Amals - how worn is worn out?

Joined
Jul 18, 2004
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327
Hi Guys,

I always run into this problem: manual states " if worn, replace" ?!
How worn is worn?

Slides:
Can anyone give me some rules of thumb on throttle slide play to carb body. Is there a measurement I can use as a ball-park figure, slip in a feeler perhaps? I notice on the AMR site they make mention of " original tolerance" so a measurement must exist. :?
I've got an extra set of Concentrics, they are obviously shot, they rattle, have deep grooves in the bore and on the slider, stick at the top and look like they were attacked by a ball peen hammer. This is my reference as to a bad carb. The carbs I am using are in pretty good shape, just a little play when closed and some vertical ribbing starting to form on the slide and body. I can see the wear that has occured from just a few seasons riding - these things really are made from sawdust and glue.

Any thoughts on using chrome slides (without a rebore)? If my bodies are in good shape (and I think they are) chrome would be a good first step before going to a rebore & brass slide a la Triton or AMR.

Needles & jets
I cant see any signs of wear on my needles or jets, should I be able to visibly see any signs of wear on the needles? They are cheap so replacing them is not an issue, I just want to be sure I am chasing the right problem.

Synch:
Any thoughts on using vacuum gauges to synchronize carbs. Is it overkill?
Does a product like Carbtune http://www.carbtune.com/carbdtls.html work on a Norton? I've done it manually for the last few seasons...

Strobe:
I have manually set timing, should I set is with a strobe before trying any tuning? (I know the answer is probably yes, just have to bug my friend with a strobe..)

ok - that's the end of my questions, thanks in advance!
:D
 
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Oct 19, 2005
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Fastback, Carbs on a Commando seem to have a harder life than on any other British bike due to the considerable movement on the isolastics at lower revs, thus shaking the carbs and wearing the slide to body fit. Many owners reckon to change their carbs at about 10,000 miles as a matter of course. I have had fairly good results on freshening up carbs with an unknown provenance by simply replacing the slides with chrome ones and also replacing the needles, needle jets and main jets. Petrol is actually very abbrasive over time so these jets do wear out even though there may be no actual contact. As you point out if you freshen up the existing carbs the parts are fairly reasonable and if this doesn't do the trick then you can take the more expensive step of complete replacement and then keep the new parts in stock for future use.

Regarding timing I would definitely do a strobe-check, my timing was quite a bit out when I did a static followed by a strobe timing exercise. The bike ran quite a bit better after the strobe. One tip is to do this with another person helping, have them sit on the bike with it off it's stand to rev it otherwise you will be chasing it around the workshop as it moves backwards on the stand at higher revs.

In synching the carbs make sure that they open at the same time and also that they both achieve full throttle. I have had a number of allegedly identical cables that actually have a different inner or outer length (it only takes a small amount to be out). I take off the filters and put two small drill bits of the appropriate size under the slide and watch them move in unison as I open the throttle. Sometimes the choke slides (if fitted) do not open fully.

Good luck
 
Joined
Apr 7, 2004
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Fastback, as a guide there is an engineered .0025-0035 clear slide to body. Don't ever run one tighter.If you have doubled that setting the idle gets tricky. Channel locks and a rag work wonders on the bodies in the right hands. Over tightened screws is problem#1 And a .016 drill bit epoxied on to the end of a red spay tube is indispensables.
 

L.A.B.

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fastback said:
I've got an extra set of Concentrics, they are obviously shot, they rattle, have deep grooves in the bore and on the slider, stick at the top and look like they were attacked by a ball peen hammer. This is my reference as to a bad carb.

That pretty much sums up a worn carb really! I personally would go by the visual signs rather than measurement. The throttle slides have a reduced diameter area machined at the top, if any scoring can be seen on this reduced area then that indicates that the slide is worn.

fastback said:
The carbs I am using are in pretty good shape, just a little play when closed and some vertical ribbing starting to form on the slide and body. I can see the wear that has occured from just a few seasons riding - these things really are made from sawdust and glue.

General reports suggest that the quality of materials and machining of new Amal carbs can be a little inconsistent. (Amals now made by Burlen Fuel Systems: http://www.burlen.co.uk/ ), and many owners prefer to have their original carbs re-sleeved,


fastback said:
Any thoughts on using chrome slides (without a rebore)? If my bodies are in good shape (and I think they are) chrome would be a good first step before going to a rebore & brass slide a la Triton or AMR.

Fitting chromed slides to relatively unworn bodies does appear to slow the wearing process, and there are (at least) two types of chromed slides, chromed alloy and chromed brass: http://www.amalcarburettors.co.uk/exclusive.htm the chromed brass type are supposed to be the better option, I use the chromed alloy type and they seem to wear fairly well.

fastback said:
Synch:
Any thoughts on using vacuum gauges to synchronize carbs. Is it overkill?
Does a product like Carbtune http://www.carbtune.com/carbdtls.html work on a Norton? I've done it manually for the last few seasons...

I use a Morgan Carbtune (by fitting the gauge pipes to the inlet balance pipe stubs after removing the balance pipe) and the job is quick and easy with the Carbtune (although you may have to use it in the inverted position to get proper readings from the Amals (see Carbtune instructions).

fastback said:
Strobe:
I have manually set timing, should I set is with a strobe before trying any tuning? (I know the answer is probably yes, just have to bug my friend with a strobe..)

Ideally = Yes, although a decent quality strobe shouldn't be too expensive to buy these days.
 
Joined
Jul 18, 2004
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327
Thanks,

I will try new needle and jets, and a chrome slide.
I read more then 20 thou as a good guide line for slide replacement.

fstbk
 
Joined
Apr 7, 2004
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No more like .008 slop would start flowing so much air that the idle starts to wander .0025 is minimum, 0035 is as new, double that is .007, anywhere from .008 you could start to develop typical symptoms. IMO
 
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