Single carb. conversion using Amal Mk.l

Hi there, I'm currently running a single 32mm Mk1 on my 750 with a 106 pilot, a 260 main, 3.5 slide and needle on top groove.

The only thing I found with the single manifold that I have is that you can only use the 2 outside boltholes on the head as the inner ones are a bit difficult to get bolts into, but it's not caused any problems with air leaks, I made a gasket out of some decent material and moved the heat insulator between the manifold and carb. The bike is still in the running in stage but is pulling easily past 4500-5000.

Hope this helps.

Mac.

My 1 into 2 manifold uses socket head bolts inside. Make sure they are tight (loctite) or your engine might try to swallow one. Mine tried and failed...luckily didn't get in far enough to jam a valve open. I am glad I did not try to limp home.

The jet settings should be identical. I set up my twin carbs (slides and main jets) by changing bits when running with single carb. Then set the other one up the same way. Cheaper than buying pairs of slides and not using them...

With your 750 Commando I suppose you can get away with one carb. On a 500cc Dommie SS I want the extra urge even if it's only for hill climbing two up.

I have 2 types of 2 into 1 manifolds. An original Norton one which has 4 socket screws holding it and an aftermarket one which is just held by the outer 2 screws - no provision for the inner ones. Also there is an abrupt change of plane where it joins the cylinder head. Funnily enough, although the aftermarket one worked OK, I am using the superior original one. Get one if you can. I used one of the original carbs when I went to a single carb setup which leaved me a complete spare carb. No change of jetting required. Gordon.

I have 2 types of 2 into 1 manifolds. An original Norton one which has 4 socket screws holding it

An "original Norton" 2 into 1 manifold does not exist, because it is technically disadvantageous. Due to space restrictions between Commando head and frame, the single carburettor needs to be positioned much too near the inlet tracts. These were never designed to take a single carb manifold and are, therefore, relatively wide apart. For this very reason Triumph made different heads for Bonneville (twin carb) and Tiger (single carb).

Therfore, the 2 into 1 manifolds are too short to allow for straight paths to the inlet valves and force the inlet charge to go round 90? bends twice on their way towards them, the carb actually pointing at the back wall at the centre of the manifold.

While this works sort of o.k. up to about 4.500 to 5.000rpm, one looses top end performance. You actually castrate the Commando by putting a single carb manifold on. If you want to voluntarily restrict your poor Commando to about 35bhp, get a single carb manifold!

Previously wrote:

I have 2 types of 2 into 1 manifolds. An original Norton one which has 4 socket screws holding it

An "original Norton" 2 into 1 manifold does not exist, because it is technically disadvantageous. Due to space restrictions between Commando head and frame, the single carburettor needs to be positioned much too near the inlet tracts. These were never designed to take a single carb manifold and are, therefore, relatively wide apart. For this very reason Triumph made different heads for Bonneville (twin carb) and Tiger (single carb).

Therfore, the 2 into 1 manifolds are too short to allow for straight paths to the inlet valves and force the inlet charge to go round 90? bends twice on their way towards them, the carb actually pointing at the back wall at the centre of the manifold.

While this works sort of o.k. up to about 4.500 to 5.000rpm, one looses top end performance. You actually castrate the Commando by putting a single carb manifold on. If you want to voluntarily restrict your poor Commando to about 35bhp, get a single carb manifold! On my 750 commando i have a norton atlas inlet manifold i cut the rear flange off and welded on a round tube spigot on this i have a CV mikuni that came from a bank of 4 carbs from an fj1200 yamaha ,the engine is stock apart from a big valve head and high compression pistons and i can redline it in every gear,it is harder to start in cold weather i have kick it over 2 or 3 times ignition off then start it but i can live with that for a perfect tickover and perfect pickup and revving like a banshee when required regards nick

dont forget most people use a slide mikuni,my one is a CV also i am not sure this setup would fit a standard frame as my frame has the gusset removed that bridges the frame above the airfilter,the only reason i did this was because i couldnt afford the mikuni conversion and i had just fitted brand new mk1 amals and i was never happy with them so i used some parts i already had and was surprised at the results regards nick