Amal MK2, how to tune, start to finish

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So I have this, new to me, 74 Commando Roadster with a single MK2 Amal (My other two Nortons have twin MK1 Amals) The bike runs pretty good at it's current carb settings (although my plugs are consistently black). It starts easy, idles nice and runs great (at least to me) up to about 3/4 throttle. At 3/4 to full throttle the engine cuts out. I think I read in the Amal lit. that the main jet is responsible for 3/4 to full throttle and that if the engine is cutting out it means you need a larger main jet. Does this make sense and if so how much bigger do I go? Or what should be my next step to work this out? Thanks!
 
Yes, main jet above, 3/4 throttle. Try the next size up. Not a very expensive part to experiment with. They make a jet wrench that you don't have to drop the float bowl to change jets.
 
What main jet is fitted?

Is there one fitted?

Is it screwed in properly?

You need to have a look inside and let the experts know what yer got before you start buying random jets...
 
I just installed two new Amal carbs (premier), idles super high. Can someone give me the ballpark starting point for the two idle/air adjustment screws, ie both 1 1/2 turns out?
Thanx
 
I think the idle screws on my Mk2 Amals adjust the fuel. I just lean-off until I get the miss, then back off until I get the smooth idle. It is important that the two slides hit bottom at the same time.

The comment that the plugs are black - what is important is the appearance of the porcelain, not the metal part. There should be a black ring on the porcelain, right down inside where it meets the metal. The heat range of the plug and the fuel mixture determine how far the soot burns off. I'd use 8s for tuning and 9s for running. That way you stay safe.
 
I just installed two new Amal carbs (premier), idles super high. Can someone give me the ballpark starting point for the two idle/air adjustment screws, ie both 1 1/2 turns out?
Thanx

Leave the air screws at 1 1/2, adjust the idle screws for around 900 or so, then fine tune the air screws, adjust idle again.
Air screws are horizontal and control air, idle screws are upward and control the slide position.
 
MKII mixture screws control the air same as MKI. In for richer, out for leaner. Start at 1 1/2 and should need no more than a 1/2 turn either way. Original poster was talking about above 3/4 open performance which is main jet territory. If you want to talk idle start another thread.
 
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