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MG MGB Technical - Float Needle & Seat Problems

We have a 1974 B/GT with the HIF-4 carburetor's and 97K miles completely stock from new. I recently had the cylinder head off for valve seats, valves, springs and seals. While apart I did a quick re-fresh on the carburetors. Cleaned things up with (Gum-out), replaced the floats, needles & seats, and new gaskets.

The problem; the front carb needle (SU viton tip) is sticking and overflowing the bowl. I removed the carb to recheck, and everything seems to be in order, and working again. Went out this evening to do some tuning, and the front carb is overflowing again.

The gasoline is fresh, and treated with Sta-Bil. Is it time for Grose-Jet's?


Larry C. '69 Midget, and '74 B/GT
Larry C '69 Midget

Larry - It has been quite a number of years since I fussed with HIF carbs, but as I remember, there is a float lever adjustment that, if not adjusted correctly, will cause the needle to drop too far and jam against the lever. Although the arrangement is different in a TD, see the article Float Lever Drop Adjustment in the Other Tech Articles section of my Homepage at: to see what I am talking about. The other thing to check is to see if the float itself is leaking and not coming up far enough. Cheers - Dave
D W DuBois


Float drop lever angle was of concern with the small float tab located, and pointing towards the center of the "C" shaped float. It is difficult to get what should be a proper adjustment angle on the needle while maintaining the proper (recommended) float height adjustment.

The devil in the mix is a small spring loaded pin in the base of the needle itself that rests on the float tab. I believe that's where the problem may be in this case. The original needles & seats had a small shim at the base of the brass needle seat the new ones do not. I'm going to have another look through my parts bin for those shims to see if I can get a better adjustment on the float tab to avoid jamming the needle.

Thanks for your help,


Larry C.
Larry C '69 Midget

Grose 'jets' have been recommended against for some time now, since their quality deteriorated and the Viton-tipped needles improved. Jets and floats are handed on the HIF.
Paul Hunt


I'm in agreement with you, and Dave. I found a pair of Grose-Jets in my parts bin from the 1990's, but they are for the HS "side bowl" type. So they are of no use anyway.

I think I need to now go back now, and try to adjust the lever angle on the floats to avoid binding of the shut-off needle. When I sketch this out on paper it looks like the float tab needs to be pointed downward slightly at rest so that when the bowl fills and the tab is lifted with the float it's more parallel with the base of the needle seat when full. That should relieve the binding problem.


Larry C.
Larry C '69 Midget

Problems continue with the HIF's in testing phase.

I finally sorted the vacuum leak to be a bad gulp valve, and thought I had the shut-off needles corrected. With no further flooding of the front float bowl, and engine idle seemingly restored, I fitted the air filters for a test drive.

After about a mile she started to run rough again so I turned her back around, and into the garage. The first thing I noticed was the temperature gauge needle above "N", and when I lifted the bonnet their was a good bit of condensation (humid day) on the front carburetor air chamber bell. It felt cold to the touch, so way too rich. When things cooled off I checked the spark plugs and numbers one and two were sooted. My guess is the needle stuck/jammed again.

Both carburetors are now off again for a complete teardown and cleaning. So far I cannot see any reason for the condition including the cold start valves which were installed correctly. So I guess I'm going to replace both float shut-off needles and seats (bad batch?), and start again. Suggestions welcome.


Larry C.
Larry C '69 Midget

This thread was discussed between 04/07/2014 and 10/07/2014

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