commando dry sooty spark plugs

Hi it is dusty rider a Norton rider in Australia for over 60 years Racing a ES2 single in1951 so I have learnt a little in that time But I need help I have a 1973 commando and know of four others that soot up with dry black soot with 100ks I HAVE CHECK THE BOYER IGNITION ,BEEN UP AND DOWN IN ALL JETS (ie main needle jet and piolet jets plus plugs NKG 7-6-5-but no good and don't won"t to melt pistons Can it be fuel ??? I have tried all I can think of Help required
Dusty

Hi Dusty, we'll need more info... Compression test please, post the numbers, fuel mileage (several tank average), oil consumption, etc. does it need/want/like choke when cold? Does choke make it run horrid when hot? :?:

Dry soot is better to find than oily coking but end result about the same. With your life time on real Nortons I can't imagine you over looked float level or confused on choke lever position so may be a local gasoline quality issue. I'd call area airport shops and mc shops to see if they have a clue to offer. Might try some aviation gas for a while to get a sense of its effect or not. I've put in richer slide number, less cut out to get a bit more off idle response but it didn't make extra soot to note. Old tradition to de-coke is spraying water in carbs while blipping good, which turns carbon soot to a greyish soft powder that blows out harmlessly.

Old blocked air filter, if fitted :?:

Hi

i have a 73 commando too, starts v well, idles lovely and seems to run okay but sooty plugs too so I've started experimenting . .
I read somewhere that worn needle jets can give over rich for low to mid throttle so after checking the set up generally, i switched in a new pair and so far plugs are looking a bit better after 2 days running. For reference my twin carbs are R&L 932/26, 220mains and 106 needle jet -the amal site shows these are carbs for the combat (but the bike is late 750 not combat)

a cheap fix so mibe worth a punt ?
Stu

Combats, [which may draw in more air than standard 750], with these 932's on no-lead pump gas in the states, tend to like 240-260 jets as new gas is lean burn here. Takes a good bit of WOT though to get into main jet only zone and this seasoned Nortoneer said he's been up.dn that obvious route. If tossing out the soon worn AAU , I am collecting them.

For my own refreshment copied this sooty summary, already covered in post, that ignores shoe eve's mischief of course.

Basically, soft, sooty carbon deposits, have a dry, black appearance. If only one or two plugs in a set are fouled, it is a good practice to check for sticking valves, a cracked distributor cap, or bad secondary ignition wires. Fouling of the entire set might result from an incorrect heat range spark plug or an over-rich air/fuel mixture caused by a clogged air cleaner filter element, a sticking heat riser valve, or a faulty choke. Fuel injectors that malfunction can also lead to this condition. Other causes include weak ignition system voltage or an inoperative pre-heating system (carburetor intake air) or poor cylinder compression.

dusty rider said:

Hi it is dusty rider a Norton rider in Australia for over 60 years Racing a ES2 single in1951 so I have learnt a little in that time But I need help I have a 1973 commando and know of four others that soot up with dry black soot with 100ks I HAVE CHECK THE BOYER IGNITION ,BEEN UP AND DOWN IN ALL JETS (ie main needle jet and piolet jets plus plugs NKG 7-6-5-but no good and don't won"t to melt pistons Can it be fuel ??? I have tried all I can think of Help required
Dusty

Click to expand...

Yes it can be the fuel - lots of reports of Oz fuel causing this. (lotta fuel is imported ?).
What fuel are you using ?
Some folks say that different brands are different.
And some folks say that ethanol in the fuel can - or cannot !! - do this.
And some folks say that low octane does this, but not the better stuff.

Note that a bit of oil burning can also cause mildly sooty plugs.
How many miles has your bike done - and the others you mention ?

A quick-n-dirty test for this is to try some avgas in it (which is illegal, note).

Tell us more about this racing ES2 ?
Got any pics ?

dusty rider said:

soot up with dry black soot with 100ks

Click to expand...

Gooday Dusty,

Tune for best performance. Don't use 98 (for injected motors). Use 95. Around town I get sooty plugs quickly. Up the freeway it burns off pretty quick. Do a plug chop on the freeway, it should be clean.

Cheers

No chance of melting pistons. Amal sells a kit with matching needles and needle jets. New viton tipped float needles whilst you're a' spending.

I would doublecheck the Boyer. I have seen this before and the guy went leaner and leaner but the plugs still sooted up. The answer was the hot wire to the black box had a bad connection though it looked good. There is an extensive troubleshooting guide on the Boyer in the tech digest put out by the INOA and it covers this.

It is perhaps also worth commenting that depending on the mileage the amals have done, the jets and needles do wear - it is perfectly possible to have jetting done to factory numbers, and it still running too rich. Fitting new needles and jets can restore it back to how it should be. Worth a try, if not done already ?

Some other makes of carbs have easily detachable or drainable floatbowls - it can be surprising how much dust and grit can come out of these - out of rusty fuel storage tanks and tankers, perhaps ?? Fine enough to go through most filters too, unless they are exceptionally fine...

Dusty rider
Apart from the Boyer and worn jets, Australian unleaded fuels, either 95 or 98 require about a 10% reduction in jet size on the original leaded fuel that the amal was jetted for. Shell optimax is probably the thinnest fuel and will result in a richer mix than other fuels.
Original jetting will probably be close to correct with E10 fuel. E10 is not nice to the plastic in the amal but you could try a run on E10 to see if that improves things. If you get an improvement on E10 try a smaller needle jet as that is where most of your running is and reduce main jet by about 5 - 10%
Ando

A half fast clue too is proper carb tune should need a tickle or choke to start cold or its considered to rich. Modern fuel and ethanol spiked fuel are leaner burn so generally jet set richer than olden days, not to say you ain't over rich even with these fuels.