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MG MGB Technical - HIF MYSTERY

With the air filters off, if I cover the front carb the engine stops (as expected), if I cover the rear carb it does not stop. I can feel air flow into the front but only a little on the rear carb. If I increase the RPM the pistons of both carbs rise and stay risen (until dropping the RPM). The sparks plugs are new, I adjusted the valves. All the carb mounting gaskets are new. The compression is OK. Manually raising the piston on the rear carb has little effect. The jets are at about the same height, the needle and seat are new.

Why can I cover the air to the rear carb with almost no effect??
William Webb

Because you have the rear thottle plate closed more than the front one!
Chris Betson

Thanks Chris, it sounds so simple when you know the answer. I'll work on this.
William Webb

Sounds like a syncronicity problem. Get out your widgets and fiddle away.
Bob Muenchausen

You need to balance the sirflow and mixture from scratch. Not a difficult job but needs care and a logical approach. http://www.mgb-stuff.org.uk and clicking on 'Spanners', 'Fuel' and 'SU Carbs' should help.
Paul Hunt

The HIF carbs IIRC have a o ring seal on the choke these are often overlooked and perish leading to a rich mixture and virtually impossibile to set up and balance, worth checking in any event.
HTH
Mike.
mike

This thread was discussed between 16/12/2002 and 21/12/2002

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.