32mm carbs on earlier head

htown16 · Mar 12, 2016

Can 32mm carbs be used on the earlier rh1 28.5 head? I have a set of the 32/30 mm intake manifolds from a 74 that had an rh10 head.

peter12 · Mar 12, 2016

Not an expert but don't see why not.
I had 32mm's fitted to a 750 many years ago, if the manifolds taper to 30mm I would have thought that was fine. Its all in the jetting. Took me a while to get the jets sorted as it was running v rich at first.
Good luck.

CanukNortonNut · Mar 13, 2016

htown16 said:
Can 32mm carbs be used on the earlier rh1 28.5/30mm head? I have a set of the 32/30 mm intake manifolds from a 74 that had an rh10 head.

Hi htown
You shouldn't have a problem. You will probably need to change carburetor jetting components to suit the engine.
Cheers,
Thomas
CNN

htown16 · Mar 13, 2016

Should have been clearer, I'm refering to the early Commando head with the Birco and 06-0380 casting marks and 28.5mm ports.

peter12 · Mar 13, 2016

Might be best to get the ports at the manifold tapered to 30mm to match the manifold, don't think a step is a good idea.

Deckard · Mar 14, 2016

That's actually the ideal way to mount 32mm Amals to a non Combat 750. The smaller ports flow better. I did mill the head to come up to 10:1 and added the 32mm Amals, and boy did that engine come alive. With the stock cam it had a nice wide power band. Dunstall mufflers helped too. As stated, the main jet will need to be sorted out. Dunstall mufflers required richer jetting even with the 30mm carbs.

johnm · Mar 15, 2016

peter12 said:
Might be best to get the ports at the manifold tapered to 30mm to match the manifold, don't think a step is a good idea.

You might be surprised. On the dyno one day going through carb options and a step turned out a very nice idea ! :roll:

Fast Eddie · Mar 15, 2016

Gentle radiusing of the step gives best results according to Comnoz' head flow tests.

I would use 32-32 manifolds and gentle radius the step in the head by hand.

acadian · Mar 15, 2016

I'm have 30mm manifolds ported to 32mm at the carb end with jim schmidt's older 32mm flatslides, works well enough

32mm carbs on earlier head

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