Lifetime of Amal carbs

This week I brought my newly bought Commando Production Racer to the dealer for a complete check. As I don't have much experience with Nortons (yet), I thought it to be preferable instead of the "trial and error" procedure. So today they informed me that a regular idling is impossible to achieve as carbs are badly worn and adviced to install new ones. :cry:
They advised Amals and personally, I prefer those above Mikunis as well because of their originality. Using the "Search" function, I read a lot of interesting information about carbs for Commandos. Mikunis seem to have a longer lifetime than Amals (please correct me if I'm wrong) but what may I expect as lifetime for Amals ?

That is a bike that should be kept as original as possible. Your best bet is to have your original carbs re-sleeved and have the needles and needle jets replaced. (The needle jets at least need replacing anyway every 5000 miles or so to have it run smoothly at constant speed through town.)

The re-sleeving takes care of the wear caused by the pot metal slides rattling in the carb body. The carb body is bored out slightly and sleeves made of a dissimilar metal like brass are pressed onto the slides. (There are many variations depending on who does it.) It will be better than new.

This is what I would do but there are other options like buying new carb bodies and getting chrome plated slides. Burlen is now making new Amals and parts but some have had quality problems with these. I've gotten parts from them and they've been fine.

How many miles are on it now? Would say the 11-12K miles is about right but there is no reason they can't be made perfectly usable again. I have a 276 carb on my '51 Matchless with a machining job that is like new now. (On these there is a new oversize slide made of stainless since they can't do a sleeve.)

No way Mikuni on a real Production Racer please!!

The odometer indicates well over 20 000 miles but I have no idea when the 850 cc engine has been replaced by the Combat 750. Moreover, the Amals might have been the ones that were fitted on the 850. There are more question marks about the origin of the Combat such as the failing engine number. Does it mean that the crankcase have been replaced ? No idea. I can only hope there won't be much negative surprises waiting...
The bike looks absolutely fabulous from the outside and today I was told it runs well but I keep sleeping badly untill everything is clear.

By resleeving the carbs and fitting disimilar metal slides you at least triple the lifetime of an amal carb. Have 2 rubbing surfaces made from the same metal is an engineering no no, at a molecular level the surfaces bond and then rip pieces from each other as they move causing rapid wear :shock: .

Paul said:

the Amals might have been the ones that were fitted on the 850.

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Amals fitted as original equipment normally have a build number stamped on them next to the body size "932" number on a raised pad on their right hand side?

That number identifies the carb's unique specification, so the model of bike it was originally fitted to can generally be identified by the build number.

Paul said:

There are more question marks about the origin of the Combat such as the failing engine number. Does it mean that the crankcase have been replaced ? No idea. I can only hope there won't be much negative surprises waiting...

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Not quite sure what you mean by a "failing" engine number? Can you supply us with more info please?

Paul said:

The bike looks absolutely fabulous from the outside and today I was told it runs well but I keep sleeping badly untill everything is clear.

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I suggest you ride it as soon as you can? Then you will find out if the supposedly worn Amals (or anything else?) are likely to be a problem you can't live with?

In the UK, carb re-sleeving is a popular modification, instead of perhaps buying a new set of Amals which may wear out again in a few thousand miles? Mikunis are fine, but they are more difficult to set up.

Carb life will depend a bit upon filtration. With a decent filter, I used to reckon on about 20,000 miles with perhaps a slide change in between. It will be less with the open carbs that you have. I also doubt if you'll get it to run cleanly at the bottom end with those screw-on bellmouths which include the pilot air intakes. The proper Amal velocity stacks which are concentric to the carb bore work more efficiently.

I've only used Martyn Bratby in the UK for carb re-sleeving but thoroughly recommend him. He's usually at the Wieze jumbles.

Belgians have some of the world's most liberal attitudes when it comes to 'fiddling' with frame and engine numbers and Commandos registered as Jubilees are not unheard of. The former importer Poidevijn told me that there were no type approved 1973 750s as it wasn't worth his while to go through the procedure for a stop-gap model. All '73 750s registered new in Belgium were 850s ! Simple really.

If there's anyone on this forum who has a 'thing' about matching numbers then he's keeping his head well below the parapet. Don't worry about it, get out there and enjoy it.

"failing" engine number: I meant "missing": there's no more than a "1" where the number should be stamped.

Before I bought the bike, we had quite some problems to start it (after 6 years). Eventually, I found that a bad coil connection caused ignition failure but meanwhile, one of the spark plugs had to be replaced and we only had one with a different heat range. Eventually, the engine run but idling was either impossible or at a much too high speed.

This was confirmed by the dealer today. Unfortunately, I couldn't be present when he worked on the bike (his workshop is 125 miles away and he couldn't start working on it when I brought it) As I told before, he called me today and stated that it is impossible to get a proper idling because of the carbs condition.
Remember the Production Racer doesn't have an electric starter so I really want it to idle perfectly. After all, it's rather unpleasant when the engine stops in a trafic jam...

I mentioned re-sleeving but this was not recommended. maybe because other parts (needles etc.) should better be renewed as well. (don't forget labour costs !)
Would it be advisible to mount crome plated slides ?

I'll call them back tomorrow...

@79x100: once more very interesting information !
Unfortunately, Poddevyn passed away so it won't be possible to question him about this anylonger...

So - if I understand you well- could it be that the Combat engine was the original one ? (the registration papers say "850 cc" ?)

As son as you say "racer" it probably means a replacement engine case.
With no number that pretty much confirms it.
You could always get some replacement Amals and fit a chrome slide later.

Many 750s have been rebuilt after major damage using the latest pattern (MkV) crankcases which even now turn up new unstamped on eBay. Some close-up photos would assist in seeing what you have.

Probably not much point in just fiting new slides to your carbs as the bodies will not be worn evenly and you'll end up with slides which stick open. This is far, far worse than an uneven tickover !

The cost of a re-sleeving and replacement of all wearing parts together with ensuring that all faces etc. are flat would normally be less than that of new carbs and will give better results. That's why most of us prefer it. It is however an operation that requires some expertise and most 'dealers' would probably prefer to sell a new pair of carbs.

To be honest, whilst a bike with worn carbs can be a bit unpleasant to ride, I've never known it make a bike unrideable. At full throttle it makes no difference at all so big handfuls help disguise the problem as will a slightly faster tick over. Most production years of ex-works production racers were fitted with Amal GP carbs and I don't think that they had a tickover facility at all.

If it were me and I wanted to get on the road quickly, I'd probably put a new pair on and then have the originals reconditioned for when the new ones wear. That way it won't matter if it takes a while.

Of course, I meant chrome plated slides into new carbs, not in the old ones.
I think it's a good advice to go for new ones now and to have the old ones reconditioned later. I really couldn't stand it to wait untill the autumn before I can ride it.
Thanks !

Paul said:

@79x100: once more very interesting information !
Unfortunately, Poddevyn passed away so it won't be possible to question him about this anylonger...

So - if I understand you well- could it be that the Combat engine was the original one ? (the registration papers say "850 cc" ?)

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The answer is that I don't know but probably not as the unstamped cases suggest a replacement unit. I know the old gangster has gone and to be honest he would say anything for a couple of thousand franks in his top pocket but this was on one of his rare friendly moments.

As I understand it, at the time when Nortons were in difficulties he was in the habit of filling a van up with spares at the factory in lieu of repayment for warranty failures so anything is possible.

I really wouldn't worry too much if you've got documents with at least one correct number on. Is your gearbox numbered ?

Frame and transmission numbers will help identify what you have - maybe. There were not many genuine production racers made. But it is not hard to buy the bits to make any Commando into a look-alike production racer.

I have seen some very "creative" individuals trying to sell off these bitsa bikes as genuine production racers. Not trying to scare you but it would be good to track down as much of the past history as possible using the serial numbers you do have on the bike.

I think you have a good plan. Dealers worry me though so you are doing the right thing by participating in the decision making process! The more you can learn and do yourself the better.

Russ

I have seen some very "creative" individuals trying to sell off these bitsa bikes as genuine production racers.

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To make things even worse, a genuine production racer would no doubt have undergone many modifications in the quest for more speed! You could spend years trying to confirm your bike originated as a proddie racer. Does it really matter? It is one now, just enjoy it.

Just to support 79X100's suggestion of putting a new set of carbs on while the old ones are sent away for repair. I think new carbs come with alloy slides so you will probably have to specify that you want chromed ones. New Amals are still quite cheap when you compare prices of parts on new bikes.

batrider said:

I have seen some very "creative" individuals trying to sell off these bitsa bikes as genuine production racers. Russ

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I need to correct this misunderstanding. I posted this before (but of course, not every one is supposed to read everything.):

The bike I bought was originally a MKIII that was bought secondhand by the previous owner. As in the seventies he raced with Commando Production Racers, he wanted to modify the MKIII into a -lets say- Production Racer Replica to participate in classic races. His "dream" was postponed for a long time though untill, 6 years ago, it was more or less finished. In the meantime, he suffered more and more from arthritis and had to give up his "come back" on the race track. The only ride he can bear now for a couple of hours is on a comfortable HD Electra-Glide with air suspension (he's a HD dealer). As initially he rebuilt the bike for himself, he renewed really everything that wasn't in an excellent condition. He also has a good reputation and so I took the risk...
I called him yesterday and he claimed that if he had kept the machine for himself, he would have changed the Amals for Mikunis. (which I won't)

The Ducati MHR I have is not the original "Mike Hailwood" either, much less resembling like that one than a "Commando Production Racer Replica" resembles a genuine Norvil but still a nice bike to ride.

So I am fully aware that it is "only" a copy ! Moreover, I even prefer this look-alike as I want it to be reliable: the aim is not to display it in a private museum but to ride it.

This morning I called the dealer again. As I expected, the costs for repairing the old carbs (including labour costs) would be higher than the price of new ones so the decision was easily made. I asked to mount chromed slides though which seems me to be the best way to go.
As Dave said, the Amals are still quite cheap compared with the "modern" parts.

Paul, Do make sure that you get the old carbs back from the dealer, you may ultimatley find somewhere in the US or elsewhere that can do the repair at an economical price, especially if you are not in a hurry because the bike is operational with the new carbs.

dave M said:

you may ultimatley find somewhere in the US or elsewhere that can do the repair at an economical price, especially if you are not in a hurry because the bike is operational with the new carbs.

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79x100 recommended Martyn (or Martin?) Bratby, as he has a good reputation for doing Amal resleeving work.


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