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one carb or two?

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750 with RH6 head. Not going to be flying around the place. Will one 32mm carb be sufficient or is a two carb set up to be preferred? Ta.

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One carb is great for mileage and, if you're never going to break the speed limit, adequate as it's mostly top-end that suffers. One carb doesn't need balancing either. You need a carb with a bigger fuel inlet in the float bowl, used to be called a "dope bowl" (for alcohol) otherwise you'll suffer fuel starvation. And when it runs onto reserve you'll really notice it.

That said, for the way they're used 50 years on, it really should have two carbs like they were built.

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.. that a single carb is better at anything other than wide open throttle as the gas flow is more consistent. With twin carbs, the flow is interrupted for each carb for about 3/4 of each cycle; this is reduced to 3/8 for a single carb. This means that carburation is cleaner. Plus of course the other things mentioned by Stan. I don't actually believe you need a bigger inlet for the float bowl.

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To add a little more detail, I had a Stewart Engineering single carb manifold on my '74 MkIIA Interpol in the early '80s with a 932 Amal. I could get 70mpg which gave a 350 mile range from an Interstate tank; remarkable at the time, unheard of now. Top speed of 100 and would cruise at 80+ (it had a chronometric speedo) which was pretty decent with that big fairing. Plus the throttle was really light with only one spring to lift and you got a spare carburettor.

It was my daily commute and I would go touring two-up. I don't remember thinking it was slow. Mind you, it had the Norton-Lockeed front disc and I don't remember thinking that was feeble either.

But times change. I don't do enough miles on it to worry about fuel consumption or range. And even a Transit van will do the ton, so I like that twin carbs have a bit more get up and go.

I don't know whether the float bowl really needs the bigger inlet, - you know, the brass bit that the float needle seals against, there has to be a name for it but I can't think of it. But everyone said you needed bigger and stuff was readily available then. I never tried it with the standard bowl.

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I used to race the Dominator at East Fortune on one carb. Did ok too. Same bike, now with an Atlas engine and still just the one carb. Goes rather well and so much less of a guddle to set up. You know the one I mean. All set for the season once more, just waiting for the restrictions to lift.

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Unless your going the S.U. route keep to two amals, replace needle jets and needles when enthusiastic riding causes fuel to disappear at 50mpg or less...

Good to hear from you Gordon. Hope you're keeping away from people just now.

I contracted something which had me wiped out for a week. nasty. Once the situation improves I'll take a run up on the Commando and see you. Take care.

 

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