n°2 black spark plug

[waltergs1000]

Ciao to All, my bike works very good (gs1000g) but I have problem with N°2 spark plug, it be wet, black and stinking of fuel. I have rebuilt N°2 carburetor, float height ok, o-ring pilot screw new, pilot screw turn out of 1 and 3 / 4, pilot jet plug new. Fuel petcock is new, I have also opened Therefore, being all perfect. Coil + wire + spark plug cap new. What to look again?

excuse my English, google translation

[Steve]

I see from earlier posts that you have a 1980 bike. That will have the BS series carbs. If you are counting properly, from left to right (clutch hand to throttle hand), your #2 carb is the one that supplies vacuum to the petcock to turn on the fuel. Check the diaphragm in the petcock for a leak. If it leaks, it will provide extra gas to #2, causing it to run very rich.

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[supersonictoys]

I agree with the post above. try putting a vacuum cap on the vacuum port on the petcock and plug the end of the vacuum line with a small bolt then turn the petcock to prime so that no vacuum is required to flow fuel to the carbs and run the bike again with a new plug in that cylinder and see if it cleans up.

[tkent02]

Or just draw a vacuum on the vacuum port of the petcock with a syringe or something and let it dangle for a while, see if any gas comes out. (Block the fuel line first) It should stay dry as a bone.

[waltergs1000]

ok I try it and inform you thanks!

[81gs1100]

Or just get some clear (trasparent) fuel line to use as a vacuum from your petcock to intake, that way you can look and see if there is any fuel transfer.

[waltergs1000]

petckock is perfect. I tried for several hours as in photography, and syringe
be perfectly dry. I have 4 Carburetor gs1100g, dismount a pilot
screw from here and install on my gs1000g...?

[Big T]

I understand the problem, but I don't understand what solution you are proposing.

It may be that the tip of the needle is broken off. Check that also.

[waltergs1000]

I have replaced needle and again o-ring, I have to just try, I hope next weekend

[KEITH KRAUSE]

Looking at your plugs, number 3 looks just as dark as number 2. Number 1 and 4 look much lighter and I assume burning correctly (hard to rely on pics).
I'm wondering if you have a weak coil to 2/3 and minor differences are making number 2 foul out but actually both 2/3 are firing weak. Weak spark will allow raw fuel to exist too.
Not sure about bypassing the infamous '80 petcock. Most petcocks with a suspected vacuum line leak you simply plug the vacuuum and run the bike on prime to see if the problem clears. On the '80 petcock, the factory manual says that even on prime the engine must be cranked to initiate fuel flow, which means you'd have to have the vacuum line connected(?). I've never actually worked on an '80 petcock so I don't know for sure.
Looks like you're trying some tests on it and it's OK? If so, check out the coil to 2/3.

[waltergs1000]

coils with wires and plug cap be new (500 km), possible bad coil?
how to check?

I can not test drive it rains here!