Amal Mk2 Jetting

Hi chaps - I have a 920 Mk2A fitted with a single 36mm Mk2 Amal - the bike runs well but 'hot-starting' can be a bit hit and miss. I fitted a Gunson Colourtune and found that the idle mixture was way too rich. I had to turn the pilot screw right out to get a good 'colour' - the pilot screw is so far out that it's only holding on by about half a screw thread. I realise that the screw regulates air rather than fuel but does the internal brass jet do the same or does it regulate fuel ? I ask because I realise I'm going to have to change this brass jet to try and set things up properly.

Cheers,

The idler jet passes fuel, so a smaller one gives a weaker mixture.

What size pilot jet have you got in there? Has the cold start jet been fitted by mistake?
Cash

Check your cold starting circuit is shutting off completely. There should be a witness ring indented in the rubber in the end of the plunger.

Hi Mark

Choke is the thing to look at. I disconnected mine & put a piece of rubber in to pad it out. It seems they wear the rubber on the seating area so dont shut off.
Chris

Check your cold starting circuit is shutting off completely. There should be a witness ring indented in the rubber in the end of the plunger

Click to expand...

Yes Chris you're right there, I've known the rubber pad to drop out and disappear. On a wet cold day the carb would freeze up.

Cash