Britbike forum Forums British motorcycles in general British motorcycles in general Amal Concentric throttle slide to body clearance

Can somebody give me the running clearance of the slide in the Concentric body?
Cannot find it with the search function.

Thank you, Martin

.0035" to .004"

I'm curious as to your asking.

Recently I was working on a friends bike. His original slide in the matched body was too slack and it rattled. I fitted a good slide in the body and it nipped up. It was obvious that the body was warped as well as the slide being excessively worn.

Slides are fairly inexpensive so I would start by checking the bore is round. If you have a known good slide, you can:
1) cut away the locating nib and the bottom of the slide so the bottom is flat, then open up the needle hole large enough so it will sit over the spray tube.

2) get some bar at the correct OD to match the ID of a good body, and fit that into the bore ( I think John has done an article on bringing the bodies back to true. )

Until you know your carb is true, measuring clearence might be a waste of time, as you could have good clearence in one spot, but it still can suck air.

The friends carb I mentioned earlier was running lean ( the engine was fitted with a big bore kit, so we took carb settings as red) we were up to a 190 main jet and looking at going richer before I noticed the slide issue, after fitting a gknown good carb, we were back to a 160 main jet which was the same as a standard setup.

HTH

Thank you John and thank you Allan.
I know the problems with the bores.
But I asked because we want to sleeve a carb and needed the right clearance.

But we will trueing the body before, don´t worry.

Thank you and best regards, Martin

The clearance is important, a good machinist friend relined his concs to a very precise fit probably about one thou. The bike would not run correctly until he fitted an old worn pair of concs I had on the shelf. Stock amals are about 3.5 thou slack when new.

Most are aware a worn carburetor bore, or slide, will cause the AMAL to provide a lean mixture at low throttle openings. It is just the opposite when you close up the clearance. With less air flowing around the slide, the vacuum signal on the needle jet will be stronger drawing more fuel into the venturi.

If you want this carburetor to work as designed, and be safe to use, it is important not to close up the slide clearance!