Amal 36mm MK2 baseline main jet settings

Fast Eddie

Fast Eddie

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Can anyone assist with baseline main jets settings (just to get me started) for 36mm MK2 Amal’s on a 1007cc stage 3 Maney motor, 11:1CR and a Maney 2:1 pipe?

Acotrel… please do NOT respond…
 
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Kinda thinking that engine and exhaust is not very common for the members on this site. :)

Anyway maybe Andy Molnar knows something useful since he sells parts to build similar engines.
 
Fast Eddie said:
Can anyone assist with baseline main jets settings (just to get me started) for 36mm MK2 Amal’s on a 1007cc stage 3 Maney motor, 11:1CR and a Maney 2:1 pipe?

Acotrel… please do NOT respond…
Click to expand...
Haven't a clue, would be interested in where you end up..
 
If Mikuni is a copy of Amal, which I find hard to believe, the standard jetting is listed on the MAP Cycle page for 36mm Mikuni carburetors. 310 is the main jet listed for the VM36 Mikuni. 330 sounds like a good place to start though for a larger displacement engine.

www.mapcycle.com

Mikuni VM36 Round Slide 36mm Carburetor

Standard Jetting Specifications Carburetor # Venturi Size Main jet (VM4/042) Pilot Jet (VM22/210) Needle Jet Jet Needle Throttle Valve Air Jet Needle Valve VM36-4 36 310 35 Q-5 6FJ06 2.5 2.0 3.3 Mikuni's VM Series,
www.mapcycle.com www.mapcycle.com
 
Fast Eddie said:
Well my current guesstimated start point is 330s…
Click to expand...
My 750 with 36mm Mikunis is currently on 210s, have used up to 230. But....I don't think they relate to Amal jet numbers.

The other issue with Mikunis is that the main jet choice varies with the air jet used, so I think this is purely a confusion factor.
(MAP don't actually list what air jet size they fit, so it will be a 2.0, and wrong for pretty much any 4 Stroke twin!)

Decades ago, on an 850 I was running 36mm Amals (Both Mk1 and Mk2 at different times) with low 300s. Go with your 330.
 
SteveA said:
My 750 with 36mm Mikunis is currently on 210s, have used up to 230. But....I don't think they relate to Amal jet numbers.

The other issue with Mikunis is that the main jet choice varies with the air jet used, so I think this is purely a confusion factor.
(MAP don't actually list what air jet size they fit, so it will be a 2.0, and wrong for pretty much any 4 Stroke twin!)

Decades ago, on an 850 I was running 36mm Amals (Both Mk1 and Mk2 at different times) with low 300s. Go with your 330.
Click to expand...
No mikuni and amal jet numbers do not relate
 
Hmmm, the air jet is listed on the MAP Cycle site as a 2.0. You have to actually use your mouse to side scroll and extend the specs.
Below is an image with the VM36 specs side scrolled to show the Air Jet.

Screenshot_16-6-2026_75826_www.mapcycle.com.jpeg


If a 310 main is listed as standard for the VM36 my guess is the main jet specs for the two 36mm carburetor types are fairly close. Would depend on a lot of other things like the needle jet, needle, and more, but it is a flow number that a tuner could make some sense of. Then again maybe not.

I don't use a phone for the internet, so I might see more than people that only use phones.
 
I've been wondering if you are replacing the Keihin FCRs with the Amal MK2 carburetors? The engine and exhaust configuration sounds like your track bike, but I guess it could be someone else's project.

If you are replacing the FCRs, any chance you could explain what issues you were having with the FCRs that prompted the change?
 
Schwany said:
I've been wondering if you are replacing the Keihin FCRs with the Amal MK2 carburetors? The engine and exhaust configuration sounds like your track bike, but I guess it could be someone else's project.

If you are replacing the FCRs, any chance you could explain what issues you were having with the FCRs that prompted the change?
Click to expand...
I’ve been wanting to try Amals for a while to see how they compare.

A small niggle with the FCRs prompted it this time. It feels like over fuelling at low throttle openings, on one carb only, I’m sure it’s something simple, just haven’t found it yet!
 
Fast Eddie said:
I’ve been wanting to try Amals for a while to see how they compare.

A small niggle with the FCRs prompted it this time. It feels like over fuelling at low throttle openings, on one carb only, I’m sure it’s something simple, just haven’t found it yet!
Click to expand...
It's always something, and I mean that in a most supportive way.

At one point in time I had one carburetor slow air adjustment set richer. I was getting a false full stop of the adjuster, so the adjustment ended up off. One other odd thing I ran across due to not riding that much is a ring of green I don't know what on the needles. Once cleaned off everything was better. Biggest recent improvement was getting rid of smaller diameter fuel filters and going with filters that have a 5/16" ID at both ends. It was a huge improvement. Different motor though, so all probably irrelevant. If the Amals are like Amals and you decide to go back to the FCRs. I'm sure you'll run down the problem.
 
Fast Eddie said:
Can anyone assist with baseline main jets settings (just to get me started) for 36mm MK2 Amal’s on a 1007cc stage 3 Maney motor, 11:1CR and a Maney 2:1 pipe?

Acotrel… please do NOT respond…
Click to expand...
When I started out on my RTW on my 850 w Maney 2:1, I was using 2 x 36mm Mk 2s. I later changed to a Phoenix SU to allow for on the fly altitude driven mixture adjustment. In the 36 Mk2s I was running 270 mains at sea level , 106 needle jets, 35 low speed. I had to fit the heavier Amal chromed brass slides (No 3) to stop the stock slides hanging up. I had an Innovate AFR meter fitted, so could see my AFR. I have to confess I was new to AFR meters and safe Commando AFR settings, and was naive / idealistic, and probably causes my first Nikasil (on stock barrels) seizure with a lean setting. Comnoz put me straight on this. It would have been the needle setting that was too lean. 270 Mains were about right.

Edit: I meant to add.. When I was racing my own 920 (w home built 2:1) a million years ago, I was running 2 x 36mm Amal Smoothbores. It also was happy on 270 mains. When we were dynotesting / jetting bikes at Thunderbike we learned that increasing displacement often didn't require larger jet sizes - it seemed to me that the bigger displacement engine seemed to just suck harder (greater depression) and pulled more fuel through the same jet size as the stock engine.
 
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johnfitzw said:
When I started out on my RTW on my 850 w Maney 2:1, I was using 2 x 36mm Mk 2s. I later changed to a Phoenix SU to allow for on the fly altitude driven mixture adjustment. In the 36 Mk2s I was running 270 mains at sea level , 106 needle jets, 35 low speed. I had to fit the heavier Amal chromed brass slides (No 3) to stop the stock slides hanging up. I had an Innovate AFR meter fitted, so could see my AFR. I have to confess I was new to AFR meters and safe Commando AFR settings, and was naive / idealistic, and probably causes my first Nikasil (on stock barrels) seizure with a lean setting. Comnoz put me straight on this. It would have been the needle setting that was too lean. 270 Mains were about right.

Edit: I meant to add.. When I was racing my own 920 (w home built 2:1) a million years ago, I was running 2 x 36mm Amal Smoothbores. It also was happy on 270 mains. When we were dynotesting / jetting bikes at Thunderbike we learned that increasing displacement often didn't require larger jet sizes - it seemed to me that the bigger displacement engine seemed to just suck harder (greater depression) and pulled more fuel through the same jet size as the stock engine.
Click to expand...
....and we have a WINNER!
Dumb old carburettors will simply mix at a RATIO... if you pull a slight amount more air through it... it will just mix more for you.
 

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