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MG MGB Technical - 1974 MGB runs very very bad

my 74 MGB starts but idles/runs very rough; exhaust has a distinct flutter. kinda/sorta like an exhaust leak. exhaust system is okay (had a pressure test done). compression on all cylinders is at 150. timing and dwell are okay. vacuum gauge flutters at 10.
removed and flushed both carbs. valve clearances are a tad loose (can fit a .017" feeler gauge).
Is it time to remove the head? (just had the head replaced about a year ago).
any help with this one would be very much appreciated.
THANX!


L Rousselle

The fluttering vacuum gauge usually points to a bad valve, but you may simply have a leak at your intake manifold. Check all of your vacuum lines, including your distributor's vacuum advance capsule, as well as the plugs in the end of the intake manifold. RAY
rjm RAY

10 is very low vacuum, want 16-18-20
Most likely massive vacuum leak, Most likely loose manifold, possible terminal manifold gasket. Late cam timing possible but rare.

FRM
FR Millmore

Doesn't sound like a head problem with those even compression readings. It does sound like an air leak. Besides checking out the all the inlet gaskets etc., and the dizzy vacuum unit, as mentioned above, put your vacuum tester on the servo pipe and see if the servo unit holds a vacuum. If you have HIF's check out the butterfly poppet valves as well, or better still get rid of them!!
Allan Reeling

When you get the engine running and up to normal operating temp, spray some carb cleaner/brake-kleen around the mating surfaces of the carbs, intake manifold fitting, etc. If you get a significant but brief change in idle, you found your leak. Often times you get a hose that splits, or a fitting that has failed.

Let us know how it turns out

cheers

Gary
79 MGB
gary hansen

Thank you for everybody's input. I removed the intake manifold this morning.........and discovered a teeny tiny hole in the intake manifold..........

Now to find a replacement............
L Rousselle

Is the hole in a location and in a thick enough section that you can drill, tap, and pipe plug it?

Charley
C R Huff

This thread was discussed between 10/07/2012 and 16/07/2012

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