Grey smoke, fouled plugs

[Thunzie]

Hi folks. I'm new here and I come seeking advice on a problem thats recently surfaced which hass me doing some head scratching. I have a 79 model XS650 which I have hard tailed. Running VM34's and straight pipes. The bike has been running fine in this configuration for quite some time but over the past few weeks, from a cold start I'm getting a very light grey colored smoke out the right side exhaust and it's also fouling plugs on that side now. If I start the bike and let it just sit there idling to warm up it will foul that right side plug, but I've found that if I keep the revs up enough while the motor reaches operating temp, then go for a bit of a ride to really get the motor at normal riding temp there's no more smoke, all is normal.

Yesterday I put in brand new plugs, went for a ride and everything was perfect but I decided to look at the right side plug after the ride and sure enough, it was a little wet. Hard to say if its fuel or oil wet though, there wasn't enough of it but from a sniff I couldn't smell fuel.... so I'm guessing oil... guessing.

 

[CDNTX650]

head gasket perhaps? they can suck oil from the camchain tunnel. Or valve stem seals.

 

[Thunzie]

If you're right would you agree that the warming up of the engine expands things enough to seal the leak and thats why the smoke goes away? It seems to only wet that right side plug during the warm up...

 

[5twins]

This could also be caused by an over-rich condition caused by the float bowl over-filling. There is an o-ring around the outside of the float needle seat that seals it into the carb body. That can go bad and when it does, fuel leaks past the outside of the float needle assembly, over-filling your bowl. The gray smoke you're seeing could be the excess fuel washing the oil off the cylinder walls. Easier to check than taking the motor apart, lol.

 

[Thunzie]

This could also be caused by an over-rich condition caused by the float bowl over-filling. There is an o-ring around the outside of the float needle seat that seals it into the carb body. That can go bad and when it does, fuel leaks past the outside of the float needle assembly, over-filling your bowl. The gray smoke you're seeing could be the excess fuel washing the oil off the cylinder walls. Easier to check than taking the motor apart, lol.

5Twins thanks for your input. The o-ring should be ok as these carbs ar only 6 months old but it's still worth me inspecting it - thanks, will do. I suppose it's worth mentioning that this pale gray smoke from a cold start is some days much worse than others, which to me would suggest that this is an intermittent problem, a dodgy o-ring could definitely result in such symptoms.

 

[5twins]

I would also verify that your float level is correct and that the rubber tip on the float needle is in good shape. Either could be causing the bowl to over-fill.

 

[HooliganCycles]

I would guess valve stem seals, oil leaks past the stem seal into the cylinder then when you fire up the bike and it warms up it continues to burn off the oil.

 

[Thunzie]

I would guess valve stem seals, oil leaks past the stem seal into the cylinder then when you fire up the bike and it warms up it continues to burn off the oil.

But this bike only blows the light grey smoke when completely cold, and once warmed up - good as gold. A bit more info; It only seems to happen on a fully cold start (been sitting all night, about 14 hours). Doesn't happen when I ride home for lunch (been sitting about 4 hours) or back home that night (another 4 hour rest).

Looking into 5Twins float suggestions... stay tuned (pun intended).

 

[bbillington]

But this bike only blows the light grey smoke when completely cold, and once warmed up - good as gold. A bit more info; It only seems to happen on a fully cold start (been sitting all night, about 14 hours). Doesn't happen when I ride home for lunch (been sitting about 4 hours) or back home that night (another 4 hour rest).

Looking into 5Twins float suggestions... stay tuned (pun intended).

You could pull the exhaust and carbs after the bike has sat overnight and that should clue you in.

 

[Thunzie]

You could pull the exhaust and carbs after the bike has sat overnight and that should clue you in.

It would if I knew what to look for in the pipes and carbs, wish I knew the forensics of it to know what to look for.... unfortunately as keen as I am to learn about my XS I'm not yet quite that cluey. PS: I dig your Slayer icon "Infamous! Butcher! Angel of Deeeeath!!!!"

 

[bbillington]

Just have a look at the valves for oil accumulating on them or evidence that it has burned off. You could also just pull the spark plug on that side and rotate the engine to TDC and have a look with a flashlight to see if there's evidence of oil on top of the piston. If it just started, you probably won't see much.

I'm no expert either, but you'll know if something doesn't look right and you'll be smarter for having tried. You can always compare the smoky side to the other cylinder as well for reference.

coils of the serpent unwind
buried beneath you will find
deep in the halls of the damned
spark plug covered in black til the end

 

[CDNTX650]

i can tell you white/grey smoke on mine was valve stem seals.

 

[HooliganCycles]

You can also check your oil, if it's stem seals or something along those lines your oil level is gonna go down, obviously it will depend on how much it is burning. Another thing to remember is grey or light smoke is oil, black smoke is fuel

 

[Bryn Turner]

Hi. I know it was 7 years ago but --- Did you get to the bottom of this problem? I have the same issue.

 

[Thunzie]

Yeah mate, it was all because the engine needed a top end rebuild. After that, I had no further issues with anything.

 

[Bryn Turner]

Thanks for your reply !

 

[Thunzie]

Also keep in mind I was running VM34's because t

Thanks for your reply !

No worries Bryn. Mate, I wasted SO much time trying to sort that problem out thinking it was probably ONLY the carbs. But now in hindsight it's clear to me that it was a bit of both the worn top end and the original carbs; the original carbs were definitely worn, so I replaced them with the new VM34's, which made some difference. The VM's are great carbs for the XS! But make sure you get the genuine Mikuni's and don't go for the cheap knock-offs that exist. If you have smoke issues beyond that, assuming the new carbs are properly balanced (click here to see I video I made for a cheap, easy and very accurate way to balance carbs), odds are you probably need a top end rebuild. My top end rebuild from memory consisted of a re-bore to first over size, new pistons, rings, conrods, timing chain, gaskets of course, valve job, and man... from then onwards that bike was solid as a rock. Wish I still had it! I sold it a few years ago.

 

[Bryn Turner]

That should keep me busy for the next few weeks ! You should of kept that it ran and sounded beautiful. What do u ride these days ?

 

[Thunzie]

That should keep me busy for the next few weeks ! You should of kept that it ran and sounded beautiful. What do u ride these days ?

Another late reply haha. Since then I've restored a 1972 Honda CT90, which I still have. Had a GSX1400 for a few years. And now I have another XS650. Same model as my previous one, a 1979 XS650SF. But this one will not be chopped! It will remain almost stock - So, did you sort out your problem?