I thought maybe the battery, but I would think that both plugs would be black sooty if it was a weak battery.
Any thoughts?
Thanks,
Joe
Outstanding HDF Member
Joined: Jul 2006
Posts: 2,876
Likes: 3
From: Washington State
Ok, inquiring minds wanna know.... What's with spraying wd-40? Where are you spraying it, and do you do it while it's running?
Thread Starter
|
Intermediate
Joined: Feb 2011
Posts: 47
Likes: 0
From: Washington
Spark Plugs
Thanks,
Joe
Outstanding HDF Member
Joined: Jul 2006
Posts: 2,876
Likes: 3
From: Washington State
I'm no mechanic, but maybe an air leak will cause some issues with your plugs? As simple as these things are, I'd look into the manifold leak and then work your way through; plug wire may be the culprit, but why is one too lean? You have something strange going on. I can see this happening on a EFI bike, but a simple carb'd bike? I'd say you have some air getting in, but again, I'm no mechanic. I hope you figure it out, cause I'm sure it will help us all someday.
Seasoned HDF Member
Joined: Dec 2010
Posts: 7,736
Likes: 1,524
From: Coromandel Peninsula New Zealand
If it was weak battery they would be black and wet.I ntake may have a leak and that is why front plug detonates, or there may be some rubber hanging down that blocks front cyl and diverts gas to rear making it run rich.
Check your timing, check your compression too.
Check your timing, check your compression too.
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Road Master
Joined: Apr 2009
Posts: 1,123
Likes: 43
From: NJ
If your intake is leaking it will change the mixture on that particular cylinder, thus the difference in plugs. Don't use carb cleaner, it makes a mess on the black wrinkle of the motor, spray it right where the intake meets the cyclinders, do the back of the carb also.
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Road Master
Joined: Aug 2010
Posts: 1,205
Likes: 18
From: SE Michigan
Did you try snugging all the carb mounting bolts and intake bolts? Really sounds like an intake leak on front cylinder. The extra air coming in leans out the mixture ( radically in your case) causing the symptoms you have; preignition, overheating,and plug failure. I would not ride it until it was fixed or you'll burn a hole in that front piston.
On a normally running Twin ( with carb) the rear cylinder plug will always look hotter as that cylinder has a harder time getting air to cool it.
On a normally running Twin ( with carb) the rear cylinder plug will always look hotter as that cylinder has a harder time getting air to cool it.