carb comparison

The Mikunis work OK but I don't like the way they are splayed out. And the single carbs are too slow. We all know what happens when Amals get worn (flat spots) and the Premiers really aren't much of an improvement because they are still basicially the same carb and run about the same as original new Amals. The FCRs are top quality but too big and expensive. So far the best I've tried are the JSM flatslides because they give more power, a smooth idle and they fit. I'm interested in the Keihin CRS twins like Matchless is using but they don't fit without modifications. Does anyone else know of another twin carb kit that fits without mods and runs well? Or has this reasearch run its course?

Funny, both my commandos have the original carbs. The 850 has done a lot of miles. The carbs are worn, and I have set them up to run economically. I get 63 mpg out of the 850 on a good day. Neither has flat spots, and they both idle well, though I don't rely on the 850 idling cold or hot. To me the idle doesn't matter so much because I live in a country area and don't stuff around. Generally though the 850 does idle smoothly.
What am I doing right that others may not ?
I have heard that the new Amals have a different material in the construction of the slide. Apparently this is far better, and does not wear so much.
Lets face it. All carbs wear. Even the best design out [ the SU ] wears its throttle shafts. Throttle shafts are easier to fix than carb bodies I must admit.
Dereck

We all know what happens when Amals get worn (flat spots) and the Premiers really aren't much of an improvement because they are still basicially the same carb and run about the same as original new Amals.

Click to expand...

with all due respect, you are wrong

Amals "used" to get flat spots due to british pot metal softness and quickly became poor idling

Like many people on this forum I have the new Premiers and they are indeed a significant improvement over old Amals because they have a greatly improved idle circuit and a better and harder slide.

The new Premiers are very good carbs that start, idle like a rock, flow to redline and are better built to last

but better than take my word for it, do a forum search on Amal Premiers and read what the owners think

FCRs fit fine. Is there a lot of clearance? No. But they do fit. And they're awesome. I'm not aware of anything that's even close on performance, by which I am referring to responsiveness, idle, starting, top end, the whole nine yards.

Buy something cheaper if you will, but do it because they are cheaper, and for no other reason, as there is none other I'm aware of.

Best of luck.

Trying to spend others money is fun, so lookie here
http://www.bikeexif.com/norton-cafe-racer
http://www.allensperformance.co.uk/crs-35-860.html

+ 1 on the FCR's they work very well .

+2 on the FCRs...

Well all I can say is that I have the JSmotorsports flat slide single, which I`m quite happy with at the moment, but I just hapened to be going over the CNW web site and it seems that theynow offer a custom manifold to make the FCR's fit in the space better & possibly flow better. Anyway that looks to be the way to go for all out , top of the line , best performing carb

The Keihin FCR's are beautiful carbs, and I'm sure they'll outperform anything else on the planet, but it seems to me putting these $1400 carbs on a 70's pushrod, air-cooled, british twin that makes maybe 60-65 HP (in good tune) is a little over-the-top (not that there's anything wrong with that). It seems there are lots of ways to spend money to make these old Norton's perform more like a more modern bike. It's a slippery slope. I love both my old Norton's but I know at the end of the day, a good used $3500 SV650 will out perform them in every way.

I run a set of PWK's on my 850 and they perform well and while the engineering in them is great, I'm not entirely satisfied with the quality of these copies (I've covered that issue in a previous post). There's just no comparison when I examine the Keihin flat slide on my KTM. I like the rubber spigot mount. I can pop them off in a couple minutes as opposed to the Amals. The rubber mount is great at isolating heat and vibes too. I don't like the inaccessable air screw and choke plunger on the RH carb.

The Premiers look good. I wouldn't hesitate to buy a set if I was replacing a set of worn-out Concentrics, and I was concerned about keeping it looking "stock".

My 850 was purchased with a single Mikuni installed but it's gone now. It didn't perform very well with this setup. I suppose I could have spent some time getting it dialed-in better but I didn't care for the way it looked. I like dual carbs on Norton's. That's just me.

The perfect combination (bang for the buck) would be genuine Keihin (PWK style) flat slide carbs + manifolds that come in RH and LH versions, with a linked choke lever for around $500.

I'll agree that the FCRs are the probably the best running carbs on the market - but the cost seems out of line. I haven't experienced them so I'll reserve judgment. They just seem a little over the top, kind of like having your motor attached to a set of carbs instead of the other way around. I've tried every other carb that fits. Of course I've run the Amals for many years and they just aren't good enough for me and neither are the premires. They may be good enough for some but I don't like the crude design, the tendency to warp, the leaks & stains and the gas stink on my fingers from the ticklers. I don't care about finish quality or brand loyalty or any opinion about what is wrong or right. All I care about is how well the carbs actually work in the real world and how well they stay adjusted. I think most people will agree that the most refined design is the Keihin. They look the best to me. So I will just dream about the FCRs or opt out for the Keihin roundslide CRs (with modiications) or stick with my little JSM flatslides.

The reason I fitted CRs is because they were offered at the right price. They are very well made & because they are linked, they should stay in tune longer. If they hadn't turned up, the next choice would have been Jims flatslides or MK 2 Amals. I really do think that MK 1s are fantastic carbs for the money though. I have tried others, including a single 34mm MK 2, single 32mm MK 1, & the Pheonix S.U. conversion, all too slow.

Ed The Tomato Man Ostack send this FCR summary to keep this flow going
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1977-Earlier Norton Commando Keihin FCR35 Carburetor Kit
The Keihin FCR carburetors are the industry standard when it comes to carburetion. No one makes a better carburetor and Keihin is the carburetor everyone else tries to duplicate. They've been the choice of champions for over 40 years!

These FCR35 Norton kits for the 1977 and earlier Commandos are easy bolt on horsepower. The increase in throttle response is almost worth the cost itself, and throw in a tremendous HP increase on top of that. Please see the detailed description for more information. Our carburetor kits ALWAYS ship FREE!
Price: $952.99
Retail: $999.00
- See more at: http://www.power-barn.com/servlet/Categ ... VTOLA.dpuf 1977-Earlier Norton Commando Keihin FCR35 Carburetor Kit
The Keihin FCR carburetors are the industry standard when it comes to carburetion. No one makes a better carburetor and Keihin is the carburetor everyone else tries to duplicate. They've been the choice of champions for over 40 years!

These FCR35 Norton kits for the 1977 and earlier Commandos are easy bolt on horsepower. The increase in throttle response is almost worth the cost itself, and throw in a tremendous HP increase on top of that. Please see the detailed description for more information. Our carburetor kits ALWAYS ship FREE!
Price: $952.99
Retail: $999.00
- See more at: http://www.power-barn.com/servlet/Categ ... VTOLA.dpuf 1977-Earlier Norton Commando Keihin FCR35 Carburetor Kit
The Keihin FCR carburetors are the industry standard when it comes to carburetion. No one makes a better carburetor and Keihin is the carburetor everyone else tries to duplicate. They've been the choice of champions for over 40 years!

These FCR35 Norton kits for the 1977 and earlier Commandos are easy bolt on horsepower. The increase in throttle response is almost worth the cost itself, and throw in a tremendous HP increase on top of that. Please see the detailed description for more information. Our carburetor kits ALWAYS ship FREE!
Price: $952.99
Retail: $999.00
- See more at: http://www.power-barn.com/servlet/Categ ... oem=Keihin

So $953 + $170 for a manifold kit (but hey, they ship for free).
Christmas is right around the corner...

My PWKs have been on my Norton for about 5 years now and have had no problems with them easy to set up and I have only tuned them when i fist mounted them, they have stayed tuned, starts first kick every time and performs great with the Joe Hunt, I have just on 25,000 miles on them now and they work great through out the whole rev linem, my old Amals were still good but I had some spare money and went for Jims PWKs at the time, I would never put a single carb on my motor, I have never had any problems with tuning dual carbies and having enough fuel right to the end when needed and so much better pick up when you hammer it.

Ashley

What is the difference between the CNW FCRs and the Power Barn FCR35?

Honestly, I kind a like the old gas stink finger from the ticklers.

Gas smelly fingertips tickling for me too, so be it. :|

Duh Dudes call the vendors and tell them you don't know which to spend on so please sale pitch why theirs not someone else's and let us know too. Seriously may learn something about sales pitches or facts of the matter.

kerinorton said:

Funny, both my commandos have the original carbs. The 850 has done a lot of miles. The carbs are worn, and I have set them up to run economically. I get 63 mpg out of the 850 on a good day. Neither has flat spots, and they both idle well, though I don't rely on the 850 idling cold or hot. To me the idle doesn't matter so much because I live in a country area and don't stuff around. Generally though the 850 does idle smoothly.
What am I doing right that others may not ?
I have heard that the new Amals have a different material in the construction of the slide. Apparently this is far better, and does not wear so much.
Lets face it. All carbs wear. Even the best design out [ the SU ] wears its throttle shafts. Throttle shafts are easier to fix than carb bodies I must admit.
Dereck

Click to expand...

I use MK2 Amals on my bike. I believe they are a copy of the VM Mikunis which are basically a two stroke carb. When you use them you need to tune carefully right across the full range of throttle openings and for the various load conditions. I effectively cheat and use methanol fuel for racing and because I'm using standard comp. ratio the jetting stays within the range at which the carburettor can cope. If you get it wrong with methanol, the bike will still be quick enough for it's racing purposes. Back in the 50s there was a Triumph Thunderbird which was fitted with an SU carb. Because I never had old British cars, I never knew how to tune them, so I replaced the one on my bike. In fact when an old Brit racer told me how good they were, I thought he was an idiot. My feeling is that the constant velocity carbs which were fitted to many bikes in the 70s were a much better option than VM type Mikunis or Mk2 Amals. I don't like butterfly throttle valves, however with the latter two carbs there is an air jet in the bell-mouth which affects the depression on the needle jet - how do you know when you've got that and the pilot jet right ? With my own bike, my next step in improving the tuning will be to try several of the various taper Mikuni needles which fit the Mk2 Amals, as well as tuning to a calculated ignition advance curve. I think that 'pumper' carbs are silly stuff - how can you control that? Even the slightest bit rich at mid-throttle can make the bike sluggish. Jim Comstock's fuel injection system has to be the way to go for a road bike ?