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Rear Cylinder Plug Fouling

Engine, Fuel and Exhaust

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Old Dec 31st, 2008, 07:53 PM     #1
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Rear Cylinder Plug Fouling

Well, I picked up my 2000 Fatboy earlier this year and have pretty much been plagued with the rear cylinder plug fouling out to the point of the bike becoming unrideable within @ 100 miles of operation. I've been through the carb and cleaned it out, along with the tank (had it cleaned out at an Indy shop due to rust). Slow jet is a 45, mid is 2 clips up and main is an 85. Added an in-line fuel filter. Ran, same problem... Had the Indy shop check out and set the carb with their computer/analyzer. Ran, same problem... pulled intake and checked seals, no problem, replaced, of course, same problem. I pulled a compression check today and both cylinders checked at @ 90 initial and went up to @ 145 psi. Went ahead and cheked with a shot of oil to each and the pressures were about the same. The rear cylinder does have light black smoke on start-up and smokes light black smoke when I hit the throttle. The front plug is relatively clean with little color change. Black on rear plug is sooty, not oily. I'm at the point of thinking the valve seals are gone...The bike only has @ 10, 000 miles on it. Ideas?
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Old Dec 31st, 2008, 08:13 PM     #2
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Re: Rear Cylinder Plug Fouling

Quote: Originally Posted by Shifter View Post
Well, I picked up my 2000 Fatboy earlier this year and have pretty much been plagued with the rear cylinder plug fouling out to the point of the bike becoming unrideable within @ 100 miles of operation. I've been through the carb and cleaned it out, along with the tank (had it cleaned out at an Indy shop due to rust). Slow jet is a 45, mid is 2 clips up and main is an 85. Added an in-line fuel filter. Ran, same problem... Had the Indy shop check out and set the carb with their computer/analyzer. Ran, same problem... pulled intake and checked seals, no problem, replaced, of course, same problem. I pulled a compression check today and both cylinders checked at @ 90 initial and went up to @ 145 psi. Went ahead and cheked with a shot of oil to each and the pressures were about the same. The rear cylinder does have light black smoke on start-up and smokes light black smoke when I hit the throttle. The front plug is relatively clean with little color change. Black on rear plug is sooty, not oily. I'm at the point of thinking the valve seals are gone...The bike only has @ 10, 000 miles on it. Ideas?
Sooty is over rich .. If it was valve seals it would be oily.. Check your spark plug wires or coil .. could be heating up and breaking down
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Old Dec 31st, 2008, 08:35 PM     #3
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Re: Rear Cylinder Plug Fouling

Sorry, forgot to mention...checked out coil initially, was bad and replaced it, wires too, one of them checked bad and put new wires on. I've been working this off and on for a while. The engine is stock and I don't think anything was done to if before I got it from a local hock shop. Previous owner had hocked it several times before he just sold it to the shop out right to keep his business going. I've had several sets of plugs in it and set them @ .040. Bike came with staight stock pipes originally, mufflers removed. Put on another stock set, too restricted and quiet. I now have on V&H Straight Shots, baffled. Intake filter is a K&N.
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Old Dec 31st, 2008, 08:48 PM     #4
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Re: Rear Cylinder Plug Fouling

Quote: Originally Posted by Shifter View Post
Sorry, forgot to mention...checked out coil initially, was bad and replaced it, wires too, one of them checked bad and put new wires on. I've been working this off and on for a while. The engine is stock and I don't think anything was done to if before I got it from a local hock shop. Previous owner had hocked it several times before he just sold it to the shop out right to keep his business going. I've had several sets of plugs in it and set them @ .040. Bike came with staight stock pipes originally, mufflers removed. Put on another stock set, too restricted and quiet. I now have on V&H Straight Shots, baffled. Intake filter is a K&N.


Hd Plug or another make?
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Old Dec 31st, 2008, 08:52 PM     #5
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Re: Rear Cylinder Plug Fouling

Harley plugs and several others...NGK, Champions also come to mind
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Old Dec 31st, 2008, 09:10 PM     #6
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Re: Rear Cylinder Plug Fouling

I assume you meant #185 main and not 85. Check functions in the carb like the slide and diaphragm to assure the slide isn't hanging up. Jets in the carb securely and the emulsion tube in properly?
Does it use any oil?
Have you checked the intake manifold for any leaks with some W 40 besides doing the intake seals. It could be the mixture is rich or dumping and the front is actually running lean if it were leaking and this is causing the rear to appear rich.
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Old Dec 31st, 2008, 09:39 PM     #7
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Re: Rear Cylinder Plug Fouling

Right...185, as read on jet. Slide operation is smooth, no hanging, checked several times. All secured internally in carb. I've jetted up and down with the intermediate clip and the main in the carb. Jetting it richer made the rear foul up quicker and started to foul out foward plug. The intake gaskets have been replaced in the last two weeks, even though the leak check of them checked good prior.
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Old Dec 31st, 2008, 09:45 PM     #8
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Re: Rear Cylinder Plug Fouling

By chance do you have a vacuum operated fuel valve on that bike?
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Old Dec 31st, 2008, 09:55 PM     #9
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Re: Rear Cylinder Plug Fouling

Quote: Originally Posted by Gary12850 View Post
Get a gremlin bell...I'm outta options
Man, you said it! So am I. I am pretty good at changing out plugs though!
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Old Dec 31st, 2008, 10:49 PM     #10
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Re: Rear Cylinder Plug Fouling

Quote: Originally Posted by glider View Post
By chance do you have a vacuum operated fuel valve on that bike?
Sorry Glider, I missed your input. Yes, fuel valve is vacuum operated??!!
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