curious carb question

Not open for further replies.
Aug 6, 2005
I am curious after years of reading lists and forums and seeing the great debate of a single mikuni come up time and time again, why no one really ever does a single 32mm amal. I bought, not to long ago, as a back up plan, a single amal manifold to bolt on to the head and fit a stock 32mm amal carb for my commando. After finally getting the dual carbs to work right and riding the bike for a nice long weekend I sat and thought about practical use of the bike and future adjusting and problems and if I really wanted to have to mess with the carbs or ride the bike happily. I have never liked the looks of a mikuni on a British bike, only my opinion, sorry if that offends, but I just don't like em. From what I've read and the one I do have on my single Ducati, they are more dufficult to set up than an amal, there are more components than an amal. So I sleeved an old 32mm amal, modified the idle curcuit so it is accessible, put in a new needle and needle jet, set the air screw to the book at 1.5 turns out and kept stock jetting, bolted it on because I needed to see what , if any performance differences I would have and guess what. For "my type" of riding, street riding, norml speeds 0-80 mph, 0-4500 maybe 5000rpm's I had absolutely no difference in performance. It does idle better and it only took about 20 seconds to make sure it was set right and it was road ready. I figure I have eliminated about 80% or more of any carb related issues I may have in the future from a cable binding, stretching or slide doing the same. I don't have cable routing issues and a well set up amal is a beautiful thing, so simple, so functional. So I spent 50 bucks for the sleeving, 14.00 for the needle jet and 8.00 for the needle and I'm good to go and the bike still looks stock. I bought a used air box plate and modified it for one carb and even have the horrible ugly space filled in that a mikuni leaves open like something is missing. So the question is. Why hasn't the single amal been a hit and why the mikuni such a rave. I appologized in advance if this post offends anyone who is pro mikuni or a dual carb purist, but I've tried all of the options successfully and the single amal is so sweet and easy I just didn't get why I'd never really heard of the single amal option.
A great idea, story and a HAPPY conclusion.. who could ask for more??

oh yeah, me... please share as to the 50$ sleeving job??

Thank you and would you consider a MPG test for us??
It's done more than you think, it's just not talked about. Our favorite controversial supplier, Norvil has the manifold and the single carb backing plate for the stock look.
Manifold #069961
Backing plate #069767SS
If I'd of known an amal single manifokd existed years ago, I'd of changed over, this is the type of thing that needs to be passed along to new norton owners just in case they don't like the mikuni alternative and want to remain semi stock. There are several American dealers that have or can get the manifold, but I believe RGM in England casts them. The 50.00 sleeve job was a friend of mine, 30 year mechanic and machinist that made the tooling for us to do all of our amal carbs. He is tooling up for trident carbs now. I paid him the money so he could get back a little of what he had in the tooling. I provided the sleeve material and he did the machining. Did a heck of a job and they work great, plus he is only a few miles away from me.
Excellent... Any chance he would like to more sleeve jobs??

I have a few I wouldn't mind having done.

Depending on which corner of the planet ya'll are that is...

Thank you for following up!

I don't think the thought of doing others occurred to him or I. The tooling was made to supply our needs as we have them, but I could ask and see. I don't even know what he could reasonably do them for. I imagine it's one of those things where one is not worth the time, but more than one is good once set up and doing them. I'll post back if that isn't against forum rules. I do not want to step out of line here. If anything I could post there would be an interest and give my personal email for inquiries and details.
Amals work good but are very coarse in thier adjustments. When close isn't close enough. Get a Mikuni. From another board Panic explains:Each letter of Mikuni needle jet (O, P, Q) is .002". Each number (-4, -5) is .0002". Each Amal size is .001", so there are about 5 Mikuni sizes between 106 and 107."
So do you need a micromater or a scale to set your flow? This is a choise of which tool to use it's not a style thing. Mikuni's cheapness made them the carb of choise on a market unprepared for the adjustments they have to offer. Cutting it that fine isn't somthing most of us can do. You might look at this tool as a way of seeing what you would really like an Amal to do. But kissing them of because they don't look right? You can also use the Amal mark two which looks better and flows better than the Concentric But it doesn't have ticklers and behaves much more like a Mikuni. Agian you loose the very fine adjustments. Bottom line if you can get 50 plus MPG and you like the way it runs... I have used them all.
When I was at N-V Wolverhampton, my 40-mile ride-to-work was a Company 650SS.

Originally it had the stock twin Amals, but in response to a sidecar driver, we looked at a single carb alternative. I think we went up a few millimetres in choke size, and the low rpm torque was significantly better. Since that wasn't the 650SS' normal operational regime, (it was a "Super Sport after all, not a taxi) we didn't pursue it further.

I think that was the same customer who complained about fuel consumption. It was so bad (about 40 percent of typical) that the factory invited him to visit. He had been looking at magazine road test fuel mileage. He didn't tell us he was pulling a double-adult sidecar and usually had at least one adult and three kids in it.

I had an interetsting experience after I put the twin-carb package back on. I hadn't realised that the slides were individually lapped to fit the carb body, so I hadn't marked which carb they were from. Mr. Murphy ensured that they went back wrong. Shortly thereafter, accelerating round some traffic in Wolverhampton, I shut the throttle as I came in behind a bus, only to find that one slide had hung up and I still had about 75% power. I was very glad that bike had magneto ignition and a kill switch beside the throttle grip. 75% power in second gear when about 10 feet from the back of a double decker certainly gets your attention.
curious carb question,

I have a 1970 fasrback 750. Why do you ignore the Amal Mk11 for single carb use. I have used a 34mm for the last 7-8 years and have had no problems. The manifold and carb supplied by RGM in england. It works as well as a mikuni, easy to tune, good fuel consumption. I replied about this on a previous forum.
I don't ignore the use of any carb that works well. I like the somewhat original look that the single concentric gives, thats all. I don't like fiddling with two carbs and two cables and routing and the chances of something going wrong with either or both thats just me, to each his own. I was just asking to get opinions. I don't have any experience with the MK2's, but would like to try them sometime maybe on a special I plan to build in the next year or so.
Britbike220: I am planning on doing a single amal conversion to my 72 750 Combat. You said you left the jetting stock, as in 106 needle jet, standard 750 needle, 230 main, and the #3 slide? Your bike is a 750, correct? Also, were you able to use your old twin cable setup and just disable the cable junction? RGM motors' single intake manifold, does it require a rubber mount conversion, or does the carb actually "bolt" up to the manifold? What temperature and elevation do you ride in? Sorry for all the questions, but thanks in advance. :D
72fastback - The single manifold from RGM allows the carb to bolt up with the standard heat insulating washer. Mine was bought used, so I had to remove the studs from one of the standard manifolds to use on the RGM (not sure if new ones come with them or not). In order to test the setup, and prior to making it a bit neater, I removed one of the "y" junctions from the standard throttle and choke cables for use with the remaining Amal MK1. I left all the jetting stock and just adjusted the needle position a little. Mine is a '73 850. I know some people have gone up a size or two on the main jet to compensate, but I haven't needed to do that.
A single MK2 will require a different manifold where the carb mounts with a rubber adapter and clamps (same as the Mikuni). You'll need a new throttle cable too.
A little thought with the cable routing will get everything operating smoothly with the single MK1.
I'm very happy with my set up - smoother and more reliable tickover with very little maintenance to keep it that way.....some people don't like the "naked" look where the stock air filter housing used to be (and you have to remount the ignition lock) but you fail to notice it after a while!

I struggled with a single MKII conversion for about three weeks - I could not get it to stop flooding. Not sure what was going on but all the changes in the world to the internals plus float height would not stop it. I just came to the conclusion it didn't like being rubber mounted (the MKII moved around considerably more than a bolted-up MKI when the motor was running). No regrets with going back to a single original carb - give it a try!
Not open for further replies.