Mystery plug and pipe temperature

[Kara25]

Greetings guys first time posting here. I recently aquired a GS550E. The bike was rebuilt from scratch into a cafe racer from the previous owner. When I got the bike home before starting to change fluids etc etc as a new owner I noticed something weird. Pipe No3 was running hotter than the rest. I took out all the plugs(was gonna change them with brand new anyways) and I discovered that the No3 spark plug was different from all the other 3 (!). It’s like a small 2-stroke plug. Obviously previous owner messed up the threads and did some patch work so it can fit some other size plug in there. What baffles me is that the bike runs good has power in all range but this is making me uneasy knowing some foreign plug is in there. Is that why the No3 pipe is getting hotter? Oh and btw this particular plug is filled with dark carbon deposits dry ones indicating I assume a rich mixture.. All the other 3 all look good cream colored...Looking forward for some wisdom from you guys.!

[GregT]

What are the heat range numbers on the plugs - and the brand please.

[Kara25]

All of them are NGK. 3 are B8ES and the different one is D8EA.

[GregT]

Even given the different plug, there shouldn't be a marked difference in cylinder temp, all else being normal.

I'd do a carb balance as a first step.

[Kara25]

Thanks a lot man.! I was thinking about taking the carbs out for cleaning just to keep my mind at ease and I think I found the culprit of my problem.. The o-ring in the boot of the third cylinder looks beaten and cracked. I assume air was passing through that and thus the high temp. Let’s see what will happen after I replace it put everything back together and balance the carbys.!

[standswithabeer]

heat range and reach for B8ES and D8EA are the same, the only diff is thread size, 12mm vs 14mm. not sure what you mean by "patch-work", usually helicoil repairs don't change thread diameter. i think the carb mix needs needs adjustment on #3. i also have a gs550e, do you have pods or modified exhaust?

[Kara25]

After removing the carbs cleaning them thoroughly and replacing the No3 carb boot that goes to the cylinder everything worked well all plugs have nice tanned colour and all pipes heat-up the same. So I think the leak on the boot was the culprit.!

[steve murdoch]

Glad you got it sorted.
Also, glad that you did the follow-up. We could all do better in reporting back after solving problems.