Ok, my 68 XLCH is fouling plugs after only a few minutes running..The plugs turn a sooty black that you can almost wipe off easy..I have checked the seal around the carb by spraying WD40 while idiling with no change.150 PSI out of each cylinder before and after a squirt of oil..147 and 145 PSI after engine is warm.I had milwalkie twins on the bike before i put on drag pipes with the same problem.I have a clear plug to check timming but have found that to be absolutely impossible to see the timming marks at all..So im not sure if the timming is off..Im getting troubled to a boiling point with this bike.As im riding it if i get on the gas it it starts to miss and backfire,but if i ease on the gas until it gets up to speed it runs smooth..I diassmbled and cleaned the carb,It looked good but it may be a carb issue and i am not sure how to get this machine adjusted to run right...Any help would be appreciated

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traxsmax........From your description it sounds like a definite carb issue to me.
Yes, the timing mark is hard to see thru the clear plug. Try to view through it at an angle if straight on does not reveal the mark. All you have to do is see the mark within that hole. Perfect center is right on but anywhere in the hole is close enough.
If you have sooty fouling of the plugs that you can easily wipe off then it is fuel fouling.
To start with, what brand of carb do you have on the machine?
Does the carb say only Harley Davidson on the body?
Does the carb have an accelerator pump?
Does the bike idle smooth, or is it erratic? If the idle is smooth and the bike runs well up to about 2000 rpms, then the low speed is OK and the problem may be with the high speed end of the carb.
Let me have a little more info and I will try to give you a hand with solving the problem.................pg

 

It has the original zenith carb,It does have an accelerator pump..The bike does seem to idle good but as i am riding it along it does ok till i get on the gas and it starts missing "cutting out sounds more like it" and sometimes will backfire..I tried adjusting the carb while riding it and at one point it will do nothing but backfire then as i adjust it back the other way it fouls the plugs.Also it seems to never foul the front plug,it has once or twice but it always fouls the rear plug..

 

transmax.......Pull the main jet assembly. This is the brass hex bolt on the bottom of the float bowl and can be easily removed from the carb.
What condidtion do you find the rubber O-ring in on this assembly?
A cracked or deteriorated O ring could be the problem. This condition allows fuel from the float bowl to get past the main jet and dump raw fuel into the carb venturi. The result is rich fuel fouling of the plugs at high speed.
You do not need to buy a carb kit to get this O ring. Just go to Lowe's plumbing department and buy a ten pack of #5 O rings and put one on the main jet assembly and reinstall in the carb.
Let us know if this solves the problem.....................pg

 

When i disassmbled the carb about 3 months ago i replaced this oring because it was in bad shape..Could you maybe give me a starting point on the adjustments and maybe some routine you have proven to work for you on adjusting this carb..I actually got it running a little better today and it didnt fould a plug on at leat 30 min worth of riding today but the plugs are very black and sooty looking..Also on another note is there someplace online maybe i can get an exploded view of how the pushrods, covers and gaskets go on this engine..Once again thanks for all the help and this FORUM RULES...

 

traxsmax.....If you replaced this O ring three months ago because it was in bad shape, I urge you to pull it out and look at it again. This sounds like what is causing you the fouling problems. I also assume that you have your float level set correctly.
I have had the same problem before and it was that stinking little O ring every time.
To adjust the carb, follow this drill: The low speed needle is the screw on top close to the inlet manifold flange. Turning it in leans the mixture and turning it out richens the mixture,
Turn the low speed needle in clockwise until it lightly seats. Turn it out CCW 1 1/2 turns. This will allow the bike to start but most likely will be too rich.
Crank the engine and allow it to warm up FULLY. Set the idle speed to a nice idle of about 900 to 1000 rpms. Turn the low speed needle in until the engine starts to falter. Stop. Turn the low speed needle out until the engine falters. Stop. Turn the needle back in to the mid point between these falter spots. There, low speed adjusted. The carb came as a fixed high speed jet carb, so there is nothing to adjust there.

I have attached a view of the push rods/cover make up. The forum supports jpegs, so I had to scan it and save as a jpeg rather than a PDF. If you need more infomation, send me an email and I will be glad to send you what you need as a PDF.
As always, let us know how this works and does it solve your problem?...................pg

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Update...Finally got this beast running like a RAPED APE..Done a carb adjustment from scratch and got it where it needs to be..These old sporty`s run great when there running right..

 

Job well done! Thanks for the news and glad to hear it is running nice.......pg