Smoke coming from cylinder head

I got my new (to me) engine running on my 1982 KZ750 LTD. I replaced the engine with a 1980 KZ750E engine with unknown miles. I bought it from ebay and all the guy could tell me is that it came from a running bike so I don't know very much about it.

I checked the cold compression after I got the engine installed and every single cylinder was at 130 psi - dead on the money too.

I got it started today and let it idle for about 10 minutes to get the new oil to move around and I took it out for a quick 5 minute ride to see how it shifted and everything.

The ride was fantastic, especially compared to what it used to be like, but I did notice a little bit of smoke coming out from the cylinder head around cylinders 3 & 4. It wasn't thick heavy smoke - think like steam or something. It had a smell that was a little sweet, but I don't know what burning oil smells like. The engine had been sitting outside of an engine frame for a while (at least a year and a half - I only had it in my garage for about 3 months) and was covered in mud, pine needles, and all kinds of other junk. I cleaned it as best as I could, but all I had were some brushes, Gunk engine degreaser, and a bucket of water (no hose or power washer) so I couldn't get everything off.

Is this something to be concerned about?

Or could it just be dust and debris that are in and around the engine that are finally getting burnt off because it sat for so long. Before I had the engine, it was sitting without any rags or anything to plug all the open orifices. Could it be due to that?

How do I know if my exhaust is leaking? I suspect it could be maybe be that as well since I have a brand new exhaust on this engine as well.

Did you pull the valve cover off and adjust the valves? Replace the valve cover gasket and replace, or at least reseal, the rubber cam plugs before buttoning it back up? Reason for asking is first, this is critical maintenance and must not be neglected. And two, you may have a valve cover leak.

An exhaust leak typically sounds like a valve tic noise. Hope you replaced the exhaust gaskets before installing the exhaust system.

If you didn't do the valves that's the first order of business. Clean everything really well before installing the new OEM gasket. Then go ride to heat the engine and burn off any residual residue on the engine which could be smoking. If you must, sprinkle some foot powder on the engine and look for oil leaks.

It could be remaining schmuck burning off, or it could be a dried out and leaking o-ring or gasket. With the engine cold ( has not run in several hours), grab your torque wrench and service manual and insure that all the head nuts are at proper torque. Some folks prefer to back each nut off a bit, before retorquing.
Go for a longer ride. If it is a weeping gasket or o-ring, you should be able to get an idea of where the problem is. A common place is where the tachometer cable enters the head. As I recall, there are two o-rings and a flat seal involved. Oh, I am assuming your bike has a mechanical, not electrical, tachometer.

+1 on what Nessism said.

The exhaust came with new, copper gaskets that I installed. But thanks for reminding me about the valve heights. This was something I wanted to check, but I have completely forgot!

I'll check them this weekend and order a gasket and some cam plugs.

I don't have a tach at the moment - I had ordered one but it was discontinued and I couldn't find one that was similar/matched my speedo. Could it still leak from there without any cable attached? I'd assume so, but this is the first bike I've become intimately involved with so I don't have a much experience.

Also, heads-up that 10 minutes is an awfully long time to let an air-cooled motorcycle engine idle. I think most folks would recommend no more than 3-4 minutes.

Aside from running lean and needing to sync the carbs, I think it's leaking from the cylinder head. The cooling fins are wet and that's about where the smoke is coming from.

I don't need to remove the engine to replace the head gasket, correct?

The tach housing o'ring(s) and tach shaft seal are common leak sources that can be replaced without removing the engine head.

Good Fortune!

If not already done, I would suggest torquing the cylinder head using the factory prescribed pattern when the engine is stone cold after sitting overnight.

Good Fortune!

Patton wrote: If not already done, I would suggest torquing the cylinder head using the factory prescribed pattern when the engine is stone cold after sitting overnight.

Good Fortune!

Agree. Crack the nuts loose to get them moving and then make them up. The nuts always seem sticky due to static friction otherwise.

Nessism wrote:

Patton wrote: If not already done, I would suggest torquing the cylinder head using the factory prescribed pattern when the engine is stone cold after sitting overnight.

Good Fortune!

Agree. Crack the nuts loose to get them moving and then make them up. The nuts always seem sticky due to static friction otherwise.

And make sure the threads are lubed.


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Its probably left over sap from pine needles and gunk degreaser burning off