Oil fouling plugs

[GS-H]

I've got a '79 GS 750. 24,XXX miles. I'm getting some serious oil fouling of the plugs. I've been having to clean the plugs after just 15 mins of running the engine. Some of you engine gurus can probably tell me real quick what's causing it. I'm thinking it's valve seals but not positive. Please give me your ideas and info on how difficult it might be to fix. Thanks in advance.

[Nessism]

Are you getting major blue smoke out the tail pipe? To foul a plug so fast there must be incredible smoke.

[UK-GT]

Is it just one plug or all of them, if its just one, when were the valve shims checked, if you have no gap between the shim and cam it would mean the valve is always open that would cause oil to leak into the cylinder, it would also mean a loss of compression in that cylinder.

[GS-H]

Thanks for the replies. To answer both of you.
Not getting much smoke at all. Here's the scenario. I clean the plugs. It will start right up and run smooth. I'll run it for approx 10-20 mins. The whole time it runs great. I turn off the engine and let it cool down. I'll try to restart it an hour later. It becomes hard to start and when it does start of course the plugs are fouled and it runs very rough. It is all the plugs. As far as the shims, I haven't done any work to the engine besides install the dyna elec ignition. That's why I've posted this thread. Hopefully you experts will tell me the things to check and I'll do that until I find the problem/s.

[hjfisk]

Are you sure it is oil, and not fuel fouled? If it were oil and as bad as you say you should be able to rent it to towns and city's for mosquito fogging . Seriously if it were oil it would smoke blue badly.

[habsdoc]

plugs

Is it all the plugs or just one??? Petcock could be bad if it is always #2 plug looking fouled. Check your valve shims and get them in spec 1st.

[tom203]

Oil level rising??? check your petcock to make sure it's off when engine is off- you probably got tired needle seats too, but it sounds like fuel fouling.

[Steve]

Is it just one plug or all of them, if its just one, when were the valve shims checked, if you have no gap between the shim and cam it would mean the valve is always open that would cause oil to leak into the cylinder, it would also mean a loss of compression in that cylinder.

Please explain how this happens.

The only place that oil can get into the combustion chamber is past the oil seals on the valves, and valve clearance has nothing to do with that.

Back to GS-H, take a GOOD look at the plugs when it's hard to start. Look paraticularly at the color and 'texture' of the ceramic insulator. If it is black and shiny, it is probably oil. If it is black and sort of powdery,dry, it is fuel, you are running very rich.

When you "run it for 10-20 minutes", are you just running it in the garage or are you out riding it? If you are just running it in the garage, are you using the "choke"? If you are running it in the garage, are you using a cooling fan? If you are running it in the garage, it is idling the whole time or are you varying the engine speed and load? What spark plugs do you have?

.

[UK-GT]

I read somewhere that if the valve does not close all the way, the compression from the cylinder leaks past the valve and can cause the seal to fail/leak, but it will not be the first time I am wrong and I doubt that will be the last!
I would still check valves and compression, if it is all four plugs, I would agree with Steve and say it was fuel related, have a look on the Web for a spark plug colour chart and cross reference you plugs.

[mvalenti]

My experience with plug fouling on my GS was more than likely a poor coil connection which I found when I tore the machine down for a re-ring. I was only seeing a fouling on my #1 cylinder. I chased the carb (dragon) thinking the problem was there... Coil finally made sense to me as I got break down when revving past 1/2 throttle. Bike would eventually run rough, and wouldnt start untill I cleaned the plug. my 2 cents. But listen to these guys too, they r smaht...

[GS-H]

This is the reason I love this forum, always many folks who have good info. Upon a good bit more of inspection and research, I think it is in fact fuel fouling instead of oil. Guy I bought the bike from said he'd done a good bit of work to the carbs rejetting and such. I'm planning to rebuild the carbs to stock specs, remove the pods that came on the bike, buy and install a stock airbox. Winter project I guess.

As far as the coil question, I installed the Dyna S ignition last week along with new coils. It gets plenty of spark and zapped me a couple times while I was testing that. I bought the bike in April and plan on making a cafe out of it. I want to get the engine dialed in before I spend a lot of time doing the rest of it. I'm a function over form guy. It has to work good first before I worry about it looking good.

Thank you for all the info and quick responses.

[UK-GT]

Where in the world are you as I have a box of spares for a GS650 and I think I have air box.

[tkent02]

I read somewhere that if the valve does not close all the way, the compression from the cylinder leaks past the valve and can cause the seal to fail/leak, but it will not be the first time I am wrong and I doubt that will be the last!

confusion...
It is the seal between the valve and the valve seat that fails, not an oil seal. The oil seal is on the top of the head, where the oil is, not down there where the flames are.

Read this, might clear up a little bit about valve clearances. Wrote this a while ago for someone else, but it applies here...


Why you need to adjust your valves, especially if they aren't ticking...

Valves heat up and like anything else they expand, they get longer. The clearances are set cold with this expansion in mind, so the valves can still seal even if the engine gets too hot. Now as the engine runs several thousand miles, the valves contacting the seat eventually wear into the seat. After a while it can go farther in before it contacts the seat, the valve actually recedes into the head. This leaves the stem poking out a little bit farther, hence the clearances tighten up as the miles add up. Not always, there are other things in there wearing too, but they usually get tighter.

The only path for heat to get out of the valve itself is through mechanical contact with the seat, which is connected to the head, and to the cooling fins. Maybe a little bit by contact with the valve guides, but not much. There is no other path for heat to get out of the valve. Now if you neglect the valve clearances, and if they get tighter as they generally do, the valve eventually doesn't contact the seat as well as it should, so the valve doesn't cool itself as well as it should. It gets hotter than it should be. When it gets hotter, the valve stem gets longer, and so the valve contacts the seat even less, and the valve gets even hotter. It is a vicious circle, the valve gets hotter and hotter, longer and longer, and cools less and less...

The end result is a burnt valve. When the valve/seat contact is so poor that actual flames start to leak past the edge of the valve under pressure, the valve gets extremely hot in that one spot. Sometimes the edge of the valve gets messed up, then it can't seal so well. Sometimes a pie wedge shaped piece of the valve burns away, but even if it's not that burnt, it won't seal again as well as it should. The cylinder may still run, at least until it burns more, but it won't run right.

Anything else that makes the engine hotter than it should be makes the problem worse, such as a vacuum leak or other lean running problem, or retarded timing.

Adjust the valves correctly, then check the compression. Hopefully you caught it before any damage was done.

[GS-H]

I'm located in Virginia.