Mk1 amal single carb conversion

Hi chaps
I'm sure this will have been covered here before but I can't find it I'm afraid....
I have just fitted an SRM 2:1 manifold to my 1973 Commando 850 (non electric start) and have fitted one of the old Amal 932 carbs
It now will only run with full choke on so i guess i need to think about re-jetting and what air filter I should fit?
Would tweaking mixture screw help or do i need to replace jets and needle etc?
Anyone advise on jets/needle/slide cutaway changes I might need.

Any help gratefully accepted - do be gentle with me I'm a Commando virgin!

Regards
Tony

Tony,
There's a good chance it's caused by an air leak or a blocked pilot jet and there is tons of stuff on that issue. The only changes required are usually with the needle and main jet, but a single 32 will kill the top end.

Best of luck,
Cash

I will try to be gentile. I do not want to be the one to tell you forget it and that it will never work because I am all for fiddle farting around with this sort of thing.

That being said, forget it, that will never work!

You would be very lucky to get it run on a 750 much less an 850. If you are going to run an Amal carb, you will need at least 2 of them. Even a single 34mm Mark II will cause a 750 bog down before 5000rpm. Nortons love and need to breathe. A single 32 is like duct taping your mouth shut and plugging one of your nostrils and then go running up steep grades while fight a sinus infection.


Your logical solution is determine the ID if the 2 to 1 manifold and match it with a Mikuni 36vm or 34vm if it is big enough. Or go with the original twin 32's.

You might want to explain your position as to why you are doing this.

Ooer, perhaps I'm on a looser here?
Manifold is from SRM and a 932 bolts straight on.
I am looking for a simple single carb solution that will be reliable, good idle and easy to start. Tuning for power isn't really of interest as more than 70mph doesn't thrill these days.
Whilst I can well understand that a single 932 will be restricting I wouldn't have expected what I get at the moment - will only keep running on full choke unless throttle held open past about 1/4 open.
Tony

Not so. It can work just fine. Mike Taglieri who is on the Yahoo INOA list and runs the BritIron-L list has had his bike with a single 932 for years and loves it. His bike is a '72 Combat. There are quite a few others that have followed his lead. I'd be among the first to try to talk you out of it because I feel a Norton Commando should have twin carbs but it can work, and as I remember there is very little that needs to be changed.

Hi , sorry I cannot put the hand on the paper , but normally if you had bought it from RGM, they should had sent you the spec to tune your carbie, as far as I remùenber it should be a slide with 2.5 cutaway, and a bigger mainjet something like 280, keep the needle as is and the needle jet , except if they are worn out, but if you are running with the choke on , some foreign crap is blocked somewhere in that tiny hole , try to clean it with a guitar strand or with strong air flow........good luck!

tony.pattison said:

Ooer, perhaps I'm on a looser here?
Manifold is from SRM and a 932 bolts straight on.
I am looking for a simple single carb solution that will be reliable, good idle and easy to start. Tuning for power isn't really of interest as more than 70mph doesn't thrill these days.
Whilst I can well understand that a single 932 will be restricting I wouldn't have expected what I get at the moment - will only keep running on full choke unless throttle held open past about 1/4 open.
Tony

Click to expand...

I would start by going to the extremes on the needle clip. There are two different needles available. Get the one you do not have and try it also. Change the need;e jet, trying a 105 or a 107.

If you have a donor main jet laying around and if you have a set of number drills, you start experimenting by drilling the donor jet out till you have some sort of favorable response. I do not condone drilling mains but this is for trial and error purposes. Once you get somewhere, try to match it with a non bastardized jet from Amal.

The other extreme to go for is the slide. Depending on what you have, try a size on either side, 4 or a 2.5. Probable the latter but who knows.

What ever air cleaner you use, it should be the biggest you can fit or maybe just a stack. Go to the K&N web site and size one up. Get it running without one first.

You have knowthing to loose here and many option to try. Log what you do and let us know waht you come up with.

You see, just because i do not think it will work doesn't mean you shouldn't try.

Found this in the INOA yahoo archives. Mike T describing his single Amal setup:

> --- In INOALIST@yahoogroups.com, "Michael Taglieri" <miket_nyc@...> wrote:
>>
>> I kept my single Concentric the same as it was before for quite awhile,
>> but what I had before was not normal. I had 932 carbs that had been sleeved
>> by Triton Machining and were set up stock with a 220 main jet, .106 needle
>> jet, and needle in the middle position. However, my carbs also have a 3 1/2
>> cutaway and a stepped spray tube because they were originally on an 850,
>> but I never changed them because they seem to run fine that way. Also, I
>> have a '72 Combat on which I "un-Combated" the engine by lowering the
>> compression and installing a standard cam, so I've always used the standard specs,
>> not the Combat specs.
>>
>> Anyway, when I changed to one carb, I kept all this unchanged for about
>> two years, then I increased the main jet from 220 to 230. There was no great
>> amount of logic behind this; I'd just rather be too rich running wide open
>> than too lean and I finally found a 230 jet to install.
>>
>> I'm not sure what you mean by "dialing in the pilot jet." These
>> late-model Concentrics have a permanently installed pilot jet that is not
>> interchangeable, but Amal retained the threaded place where jets were
>> formerly installed. If you're putting a second pilot jet on top of the
>> one that's already in there, this could cause odd problems. Also, make sure
>> the pilot jet and the passages behind it aren't clogged. I cleaned out my
>> pilot jet with a #78 drill, which is the recommended size. Finally, it's
>> important to adjust the float so the fuel is .170" to .240" below the top
>> of the float bowl. I've found trying to measure float height physically is
>> not reliable -- you should connect thin tubing to the bottom of the carb and
>> see the actual height that the fuel rises to when you hold the tube up next
>> to the bowl.
>>
>> Mike Taglieri miket_nyc@...
>>
>> Everyone has his reasons.
>> - Jean Renoir "The Rules of the Game"
>>

Hi Tony,
I'll throw my two cents in. I ran a single Amal for a number of years and as I recall I did not have to change a thing. First riding impression was that there was no power missing at all, in fact throttle response was improved. However, I have to admit that my bike has never seen full throttle or more than 5000 rpm (at least in my hands). A couple of used Ebay Mikunis later and I am presently running A 34mm flatslide TM Mikuni. One carb gives me all the carburation I need although I am sorely tempted to invest in a set of JS's twin carb set-up.

GB

A single Amal 32mm concentric will work just fine on a 850 Commando MK2. Sure you lose some topend power but hey I don't push my road 850 to the limit. About 40.000 miles ago I mounted a 2 in 1 manifold, new concentric 32mm with chromed brass slide(3,5), 250 main jet, 106 pilot jet, conical K&N filter. Runs smooth and steady eversince. True 2 carbs can't be beaten in performance but I got fed up with unsynchronised carbs way from home.

Hey Tony, do it if you want to, but the original Mikuni conversions ( 40 years ago, or more ) were done for a reason,
long lasting, trouble free motoring.
As several have said, the Amal conversion will work, but if you have to start spending money to tune the Amal,
you will need a single cable and a filter, then you might as well spend that money on a Mikuni, and it won't wear out for a long long time.
Plenty of specs here on Mikunis and filters etc.
The Mikuni will be fitted by means of a rubber mount and hose clamps, all you need is a Phillips head screw driver
to turn it side ways to work on, or completely remove it.
Fuel line off,Tank and seat off, unscrew top of carb and remove slide, adjust needle setting, (no tool required), turn carb sideways,
remove float bowl with the same screw driver, remove and replace Pilot jet, (small blade screw driver), and Main jet, Bowl back on,
straighten him up, Slide back in, tighten him up, Tank on, Seat on, Fuel lines back on. Job done. Your beer is still cold.
You can then try it, do it again if nec, do it again if nec, the same morning.
Second hand set ups are around and OK.
If you want to stay British, keep the Amal.
Good luck with your decision.
AC.

Hi folks
Thanks for your inputs on this, it has given me hope that it is at least a 'possible' way to go!
The cost of the change so far is just £40 for the 2:1 manifold so no big deal and I could easily adapt it to take any single carb to be honest (SU, Mikuni etc).
I have stripped and checked the two 932 carbs and they are all in very good condition with 250 Main, 106 needle and 3 1/2 slide so with a conical K&N from the 'misc' box under the bench it looks like it should at least run!
As with any of these 'boys-toys' we all have our own ideas of what we want from them. I will be happy to have a mild mannered Commando that will handle well and get briskly upto 60 or 70. Storming down the road at a ton plus with the old engine ready to explode isn't for me these days. Even in my craziest days (30 yrs ago) I couldn't handle 90 plus speeds with no fairing so I'm sure not up-for-it these days...
Will assemble the whole shooting match at the weekend to see what happens.
Watch this space.
Tony

Once I met an owner with a 70 who was running a 30 mm single Mikuni to a 28.5 inlet head (if memory serves) and it ran well and idled fine too.So there ya go.

tony.pattison said:

Hi folks
Thanks for your inputs on this, it has given me hope that it is at least a 'possible' way to go!
The cost of the change so far is just £40 for the 2:1 manifold so no big deal and I could easily adapt it to take any single carb to be honest (SU, Mikuni etc).
I have stripped and checked the two 932 carbs and they are all in very good condition with 250 Main, 106 needle and 3 1/2 slide so with a conical K&N from the 'misc' box under the bench it looks like it should at least run!
As with any of these 'boys-toys' we all have our own ideas of what we want from them. I will be happy to have a mild mannered Commando that will handle well and get briskly upto 60 or 70. Storming down the road at a ton plus with the old engine ready to explode isn't for me these days. Even in my craziest days (30 yrs ago) I couldn't handle 90 plus speeds with no fairing so I'm sure not up-for-it these days...
Will assemble the whole shooting match at the weekend to see what happens.
Watch this space.
Tony

Click to expand...

as mentioned it should/will work fine - i have done similar to this w/ commando's and triumphs and have found that sometimes you need a slightly larger pilot jet (though not always) and may have to increase the main slightly - always seems to be a bit different on ever bike - but it will work no problem and i think you'll be pleasantly surprised about acceleration/top speed achieved

Try tickling the carb while its having this problem. If it runs better, or can't be tickled, you know its something to do with fuel feed or fuel height. Or if you can see and hear that the tickling is working, and it makes no difference, then the problem is somewhere else - and very strange.
It does sound like blocked jets.

Almost every model of Norton twin has had a single carb version ( even the Commando, with an SU) and worked OK, WITH the same size carb. You won't get every last ounce of performance compared to twin carbs though.

P.S. Make sure the throttle needle is still fitted correctly, and hasn't fallen down.

Tony,

The pilot idle passage is a critical step to making the Amal work. You said it would not go under quarter throttle, that sounds like the idle circuit is not working. Usual cause is sediment build up in the pilot passages, I suggest you google bushmans Amal site, all is explained there, get yourself a #78 number drill, glue it onto one of those tubes you get with WD40 spray cans and check the jet is clear. Also check the two little holes that lead out of the jet cavity, infront and behind the throttle slide. Hope this helps Richard

Hello chaps
Well it's all a bit of a mixed bag really is this conversion...
I bought the very nice Commando a few months ago and it ran pretty well though I could feel compression was low on one cylinder and eventually it blew out a plug. Tried helicoil-ing the hole 'in-situe' but couldn't get a good result so removed the head. Sorted threads OK and refitted head but decided to 'fettle' the machine whilst rebuilding. Moved ignition switch to headlamp, rewired the machine etc. etc. I then decided that a single carb would make things much neater and more rugged so bought an RGM manifold....
Well I have tried everything I know and taken loads of advice but couldn't get the thing to run with single 932 amal. It would run sometimes but coughed and farted so badly it was unridable and gave all sorts of problems - some detailed above. Both 932 carbs gave problems and it never seemed like a carb 'tweek' was needed it really was an unrunable engine!
In the end I decided to revert to twin carbs so i could at least know if it was a carb problem or something else that I had done (engine re-assembly problem, ignition, wiring????)
Fitted carbs last night and this morning it started first kick and sat there idling before I even touched the pilot screws which were way-off as it happens. The shock nearly gave me a heart attack, I just stood and looked at it!
Two mile ride to warm her up, adjusted pilot screws (which all worked as 'in the book') then off for another couple of miles and it's running perfectly!
The only thing I can see that could have given me all the greif is a leak on the 2:1 manifold though I couldnt find anything at the time.
Might give it another try at some point but don't feel inclined to bother at the moment - mind-you i don't really want to re-fit the awful standard air filter so need to attend to that problem.
- Wonder what idiot thought that an ignition switch mounted on the air-box and facing all the rain and crud was a sensible idea?
Thanks for all your pointers whilst I've been fighting with all this nonsense.
Have a good Christmas and ride safe.
Tony
P.S. Just received a £10 Mikuni VM34 I won on ebay! Will put it under the bench for another day methinks?

Been reading this thread with interest.
I have some carb issues, as mentioned elsewhere...... starts and idles - but idle screws need to be screwed right in.
Will not rev at all, just dies.

Just recieved my #78 drill bits through the post, so will attack the idle jets over the holiday, see if that helps.

To be honest was looking at buying some new parts for the old Amals, stay up floats/gaskets/needle valves, would still have a pair of 40yr old worn out carbs though. :?
Then thought for a couple of hundred quid I could either replace them with a pair of new Amals or a Mikuni conversion - which to go for though ??

That couple of hundred quid will get you a great set of JS Flat slide Kehins!!!
See all the threads on them that are running at the moment. reat value for the time and money spent
Regards Mike