Best carbs for Nortons

NPeteN

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What I mean by a pumper carb is a carb with a diaphram that gets a pulse from the engine sump. The pulse hits the diaphram and the diaphram forces a squirt of fuel to the intake charge, after the pulse a needle shuts off the plumbing until the next pulse - sort of like fuel injection but without electronics. No float bowl. These type carbs were popular on McCulloch go cart engines and I saw a magazine article where one was adapted to a BSA 441. That BSA used a pulse from the exhaust pipe with a line tapped in near the riders foot. They measured a HP improvement but that's as far as it went.



Come to think of it - this is one of the few carbs that would fit in the Norton twins restricted space and it might be a great alternative as a twin carb setup.

I used to cut wood for a living and I have one of these racing motors in my chain saw and it absolutely kicks ass as shown below.

Hell yeah!
 
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Diaphragm pumper carbs were used on gokarts with proportionally large IDs specific for karting. That's where my racing career began.
 

Fast Eddie

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Has anyone grafted a twin choke Weber onto a Norton twin before?

I realise there’d be space issues on a Commando, but minor details like that wouldn’t stop a determined Norton owner I’m sure!

Just wondering if it’s ever been done...
 

baz

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Has anyone grafted a twin choke Weber onto a Norton twin before?

I realise there’d be space issues on a Commando, but minor details like that wouldn’t stop a determined Norton owner I’m sure!

Just wondering if it’s ever been done...
Yep I've seen a twin choke on a commando chop
The carb twixed the backbone of the frame
It ran very well
Funny enough I fitted a twin downdraft 38 weber to a 1500 wing at the weekend
I once read somewhere that car carburettors can't be used on bikes
Somebody replied "how does the engine know where the carb came from?"
Made me chuckle!!
 
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Has anybody ever used a Keihin CV carbs as used on some Kawasaki twin bikes? I think they are very good as my bike revs to 10500, what more do you want? Adapting them to fit would be an issue as they are too wide but at 35mm bore they are big enough for a 750cc. NB just make sure you have the unrestricted version- ie throttle slides will go wide open.
 

Chris

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Hi Nige
Nigel Hall Smith ran a weber on his 8 valve. Steve Mandy said his Amals 38mm smoothbore gave him the edge. Nigel however said once he got it set up on a rolling road that was it. Pretty much maintenance free.
We ran one on the sprint bike. It touched the rails on a featherbed so I had a manifold made at Ricardo. Nice performed well.
 

Fast Eddie

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Hi Nige
Nigel Hall Smith ran a weber on his 8 valve. Steve Mandy said his Amals 38mm smoothbore gave him the edge. Nigel however said once he got it set up on a rolling road that was it. Pretty much maintenance free.
We ran one on the sprint bike. It touched the rails on a featherbed so I had a manifold made at Ricardo. Nice performed well.
Yes I remember Nigel running one on his Nour-ton. Top bloke he was, especially with 8 valve stuff, RIP.
 
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Yeah the Webers are sexy. But way too big. Only two brands of carbs will fit on a Nort - Amals or Keihins (or Chinese copies of Keihins such as the PWK). Amals are too crude, the 35mm FCRs rub the frame, 31 to 33mm CR smoothbores are wonderful but you need to redesign the throttle wheel etc, 32mm PWK copies would be perfect if the finish quality was better and consistent. The genuine Keihin PWKs are too big.

If Sudco came out with a small bodied 33mm FCR twin kit then it would at least fit - but expensive. Better yet if they set up the CRS Keihin twin kit with a throttle wheel & bracket that cleared the frame.

Its frustrating as hell.
 
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I use two alcohol-kitted 34mm Mk2 Amals. But I DO NOT use Amal needles. I use Mikuni 6D needles, which are the leanest taper for that size carb. And I make my own needle jets from brass hex, using a combination of metric and number drills and a 0 BA die nut. I take the final cut out of the jet ID, with one twist of a hand drill. However you cannot do that if you are using petrol - with methanol, the effects of errors in jet size are not so bad. My carbs are not flange mounted, they are the type which plug into a rubber mount.
 
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Yeah the Webers are sexy. But way too big. Only two brands of carbs will fit on a Nort - Amals or Keihins (or Chinese copies of Keihins such as the PWK). Amals are too crude, the 35mm FCRs rub the frame, 31 to 33mm CR smoothbores are wonderful but you need to redesign the throttle wheel etc, 32mm PWK copies would be perfect if the finish quality was better and consistent. The genuine Keihin PWKs are too big.

If Sudco came out with a small bodied 33mm FCR twin kit then it would at least fit - but expensive. Better yet if they set up the CRS Keihin twin kit with a throttle wheel & bracket that cleared the frame.

Its frustrating as hell.
Colorado Norton Works do FCR 35 kits with their own manifolds but with the airbox removed they seem to fit a treat. Am told can also source through Holland Norton Works for us this side of the Atlantic. Really tempted apart from the price! Would they be that much of a performance enhancer for my '72 Combat?
 

Fast Eddie

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If your Combat is a Combat, ie 32mm ports, 2S cam and high compression I would suggest that the cNw carb kit would work bloody BRILLIANTLY !

I’ve had them on an 850 and now on a 920. To quote my dyno man when I was dynoing the 850:
“I think that’s the cleanest fueling we’ve ever seen on any carburated bike”.

Easy starting too, with no flooding and no choke to worry about, just twist the throttle to pump some fuel in, kick and go...
 
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I worked for a while in an Alfa Romeo dealership in the early 80's........There a bloody nightmare to tune even with factory equipment....and they go off tune so quickly.
and the car boys used to like fitting an Amal per cylinder for max power!
 

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