Carburettor resleeving

[david.anderson]

I have been running a 32mm concentric on my VH for some time. A few months ago the tune seemed to change. I had to richen the idle but seemed to have a flat spot just above. I went from a 3 1/2 cutaway down to a 3 with initially some improvement. Then I lifted my needle which helped a little but I was clearly running too rich with more throttle opening and the flat spot down low got progressively worse. The carb body was well worn so today I decided to bore out the body and sleeve the slide. While most resleeving seems to be in stainless I could not get any suitable size tube locally so I decided to just use steel.

I bored the body about .012” oversize.

I turned the slide down leaving about .020” thickness at the choke area.

I turned a sleeve and allowed .002 interference fit. It was into the freezer with the slide and then heat up the sleeve and press it on with the vice.
I then finish turned the slide with the sleeve on, filed the cut away back to match the slide, and filed the angle slot for the idle stop.
While the carburettor was off I redressed the flange and checked the O ring which was standing .028” proud. I decided that was way too much and was clearly the reason for the warping of the flange so I set the carb up and deepened the O ring groove so the O ring will only be .010” proud. I mounted the carb on the bike and was able to tighten the nuts without fear of the body warping and the slide sticking.
It was then time for a test run. I had to first lean the idle and then return the needle to its original position then off for a ride. The bike was back to its old self. Perfect throttle response from down low and right through the range.
The lesson is that if the tune on your bike changes and the slide is loose it might be time to consider resleeving.
David

[Danny.Lee]

so what sort of thickness was the sleeve?

[david.anderson]

Danny
the sleeve ended up .025" thick. I rough turned the outer oversize and finish turned to size after pressing on to the slide
David

[nevhunter]

SEEMS like a good fix. Mikuni's etc use a chrome plated slide thatwears well. I think it's brass with the chrome added. I'm not sure how to get it even thickness without grinding it to size. Nev

[adrie.degraaff]

The sleeve should be glued on with baring glue otherwise when turned to size it will take the shape of the slide.

[john.nash]

The new Amal concentrics can come with a hard anodised slide (I have one here in front of me) or you can get a chrome one from Surrey motorcycles.

As a matter of interest, the "wassell" amal knockoffs (allegedly, I read, made in the same far east location) are alot cheaper than an Amal concentric:

http://britishbikebits.com/carburettors ... rburettors

Not used one yet ....(they weren't making the 626 that I needed recently ..)

[david.anderson]

Adrie
yes I did not mention that I used a couple of drops of loctite bearing lock in the sleeve.
John
A few years ago amal thought it would be a good idea to chrome plate the zinc pot metal amal slides. The result was predictable, the chrome peeled and went through the engine. Ouch. The Mikuni slides (and side bowl amal slides) have chromed brass slides and being chrome on brass, peeling chrome is not a problem, and the wear rate is far less than the zinc metal on zinc metal of an amal. Be careful that any chrome amal slide that you use is not chromed zinc pot metal.
David

[brenton.roy]

Hi David, thanks for the great photo's and advice.
A few years ago I got as far as boring a brass 289 body to an oversized slide and it did make a big difference.
Re slides, I was wondering if you or anyone had had success with Teflon? http://www.gncoatings.com.au/lowfriction.htm
I've heard about it, but not seen it used.
Also, I found this. I'd never heard of it before. http://richstaylordporting.com/vintage_Venturi.html I guess an oval slide is a similar concept.
Brenton

[john.nash]

A few years ago amal thought it would be a good idea to chrome plate the zinc pot metal amal slides. The result was predictable, the chrome peeled and went through the engine. Ouch. The Mikuni slides (and side bowl amal slides) have chromed brass slides and being chrome on brass, peeling chrome is not a problem, and the wear rate is far less than the zinc metal on zinc metal of an amal. Be careful that any chrome amal slide that you use is not chromed zinc pot metal.
David

Sorry. They are Chromed brass slides:
http://www.surreycycles.com/catalog/pro ... cts_id=181

I don't point this out to denigrate your work (which is way beyond what I could do) but to mention that if you are buying new, then there are better options than the standard slides that will last you longer.

[Danny.Lee]

David

how do you know the ally used for the sleeve is compatible with the original parts in terms of coeficients of expansion? is there not a risk of the bits expanding at diff rates as it warms up?

Seems to me the risk is either it drops out, or, it will distort and grip the slide...hopefully not at ful throttle.

Otherwise, a very neat fix, I just made a sleeve to take up the slack in the hole where the valve lever pin fits in the crankcase, and I admit I had to have several goes before I could get it accurate enough.