G2 Spark Plugs go bad quickly

[slowdog]

My 1990 G2 spark plugs are going bad after only a few hours of use but the electrodes are not fouling out with carbon.... The engine has been running somewhat rich for several years as the plugs are usually black, but not fouled and no carbon buildup and has run fine until recently. I have replaced the plug four times in less than six months (about 6-8 hours of use total). We use the cart around the yard and garden so it may sit for a couple of days between uses, but that is the way we have used the cart for ten years. I have tried using NGK BR4ES and BR6ES and Champion RN 4C plugs, all of them going bad in just a few hours....

Will rich mixture cause internal damage to a plug?

Any ideas on what is killing my plug?

Thanks!

[rib33024]

Click the link and tell us which pic looks like yours. have you ever took the carb all apart and cleaned it? when is the last time you changed the air filter? how old is the gas? did you gap the plug before you installed it?



http://ngksparkplugs.com/tech_suppor...qs/faqread.asp

[1989Marathon]

Can you post a good picture of the last plug that went bad?

[slowdog]

Sorry but I have already replaced and tossed the last plug. A new plug once again makes the cart run fairly well, like the four times prior.... The closest that the discarded plugs looked as compared to the NGK chart is the "Wet/Dry Fowling" plug that they show, but like I mentioned, the plug that originally came in the engine when I bought the cart ten years ago and that ran fine for five years was also colored black. The same with the second plug that I installed that also ran fine for several years. I would clean those plugs about once a year, but they always worked. It was only in the past six months that plugs began to go completely bad quickly....cleaning them did not help.

Having done some more research on these forums and having borrowed a compression gauge I have discovered that my compression is down to about 75. I have read that that is too low....also, we did a leak-down test using my air compressor and have determined that I probably have a bad intake valve as I am losing compression back through the carb....so I am going to pull the top end down and take a look as soon as I get a chance....

However I am still a bit confused because, once again, with a new plug it runs pretty good...just not for long??? Will low compression due to a bad intake valve cause a plug to go bad when the plug does not appear to fouled by thick carbon deposits? Maybe so...

As for the carb, I rebuilt the carb about two years ago in an attempt to stop the engine from running rich, but it did not help much....I may just buy a new carb. The fuel is new and the air filter is new also. The air filter cannister did have some fuel in it and the air filter was wet with fuel which is what directed my research resulting in my checking my compression and discovering the leak past the intake valve....these forums are pure gold!!

At any rate, I am now confident that my problem probably lies with that bad valve or valve seat....but any other offers of advice are certainly welcome!