fouled plugs

[Davy]

Hello!
I topped up the oil on my 1978 gs750 with semi synthetic oil, and after a short run it immediately fouled the plugs with oil. Compression test was fine. Changed the plugs and started up fine.
The bloke at the garage said old bikes don't like synthetic oil, drain it and use mineral. Can this really be the case that its so sensitive to synthetic oil or could it be another problem, (oil scraper rings?).
Any thought appreciated!
PS thanks for all your suggestions on my gs550 over charging problems, sorted it now. Davy.

[koolaid_kid]

The bloke is incorrect, motorcycles have no issues with synthetics as long as they are the proper type.
Most likely you overfilled the engine with oil. Check your oil level as specified in your owner's manual.

[Guest]

Motorcycle's run synthetics all the time with out fouling problems. I have had a problem with a old bike that always had,had non synthetic in it and I changed over to synthetic and the clutch started acting up,[slipping]. changed the oil back to non synthetic and the problem stopped. I attributed that to a dino oil soaked clutch not liking the synthetic oil.

[koolaid_kid]

Nope. It is due to the additives in the oil, be it dino or synthetic. "Energy conserving" oils are bad on oil-bathed clutches. Use oils such as diesel oils of any type, and you will be fine.