Intermittent issue

Always worst.Rather total failure,so at least you can troubleshoot!
Ok this is my 1970 roadster that I restored last year.Spec as follows
750 Commando
PW3 Cam
Single Mikuni courtesy of CNW
Comstock Crank breather
Anti wet sump valve courtesy of HNW
Pazon Surefire
Electronic tacho/speedo
Oil filter fitted
5 ohm coil pack
LED rear light courtesy of CNW
LED Indicators(barely used)
Bike is a first time kicker.Rides wonderfully.However, this issue kicked up (or was noticed) after a few weeks.During SOME rides, especially whilst idling at lights I would notice a puff of smoke.
Initially I didnt pay too much attention.It got worse on occasions.Now considering the amount of additional electrical items, I considered that it may be the battery not being able to feed the Pazon enough
current, and it compromised its spark.Especially as on one occasion the tacho developed a mind of its own and was going haywire.Today I thought Id try and induce the fault, then measure the charging output.Well she behaved perfectly.Got back to garage and then decided to let it idle whilst indicator and headlight were on.After 3 minutes, the left pot(always the left) let a puff of whitish smoke.This became steadily worse,and I thought it was going to stall.I measured the battery charging output at 12.2v.Tad low,(its usually 13.5ish without lights on)However sufficient enough to charge battery.She eventually stalled,as smoking got worse.the ammeter was showing between middle of gauge & zero.
I spoke to guy who built the loom (this is ALL he does) he concured numbers seem fine.However the sum of ALL the excess drain may cause just enough voltage drop to rob the Pazon momentarily
Naturally all the usual suspected parts have been checked.The engine is running very rich.Plugs are black.My last thought is that perhaps there is an issue with the Mikuni ?
Natrurally any input always appreciated.

Single carb wouldn't smoke on just one cylinder. Sounds like oil consumption.
That doesn't mean you're not also running rich, but that's not what's causing smoke.

White-ish smoke is burning oil. Excessive fuel is black smoke... It's not electrical.

When you leave it idling is the bike tilted to the left on it's side stand maybe? or on the center stand?

Top guesses, knowing nothing except white smoke:

-retorque the head maybe your torque is off and you are getting some oil seepage from the left pushrod tunnel
-loose valve guide
-tiny crack in the head that only leaks around the guide when you let the bike get hot by idling excessively
-cracked intake valve seal
-partially pluged head rear drain passage
-left rocker arm weep hole is facing the wrong way
-poor fitting exhaust valve and guide on the left side
-keebler elves are at work again...

o0norton0o said:

White-ish smoke is burning oil. Excessive fuel is black smoke... It's not electrical.

When you leave it idling is the bike tilted to the left on it's side stand maybe? or on the center stand?

Top guesses, knowing nothing except white smoke:

-retorque the head maybe your torque is off and you are getting some oil seepage from the left pushrod tunnel
-loose valve guide
-tiny crack in the head that only leaks around the guide when you let the bike get hot by idling excessively
-cracked intake valve seal
-partially pluged head rear drain passage
-left rocker arm weep hole is facing the wrong way
-poor fitting exhaust valve and guide on the left side
-keebler elves are at work again...

Click to expand...

I dont have centre stand,so yes bike is on side stand.However, it has also been noticed whilst out on road,at traffic lights etc.Engine was built by one of the top guys in UK.(if not top)However shit happens as we know.Ill start with the easy stuff first obviously

Not ignition.

Cylinder head oil control anomaly.

coomo said:

I dont have centre stand,so yes bike is on side stand.However, it has also been noticed whilst out on road,at traffic lights etc.Engine was built by one of the top guys in UK.(if not top)However shit happens as we know.Ill start with the easy stuff first obviously

Click to expand...

If he's "one of the top guys", he should find the problem in short order. It's not all that hard to narrow down an oiling issue from smoke coming out the exhaust. Unfortunately, the fixing always requires some disassembly to repair... That's just the nature of it.

If it's an valve stem seal, it's not too deep of a fix. If it's cylinder rings, then you are going in deeper.

Maybe,.... change the oil and inspect the oil for excessive amounts of metallic grit, or some metallic crumbs... It's always reassuring to see there's nothing breaking up inside your engine when the engine is smoking.

If it turns out to be a clogged rear drain hole in the head, you can poke it clear with a guitar string and air pressure hopefully. The fact that the smoke happens on the left side and you only have a side stand, may mean that it is indeed a head rear drain hole issue, which submerges the left intake valve in oil rather than the right cylinder because the bike is tilted to the left on it's side stand.

I'd call that "top guy" and ask him to have a look...

Thanks for the input guys.I was going to work through this today, but a welding job took longer that Id predicted.I did remove the side cover to check contents of catch tank.As I no longer have the standard air filter box, the oil tank breather would exit directly to atmosphere.To curb excess oil being thrown over the carb/rear of engine, I brazed a spigot on the breather hole, then ran to a catch tank.Fair bit of water/oil mixture in there.

o0norton0o said:

White-ish smoke is burning oil. Excessive fuel is black smoke... It's not electrical.

When you leave it idling is the bike tilted to the left on it's side stand maybe? or on the center stand?

Top guesses, knowing nothing except white smoke:

-retorque the head maybe your torque is off and you are getting some oil seepage from the left pushrod tunnel
-loose valve guide
-tiny crack in the head that only leaks around the guide when you let the bike get hot by idling excessively
-cracked intake valve seal
-partially pluged head rear drain passage
-left rocker arm weep hole is facing the wrong way
-poor fitting exhaust valve and guide on the left side
-keebler elves are at work again...

Click to expand...

Quick update on this.I checked rear drain.It was clear, as I presumed it would be.Decided to re torque head.I used 2 spanner technique and pulled down by feel.3/4 took about 1/8th turn.
Have now completed about 120 miles., in various riding conditions.No indication of any burning oil/smoke whatsoever.Heads up to all the (as usual) great advice here.

The electronic gauges going haywire or doing sweeps through the range is indicative of low battery power.

It’s still rich though I assume? Dig out the paperwork, or ask Matt what he supplied it with then ask folk on here for alternative settings. No carb can be supplied as perfect for all possible tuning combinations. There are Mikuni experts on here that’ll give good advice.

Fullauto said:

The electronic gauges going haywire or doing sweeps through the range is indicative of low battery power.

Click to expand...

Can also be an early warning of a connection issue, as I have discovered.

Fast Eddie said:

It’s still rich though I assume? Dig out the paperwork, or ask Matt what he supplied it with then ask folk on here for alternative settings. No carb can be supplied as perfect for all possible tuning combinations. There are Mikuni experts on here that’ll give good advice.

Click to expand...

Thanks.Yes still a tad rich.I did mail Matt about this.No response as yet.Ill pull the jets see what ive got.However, I can call Allens Performance.They are top Mikuni guys, who can recommend settings

If you get the smoke puff from left side, only when blipping throttle, then likely an intake valve seal. Mine did this and the seals crumbled away as I removed them. I did the replacement with head still on bike using a nifty tool donated from a fellow member. Search forums for the method used.

The oil drain later became another issue for my bike. Needed a thorough poking/spraying with very long spray tube to reach timing chest from above. Clearer up a left misfire due to foul plug and more smoking.

Steve at Motocarb is a Mikuni supplier as well. Very clued up re jetting.