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MG MGB Technical - New HIF4s - B won't start

I bought a freshly rebuilt set of HIF4 carbs from someone on the BBS quite some time ago, and just got around to putting them on my B in place of a VERY tired set of HS4s. The engine would start and run without major problems with the old HS4s, but with the new HIF4's it will not start. The jets were set at .090 below the bridge and I've lowered them to approximately .120 since (roughly 2 turns of the adjusting screw). Pistons move freely. Fuel is flowing. If I spray a little starting fluid into each carb throat, it starts, but will not run.

Is the HIF4 choke supposed to operate the same way as the HS4 choke? If yes, then something is wrong. The fully open choke does not move the jets down at all.

Any suggestions?

~Jerry
Jerry Causey

Jerry, The HIF a has cold start enrichment device for starting and it doesn't move the jets down. What you see is normal. Look at the diagrams on page 80 of the Haynes MGB manual for a drawing of the cold start device.

You say fuel is flowing, do you mean it's flowing through the carburetors and wetting the spark plugs or do you mean it's flowing to the carburetor inlets? It sounds as if it is not flowing throug the carburetors since you can onlt get the engine to fire by using starting fluid. It also sounds like the float needle valve may stuck in the closed position. I would suggest removing the fuel bowl covers and examine the needle valves and set the float levels, the bad part is you need to remove the carbs to do this. If it has Grose jet float valves, I have had some problems with them shutting off fuel in HIF carbs, I removed them and threw them in the trash several years ago and had no problems since. The standard needle valves work fine. An initial setting of around .060 down on the jets should work fine for initial starting. Good luck, Clifton
Clifton Gordon

The choke on the HIFs does not move the jet, instead it is an "enrichment device" that opens a metered passage to allow more fuel into the air flowpath. If you look down through the jets, can you see the fuel level in the bowl? You have to remove the slide to do this.
gerry masterman

Oh, something else. I knew someone who had the same problems years ago. He had the fuel line hooked to the bowl vent. Got gas, lot's of gas!
gerry masterman

Gerry, Thanks for pointing out a simple way to check for fuel in the bowls of the HIF I learned something useful from your post. Sometimes we get carried away with details and don't think of simple and easy checks. Clifton
Clifton Gordon

If you blow gently in the overflow and the float chambers are 'full' it will come up out of the jet, you can see this just by removing the air filters and overflow pipe.

Paul Hunt

Just one comment:
Be sure to put drain hose or pipes on the carb vents and run them out the bottom of the car.Stops the problem of a possibility of a fire.
Dale & Barb Mast

Thank you all. The proglem was indeed no fuel in the float chambers. I pulled the carbs, opened the float chambers, and removed the needles from the seats to free them up. The rear carb still seems to have a problem. When I blow through the fuel line (carbs still off), the rear carb seems to be restricted.

I guess it's back to the leaky HS4s for a while.

Thanks again for your help.
~Jerry


Jerry Causey

This thread was discussed between 22/08/2004 and 23/08/2004

MG MGB Technical index

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