Carbon Fouled Plugs

[Guest]

Hello, All.

I got some great advice on a carb rebuild on my '78 GS750 a few months ago. Got the bike running recently and have taken it for a few rides. I'd like to list some of the symptoms and what I'm planning on trying as solutions.

Symptoms

- Engine hesitation, stalling when idling
- Spark plugs carbon fouled after riding (dry)
- Slight hissing noise with throttle

I've only noticed the hissing noise recently when I rev the throttle. I turned the air screws 1/2 a turn out on each carb to lean the fuel mixture. Now one of the spark plugs stays white after riding. I've been carrying a set of clean plugs and a socket with me to get the bike back home when it craps out.

Here are some things I'm going to try:

- Turn the remaining airscrews on the carbs out 1/4 turn at a time? Maybe turn the fuel screws in (I know the tips are sensitive)?
- Drain the gasoline (I'm currently only using premium)
- clean/replace the petcock
- change the oil
- run Seafoam through the engine

The Seafoam treatment was something I'm iffy about, and wanted to get some opinions on before trying. The last resort was going to be taking off the carbs and readjusting them. Since I'm still very new to this, I wanted to eliminate maintenance issues before taking my bike apart again.

Any advice or related experience would be a big help.

[chef1366]

Hissing may be a compression leak. Check the seal on the plugs and the head gasket.
Oh and check compression.

[eil]

Random notes/questions:

Did you rebuild and clean the carbs thoroughly as per the tutorial? (Completely disassemble, soak in carb cleaner, new o-rings, etc?)

By "premium" do you mean "high octane"? (Premium does not mean better gas.) The engine should run fine on all grades available at most pumps, but you'll usually get better preformance and mileage from the lower-octane grades. Something to note, though I don't think it's a major contributor to the issues you describe.

If your carbs are still gunky, seafoam isn't going to do anything. (And certainly doesn't do anything inside the cylinders except make a bunch of smoke.)

Carbon-fouled plugs could indicate either an extremely rich mixure or oil getting past the rings into the cylinder. How many miles on the engine?

The hissing could also indicate an air leak in the intake boots, carb boots, airbox, etc. Do you have new boots? Sealed the airbox up good and tight?

I'm not an expert either, so take these suggestions with a pinch of salt. With symptoms like these, the only way you'll find the culprit is through the process of elimination.

[Nessism]

A lot of stuff going on here. Best check the Newbie Mistakes thread linked in my signature for more info.