Sooty Plugs

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Mart UK

Mart UK

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I recently had some misfiring. Both plugs were sooty black. I replaced both and this sorted it.

In the previous couple of hundred miles I had retorqued the head. They all had some movement and the front centre bolt was almost 1/2 a turn. I also adjusted the valve tappets, all were tight and the inlets had no gap at all. Finally I checked the head oil drain was clear with a guitar string. I then lowered the (single carb) needle one notch, for lean, and adjusted the air pilot screw for best idling and pick up on the throttle.

I've now run both new plugs for about 70 miles, riding higher in the rev range than I normally would to get beyond 1/4 throttle. Bike is running fine, but I have some slight deceleration popping. I didn't do a 'plug chop', but switched off as soon as I pulled the clutch in my drive. Both plugs have a very slight dark rim at the top (electrode end) of the threads, but the electrodes look lean, almost white. Both plugs look the same.

Is it reasonable to think the soot on the previous plugs could have been down to the head not being tight enough and possibly the valves out of adjustment? I am thinking I will move the needle back to where it was, to richen it up and run it for a while to see if the plugs settle down. I'm hoping I don't need to check valve seals, don't fancy taking the head off. Compression feels excellent from how difficult it is to turn the engine over with the kickstart. I don't have the kit to check that though.
 
Cudda been oil seepage… 1/2 turn is a LOT in terms of clamping force.

Its also quite a lot in terms of distance… that’s why the tappets should always be checked after re torquing if there was any significant movement.

Cudda been many other things of course… a quick test with the needle raised again won’t hurt will it.
 
May be the plugs just needed replacing and have gone past their life, a week spark will cause them to soot up.
 
Mmm, doesn't look too bad Mart ...
Sooty Plugs
 
ashman said:
May be the plugs just needed replacing and have gone past their life, a week spark will cause them to soot up.
Click to expand...
Only 1500 miles, or so. Manual spec Champions. They didn't respond to a clean up.
 
Quick test yesterday afternoon. Needle raised 1 notch, to middle of 5. The only difference I noticed was wheel spin at 5,000rpm, throttle wide. Roads a little damp, TT100s. I don't think it was clutch slip. I'd say it's running well enough for my normal riding style. Will just keep an eye on the plugs.

Gap in the weather at the moment, so plan to ride today. It's good to get out on it.
 
Rode to a nearby town, a nice 20 mile route (+20 return). Some hesitation at tickover. Half way, thought I'd try some fresh fuel and the hesitation disappeared. Ran lovely and even tickover resumed. I'm only using E5 premium and I've tried several different petrol stations. The initial fuel was less than 3 weeks old and I had 2/3 of a tank left.

Not sure it's useful to whip the carb off again to clean it. Also, I replaced the needle and jets under 3000 miles / 8 months ago and the carb has only 6,000 miles of total use. I think I'll just live with it and change my plugs every 1500 miles or so. Maybe it just struggles with a single mk2 Amal if everything's not perfect, including the freshest fuel.
 
Mart UK said:
Rode to a nearby town, a nice 20 mile route (+20 return). Some hesitation at tickover. Half way, thought I'd try some fresh fuel and the hesitation disappeared. Ran lovely and even tickover resumed. I'm only using E5 premium and I've tried several different petrol stations. The initial fuel was less than 3 weeks old and I had 2/3 of a tank left.

Not sure it's useful to whip the carb off again to clean it. Also, I replaced the needle and jets under 3000 miles / 8 months ago and the carb has only 6,000 miles of total use. I think I'll just live with it and change my plugs every 1500 miles or so. Maybe it just struggles with a single mk2 Amal if everything's not perfect, including the freshest fuel.
Click to expand...
Winter fuels (now) are a different formula than summer fuels. Don't know specifically the difference.
 
Mart UK said:
I recently had some misfiring. Both plugs were sooty black. I replaced both and this sorted it.

In the previous couple of hundred miles I had retorqued the head. They all had some movement and the front centre bolt was almost 1/2 a turn. I also adjusted the valve tappets, all were tight and the inlets had no gap at all. Finally I checked the head oil drain was clear with a guitar string. I then lowered the (single carb) needle one notch, for lean, and adjusted the air pilot screw for best idling and pick up on the throttle.

I've now run both new plugs for about 70 miles, riding higher in the rev range than I normally would to get beyond 1/4 throttle. Bike is running fine, but I have some slight deceleration popping. I didn't do a 'plug chop', but switched off as soon as I pulled the clutch in my drive. Both plugs have a very slight dark rim at the top (electrode end) of the threads, but the electrodes look lean, almost white. Both plugs look the same.

Is it reasonable to think the soot on the previous plugs could have been down to the head not being tight enough and possibly the valves out of adjustment? I am thinking I will move the needle back to where it was, to richen it up and run it for a while to see if the plugs settle down. I'm hoping I don't need to check valve seals, don't fancy taking the head off. Compression feels excellent from how difficult it is to turn the engine over with the kickstart. I don't have the kit to check that though.
Click to expand...
I would recommend iridium’s (BR8EIX) - much less prone to fouling and much longer life (no joe hunt knowledge here!)

You could also consider replacing your 3/8” head bolts with waisted (5/16”) items (eg: ARP) which will reduce creep damage to your head and keep good clamping pressure.
 
Last edited:
From the linked article above:
"Despite those higher prices, summer gasoline contains about 1.7 percent more energy than winter gasoline. Warmup times aside, that’s why you could measure reduced fuel economy outside the summer months. Winter gasoline varies widely in volatility throughout the season. Refiners constantly adjust their RVP to as high as 15 psi—higher than sea-level atmospheric pressure, which is 14.7 psi—to help the gasoline ignite more easily in colder temperatures. The vapor pressure varies by month, region, and octane. In frigid temperatures, higher-volatility fuel is essential and does not cause the smog effect it would in the summer. Using low-RVP fuel is a nonstarter in freezing weather; the engine won’t turn over or might misfire."
 
I don't recommend Iridium plugs. They cost 5 times as much each and wont last any longer with these bikes. I did a long run to a rally in South Canterbury and it became very hard to start the closer I got. I fitted clean n7Y plugs and got going again. Apparently modern plugs don't have the resistance to fouling that the plugs available in the 70"s used to have, Could be an old wives tale but could be true.
I did a lot of work on my carbs years ago to get the economy better. [ up to 63 mpg imperial ].

Don't waste your money on iridiums.

Dereck
 
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