3 lean plugs, 1 black plug....

If they are VM's turn the pilot fuel screw in a 1/4 turn and see if the black plug lightens up a bit. If it does, you might want to turn the other three out a bit until they are all are the same color, chocolate brown would be right. If the others do not darken up, your jetting may be too lean. If the pilot screws are still painted in so they don't turn, you are long overdo for a complete strip down, a good soak and clean and new 'O rings.

Sounds like it'll be something specific to that cylinder or carb rather than something common to all the pots .
Good luck and let us know what you find .

Cheers , Simon .

Thanks, I'll have a look at that site and see if I can't learn something I don't already know. I should say that I'm not a carb noob though. I've worked with Kehines quad carbs before and top-draft carbs on cars as well. Just figured I'd ask my questions here first since I'm new to these bikes and to get some input is always good.

from one newbie to another;

read this: http://www.iwt.com.au/mikunicarb.htm it will help you understand what's going on inside those carbs.

there is a section on "Carburetor Jetting Troubleshooting" that will tell you how to see where the problem is. You'll drive yourself crazy taking wild stabs in the dark at the issues (trust me, I've been there).

It's an 80 gs550.

It's not the petcock because I've had the tank off many times and no fuel leaked from the petcock nor was there fuel in the vacuum line. And after I open the choke I always push the rod on the carbs to make sure it's all the way in... I guess I'll just have to pull the carbs and see if I can find anything. The bike runs pretty good despite the issue... The only other thing I can think of as to why the other plugs show lean is because I put the dual exhaust on from a Katana, which is a megaphone style and has more openings than the stock 550 exhaust, so it flows a little bit better. The bike runs good and is smooth through the whole power band, so maybe something funky is up with that carb like a loose jet or something then... Because if the other cylinders are lean because of the exhaust system, than that cylinder should also be lean, unless something is allowing more fuel in.

I'll give everything a good looking over and I'll double check the petcock. Lucky enough I ordered a new o-ring set from cycleorings guy a few weeks ago so I have those on hand if need be!

[hampshirehog]

As above or maybe a choke that's not closing off properly (weak spring, worn rubber etc).

I had a similar problem and I found................

1 -- The main jet in one carb was ready to fall out .
2 -- The previous owner had fitted an incorrect o-ring in another carb main jet which didn't seal properly .

Fixed both and all good .

Cheers , Simon .

Pull the vacuum line off the petcock and see if there is any gas or fuel residue in it. One possibility is that the diaphragm inside is torn and fuel is getting sucked down the vacuum line into cylinder #2. If it is bad enough it might even starve the other cylinders for fuel?

[rustybronco]

The second spark plug in from the left side was BLACK. Like, completely black. I cleaned it up with a wire brush and some carb cleaner... But does anyone have some suggestions?

Depending on what bike you have (put it in your sig line) it could be because of a bad petcock.

Hey guys... So a couple days ago I was having trouble keeping my bike running. Sometimes when warming it up, it would just die for no reason and then would not restart for maybe 10 or 20min later. Well it did this on Friday and but it died after only warming up for 2min... I checked for spark and it was good and the fuel was flowing, so I went out and got new plugs and viola, she fired right up and has been running no problems... Except for what I found today....

So yesterday I had it out all day and I put about 40 miles on it through the back roads and city. I ripped on it a bunch of times and also casually drove it through heavier traffic. So today I changed the oil and filter and I pulled all the plugs to check the coloring... The 2 cylinders on the right hand side of the bike were white. As in the electrode was white with a light flaky layer on them and the center ceramic was virgin white. The outside cylinder on the left hand side (This is sitting on the bike mind you) was also white and the same as the other 2. The second spark plug in from the left side was BLACK. Like, completely black. I cleaned it up with a wire brush and some carb cleaner... But does anyone have some suggestions?

I'm getting ready to put the pod filters on in a couple of days but before I go and pull the stock airbox/filter setup off I want all the cylinders to be running the same and properly.

So a black plug, it's most likely running damn rich in that cylinder, but why? If all the jets/needles are the same... Then that must mean that maybe the float height isn't proper in that carb or the needle valve on the float is leaking? Or might it be something a little simpler?


** Could it also have anything to do with the valve adjustment? When I get my new valve cover gasket I'm going to pull the cover and check the clearances.
Thanks!