I have a '97 Heritage with a stock evo 80. I'm hoping someone can help me out. The rear cylinder keeps fouling the plug about every 200 miles or so. Blackens up and starts popping until it stops working. I only use the choke for about 1 minute to start. The front plug looks fine.

Any ideas?

Thanks!!

 

Perhaps you have a bad plug wire or coil or connection of the plug wire to the coil.
If you are using a dual fire ignition, (Which I believe is stock, I'm tired and I don't remember when Harley went to single fire...was that with the twin cam models?), anyway, if you are dual fire ignition, try swapping where the plug wires connect to the coil and see if the problem swaps to the front cylinder.
If it does move the problem to the front cylinder, check/replace as necessary the wires, coil or clean up the wire connections at the coil.
Maybe first you could confirm that you have identical, properly gapped, heat range spark plugs in each cylinder. Just to be sure.

 

I had a similar problem a few years ago that turned out to be the piston ring.

 

I didn't know you could swap positions on the coil. I put a new plug in the rear and checked the front. I swapped positions of the wires at the coil and fired it up and it sounds like it should. I also just noticed that it has burned about 3/4 of a quart of oil in the last 1000 miles. I'll let you know if the problem is swapped to the front now.

 

Chevypilot-- sorry to say this but with the oil consumption fairly high it sounds more like a ring/piston/or valve issue more than an ignition issue. I hope this is not the case of course....
Do let us know what the problem is when you find it.

Regards,
V2

 

Damn, I was afraid of that. What does that kind of work cost usually?

 

Chevypilot, I am located in Australia and rates aren't equivalent. I would take it to a reputable independent shop and ask tell them what's up and ask for a diagnosis and estimate of costs.

I do know it does not take too long to remove the fuel tank, exhaust system, pull the rocker covers and pull the cylinder for a look see.
You didn't say how many miles are on he motor, but maybe a good idea if the rings are bad in the rear cylinder to go ahead and pull the front one for a re-ring on both pistons (if that's the problem).
If other damage is present in the rear cylinder who knows. A good trustworthy Indy shop will save you $$$ and do the right thing by you wrt the repairs.

Best,
V2

 

Sorry but forgot to mention that a bad valve seal or worn guide could cause this so it may not be a ring problem.
Are you seeing any light coloured smoke on a long decel? (as in rolling off a freeway or gearing down to stop at a traffic light), and while stopped idling at the light.This is most noticeable at night with backlight.
If you try this and see smoke my money is down on a valve seal.

regards,
V2

 

The top end was done on mine at about 78,000 and during the process I had the Indy do head work, install a better cam , ignition etc.- the normal 85 hp routine. They also put on new tires and total bill was over $3000. If I would have spent a few dollars more, I could have bought a new Ultima engine rather than wait another 30,000 miles to get it.. Having the performance work done on the 80" made a big difference but not as much as installing a 113" Ultima. Keep that in mind if they talk to you about total costs, especially if you are thinking about increasing the performance as well. If the estimate for performance work starts getting pretty high, you may be better off replacing the engine.. The problem may become a "While we are at it" logic, might as well do this and might as well do that - it all adds up and although it is good it can get expensive.

 

Just my 2 cents but I had a similar plug fouling issue and it turned out to be a broken coil ground at the coil. However, my issue was also accompanied by a loss of power at acceleration and bad idle, and I wasn't burning any oil. Doesn't sound like this is your issue but I thought I would at least mention it. Goodluck