Hitchcocks Forum

Hi All, I've got a problem that i think may be the carburetta ,i have very recently fitted a new amal con mk1,the 350 bullet ticks over fine but when you blip the throttle the engine hesitates or stalls with spit back in the carb,at larger throttle opening the engine runs ok.Could the problem be weak mixture? Your thoughts appreciated.

Brian, what are the settings at the moment? That is, slide, main jet, needle position and carb size.


REgards, Mark 

Hi,Mark


           The carb is a 600series 26mm Amal concentric and the slide is a number 3,the main jet is 170 and needle is in the centre groove.The cylinder head has been tuned to accept carb


                                       Brian

Brian, it seems odd that it's just when you blip the throttle. Your settings seem ok although I would expect a 3.5 slide usually. Hesitation and spitting are signs of weakness but it's strange that it's isolated like this and running ok at top and bottom of rev range. You could try raising the needle a notch? Where did you get the carb from? I ask because I have heard of some Concentric copies (not from Amal) which have a poor reputation...


REgards, Mark 

Try adjusting the slow running jet on the side of the carb, nearest to the manifold.


Screw it fully in and make a note of the number of turns so you can return  to your starting point.


Unscrew to your starting point and then unscrew it further to enrich the mixture.


I think that the normal starting point is one and a half turns.


At smaller throttle openings the main needle does not have much of an effect and most of the fuel is drawn through the slow running jet. 

Thanks for the help lads i will try some of the adjustments you suggest, further to your earlier question the carb is an Amal made by Burlen fuels.