Plug fouling…>

1973 850 Roadster with new Amal Premiers and TriSpark ignition, original coils. I've got a new issue where my timing side plug is fouling. I'll goo out for a ride, bike runs well but something's going on at idle. When I get back after 10-15 minute ride and let it idle it will start smoking out of the right-hand pipe. After shutting down I'll pull the plug and it's black & wet. I put a new plug in, took her out and same thing happened. Today I pulled the right-hand carb and stripped it down, particularly blowing air through the pilot air passage. Float level & viton both seem fine. Got it all back together and just took it out and had the exact same thing happen again. Took both plugs out and put them against the cylinder head and used the kickstart - good spark on both sides. Not sure where to go with this. I do have my original carb, I'm thinking of swapping that in just to see if I get the same symptom. The primary side plug is a nice, even brown color.

Drop the timing side needle a notch.
It may seem normal to adjust the both carbs alike and of course should be the starting point, but knowing the no 2 Nortons breath exactly alike, neither do 2 cylinders.

Dark smoke good as implies fueling issue, white smoke bad as implies oil in chamber. Rings tend to seal better as heat soaks in and stop smoking on the road or on return so implies to me - think valve guide or porous metal issue or gasket internal leak.

Did you check the float height?

I had to set the height of my Premiers. They were set to high for the angle they are mounted on at a Commando.

I think you have an oil issue rather than fuel issue. To me, your post implies the bike starts smoking (color?) from one side after a run but idles ok. A wet oiled plug will spark for a bit and engine will run until plug's totally fouled, especially if the A/F ratio is ok. A plug that is wet from fuel is living in a cylinder that is not igniting. If the engine is running on two cylinders but a plug comes out wet, I'm thinking the 'wet' is oil not fuel.

Biscuit said:

I think you have an oil issue rather than fuel issue. To me, your post implies the bike starts smoking (color?) from one side after a run but idles ok. A wet oiled plug will spark for a bit and engine will run until plug's totally fouled, especially if the A/F ratio is ok. A plug that is wet from fuel is living in a cylinder that is not igniting. If the engine is running on two cylinders but a plug comes out wet, I'm thinking the 'wet' is oil not fuel.

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You may be right, Biscuit, but I would want to trouble shooting the "fuel/rich on one side" issue before delving into what could be an extensive problem.

Going out for a normal ride, sooting up the one side, then coming home and seeing a bit of smoke does not seem that far out of the question.

Seems to me an oil issue might manifest cold, but thenm again, when the oil get hot it would flow easier to where is shouldn't. Maybe do a DogT reversal and run some straight 50 wait and look for improvement.

Perhaps if it could be determind if the plug is wet/fouled from oil or from gas. Could be confusing because of the smell of gas when fouled either way.

It just seems to make sense to rule out the easy stuff first.

Just give the plug a sniff. Easy to tell the difference between fuel and oil.

Mark F said:

Just give the plug a sniff. Easy to tell the difference between fuel and oil.

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I thought that at first too. But if fouled it should be wet with gas either way. Maybe being fouled by oil will lave a different signiture like carbon deposit down in the electrode or something like that.

Maybe leaning out the needle and giving the air screw a 1/2 turn out may give an indication of the source of the trouble.

Good luck sniffing a missed fired plug to know if over fueled or not. Wet look better way. Its standard procedure to always look for lost keys under the street light first but generally in my case short cuts never seem to work out efficiently. I can tell ya one thing it can smoke clouds like a crop bug forger for a good while before fouling normal heat range and gap set spark plugs, ugh boy howdy can it but at some point alone with illegal levels of chem-trails it will start missing and eventually be too unpleasant or trustworthy to ride. White glove or finger wipe in muffler may give idea of oil or fuel carbon soot source though of course could now be both. If ya pull head and notice a clear section along piston rim - definite indication of oil past rings fouling combustion in that area. A bore/ring issue better than in the head I'd think. I've had oil sucked in from bad gasket seal by oil drain hole and push rod tunnels and have seen a head with gas jet cuts from bore to tunnels. Such simple machines so about anyone can get em fully fettered leak and smoke tight straightaway they tell me.

If carbs are set correctly the plugs should not be wet. Try it with fresh plugs straight after a 10/15 minute ride.

I've just re-read your original post and I see you have new premier carbs. Is your motor stock? Are carb settings stock?
If you're non stock and you have dialed in your carbs in its probably unlikely to be fuel.
I had a problem a while ago where a new valve guide seal had come off the guide. Smoked on timing side at idle. This seems to be not uncommon from the amount of posts I've read on the subject. They don't have much to hold on by.
Could also be loose/leaky valve guide or oil leak at head joint.

I had some problems with my 750 bog standard with mikuni and boyer , black wet plugs white smoke. No mater which way
I looked at it ,it was an oil problem. And when my plugs were like that it ran like a turkey,new plugs, she started easy and then back to square one.
Cured that problem and now it's blown the head gasket. Hey ho!
Best of luck with your bike

Biscuit said:

I think you have an oil issue rather than fuel issue. To me, your post implies the bike starts smoking (color?) from one side after a run but idles ok. A wet oiled plug will spark for a bit and engine will run until plug's totally fouled, especially if the A/F ratio is ok. A plug that is wet from fuel is living in a cylinder that is not igniting. If the engine is running on two cylinders but a plug comes out wet, I'm thinking the 'wet' is oil not fuel.

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+1 -- See the other thread about oil coming down or around the valve guide. Not to dispute that it could be a fuel/carb problem but this sounds exactly like what mine was doing before having the valves done right. Look in the intake and exhaust ports on the smoking side and see if there is oil on the guide.

Thanks for all the replies and great information. I'm inclined to go with the oil thinking for a couple of reasons - the Premiers were running great for the month since I put them on and it doesn't seem that any carb adjustment makes a difference. The winter build did include the head being sent out and done up with new valves/guides and springs. The pistons, bores and cam showed virtually no wear. Pistons did get new rings, so I'd be really bummed if the issue is rings. I'll proceed in terms of looking for oil coming down/around the valve guide. Tom

Its been well settled here by the most respected builders [so not hobot opinion] that there is no risk to run head w/o oil supple at normal engine temps for way long enough to see if that stops the smoke habit or not to help ID next area of hassle to recover towards the mythical attainment of a temporarily fully fettered Commando. In my events bad rings got wet sump splash that smoked bad on first firing then cleaned up in a minute or so, so I'd just ride off essentially smokeless but following rider could smell it on throttling ups. Head gasket and other head items took about 30 sec of 2000 ish rpm warm up - wet sump pump down, before oil flow hit head to get into chambers to smoke. Ugh then got bad enough head and bore wear the smoke started right away and didn't go away to point plug fouling miss firing occurred on way out driveway so turned tail to bite bullet back into it again. I've ridden a few miles on a few occassions with dual Amals choke and single Miki enrichers engaged to get ~1/10 mile down the hwy before barely responding to throttle miss firing with some dark smoke as clue what to do. If run in much over rich mix the oil washes off bores so rings &/or bore can go bad in short order.