MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Grose Float Chamber Valves/Jets

After reading complimentary reports on Grose jets on this and other sites I replaced my standard SU jets last year and have been ok to-date. Today we had an MG club meeting at Arundel Castle grounds (fabulous warm sunny day and lots of MG's) and after half an hour of running they decided to misbehave and flooded the rear carb float chamber. Inspection showed no obvious dirt or other problem so closed up and quickly continued on. On return home, same problem. On the assumption that it is not worth the hassle of continually hoping, probably in vain, for the problem to go away, the offending jet will be binned and replaced. But, do I go for more of the same or back to standard SU type? Anyone else had trouble with Grose?
Advice please.
Bruce
Bruce Mayo

Bruce

I have heard lots of grumbles about recent batches of Grose jets. Never touched them myself. The standard SU type has served me well.

Steve
Steve Gyles

Bruce,
I have regular SU jets in 4 carbs, and over 30 years have never had any problem with them.
So I would not change them on my 2 MGAs.
Cheers, Peter.
P. Tilbury

There are a few different styles of "original style" jet pins. They may be solid brass, or brass with a spring loaded tip, or may be tipped with nylon or rubber (hopefully Viton these days). Many years past I had ongoing problems with a couple different types.

I installed Gross jets in the early 90's, and all of the problems vanished, and now still running the same set of Gross jets 20 years and over 200,000 miles later. Gotta love them, never go back. I put them at the top of my Wonderful Parts list along with my 25 year old Teflon lined fuel hoses, Teflon O-rings to seal the main jets (now 14 years and 120,000 miles without drip or stick), and more recently Viton grommets to seal the float chambers (three years and counting).

However, Gross Jets can have a a few issues. The fuel must be clean. A tiny speck of rust from the fuel tank can make the larger ball stick either open or closed. If you have this problem, a fuel filter should be the solution. I drive a lot, run a lot of fuel through my car. The whole fuel system stays so clean that it will not clog a finger size sintered bronze filter in 100,000 miles.

Gross Jets are also susceptible to overpressure and certain vibration resonance frequencies. If you have an aftermarket fuel pump putting out about 5-psi pressure (or higher), using a pressure regulator to cut it back to 3-psi can banish the problem.

Also the Gross Jet patent recently ran out, and there are now kockoffs made in "other countries" that are substandard with problems. If you receive "GROSS JETS" in a brown paper envelope, they should be the real thing, good quality, and may last a lifetime with no problems. If you get "Gross Type fuel jets" in a plastic envelope, check to see country of origin. Those seem to have problems with irregular or inconsistent size of the larger steel ball. I think I would toss those into the dust bin and order the original ones.
Barney Gaylord

Thanks for the useful feedback. BUT this is where I embarrass myself!
Being uncomfomfortable with my implied criticism of Gross jets, as they do indeed appear to be a nice design idea, I spent a bit of time late last night "digging" around the carbs for some other possible explanation for the problem. Indeed, the rear float chamber was brim full, even though the float level setting was correct. Clearly overfilling the bowl, the front one being all ok. On closer inspection it appeared that the rear float was floating much lower than the front one. Not completey sunk by any means, but just flush with the surface of the fuel, rather than a bit proud.. Took it out and turns out it is leaking - front one perfect, empty and weighing 25 grms, the rear one with fuel sloshing around inside and weighing 45 gms! So that's the problem. Spoke to SU/Burlen who now supply un-sinkable, same weight, closed-cell replacement floats (mine are H6 on a Twin Cam) because they are finding problems with the brass/soldered originals with ethanol fuels these days.
Thought I should be honest and own up because, as Barney says, if we don't report problems with suppliers we won't get things sorted. This however is a retraction of a potential criticism of Gross jets!
However, noting Barney's comment re patent expiration and potential for rogue suppliers, I guess this a possible problem to come. For the time being I will back down!
Bruce
Bruce Mayo

How to repair a leaky brass float:
http://mgaguru.com/mgtech/carbs/cb116.htm
Barney Gaylord

Bruce, nothing like Barney's 200,000 mile I know, but I am well pleased with my Grose jets from Moss 3 years and 12,000 miles ago.
Lindsay Sampford

There is a nice Tech article in the latest issue of MGA which talks about the low quality made in china reprodution grose jets showing high failure rates.
Thomas Koch

Bruce,

Confirming your experience I had the same sinking float problem and went through the same sequence of troubleshooting. Have run GrosJets for ten years and also want to pass along the following. Allowing GrosJets to sit over winter after running 10 percent ethanol can result in the ball sticking in the open position. Unsticking was a chore.

Regards,

Jim Haskins

1953 TD
J. M. Haskins

Bruce,
I recently started the engine in my 1600 Mk2 for the first time and I had fitted Grose jets. Everything in the fuel system is new or rebuilt.Petrol started pouring from both the overflow pipes.Dismantled,checked float hight etc and re-assembled.Still fuel pouring out.Replaced Grose jets with SU needle valves-perfect,no problems.Any ideas?
S Ash

Yes. Check the fuel pressure.
Barney Gaylord

This thread was discussed between 01/04/2012 and 04/04/2012

MG MGA index

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