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Fouling a plug on my Ironhead

6146 Views 7 Replies 7 Participants Last post by  latham
I have a 81 Ironhead that keeps fouling a plug in the front cylinder. I had an Ultima electronic ignition put in hoping that would solve my problem but it didn't. The front plug is real black and the rear plug is clean as can be. The bike idles fine after warming it up and runs great for the first 2 rides but on the third ride when I go to take off it breaks up, spits, sputters and back fires like crazy. I run NGK BP6HS plugs with 93 NON ethanol fuel. It also has a Super E carb.
I had NGK BP7HS plugs, which caused fouling almost immediately, and according to NGK's site that was too cold and they recommend the 6 plug in the 81 XLH, which is hotter.
The carb seems to be adjusted right because if I turn the air/fuel screw either way the engine stumbles. I'm at a loss. :feedback:
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Intake manifold leak.
Tip O' the day:

Use a light coating of high temp grease around your intake seals and you'll be very happy with the results.
I would drop the main jet down a size or two, that Super E is a sewer pipe for fuel delivery. Also the air/fuel screw is only for idle, doesn't affect high speed operation.
Agreed that the intake seals could be leaking air too, common problem.
Lol. I've never heard one called a sewer pipe. But I've had several tell me that they're boy too big for sportys!!
Black from plug on an ironhead can be compression or too tight of a valve.

If valves are adjusted too tight, the engine has low compression at cold temps because valve is being held open.

As engine warms, cylinder grows and valve lash changes, allowing valve to close, reseat and compression is restored.

Switch plug wires and see if problem switches cyliders. Plugs as well....
I have a 90' Harley evo motor in my bike and had the front plug constantly fouling. I changed plugs, wires, ignition coil. Nothing changed. I then changed the rubber seal behind the carb and so far the problem went away. Ive put 200+ miles on since the seal change. Before that was changed it would foul within 50 miles.
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