Lemans 3 running fault

Ok.I start up the bike from cold and all runs well, after only a couple
of mins she starts to miss fire and pop and bang with large black smoke
and 2 ft flames withone of the most nasty smells there is out of the left hand exhaust. After 5 mins or so of hard
riding she starts to clear and run fine but leave her over night and we
start again. I have replace coils, points, HT leads,caps and plugs all
with the same result. When I remove the plug it looks like it has come
out of one of my old 2 stokes when the plug oils up. In fact we got it
to TDC and scraped the top of the piston and it came out covered in
black crap. Not only this but all of a sudden I have oil leaks all over
the engine, It’s coming out of what looks like the spark plug hole or
the nut just below. I even have oil coming out if the inspection hole in
the gearbox. I plan on taking the head off tomorrow and having a look.

Blown head gasket?

I’m trying to think how lots of oil can get into the combustiion chamber. There’s no oil feed galleries in the barrel itself. Possibilities are: Stud O-ring(s) failed so oil is being pushed up a stud by crankcase pressure. Remote Broken piston ring(s) Holed piston crown (but would be like running on one cylinder) Cracked head so oil is leaking down into combustion chamber from rocker box cavity.

Appendix ~ I’ve just remembered the pushrod tunnels and drain tunnel, so yes if head gasket is loose crankcase pressure could blow oil in that way.

Before ripping it apart, give the carb float bowls a sharp tap with the handle of a screwdriver to make sure you have not just got a stuck carb float.Guess how I know that one!!

I have cleaned out the carbs and all was ok. At the point of it running bad if I pull the choke on she will run a bit better then as I say after a few mins, she then runs fine.

There’s 2 topics running on this now ~ should we confine it to Tech Talk? Last post from Guzzi Parts:

This sounds a really strange one. Is it worth doing a carb swap, put the left one on the right and the right one on the left, just to rule that out absolutely?Ditto swap coils over?Timing? You say you have changed the points, was this before or after the troubles started?Is there anything you did to the bike before all this started?Duff fuel? - that would effect both cylinders.I assume you have the cross over on the fuel so both taps feed both carbs. That would rule out a blocked filter in the tank.Let us know what you find?

“I have had running problems on that side for some time but it has got worst now” Ah! Not that sudden then.

“When I remove the plug it looks like it has come out of one of my old 2 stokes when the plug oils up. … Not only this but all of a sudden I have oil leaks all over the engine, It’s coming out of what looks like the spark plug hole or the nut just below. I even have oil coming out if the inspection hole in the gearbox” I agree something weird going on ~ not convinced it’s owt to do with carbs, except I have had the experience where too overly enthusiastic oiling of the throttle cables merely resulted in both carb slides being soaked with engine oil! In fact when I took them out this time they were oily, albeit I’m more sparing with the oil these days. But I am digressing (as usual) …

EddieWhat did you find???

Well, all sorted. I checked for any oil in or around piston and valves and found that all was clear. So I removed carbs again and again cleaned them out, I also rewired the ignition system from points to coils then replaced HT leads and plugs ( my god they have gone up in price ) anyway set points gap and had a general check around. I fired up the old girl and she ran on both sides, we went up the road to get her warm and had no problems, gave her a tune up on my return and all seemed ok. I went to work on her today and all sorted.Thanks for all the advice people gave, this is one of the things you should join the club for.