AJS & Matchless Owners Club

Does anyone know what the best working spec would be for an Amal concentric carb for a 50's G80? I know the correct carb should be a monobloc for my year but I've been having a lot of grief with this setup and I'd like to try something else.

Basically, I bought a new monobloc last year from Amal and have never been able to sort the slow running. Tickover's also a bit rubbish but the worst bit is just coming off throttle closed position when the bike surges and feels like its missing or 8 stroking. I've stripped and cleaned the carb twice and replace the pilot jet and tried a 3 cutaway slide instead of the supplied 3.5. I also found that the carb jet body had been poorly manufactured as the two air inlet holes in the jet body didn't line up with the holes in the carb body; fixing this and the other changes improved things from the position I started with when the bike was an absolute beggar to start but I've now lost patience with the existing carb. I've even been tempted to go down the Mikuni route.

Hi, I put a concentric carb on my '54 AJS 18S and it is very good - I now have a tick over which I never had on the old original carb. I bought it from a club member who got it from Burlen some time ago, set up to replicate the original. I put a 210 (if I remember right) main jet to replace 200 supplied as I have fitted SH cams (parts list says all models in the early '50s use same settings but thought I'd play safe). Slide I think is 3.5, needle middle notch. The only problem I have is occasional popping on the over run, caused by non-adjustable pilot jet being too small - I must drill it to better size. Later production has separate pilot jets so no longer a problem. Hope this helps, Andy

Thanks Andy, that is helpful. I think I will try a concentric as I've been used to them on the Triumphs I've previously had and they never gave me any hassle and always had clean running across the rev range.

My 55 G80s came with a concentric carb when I bought the bike. I like it. First or second kick starter and lovely tickover. Can't tell you whats inside it because I have never had cause to look. W

A concentric was on the G80S when I bought it but last year I bought a Monobloc from the Club as the concentric was completely worn out and I could not get tickover at all and low speed pick up was poor making slow tight bends interesting.

But I have to say that I still haven't got the carburation quite right and appear to be running rich (from plug colour) whereas the concentric gave a nice straw/beige colour with good mid to top speed pull. On the plus side, with the Monobloc starting improved, tickover achieved and slow speed pick up is good.

Johnny B

Good news... I replaced the brass float needle with a lighter aluminium one and also moved to a hotter plug (Champion N9), and now it's running fine. It picks up nicely from a closed throttle with no hesitation or jerking and runs cleanly at 50 mph. It also starts first or second kick and ticks over like a noisy sewing machine.


I've done around 150 miles since making these changes and for the first time in ages am enjoying riding the G80.