Amal Concentric Mk1 carb on '54 18S

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Andy51
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Joined: Thu Mar 31, 2005 1:00 am
Location: BERKS UK

Amal Concentric Mk1 carb on '54 18S

Post by Andy51 »

Hi All, I have an early model 30mm Burlen Amal Concentric Mk1 fitted to my '54 18S. I bought the carb from a fellow club member a few years ago; he had bought it new a few years before but never used it. It works very well, giving good performance and tick over, but bangs and pops on the overrun. This forum and Surrey Cycles at Kempton reckoned weak mixture caused by too small a pilot jet was the issue. Surrey Cycles recommended drilling it out to 19 thou (no 76 drill is 20 thou, 77 is 18). Where is the jet? The early Concentrics did not have a replaceable pilot jet like later ones but had a pressed in drilled plug, probably located under a pressed in metal cap in the base of the main body. A copper wire can be passed right through the hole behind the pilot adjuster, and the 2 very small holes in the Venturi are larger than 19 thou, so wherever the jet/plug is, it is not easily accessible. Any ideas how I can access the offending part without causing damage, or should I richen the mixture using the pilot screw as best I can and live with any subsequent popping? Andy
bob121
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Joined: Sat Jan 14, 2017 11:48 am
Location: WEST MIDLANDS UK

Re: Amal Concentric Mk1 carb on '54 18S

Post by bob121 »

should be behind the air screw. I know they are on the T140's. I've had to get a #76 drill to try and be sure they're not blocked on a couple of bikes.
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Amal Concentric Mk1 carb on '54 18S

Post by Mick D »

Hi

Actual location of the pilot jet is detailed column 3 bottom here:

http://amalcarb.co.uk/downloadfiles/ama ... d_Tips.pdf

I'd be tempted to exhaust all other potential cures before trying to open out the jet.

Regards Mick
Andy51
Member
Posts: 742
Joined: Thu Mar 31, 2005 1:00 am
Location: BERKS UK

Re: Amal Concentric Mk1 carb on '54 18S

Post by Andy51 »

Hi Mick & Bob, thanks for your replies. I have now found a website giving all details and how to enlarge the pressed in bush that forms the pilot jet (Bushman's Carb Tuning Secrets, don't know how to post a link on I-pad). It does seem a risky action that unless done with great care could wreck the carb body, so I will only attempt it if all else fails! Cheers, Andy
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