no more guesses - can't figure it out

For reference, I started the bike up with the #2 plug out and put a square of toilet paper just over the hole for about 5-10 secs.

This is what i got - ew

? ? Oil level okay -- not too high ? ?

Good even compression figures, and good spark on #2.

From an FSM trouble shooting guide:
Valve oil seal damage;
Valve guide worn;
Cylinder head gasket damaged.


Wild guess -- Any possibility of an oil channel restrictor or o-ring having been inadvertantly omitted during reassembly? Or possible misfitment of a valve oil seal?

Is the apparent excess oil inside combustion chamber "clean" oil? Or possibly fuel soaked carbon gunge from a fuel fouled cylinder? Suppose it might help to flush out the cylinder by spraying inside with carb cleaner, and letting it sit for awhile to allow evaporation out the empty sparkplug hole? Seems like the new plug (shiny black with good spark) is producing some limited combustion in the cylinder?

Good Luck!

Toilet tissue test indicates clean oil which would seem to rule out fuel soaked carbon gunge.

Still thinking about a combustion chamber flush out with carb spray.

May yet result in being a problem inside the carb primary circuit (perhaps blocked fuel passage) which is preventing delivery and existence of a combustible fuel mixture in the cylinder.

Am still pondering.

That's for brainstorming...i think eventually we'll hit on it.

pondering if I should offer a reward for the first right answer hehe

Valve oil seal damage; - possible but unlikely, just changed

Valve guide worn; - possible, but unlikely, even if guide worn, the seal should keep oil out, right?

Cylinder head gasket damaged. - brand new one in march, also seems unlikely


the oring and restrictors are good ideas, but they are on the outside, so wouldn't they affect #1/#4, not #2? i don't think there are any oil passages by #2 on the 750....

Agreed on the clean oil, what was coming out was prestine oil, not gunky oil.

the primary circuit may still be problematic, but the cloud I was getting actually seems to indicate it was firing properly, just too oily in there. that caused the cloud and eventually fouled the plugs, yes?

i read somewhere that i may have a gouge in the cylinder wall, just BELOW TDC so that it gets good compression numbers but wouldn't seal only on the whole travel. i'm really hoping to avoid having to take the head and block off if i can avoid it...

Just to confirm, crankcase oil level is okay (not too high)?

Any repair history that could have involved damage to the oil ring on #2 piston? Such as unknowingly breaking the #2 oil ring when reinstalling a cylinder block?

Thinking a broken oil ring might not disturb compression, but allow clean oil movement into the combustion chamber.

Casting ideas -- not stones. :laugh:

I haven't worked on the bike lower than the head, but it is certainly possible that the #2 oil ring is broken at some point.

fairly certain the oil level is ok

It was low this morning and i filled it to 80% full before all the testing today.

Is my only options at this point to open it up all the way in a teardown? Should I start a poll?

May catch some flak here, but I would be desperate enough at this point, before resorting to engine disassembly, to assist #2 with some starting fluid sprayed through #2 carb intake to at least get the engine cranked and hitting on all four cylinders, and thereby afford it a long-shot chance to clear out #2 cylinder. And yes, it will most likely smoke heavily until quickly re-fouling the new #2 plug.

Any particular reason to suspect #2 carb is failing to deliver a fuel mixture or otherwise performing any differently than the other three carbs?

Good Luck!

I reinstalled #2 and started it up. big white cloud again that doesn't go away. #2 is firing, but clearly burning oil left and right.

i just wish I could confirm the need to tear into it before i do...

While grasping at straws, am doubtful that a clogged crankcase breather could cause this particular problem (in contrast to oil leakage), but suppose it wouldn't hurt to check it.

Still pondering, but options are dwindling.

Fingers crossed! Good Luck!

dnpurdy wrote:

I reinstalled #2 and started it up. big white cloud again that doesn't go away. #2 is firing, but clearly burning oil left and right. i just wish I could confirm the need to tear into it before i do...

Going to be any betting allowed in the poll? :lol:

Took the breather cover off. Inside is slight puddle of oil in the low spots, prestine metal. The hole to the airbox is totally clear.

AHHHH!!!!!!

If anyone can solve this without a tear down, you get $50 of z1 stuff from me....

If the head has to come off, no winners