Spark Plug Carbon Fouling on Cylinder #1

[janderson12]

First of all, this is the only place that would allow me to start a new topic, so I hope it is appropriate to post here.

I have a 1979 XS1100SF and I can not figure out what is causing my #1 spark plug to foul. I have done everything that I can possible think of to fix it.
My XS1100SF has pod filters and an open header exhaust. Cylinder #1 is the only plug that carbon fouls.
Below is a list of what I've done to the bike in an attempt to fix the carbon fouling.
Carb bank completely gone through and cleaned with original jets removed cleaned and reinstalled. When this did not work I installed new Mikuni pilot jets (#42.5) and new Mikuni Main Jets (#145). I also tried #142.5 Main Jets. When this didn't work I tried a completely different carb bank (cleaned) from another 1979 XS11.
I've tried a different set of pistons/rings, a different cylinder (jug), a different cylinder head and cylinder head gasket. I've also tried a new set of ignition coils. I'm using the correct spark plugs (NGK BP6ES) gapped to spec.

So what in the world am I missing here??
Thank you in advance.

[janderson12]

A couple more things, Pilot Screws are 2 turns out. I do not have the original vacuum operated petcocks. I'm running a single hose from the left side of the fuel tank that splits into a "T" which runs into both fuel lines of the carb bank.

[Bax]

janderson12 A few more things to check. Are all the needles and emulsion tubes the same? Does the float level hold properly when the bike is running using external tube to check? Some carbs had the sensing hole in the bottom of the slide enlarged for an improved performance attempt you may have the odd carb part going on. All the diaphragms and springs intact? Does the plunger on the richening circuit properly shut/seal. If not the carbs then excessive oil in cylinder, rings, valve seals.....


Bax

[bikerphil]

You could try swapping the plug wires on 1 and 4 and see if it still persists. Are you using the stock 40 year old coils or aftermarket replacements?

[janderson12]

Bax, I'll take a look at what you suggested. Thank you!

bikerphil, I'll try swapping the plug wires, but since I've tried two different coils I won't be holding my breathe. The bike had Accel coils on it when I bought it which tested good, but I also tried swapping the coils out with some new aftermarket coils that I had on hand. Same results with both coils.
Thank you for the suggestion though.

[DiverRay]

Try a leak-down test. My guess is bad valve seals, and you have just a little oil causing the problem.

[2WheelFun]

I was going to say valve seals but he said he changed the head. Odd that a different head would still foul #1. Add to that new cyl and pistons/rings and you ruled out anything I would investigate. Maybe it's not getting good spark.

[janderson12]

Some additional information. The carbon fouling on spark plug #1 seems to be occurring during start-up of a cold engine. The bike is very difficult to start while cold. After the bike is warmed up I can remove plug #1 clean it and then reinstall without carbon fouling (this is with limited amount of testing.) So should I be looking at the starter jet circuit?
Thanks