Question for you motor heads... 78 GS750

[jonr]

Greetings all:

I am in the process of major surgery on my bike this week. One of the operations on the list is swaping out the exhaust pipes. So I go into pop out the exhaust gaskets and notice just how black it is in the exhaust port on the head. I noticed there was about .01 or .02" of caked carbon soot on the wall of the port. I could also see a bit of the valve stem and noticed it was covered with a seemingly thick layer of wet grime. I assume it's oil mixed with carbon build up???

Anyway, is this normal for a 2-valve GS engine with 34K miles? I am ultra hesitant to take the top end off, but I am very concerned at the same time. Can anyone off any advice?

Thanks!
-jon

 

[Jethro]

I've been told by some trustworthy folks that everything you see is normal. The carbon is certainly normal, it will happen over time, but you have to clean it up every once in a while. The dirty valve stems are the result of detergents in the gas, and will also happen over time.

Basically, yes it's normal, but there is a time that it has to be dealt with. It takes a long time for the buildup on a valve stem to kill the valve guide and the seals, so if you don't notice lots of smoke and some power loss, leave it be. My 81 had 40k hard miles before it needed to be replaced, and even then, I could have managed to keep it.

 

[Keith Winter]

Carbon build up

Carbon build up

My 78 GS1000 has 47k on it and goes through about 1 litre of oil every 1500-2000 miles. It does not have any carbon build up anywhere in the port or stem area. It does have black soot in there, but not enough that you can't wipe it out with your finger or a rag. It's a light coating (dry) that wouldn't be enough to measure easy anyway. I consider the amount of oil mine goes through quite alot, but I got the bike in bad shape and it had been sitting a long time and as the compression is ok, I think mine is probably valve seals. It has not got any worse since my restoration, so I've just left it alone. I've been riding mine 4 years now this way with nothing getting worse so, if your plugs don't foul and the bike runs ok I would just leave it and ride it.
Keith

 

[Anonymous]

I ran some Sea Foam in a few tanks of gas and it cleaned up my exhuast area quite nice and cleaned alot of others things in the process.

 

[jonr]

Thanks for all the advice all. I'm not burning any oil at this time, so I think I'll let it fly for now. Would anyone have any concerns with running an additive such as Sea Foam and clogging up the oil passages with debris? I guess if what's coming off is in the combustion chambers, then how would it find its way to an oil passage?

-jon

 

[Anonymous]

A GS in decent condition doesn't need any additives at all. What they do need is regular trips to redline at full throttle (after proper warmup, of course). \