1976 KZ 900 #4 plug fouling

My buddy is working on getting another friends 76 KZ 900 running. He is currently fighting a fouling issue on the #4 plug. He said he has swapped plugs/wires/coils with other cylinders and swapped carbs (apparently 2/4 carbs are interchangable on these bikes?) and the issue stays with #4.

He said it doesn't smoke at all, so I would think rings or valve seals would be ruled out. He has 125 psi on all 4 cylinders. The only thing he was wonder is if the valves adjustments are tight, would that cause a plug to foul? I think he plans on adjusting #4, but just has not gotten the shims yet... He mentioned he is wondering if the timing is off somehow...?

gas or oil?

apbling wrote:

...76 KZ 900...fouling issue on the #4 plug...swapped plugs/wires/coils with other cylinders and swapped carbs (apparently 2/4 carbs are interchangable on these bikes?)...issue stays with #4...doesn't smoke...125 psi on all 4 cylinders. The only thing he was wonder is if the valves adjustments are tight, would that cause a plug to foul? I think he plans on adjusting #4, but just has not gotten the shims yet... He mentioned he is wondering if the timing is off somehow...?

Too tight valve could result in reported problem.

Don't need shims to measure existing clearance.

Likely not a timing issue.

Good Fortune!

This is a very common problem. It happened to me also. i discovered it to be the enrichening plunger not seating all the way. Even after I rebuilt the carbs it kept on doing it. I solve the problem by putting extra pressure on it to seat it to it's fullest.

Thanks for the replies guys. He'll just have to keep tinkering with it. He told me that he switched the carbs around and the problem stayed with #4, so it's got to be rings/valve seals/valve clearances or something non-carb related (or electrical because he moved them around too)

How were the carbs switched around when the housings are not the same????

I'm not sure... I'll have to ask him. Which housings are you referring to? He just texted me and said that it's not a carb issue because he swapped 2 and 4 and said they are interchangable. I'll have to give him a call and see exactly whats going on. He's a pretty good mechanic, so maybe I'm the weak link in the information chain .

Than he is lying to you. Especially 2&4 are not interchangeable. 2 is a left hand carb and four is a right hand carb. This guy is playing you. This mechanic who ever he is, is not very scrupulous with you. This is telling me that he is charging you for things that he is not performing, and he is not aware that you have this web sight as a recourse.

He's not working on my bike, it's another buddies bike. He actually is a family friend of ours and does lots of favors fr people with their bikes, and usually charges little to nothing for his time... I am guessing I mis-heard/understood him.

He isn't a mechanic, just a guy that knows how to work on bikes. I'll confirm what he's referring to and get back to you.

A single plug fouling is probably carb because plugs are wired in series so a bad coil would affect two plugs not one. Could definitely be a bad valve guide seal if oil is running down onto the plug.

How long will it take to fowl out the plug after cleaning it? If it is between 30-50Mi than it is the enrichning (choke) plunger. If you would be doing it with oil, you would be smoking like crazy.

On my twin when the valve seal failed, I didn't see any smoke at all. But a little oil would run down after I turned it off and foul the plug. Only takes a tiny amount to foul the plug and gravity was running it right onto the plug tip.