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MG TD TF 1500 - Grose Jets Sticking ?

About a year ago I had my mechanic install Grose jets in my TD carbs. He never seems to do anything quite right, by the way.

Today, after the car was sitting for 2 days, I turned on the ignition and the fuel pump didn't do its usual 5 or 6 pumps and then stop. I lifted the hood and checked the overflow hoses, and both were wet with fresh gas. I started the car up, drove it, it ran fine, and then rechecked again when I stopped it and the problem cleared
up. What could cause this on Both carbs ?

If its dirt, and I had them installed because the SU needle valves are prone to sticking when dirty, what is the best way to deal with it ? Blow it out and install a filter somewhere ? Where is the best place. The tank has always been very clean and I use good brands of gas.

I also understand that the grose jets are adjusted to slightly different specs (the float is I mean). Does anyone know that it should be. I have had to redo everything this mechanic has ever done, except oil changes, so this could be wrong also.
Larry Ayres

Gross Jets are a great improvement over the needle valve assemblies now available. However they do sometimes stick usually, I am told, in the off position. Rick Smith, the chaiman of the Safety Fast commitee of the NEMGTR, won't use them, preferring the ones with a fiber tip on the needle valve. I myself have the Gross Jets in both my TD and TF.

From your description my guess is your problem is/was dirt and a fuel filter is a cure for that. My estimate is that the best place is near the fuel outlet of the tank. This is so gravity will help the fuel thru the filter. Also not as obvious as if it's under the bonnet near the pump.
Safety Fast,
Bob
R. K. (Bob) Jeffers

I have used Gross jets in my TD and my Healey for years with mixed results. Some Gross jets were manufactured out of tolerance and the balls would stick. I have found that even with the good ones, the balls will stick after a long period of inactivity. The problem seems to be varnish accumulation from the gasoline. The fix is to remove the float bowl covers, and give the jets a good rinsing with spray carb cleaner.
Dallas Congleton

"The fix is to remove the float bowl covers, and give the jets a good rinsing with spray carb cleaner"

I meant to say give the float balls a good rinsing with cleaner.

Dallas
Dallas Congleton

The filter, if installed, should be downstream from the pump. The SU pump is quite happy with a clogged filter downstream from it, but quite unhappy with a clogged filter upstream (between it and the tank). You will save yourself a set of points and being broken down by a clogged filter if you install the filter just before the carbs. You can buy a clear one with a replaceable element and you will know if fuel is passing through it.

dave
Dave Braun

To amplify on Dave Braun's comments regarding filter placement in relation to the SU fuel pump, a filter placed between the tank and the pump that becomes clogged with debris will cause the pump to stall in a current on condition. When this happens, the coil and particularly the swamping resistor (which consists of a length of resistance wire wrapped around the outer layer of the actual coil) will overheat. The coil generally survives this overheating unless power is left on for a long period of time, in which case the insulation on the wire become very brittle and will flake off, causing shorts between the turns. The swamping resistor is the item most often damaged by the overheating, often burning in two. Since the swamping resistor is the only form of arc suppression for the early, low pressure and high pressure pumps used on the T series cars, it's burning out leaves the pump with no arc suppression for the points and results in premature burning and failure of the points. Further, since the swamping resistor is hidden inside the coil housing, it is not recognized that it is burned out and a new set of points is installed, only to burn out in a short period of time. The final result is the car's owner having bad things to say about all SU fuel pumps. I have commented on this situation numerous times over on the MGB BBS because the design of the swamping resistor in the later pumps for the MGBs makes it much more vulnerable to overheating damage than in the pumps for the T series and MGAs. It is, however a problem inherent in all SU fuel pumps and the reason that I keep counseling people to place any kind of modern, high efficiency filter down stream from the pump as Dave Braun states. Cheers - Dave
David DuBois

David -

Can the swamping resistor in the pump be tested to see if it is burned out? And if it is burned out, can an external resistor or diode be used as a replacement?

Jan

Janson Hurd

Larry,

Replaced both needle valves with Grose valves last summer. (the old needles were badly grooved)big improvement to vapour lock problems.
However after 3 months began to get intermittent missing, changed out most of the ignition system before tracing the missfire to sticking grose valves. Already have a good quality filter between pump and carbs. The Grose valves appear nice and clean, but they still stick intermittently. I only have a crude solution right now - tap the offending float chamber with 1/2 ins af spanner and the missfire disappears. If the problem persists I may revert to the old needle valve assy.
Any ideas anyone?

Regards
Graham Smith
TD/C 7822
G.D. Smith

This thread was discussed on 12/02/2006

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.