Amal problems

'72 Commando with 932's misses when accelerating briskly. If I nurse her to road speed it's smooth, but if you goose her, she cant handle the fuel. Just switched to NGK Iridiums, 'cause upon inpection the plugs were pretty black and was difficult to start. Again, if I accelerate slowly it runs fine thru the gears. Thinking about a single Mikuni, but would like to keep the bike original. Think it's just the floats ? Thanks

What is your main jet?

Not sure, just got the bike and it ran fine for the first month

hostilecarl said:

Not sure, just got the bike and it ran fine for the first month

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So it studders and boggs just during wide open throttle? Was this bogging always but not discovered or has it just developed?

I am sure it could be other issue, but for me, when this happened it seem so like the main jet were to small think I was starving it from fuel.

I went up and up and up in main jet sizes with no luck. So, I started going the other way. I hade to order smaller jet because I experimented with number drills on a set that I had duplicate, you cannot make a bigger one smaller.

Anyhow, I kept going down until I got some result and improved response. Going down a couple more sizes, the studder and bogg were gone.
The real clue here is that it happens at WOT. This sort of narrows it down.

Just to be clear, this was not done on Amals but perhaps the principal is the same.

hostilecarl said:

Not sure, just got the bike and it ran fine for the first month

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What is it the forum boys say 90% of carburettor problems are electrical . My 69 750 missed when I hammered her when it was on the dyno it came up as electrical. But do the simple things first as it costs you less.

J

check your electrics first please. Dereck

hostilecarl said:

Not sure, just got the bike and it ran fine for the first month

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How's your idle ?.

Not a fan of iridium in these old motors. What plug number did you have on the original plugs ?

If something has changed recently, it won't be hard to find.

Could be electrical as others have noted,but I run a single 32 mm Mikuni on my Norton and it starts and runs beautifully. I'm not racing anybody,I look for simplicity and reliability.

Electrical ? Idles fine, agian with sensible throttle it doesn't miss a beat. I've got some brand new Amal 930's for my '71 project, maybe I'll throw them on. I went to a hotter plug to see if that might help, I'll go back to the correct plug too. It seems to me that an electrical problem would be ever present ??? Thanks

hostilecarl said:

Electrical ? Idles fine, agian with sensible throttle it doesn't miss a beat. I've got some brand new Amal 930's for my '71 project, maybe I'll throw them on. I went to a hotter plug to see if that might help, I'll go back to the correct plug too. It seems to me that an electrical problem would be ever present ??? Thanks

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Unusual. It runs perfectly if you just roll the throttle on and stumbles if you crack it open. This change happened after 1 month of ownership.

Most carby problems are electrical but are usually more intermittent than what you describe. Have you checked the needles on the throttle slide are secure ? The clips are known to let go.

With Amals you cannot just crack the throttle open, you need to roll on as they don't have pumpers to make up for the quick air hit.