‘54 AJS 16 MS spark plug/timing issue.

[Paulie B]

Good morning.
My bike seems to be running fine, albeit with bluing on the exhaust. The old spark plug was badly carboned up ahd was replaced. Idles ok and (as far as I can see) runs nicely, although refuses to get past 55. I took it for a varying speed, 1.5 hour run yesterday with a new spark plug, with no issues at all. However, when I pulled the plug, it already has a deposit of carbon on it. Starts first kick (once I remembered to connect the plug) and idles nicely. Apart from the heavy build up of carbon on the plug, it’s not displaying (to me as a new owner) any other signs of richness. I’m thinking the next move is to change the needle position. Is this the right start or would I be better served checking the timing.

[Paulie B]

The exhaust is also black rather than grey.

[Groily]

If it won't go beyond 55mph it's possible the timing is a bit retarded I guess - I'd check that for starters. Should run up to 70-ish quite nicely I think.
It could indeed be running very rich and bogging down with larger throttle openings, but you've got to start somewhere, and preferably do just one thing at a time!

If the timing's good, and the advance and retard is operating OK, and if the plug fouling is not due to oil consumption (no excess smoke we assume?), then I'd check the carb settings next. (No harm checking the elements of the carb are 'per book', though, at any stage - pilot jet, needle jet, main jet, throttle slide etc. But if they are, I wouldn't fiddle with them until I'd confirmed the timing was good.)

It's well-known that 'all fuel issues are ignition problems, and vice versa' - but I usually start with the timing because if it's not reasonably close to where it needs to be, you could be pushing an unset jelly up the sunny side of a pyramid playing with other things.

[Paulie B]

Thanks mate. Looks like great advice.

[Pharisee]

Just out of curiosity, what model and size of carburettor are you using?

[Groily]

Interesting question . . .
The 'book' says, for 16MS '54:

"Type 76 AV, main jet 150 (or 130 with air filter), throttle valve 6/4 and needle on 3rd notch (or 2nd with filter)"

If a later machine, "376/5 Monobloc, 1 1/16" bore, 210 main, 30 pilot, #3 slide, needle on middle notch and needle jet .1065".

Plenty of concentrics to be seen on these things too, so could well be some tinkering required to get to happy.

Can't be too far off though, whatever it is, if she starts and runs and ticks over well.

[Paulie B]

It’s an Amal 276. It’s new, I’ve got the old one in a box.

[1608]

I have had bad NEW carbs from Amal/Burlen. The first monobloc 389 came with the wrong jet block and the second NEWcarb 376 I can't stop it running rich no matter what. Gave up and fitted a good s/h one. NEW one still in the box!

[Groily]

I have had bad NEW carbs from Amal/Burlen. The first monobloc 389 came with the wrong jet block and the second NEWcarb 376 I can't stop it running rich no matter what. Gave up and fitted a good s/h one. NEW one still in the box!

Not the first time I've heard that! I had to put an old needle jet in one brand new 389 to get it to run properly. Then there's the Q of whether to put a fibre washer under the inlet banjo bit on top of the float chamber or not to get the fuel height right. They say, I think, Yes with replacements, No with originals. Bit of a lottery sometimes.
Different issues with the old 276, usually to do with leaky fuel feed link on the underneath, or constant flooding of the float chamber - I ditched a new one of them, acquired at great expense, in favour of an old 376 Monobloc on my Mod 20 . . . The joy of it all!

If the carb is brand new, then maybe that's where the minor hassle is likely to be . . .

[MatthewC]

To echo the above comments, I once made the mistake of paying too much attention to Burlen's advertising about fake jets and bought a set of new ones to go in at the same time as a set of new gaskets. The bike ran filthy rich, too rich to run below about 1/4 throttle even with the mixture screw set as weak as possible without it falling out, and within a mile fouled the plug up. The old pilot jet went back in and I didn't have any more mixture trouble after that.