Carburettor fine tuning

[AdieB]

Hi. I am having trouble getting my model 14 to go anything past tickover. The slightest tweak of the throttle kills the engine. This is the same whether on full choke or full off choke. I have tried the adjustment on the air screw according to the book and tickover is sweet. As soon as I try to open up a little, she dies! A clue may be in that the engine continues to run on when ignition is turned off. Any thoughts greatly appreciated.

[Mick D]

Hi

Assuming its a Monobloc carb check the pilot jet isn't partially blocked - also check the bypass gallery is clear.

Sounds like it could also be a timing issue, either too far retarded or the auto advance stuck - was it running correctly recently and if so what have you done since?

Regards Mick

[ajscomboman]

I'd be looking at the timing Ade.

[AdieB]

Thanks for your ideas. It was running fine up until recently. I have taken out the pilot and cleaned the debris out of it, this made no difference. I'll check the timing to see if that's the problem. If it is the advance mechanism that's stuck, I have no idea how to sort that out!

[Mick D]

Hi

Page 40 of the 57-64 Workshop manual details how to manually action the auto advance - it should open smoothly and snap back closed. Drenching with WD40 and exercising should free it up if sticky, (mark the CB assembly position if you decide to remove it for access):

http://archives.jampot.dk/book/Workshop ... CHABLE.pdf

Regards Mick

[AdieB]

Mick

It looks as though the problem lies in the auto advance unit as it appears to be stuck. I will get a puller and remove it for inspection. Thanks for the link to this, it was very useful.

[Mick D]

Hi

If its the same as the heavyweights the 'extracor' is just a bolt of the correct size to screw into the thread of the ATD, (not the bolt that secures it but a larger thread at the end of the ATD spindle) - you'll have one on the bike

ATD Thread.png

Regards Mick

[ajscomboman]

Slightly different on a lightweight but principle is the same. I did get some ordered for the L/W's, they are in the tools category on the parts service website.

[clanger9]

You can improvise a puller on a Lightweight using one of the toolbox cover retaining bolts and a large socket:
https://www.ifixit.com/Guide/AJS-Matchl ... 91#s228870

[AdieB]

It's not the timing after all! Removed the auto advance unit and all is well. It was well greased (thanks Alan) and all working fine. The timing was slightly out and now sorted. My gut feeling is that I need to drop the carb needle a notch, although that doesn't explain why it was running fine a while back. Ah, the delights of old British motorbikes!