FJ1100 PLUGS FOULED WITH CARBON

[doodah]

So, my fj fouls all 4 plugs - starts straight away, but it runs rough and won't idle, as if the choke was on and within a minute or so all 4 plugs are completely blackened with carbon, and it is undriveable.

This is what I have done so far to try and cure it, none of the following has made the slightest bit of difference:

new rings and valve stem seals (initially the plugs were oiled up as well, now oiling up gone and only covering the plugs with carbon)
cleaned carbs
replaced pilot jet # 40 (European model)
float height at 23.5 mm , I have tried it at 27 to make it run lean but no different
checked chokes are shut off by attaching a hose to the pick-up tube in the float chamber and can't blow down it until you open choke valve
new float valves sealing nicely, invert the carbs and you can't blow down the fuel hose
new air filter, tried without air filter, no different
new o rings on carb mounting rubbers

changed electrical connectors on ignition circuit - ignition switch, run stop switch, pick ups, ignitor output, ignition coils, changed the 3 way fuse holder + connector
tried 3 different ignitors
re-wired pick ups + cleaned rotor arm
new earth cable
new plug caps
changed ignition coils
new plugs

Any suggestions as to what to do next?

[T Legg]

How much compression does it have?

[Pat Conlon]

Is the ignition advancing properly to flash off the plugs?
Do a suck test on the vacuum line going to the TCI ignitor. See if it holds air.
Read about the advance here: http://www.fjowners.com/index.php?topic=11690.0

I second Travis's question...how's your compression? Maybe the new rings haven't seated yet?

[fj1289]

What condition is the battery in?  What condition is the generator in?  A bad electrical system yields a poor ignition system ...

[doodah]

100 -125 psi compression - need to get some feeler gauges and check the clearances

[doodah]

battery about a year old and fully charged
swapped out the alternator - now charging at 14v

[doodah]

vacuum hoses changed, no different

[RPM - Robert]

100 -125 psi compression - need to get some feeler gauges and check the clearances

100-120 is well below the threshold of service. 128 minimum, 171 maximum is what Yamaha calls for.

[Pat Conlon]

Are those cold or hot numbers?
If hot numbers, squirt some oil in the cylinders to see if the #'s come up

Did you hold the throttle WFO when you took these readings?

I had a problem with failure on oil ring seals on a rebuild using Hank Scott Pro lite pistons.
At high rpm when I closed the throttle plates, the vacuum in the cylinders would literally pull the oil up into cylinders and oil foul the plugs....along with depositing a thick cake of coked on oil on the piston crowns and heads.

Perhaps your oil rings are not sealing?

[doodah]

Ok, so I don't think its a ring problem coz they were all brand new.
Clearances were a bit out - by 0.05 on several of the valves.
Re-shimmed - made no difference.
I remembered that a handfull of buckets fell out onto the floor, I replaced them as best I could judging position from where they lay on the ground.
I also remembered I trod on some of them.
Then I thought to myself perhaps I put the buckets in reverse order, numbering them from the left to right from the front when taking them out, and installing them when looking at the rear of the motor, thus bucket 1 was in position 8, bucket 2 in 7 etc.
So I reversed order on the buckets and re-shimmed them.
Pots 1+2 ran better, not fouling straight away 3 started out fouling then ran better. Still grey/black insulator on the plugs and misfiring, but not coked up within seconds. Pot 4 the piston was hitting the valves and heavy coating of carbon on the plug and running hot.
Compression tested pot 1 which was the worst with 100psi - it jumped to 140 after swapping the buckets around, cold with no carbs attached.
So I got 12 XJ600 buckets from Ebay for a decent price and swapped out the buckets on pots 3+4 that seemed a bit stiff / tight and re-shimmed to suit.
Now pots 3+4 running almost cold, 1+2 now running hot + misfiring, pot 1 coking up after a short time.
So the plan is next week when I get the time is to take the cams out yet again and swap out any stiff buckets on 1 +2