OK, So I bought a 76 XLCH recently (my first HD). Bike starts right up after 4 kicks. After idling for about 3-4 minutes smoke starts coming out of the front cylinder head where the exhaust pipe is connected. It also comes out of the exhaust. Not alot but its there. Could this be from sitting too long or is this a more serious problem? I have alot of questions about this bike since I will be breaking it down and rebuilding it from scratch after this season ends. For now I just want to enjoy this season with the bike as is. Right now my main concern is the smoke. Does anyone know what can cause this? Thanks. Im new to the forum and asked the same question in the introduction part of the forum so I apologize if your reading this twice.

 

First thing is that leaks at the exhaust ports, and at the intake also, are a serious problem. Must re-install that front pipe do it does not leak there. here are my intake & exhaust leaks test notes ...

Intake And Exhaust Leaks Tests

You cannot get a good tuneup if there are intake leaks or exhaust leaks.

1. Check for Intake Leaks

With the engine idling spray propane gas or WD-40 around the carb/intake/cylinder head joints. Propane is best because it leaves no mess, and is most easily sucked in thru leaks. WD-40 is said to work well because it has very fine spray droplets. Be careful to not allow any of either to get sucked in thru the A/C as this will invalidate the results.

Any change in engine RPM is a leak which must be fixed.

EDIT: Experience is that this procedure will identify larger intake leaks, but it may miss very small leaks that also must be fixed. And that propane is definetly the better choice.

2. Check for Exhaust Leaks

Pour about 1/2 ounce of oil into each cylinder thru the spark plug holes. Run the engine at idle. You will get lots of smoke for about 5 minutes.

All smoke should come from the ends of the exhaust pipes/mufflers. Any other is a leak which must be fixed.
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I do not know about the source of the smoke. It could be oil burning - from sneaking past worn rings, down the valve stem guides, oil spilled on the outside of the pipe, ... Others may be able to be more helpful.

 

If it smokes idling and not under throttle, it most likely is bad valve seals. Not a big deal.

 

If the bike was stored for along time. Just maybe the owner put oil in the cylineder heads to keep the piston's from freezing up. Alot of old school guy's use to do that dearing the winter so they can crank the pistons over to keep them free. Just my 2 cents.
Tom

 

This has nothing to do with this post.

 

1976 Ironheads do not run valve guide seals standard. Just so you know.

 

That oil would be expelled immediately.

 

The answer to your query is that you have worn valve guides. You will almost certainly have to replace both the guides and the valves to cure the problem.
You can certainly keep going for a long while with this condition, provided that nothing else is about to fail(which is unknown at this point).
Another trait of this type of wear is carbon build up in the exhaust guides, which can cause them to become "sticky" when traveling at higher rpm for an extended period. This will cause the bike to miss and carry on, and could get serious quickly.
But even that can go on for a while without attention, if things go your way.
Oh, and before I go, a little irrelevant information.
Purple monkey dishwasher.
There. That should cover it.

 

how many miles on the bike?

 

Do you know the seller, did he provide complete disclosure on the bike?