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MG MGB Technical - SU HIF4 rebuild issue

Hiya,

I just rebuilt my SU HIF4's with the propper SU brand kit.

Now when I went to start my '73 B the car wont run propperly. (Only runs lumpy with with accelerator partly pressed.)

It seems one of the carbs is set up wrong now as I notice spraying gas when I lift one of the dampners with a screwdrivers while running at 2000rpm (also when I shut it off.)

Any suggestions?

I am guessing I adjusted a float improperly as I have always found them tricky (no gas is coming from vent tubes indicating to much gas...)

How mant turns out from screwed in is a starting point for adjustment?

Thanks in advance ;)
Nathan Ward

Nathan

I'm no expert, however since no one else has replied this might help keep your thread alive. I rebuilt the HIF carbs on my 73B using a rebuild kit when I installed a rebuilt engine 3 years ago. Haynes was my guide and checking back again, the float adjustment procedure seems relatively clear - ref page 81. The jet position adjustment is via the side screw and this should initially be turned two full turns clockwise after you see the jet start moving. With the engine idling, turn each jet screw the same small amount then check the effect of lifting the pistons with the pin - engine speeds up = too rich; engine stumbles = too lean: engine speed rises then falls = OK. Turn the jet adjusting screw clockwise to richen and anticlockwise to weaken the mixture. I had never done this before and believe that my engine is running well.

Good luck.

Barry
73B
B.J. Quartermaine

Nate

I think your theory is right. To get a spray of fuel I guess you have pressure directly from the fuel pump? Sounds like your float valve is stuck open. I vaguely remember that it is possible to put the float spindle in wrongly, maybe that is it. As Barry says it is not too difficult to set the floats correctly, just a little time consuming.
Richard Evans

Use seats and needles from Joe Curto for HIFs. Not spring loaded and form a positive seal, after you reset float.
Dennis

Figured it out. Thanks for all of the help! When I looked at it with a fresh head today I noticed I had the fuel line and the wvaporative lines mixed on the front carb! I can't believe it ran at all.

Anyway, the car runs great now.

Thanks again!
Nathan Ward

This thread was discussed between 10/08/2005 and 13/08/2005

MG MGB Technical index

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