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MG MGB Technical - HIF CARBS

Engine barely runs.
With the air filters off, the front carb draws a lot of air - if I cover it the engine dies; the rear carb draws very little - if I cover it there is not much effect.
Can this be just the set-up (seems too much of a difference to be set-up)? What else could it be??
Thanks for all ideas!
William Webb

This may take a bit of explaining. Do ou have a Haynes Manual or other guide explaining SU carbs? If not check out the thread "SU CARBS" for some links to sites that will explain set up. You're going to need a unisync tool or a mechanics stethoscope. Basically you need to loosen the pinch bolt on the throttle linkage to separate each carb's function from the other. Then you'll adjust the idle set screw on each until they draw the same amount of air (use the unisync tool for this OR listen with the stethoscope until they sound about right. Check out the links I mentioned it will explain all the details.
william fox

Thanks for the input William Fox. A problem is that the rear carb draws so little air that I need to have the throttle about half open for the engine to run. This started suddenly - one day the car would run only a minute or so and stop, hard to restart and extremely rough for several minutes (as if on two cylinders - it would stall if put into gear), then suddenly ran fine until the next day when it would go through the same routine. I thought one carb may be stuck so that it did not receive fuel and initially ran on what was left in the float chamber- took them off, changed jets, reinstalled - worse.
William Webb

William,

It sounds like the piston is stuck down on the rear carb to me.

Geoff
Geoff King

Or perhaps, because of the sudden nature of this problem, your carb may have ingested something to plug the small fuel line from the float bowl to the jet. This might cause the rear carb to struggle to run suddenly.
Bob Muenchausen

William said the rear carb had little airflow; even if there was no fuel at all the engine would/should still pull air through the carb. Assuming the inlet manifold is not blocked either the throttle is closed or the piston is stuck down. The throttle seems too obvious to miss and my money is on the piston – there might still be a fuel problem but you have to get air through the carb first.

Geoff
Geoff King

Doh! Oops, wrong carb ~ thinking of the HS again. Too many worked on, brain damage. Sorry.
Bob Muenchausen

William W,

Have you fixed it?

Geoff
Geoff King

This thread was discussed between 06/11/2002 and 11/11/2002

MG MGB Technical index

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