Back to my old Amal carbs

worntorn said:
I wonder if the oil soaked air filter of the MK3 offers a tiny bit of continuous oil mist lube for the slides?
The oil tank breather also dumps into the airbox.

Glen
Click to expand...
Riding every day helps too
A mate of mine is a very high mileage rider with a t140v he swears that keeping the choke slides in help's the slides
Stops some resonance in his opinion
He now has 32mm VMs fitted
 
baz said:
Riding every day helps too
A mate of mine is a very high mileage rider with a t140v he swears that keeping the choke slides in helps the slides
Stops some resonance in his opinion
He now has 32mm VMs fitted
Click to expand...
I would agree with that from purely a physics standpoint because the added mass (assuming it vibrates as one with the slide most of the time) would lower the frequency; thus there would be fewer round trips of the slide banging back and forth in the bore per rotation of the crank.
 
baz said:
I think monoblocs like you have lasted a bit longer
Click to expand...
Monoblocs and Concentrics are both made from the same zinc alloy, slides and body.
There could be some other differences that help the Monobloc.
They do wear out too. I have a sleeved Monobloc on the BSA SR.

Glen
 
baz said:
Yes I agree
The new amals I bought had not been fettled at all
There was swarf in the float bow and the slides were razor sharp from machining
I had to go all over them with a milk stone
They wouldn't have lasted 5 minutes
Click to expand...
During assembling the cap/slide/needle into the carb after a needle height adjustment, I unknowingly twisted the slide a bit under the spring pressure which put the slide notch out of vertical alignment with the 2 top cap screw holes. Therefore I had to twist the cap a bit for the screw holes to align. This put a bit of pressure between the slide notch and the locating pin in the carb body and that wore a semicircular pattern in the slide notch. I discovered this the next removal. The throttle was working fine, but it could've created an issue.
 
worntorn said:
Monoblocs and Concentrics are both made from the same zinc alloy, slides and body.
There could be some other differences that help the Monobloc.
They do wear out too. I have a sleeved Monobloc on the BSA SR.

Glen
Click to expand...
If I remember right, Monoblocs have an internal lump that guides the inside of the slide don't they? That would maybe give slightly longer life due to better support. I know the guy that sleeved a pair of Concentrics for me in WA decades ago charged significantly more to sleeve a Monobloc.
 
I do not know about the wear aspects of carburetors, but I prefer Amal to Japanese. A lot of petrols these days contain alcohol. I use Mk2 Amals with Mikuni needles. I have used methanol in Japanece carbs. If you forget to drain them after using methanol, a white slime can form inside the bowls and block the jets. Ethanol is similar. I believe the slime is caused by high zinc concentration in the aluminium. Amal carbs are better in this respect.. But Mikuni provide a better range of needles than Amal. If you are tuning to get better performance, the needle tapers are critical. Both Amal and MIkuni needles are the same dimension on the parallel part above the taper, and Mikuni needles are available in lengths which suit Amal carbs of similar choke sizes.
With my motor, the bike accelerates quicker when you wind the throttle on slower with a slow taper needle, than it does when you wind the throttle on fast with a fast taper needle.
I do not trust Amal needles. I think they are agricultural. Japanese engineering is usually more precise, than British.
 
Probably one of the main reasons modern bikes are faster then old bikes of simiar capacity, is their engine management system. If you succeed in tuning an engine to go fast on petrol using and old style carburetor, getting it to stay right is probably a problem. If you use methanol as fuel instead of petrol,, the jets flow twice as much, so the tuning errors are halved. But even with methanol, the needles are critical. The difference between fast and slow is almost nothing.
 
Most of the slide wear comes from the 32MM Amal size as original. The 28 and 30MM....not as much. But the similar metal between body and slide causes the galling. Over tightening of the flange screws on the intake manifolds also cause warping of the bodies which causes slides to stick. Same with the float bowls and attachment screws. they warp real easy.
 
Al we are talking about Amals and long life here, as usual, I don't run methanol, it's a road running bike and 98 petrol with stock Amal needles but run 270 main jets and every thing else in stock size, none adjustable floats that came with the carbs, I always ran without chokes as in the early days I got sick of people mucking around with the choke lever and dropping the choke to find out with bad running someone has mucked around with it while away from the bike, I have been running K&N air filters since 1982.
I have never had any problems with Amal needles but when it was a everyday rider I always replaced the needles and jets every 3 or 4 years as well O rings on the air and idle screws (carby kit) just part of maintaining my Amals, I never over tighten the Amal tops.
The good thing about Amal carbs is they are so simple to maintain, easy to tune and the Norton runs so well with them, tickel, kick and go.
 
Well a lot might not believe me about my Amals or how lucky I been with my bike but everyone who knows me and my Norton knows I don't BS why would I as I have nothing to prove or gain so really you can say what ever if I am full of crap or not everyone has their opinions, if my Norton was not reliable I would have got rid of it a long time a go.
Yes it's had its failure with things breaking and sometimes been easy fix without spending a lot of money then there has been failures that cost a lot of money (replacement crank cases) but most of my upgrades spent where to make my Norton run better for more time riding, things do wear out and I will fix but fixing things without spending too much money is always a win in my book.
When all my bikes are running good I leave them alone except for maintenance when needed, I enjoy doing that as well making improvements where I think it needs it and when I have spare cash to do so, my Norton has had upgrades and improvement all it life of 46 years of ownership for reliability, better handling and lightness and over the years the dreaded blocked pilot air passage was one of the reasons I went down the PWK carb road, but I have fixed that now and the Amal are working the ways they should after a long lay up under my work bench.
If people don't believe in what I say all good with me as I just tell things as it is with my Norton and near 47 years of ownership it must be good or I just been lucky as I can't really answer that, it's not perfect but it's mine built by my hands and its been part of my life since I was 17 and I am no expert but I do know my own Norton.
If the Amals do need replacing down the road I will get new premiers but at this time why the slides are good still so I will see how they go.
 
I've had various motorcyclists tell me that their Amal Concentrics wore out at anywhere from a couple thousand to 10 thousand miles or so.
One local engine builder hated them so much that he said they should all be removed and driven over until broken into small pieces. He claimed that they wear out in a few thousand miles at most.

I've never had any significant problem with the Amal Concentrics, although the slides do wear a lot more than the new Premieres do.
I'm not convinced that the slide wear is all that critical.
The Oz Vincent came with very well worn Concentrics. I would guess they had at least 25,000 miles on, but it could be even more. I know that I put another 27,000 miles on them at which point the fuel mileage dropped from the usual 55 mpg Imp. to about 30.
The bike still ran well, no issues with starting, idling or smooth running. It did lack some power due to the rich running. But all of that was due to worn needle jets. Worn slides would tend to make the bike run a bit lean, not rich.
I'm sure that , in a pinch, those carbs could be fitted with new needle jets and go quite a distance still.
I treated it to new Premieres instead.
So I wonder if the large variation in wear is due to quality control of the cast material?
Or do some owners do as I did and put new carbs on when really it's just the needle jets that are worn out?

Glen
 
Good deal on replacing the old PWK carbs with sticky floats. Mine own bike had that problem when I bought it and that led to a fire once when I was trying to start it and a float bowl overflowed...fortunately I was able to put the fire out quickly.
FWIW it turned out the seller had installed new floats in the Amals and they were slightly too wide at the pivot, I fixed that with a file and haven't had a problem since.
 
Ethanol in petrol is no different to methanol. They are chemically very close. They both attract moisture, which can make a corrision cell, inside fuel systems. A service station in our town was hit with several law suits from aggrieved customers, who had their fuel systems reworked, after using fuel which had too much ethanol in it. Zinc is a commun additive in many casting aluminiums. It gives a different colur to the component. VM Mikunis look different to Amals, they are usually greyer and do not have the shine. Many other carbs are similar, and look as though there is a lot of zinc in the alloy. Amals never seem to become dusty when left in a moist atmosphere. Much of what was made in the UK post WW2, involved use of British MInistry of Technology materials and processes. Japanese motorcycles corrode more than British, and Italian are even worse.
There is a thing which many people do not know - cadmium is more corrosion resistant than zinc. To tell the difference - if you put a cadmium plated part into dilute hydrochloric acid, it usually does not end up with bubbles of hydrogen coming from its surface. Zinc will usually fizz slowly. When it is in aluminium, it does similar.
 
Last edited:
Never in a hundred years would I have known I could clean my Amals by soaking them in vinegar. Thank you for that.
 
Vinegar works great for cleaning carbies as soon as you put all the carb bits in a container full of vinegar it starts to work straight away, only need to soak for a few hours but I leave in for a day or so if there is any gunk or crap in your carbs the vinegar will desolve it and bring your carb up like new, will clean all passages if not fully blocked but will help to unblock.
Good thing about using vinegar it's cheap and works better than carb cleaner, it's acidic but won't harm the metal.
 
worntorn said:
I'm not convinced that the slide wear is all that critical.
Or do some owners do as I did and put new carbs on when really it's just the needle jets that are worn out?

Glen
Click to expand...
Glen,
I think you've hit the nail on the head.
I've had occasion to throw together a few carbs from junk box spares back in my impoverished years, and provided the needles & jets were replaced with new items, they've always performed well, despite sometimes being rather loose.
I was keen to keep the original carbs on my '70 Roadster, but it wouldn't rev past 3.5k. It was so bad I thought the ignition was at fault.
New needles and jets have transformed it, and it runs like new.
I can see the merit in keeping the air slides as additional support, but I generally just ditch them and blank off the cable guide hole in the carb top.
 
Damn, now I have to rethink my conversion to PWK's on the 850! I bought them used from another on the forum, so had to rely on his honesty. I tried Mikuni's on the 750 in late 70's, but went back to Amals in early 90's.
They are really easy to work on, so maybe I'll put those on the 850 while the 750 is apart for the expensive rebuild/ mods.
The Amals on the 850 are the originals, I believe. Just needed the guitar string treatment when I bought it 15 years ago.
23415 on the Veglia speedo šŸ˜®
 
Last edited:
Deckard said:
Damn, now I have to rethink my conversion to PWK's on the 850! I bought them used from another on the forum, so had to rely on his honesty. I tried Mikuni's on the 750 in late 70's, but went back to Amals in early 90's.
They are really easy to work on, so maybe I'll put those on the 850 while the 750 is apart for the expensive rebuild/ mods.
The Amals on the 850 are the originals, I believe. Just needed the guitar string treatment when I bought it 15 years ago.
23415 on the Veglia speedo šŸ˜®
Well, maybe they aren't the originals
Click to expand...
Did you have problems with the mikunis on your 750?
 
You must log in or register to reply here.
Back
Top