Which carb to go with?

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beefco

beefco

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Jan 18, 2012
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I could use your opinions. So I am thinking about buying a replacement carb for my 72 combat. I currently have a single EI flat and ride mostly in town with no hot rodding. Should I go with Sudco's ubiquitos Mikiuni round slide or the flat. Or go with Jim Schmidt's flat Keihin clone. Buy a kit from one of them or go ala cart.
 
Jim Schmidt's single

OR

Jim Schmidt's duals, just for those occasional times when you might want to remind yourself why you bought a Norton Commando
 
Im having fun with the JS flatslides lately. They are a little touchy to set up but I attribute that to my thick skull. Very nice carbs and I am really happy to have them on my bike. A definite upgrade from my original single Amal.
 
Go Jim's Flatslides once set you should have years trouble free, of course go the duel set as its a Combat it should be allowed to run freely every so often.

Ashley
 
Stock Amals dialed in work for me, but then I'm a purist. Also, I 've read of loss of horsepower with just one carb.
 
No offense but a Combat that doesn't get hot rodded is sort of like having a ...well never mind. I run twin Amals on my Combat and while I don't have a world of experience with lots of carbs, I can tell you that I get good response in low RPMs and it kicks ass when I decide to let it go. Amals get a bad rap, but they are really simple carbs that work in a large range.

Russ
 
You seem to be talking in a singular tone rather than a dual carb tone. What is your inclination?

You say you have a Combat and I do not doubt it but it is easy to have a C stamped head, 32mm intake setup and a front disc. The cam is what really sets it apart and should determine your carbs. I might suggest that the new premiers might be the best for you although many have had good success with the single Mikuni 34mm Flatsides, including myself.

You don't want to know what i use cuz it just pisses people off. It works incredible but requires slight modification which is just a No No No NO no. Bad puppy! No No No. Search my post if you care to but don't go there for fears of being alienated. No fear here!

Anyhow, I am thinking about some more R&D on twin Amal Mark 2's. A viable option. No one seem to have these on their bikes either, exept for racers. Economical at $137 each. Premiers are $170 a pop and do not have as much pop, so to speak.

Jim's single 34mm Flatside should easy peasy lemon squeezy with easy tuning and good performance.
 
pvisseriii said:
You seem to be talking in a singular tone rather than a dual carb tone. What is your inclination?

You say you have a Combat and I do not doubt it but it is easy to have a C stamped head, 32mm intake setup and a front disc. The cam is what really sets it apart and should determine your carbs. I might suggest that the new premiers might be the best for you although many have had good success with the single Mikuni 34mm Flatsides, including myself.

You don't want to know what i use cuz it just pisses people off. It works incredible but requires slight modification which is just a No No No NO no. Bad puppy! No No No. Search my post if you care to but don't go there for fears of being alienated. No fear here!

Anyhow, I am thinking about some more R&D on twin Amal Mark 2's. A viable option. No one seem to have these on their bikes either, exept for racers. Economical at $137 each. Premiers are $170 a pop and do not have as much pop, so to speak.
Click to expand...

:mrgreen:
Please tell me you are doing R&D on mk2 smoothbores!!!
 
Dkt26 said:
:mrgreen:
Please tell me you are doing R&D on mk2 smoothbores!!!
Click to expand...

I have been pricing them at this point along with the adapter/manifold configuration that suites me.

I started a thread to asked for input from others who run them. Absolutely no response. I cannot believe no one is running these. WHY? Amals. Smoothbore. Anodized slides. Better performance and price. I thought that one of the attractive attributes of the MK2 is that they fit. Am I wrong here?
 
I have some info that I discovered but it is untested. It was going to be my starting point at least. I can't post it from my phone but will post it later today for you.
 
Checked out Jim Schmidt's web site, but am a little confused.

http://www.jsmotorsport.com/products.asp

"Design by Keihin. 32mm or 34mm flat side PWK Twin Carb Kit, complete with lower cables, airfilters, curved manifolds with rubber mounts and clamps, Customized and tuned for Nortons with correct jetting and special needles designed "in house". See plumbing kit option below. No modifications necessary (more info). Customers with 30mm port heads or those buying 34mm carbs with 32mm heads see next item below. 34mm carbs will need the twist grip, cable & junction bow listed below because the original parts do not have enough travel."

What is the distinction between 30mm port heads and 32mm port heads? 750 vs. 850? Also are the 34mm dual carbs overkill for a 750? No experience with Brit bikes (I'm learning), however had a Holley 850 double pumper on an old Chevy truck that I about needed a second job to buy the gas. With the smallish roadster tank, not looking to stop too frequently.

Jim H.
 
What is the distinction between 30mm port heads and 32mm port heads? 750 vs. 850? Also are the 34mm dual carbs overkill for a 750?
Click to expand...

Jim, I suggest you either call or email Jim Schmidt of JSmotorsport with your questions.

Many of us are very happy with his products and he is quite willing to communicate with answers.
 
I just got the 32's for my 71 750 and they are awesome. Today I finally got a chance to get out and get a few miles with them. They are strong in the bottom end and just keep going up top. I was coming from a single Amal and that was decent when I had it. I never knew the top end on that single Amal though, it was never there like it is with these 32's.

I really noticed the speed of how I can get rpm's up. They are really responsive compared to the old carb I had. When I gun it the tach climbs fast.

I think the diameter of the ports designates if you can get the 34's or not. I left it up to Jim when I was looking at them. I asked what was best for a stock 750. Sleeved manifolds and 32's was the suggestion.

I'm not looking back. Today was an eye opener for me and this bike. I don't look at it like an antique anymore.

I will have to say I tinkered with them for a good week before finding the sweet spot. I am prone to tinkering though....

Cheers,
 
Hey jrh,
Most 750 Motors have the 30mm ports and 30mm Carbs, except the Combat motor from 1972 which had 32mm.
Then when the 850 was produced, it too had 32mm ports and Carbs.
"Kiehin design", yes. If they were Kiehin biult they would be twice the price.
Jims setup is exceptional value for money, for something that bolts on and works.
Twin Amal Mk 2s may have the same issues as twin Mikunis, that is, they need to be splayed to fit
as they are quite wide.
A guy in our Norton club has twin Del'ortos that work very well, if you've got the money.
AC.
 
I guess the 30mm vs 32mm makes sense as you would need 850/750=1.13 or 13% more air flow and the area of a 34mm port is 13% bigger than a 32mm port.

I'll probably stick with the single Mikuni short term if I can sort out my over rich condition (I think the enrichment circuit is not sealing fully), but would like to go back to dual carbs at some point. Does anyone know if the Jim Schmidt "Kiehin design" has an enrichment circuit like the Mikunis or a choke?

I'll probably switch to the Beemer w/ windshield when it gets too cold, but want easy starts over a wide range of temperatures.

Thanks for the info.

Jim H.
 
How much faster is any carb combination going to be than a stock 500cc current tech bike :roll: I just get out my 1000cc Aprilia if I want to go faster. :shock:
 
I took the easy way out and went with a single VM34. It fit and seems to work fine. Maybe I will add another one when the wallet is thicker.
 
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