Concentric Carb.

John B. · Post by **John B.** » Fri Jun 10, 2011 11:48 pm

Got G3L running well at every stage of opening throttle except Pilot ( zero to just open). Running very rich and Pilot air screw has no effect what so ever. Have had it all to bits to check and there is a brass jet buried down the hole ( non removeable??) All clean down there and I have set float level as recommended, just below top face of bowl. Any comments welcome. I did manage to ride it to the test station and get it done OK. Bit lumpy but hey we are getting there. JB.

SPRIDDLER · Post by **SPRIDDLER** » Sat Jun 11, 2011 12:02 am

This techy article by Amal Carbs re Concentric fuel levels may help if you haven't seen it already (scroll to bottom of page for 'Fuel Level' details).

http://www.amalcarb.co.uk/TechnicalDetail.aspx?id=13

P.S. It also mentions their newly introduced 'Stay Up' float which has been introduced to counter the deleterious effect of ethanol petrol on the older type floats. Your problem p'raps?Edited by - SPRIDDLER on 10 Jun 2011 11:06:00 PM

Chazzyb · Post by **Chazzyb** » Sat Jun 11, 2011 10:01 am

Youd think Amal would include the ethanol-resistant stay-up float in new carbs, wouldn't you.

Don Madden · Post by **Don Madden** » Sat Jun 11, 2011 6:14 pm

If the pilot mixture screw has no effect the engine is idling too fast, there is an air leak into the intake or most likely, the pilot jet is blocked. Early concentrics, 1967-68 had a removable pilot jet screwed into the bowl joint face. Later, that was replaced by a non-removable one pressed deep into the passage behind the adjusting screw. A soak in good carb cleaner as "Sea Foam" followed by a blast of comressed air may clear it. I have a #78 drill fastenen into the end of an 1/8in alloy dowel long enough to reach the jet to clean it out. Don't get too wild with such a tool, the standard size jet is about a #20 pilot, suitable for a 350cc but a #77 drill will open it up to about #25 pilot, better for 500cc-up. Cheers, Don.

John B. · Post by **John B.** » Sun Jun 12, 2011 8:06 pm

John B. · Post by **John B.** » Sun Jun 12, 2011 8:14 pm

Don, thanks for info.I have really cleaned it out well. Not done the drill bit yet. Have down loaded Conc. stuff from the Amal site and am at moment drilling and tapping the bottom of the float bowl to attach a temp. tube to positive check the fuel level,which may still be too high. Just reassure me, turning the screw out weakens and screwing in richens the mixture???? JB.

SPRIDDLER · Post by **SPRIDDLER** » Sun Jun 12, 2011 11:50 pm

quote:
turning the screw out weakens and screwing in richens the mixture
Correct.