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MG MGB Technical - HIF4 fuel leak

I have a very small problem that's causing me some very big trouble and time: After replacing the float in the front HIF4 carb I cannot stop it from leaking fuel. I am pretty sure it is leaking due to the new gasket (rubber ring) supplied with the float. I cleaned the gasket surface, and the last time I installed it (this is around the third time), I smeared a small amount of grease on the gasket...it didn't help. There's still a trace of fuel leaking at the bottom of the carb.
This is the second float I have had to install in the car. The first replacement lasted about seven years. The other carb has the original float, and is still going strong. I don't think the new floats, or the gaskets for that matter, are as good as the old ones.
Anyway, before I remove the twin HIF4s and try again, I thought it would be wise to see if anyone has had a similar experience, and what they did did to solve the problem.
Thanks in advance,
Randy Olson
Ithaca, NY
1977 MGB with twin SU HIF4 carbs
randy olson

Randy,
Set the cover down on a flat surface to see if it is distorted. I've seen covers with enough distortion so that it would not properly seal. You are correct in that the new floats are not very good quality. I replaced the floats on a minor rebuild and found that I had to eventually replace them with the original floats I had removed. Both floats eventually leaked.
the old ones are still going strong. If the gasket is not deformed, I don't relace them. I've never had one leak.
Joe G
J. E. Guthrie

I hear what you are saying. I'm thinking that the next step would be to put the old gasket back in.
Randy
PS If the cover is distorted, what is the fix?
randy olson

Randy,
The cover is available from MOSS or you might find one from a local MG club.
Joe G
J. E. Guthrie

My front HIF leaked a lot because on assembly I switched the fuel- and overflow line. I did take me a while to figure that one out.....
Willem vd Veer

Are you sure it *is* from the joint for the bottom cover? Could be from the spindle for the enrichment control which has a couple of O-rings if it is above that. Leaking from either the overflow or inlet ports should be obvious. I must say I've always replaced the bottom cover O-ring, the new ones are much more flexible and deeper and the old, seemed false economy. I don't think grease is a good idea, they should seal dry. If they don't there is some other problem which must be fixed. Covers can warp if the screws are overtightened ... in an attempt to fix a leak.
PaulH Solihull

The puzzle is solved! The leak was due to a hairline crack in float chamber cover. Upon further investigation, I know the reason the crack formed...the x%#@b& mechanic, me!
When I installed the new float, I took apart the temperature compensator. When I reinstalled the temperature compensator adjusting screw, I didn't screw it down tight, thinking it should be loose due to the spring under it...wrong. So, when I put the float chamber cover back on and tightened it down, the temperature compensator screw pushed against the cover and it cracked.
So, I now have a few solutions. I can order a new cover from one of the regulars (Moss: about $20), try sanding the cover down and applying some JB Weld (free, but possibly temporary), or have the cover welded by a local shop (which would approach, or exceed the cost of a new cover). Since it's fuel we are talking about, and it's in the neighborhood of the exhaust manifold, I'm leaning towards buying a new one. I know another solution: Use the same stuff I sealed my Jag's gas tank, and fuel rail with...maybe.
Anyway, thanks to all for the input, and special thanks to Paul for his suggestion to look elsewhere for the leak. In the sunlight, with a mirror, it was easy to spot.
Regards,
Randy
randy olson

I had a similar problem with one of my HIF4 carbs. I'd had it apart and together many times over the past few years but this most recent time it leaked through the o-ring seal at the cover.

Finally a very close inspection showed there was a tiny bit of metal left over from the manufacturing process sticking up in the ring slot on the cover. How it never got in the way of the o-ring in the past I'll never know. I tried knocking it off with a hammer and hard tipped driver but it would not come off. Finally I replaced the cover with one from my spare set of carbs.

BH
BH Davis

Well, if it wasn't so cold here in the NE I would be driving the B, but it may have to wait until the weekend. I think I stopped the leak with JB Weld...I know...but, I did it, and it will be fine. Anyway, I can't wait to try it out on a sunny day this coming weekend.
Randy
randy olson

Following up on the JB Weld fix...it seemed to work fine. For how long is the question, but I think it will last many years based on my experience with epoxy.
I'll be running the B in the spring, but I don't expect problems when I start it up again.
Randy
randy olson

Have you tried aluminium brazing/soldering? I've used it with good effect on extruded ali. They claim you can use it on any type of alloy but I have read reports that the difference between the melting point of these type of products and some cast items is so small the you have to be very careful.

http://www.frost.co.uk/item_Detail.asp?productID=8823&frostProductName=Lumiweld%20Kit%20%285%20rods%29&gclid=CLCaicmAgqUCFcH42Aod4WoTOg

Other products are available and youtube has videos on the subject

Bob Davis

Hi Bob,
I didn't try anything but the epoxy, and it worked fine. It is so easy to use that it is almost a no-brainer.
The cost of the part that was pierced was only twenty five dollars, so if the epoxy fails I merely buy a new part for the bottom of the carb...easy.
But, as I said earlier, I think the JB Weld is going to last longer than I'm alive. And, I plan to be around a long while.
Randy
Ithaca, NY
randy olson

This thread was discussed between 27/09/2010 and 03/11/2010

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