gsm Posted March 6, 2016 Report Share Posted March 6, 2016 Looking to either service or replace the MK 1 Concentric fitted to my G3C. It is currently fitted with a MK1 Concentric 626 model. Its a 1960 G3C 350cc engine, wader MAG, fitted with a pancake filter. If I go for a new carb, should I stick with the same model? Any suggestions on jet sizes, if I get another 626? Quote Link to comment Share on other sites More sharing options...
big john Posted March 6, 2016 Report Share Posted March 6, 2016 Looking to either service or replace the MK 1 Concentric fitted to my G3C. It is currently fitted with a MK1 Concentric 626 model. Its a 1960 G3C 350cc engine, wader MAG, fitted with a pancake filter. If I go for a new carb, should I stick with the same model? Any suggestions on jet sizes, if I get another 626? I would get a 24mm bore 600 series Amal. The smaller bore is ideal for these singles I have run one on my 1959 G3C long stroke in the Pre'65 Scottish for many years. I have a note of the jetting etc, but I'm not prepared to post openly on here, send me a PM and I'll let you have the settings. I use a conical filter with a rubber shield and suitable adapter. Big John 1 Quote Link to comment Share on other sites More sharing options...
jon v8 Posted March 6, 2016 Report Share Posted March 6, 2016 My 350 AJS has a recent Amal Premier carb on it with hard anodised slide and Ethanol proof stay up float etc. In the next couple of days I'll be washing the mud off it from the Golden Valley March Hare - todays event. The carb will then have a strip and clean,I'll make notes of jet and slide numbers etc, and post them up. I'll also post up a pic of one of the best mods that need doing on a Concentric Mk1. I can't say its the perfect set up,but it works on my bike,and those daft enough to have a go on it seem to think its OK. 1 Quote Link to comment Share on other sites More sharing options...
gsm Posted March 7, 2016 Author Report Share Posted March 7, 2016 Thanks. What bore carb do you run John v8? Quote Link to comment Share on other sites More sharing options...
jon v8 Posted March 7, 2016 Report Share Posted March 7, 2016 Its a 26mm bore.I steam cleaned the bike this morning,but I had work that needed doing so I've yet to get the carb off for a clean out. Try to do it tomorrow if I get my work out of the way... Thinking about it, the carb is one I bought from Surrey Cycles for my new HT5 build, I only fitted it to the AJS because it felt strangled on the 22mm carb it had before,wouldn't rev out,given time it will now scream fairly hard - I don't like doing it,but some sections like there were at the March Hare yesterday really need it. Quote Link to comment Share on other sites More sharing options...
jon v8 Posted March 9, 2016 Report Share Posted March 9, 2016 OK, took it apart tonight, main jet is a 170, hard anodised slide 2 1/2,needle is 622/124 and the air filter is a well oiled foam one.( I think the oiled foam aids very low rpm pickup.)So the body is a 626 R300.The attached pic shows the mod I was shown. The blunt scriber is pointing to the soft alloy core plug that often leaks from new.The last 3 carbs I've checked have all leaked, just spray a little liquid over the plug and block two of the three pilot holes.GENTLY blow a bit of compressed air into the remaining hole and watch the bubbles come out around the edge.BE CAREFUL DOING THIS. In the pic there is a gasket paper punch with a sharp edgeleaning on the float,stand the carb body upside down and use a punch like this to swage the plug out to make it seal.If you look carefully around the plug you will see a faint ring where I've done this. Doing this makes the carb more accurate when running on the idle circuit and therefore easier to keep in tune,good mod that costs nothing to do.Notice how clean the carb stays on Aspen fuel... 1 Quote Link to comment Share on other sites More sharing options...
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