I know this has been asked before. . .

[miles28]

but for the life of me I searched every phrase I could think of and couldn't find it here. I even seem to remember one of the Senior members stating something like "if another newbie asks this question, I'm gonna pull my hair out". And yet, I bravely march on. . .

My question is this: the spark plug on my #2 cylinder is consistently getting fouled, and I seem to remember this being consistent with a specific problem for early GS models (maybe even later ones as well). Can anyone help me out with this?

[tkent02]

If it was #3 it would likely be the vacuum line to the petcock sucking fuel through a bad diaphragm. But it's #2, that's not it.
Are you counting your cylinders left to right?
Float level too high on that one? Leaking needle?
Bad spark?

[rustybronco]

Yano...if another newbe asks a question like this I'm going to pull my hair out.
(all one of them!)

I am going to assume you are asking about the gs you have in your signature.


my question to you, is the fouling that you are seeing fuel or oil?

[Dogma]

If it was #3 it would likely be the vacuum line to the petcock sucking fuel through a bad diaphragm. But it's #2, that's not it.
Are you counting your cylinders left to right?
Float level too high on that one? Leaking needle?
Bad spark?

Interesting. I thought all the GSs pulled vacuum from #2. The 750B is different?

[tkent02]

All 4 cylinder GS with VM carbs use #3. AT least all I have seen.

[miles28]

Yano...if another newbe asks a question like this I'm going to pull my hair out.
(all one of them!)

I am going to assume you are asking about the gs you have in your signature.


my question to you, is the fouling that you are seeing fuel or oil?

Hmmm, good question. How could I tell? It seems the carbon is black, puffy & dry. . . does that help?

[miles28]

If it was #3 it would likely be the vacuum line to the petcock sucking fuel through a bad diaphragm. But it's #2, that's not it.
Are you counting your cylinders left to right?
Float level too high on that one? Leaking needle?
Bad spark?

I am counting left to right. So left side, inner plug. . .that's #2 right?

[tkent02]

Hmmm, good question. How could I tell? It seems the carbon is black, puffy & dry. . . does that help?

Good news.
That's fuel, it's running too rich for some reason...
Oil is shiny black and looks wet.
When are you going to bring that bike over here so we can get it running right?

[JTsGS650]

Hmmm, good question. How could I tell? It seems the carbon is black, puffy & dry. . . does that help?

Could also be weak spark at that plug. Do you see a fat blue spark? You may want to test the resistance of the spark plug cap or just unscrew/snip off 1/4" of wire/re-screw. Or just replace them.

[miles28]

Good news.
That's fuel, it's running too rich for some reason...
Oil is shiny black and looks wet.
When are you going to bring that bike over here so we can get it running right?

Soon I hope! I'm going on a small tour, but should be back next weekend. Maybe then?

[miles28]

Could also be weak spark at that plug. Do you see a fat blue spark? You may want to test the resistance of the spark plug cap or just unscrew/snip off 1/4" of wire/re-screw. Or just replace them.

I think I may have read this before, but what's the procedure for checking for a spark?

[mike_of_bbg]

Remove spark plug wire, remove spark plug, re-connect wire, lay against head (so the outside is grounded), crank engine.

[miles28]

ok, so I did the spark check. They all seem to have a very faint spark that travels around the lobe. I get the impression that a fat blue spark is not what I was seeing, but they all seemed to be skinny light blue sparks. Does that mean anything? Also, every plug but the one fouling had a slight yellow hue on the ground electrode, is that significant?

-Chris

[earlfor]

Interesting. I thought all the GSs pulled vacuum from #2. The 750B is different?

Yes, it pulls vacuum from #3. I'm not positive on this, but I believe ALL VM series carbs pull vacuum on #3. Its the CV setup that pulls vacuum off of #2.

Earl

[miles28]

So does anyone think I may have a bad fuel petcock?