Jetting for 36mm Amals

Folks, especially all you racer boyz…

Any well founded advice on jetting for the following.

36mm Amal mk2s (not smoothbore) on a Commando with:

920cc
11:1 CR
Maney cam
Maney stage 3 head
stock unbalanced pipes and peashooters
and / or
Maney 2:1

Bored with the FCRs already Nigel? If I were you I would just start off with the standard settings for that carb, & you will be close. I fitted a 38mm MK2 to my Big Head 612 R.E. doing just that, & was spot. Just lucky maybe?

Martyn.

Not bored as such Martyn…

The FCR 35s are 35mm, but the head is 36mm.

And the spigots require the smaller rubbers, which mean I can’t use the ‘correct’ and beautifully machined intake manifolds as supplied by Steve. I’m using DIY ‘ported’ manifolds at present which are unlikely to flow like Steve’s.

So all in all, I have carbs that are too small mounted on poor flowing manifolds !

The problem with the next size up (37mm) FCRs is a) they’re hard to find and b) they’re a good 20mm bigger bodies, and that would be a bit of an issue. Both the gusset plate and electric start would have to go !

But, I have some good 36mm Amals already, so that is a really easy set up to try out.

BTW, what size CR‘s are you running on the 920?

The CRs are 33mm on a Jim Comstock modified Fullauto head. My bike is only mildly tuned, making just 63 BHP at the rear wheel (none at all at the front)

Matchless said:

The CRs are 33mm on a Jim Comstock modified Fullauto head. My bike is only mildly tuned, making just 63 BHP at the rear wheel (none at all at the front)

Click to expand...

None at all at the front? Did you do a dyno run to verify that, or is it empirical!

Fast Eddie said:

Folks, especially all you racer boyz…

Any well founded advice on jetting for the following.

36mm Amal mk2s (not smoothbore) on a Commando with:

920cc
11:1 CR
Maney cam
Maney stage 3 head
stock unbalanced pipes and peashooters
and / or
Maney 2:1

Click to expand...

I was running 2 x 36mm Mk2s on my Comstock w FA big valve 850 10:1 Maney style 2:1 prior to setting off on my Central & South American leg of my RTW trip un 2021...
Pilots vary a/c altitude.. But usually #25
Needle jets .106
Stock needle
Mains a/c to altitude 270 to 290
Choke jet #35

Ran v cleanly, great steady idle, nice performance. Can be a little difficult to get the Mk2s to close quickly and effectively when decelerating quickly - they tend to close more slowly than I liked.. I like Baaaaaaah on deceleration... not ba-b-bah-b-bah.... Stronger springs fix it but cause RSI..

johnfitzw said:

I was running 2 x 36mm Mk2s on my Comstock w FA big valve 850 10:1 Maney style 2:1 prior to setting off on my Central & South American leg of my RTW trip un 2021...
Pilots vary a/c altitude.. But usually #25
Needle jets .106
Stock needle
Mains a/c to altitude 270 to 290
Choke jet #35

Ran v cleanly, great steady idle, nice performance. Can be a little difficult to get the Mk2s to close quickly and effectively when decelerating quickly - they tend to close more slowly than I liked.. I like Baaaaaaah on deceleration... not ba-b-bah-b-bah.... Stronger springs fix it but cause RSI..

Click to expand...

Thank you.

Fast Eddie said:

Thank you.

Click to expand...

Sorry, forgot the slides.. No 3 cutaway. Do yourself a favour and buy some chrome plated brass slides, available from Burlen..