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MG MGB Technical - su carb very little suction

hi,
my 77 gt has twin su carbs,with the air filters removed i get the hiss from the right carb at idle but very little from the left carb.
i cant get the car to idle below 1500rpm,the ignition is set at 15 deg btdc,the carbs have been mixture tuned with the gunson colortune but both idle screws have been backed off to the point where they aint making any difference.
the carbs had been stripped,cleaned and floats set up and both pistons slide up n down without any fuss,could there be a throttle issue here somewhere?

cheers
a davies

Throttle plate not mating with the bore properly, or worn throttle shaft bushings. Should be able to stall the car by backing off the idle screws.
Art Pearse

ive checked and there seems to be play in both throttle spindles,so i guess ill order the new bushes n spindles,are the bushes easy to get out?
a davies

If the throttle plates were removed/replaced, they may not be centered in the bores. Or the interconnecting linkage is holding one open and the other closed art idle. You loosen this linkage and set idle screws, then set the linkage to open carbs equally when all else is done.
And, it is impossible to set mixture correctly until throttles are synchronized correctly.

FRM
FR Millmore

on inspection,one of the disks is worn flat spots etc,fitted new disks today,tuned her up and nicely set now at 1000rpm job done,thank you.

andy
a davies

Hi a Davies- Did you acidentally mix up the pistons? Check John Twist U tube on the issue of piston fall rate. I feel a well sorted MGB should idle comfortably at 650 and even lower with manifold Vacuum. I'm currently at 450 on the Mauve car and can set it to 250 if I wanna show off. Vem
vem myers

This thread was discussed between 01/08/2012 and 07/08/2012

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