924Board.org

[ChrisMadge]

Hi I'm looking for some help please. I have a warm start issue on my UK 2.0 NA 1984 fitted with the Ciprian's Super Charger kit. Car starts cold and hot no problem. But warm starts take some cranking.

The car has had extensive work by me and the previous owner including new injectors, accumulator, fuel pump, fuel lines, hoses. I run a AF gauge, mixtures at idle and above are where they should be.

I have run the three pressure tests. The first two are good. The leak down test shows the problem. If I shut the valve off on the pressure tester so that the WUR is ignored the system holds pressure for over an hour or more. To me that suggests Everything from tank, fuel pump, accumulator, fuel lines, filter and metering head are good?

The leak down test with the valve on the pressure tester open shows the system does not hold pressure for long enough. This is the WUR leaking pressure I believe. I have checked the return hoses and fuel lines - they seem ok.

I have two rebuilt WURs.
The first one was professionally rebuilt. Heating element resistance is within spec. The leak down test shows 35 psi at the start and 19 psi after 20 mins, and dropping to zero within a couple of seconds. (This causes warm start issues after 45 mins)
The second is a vacuum WUR I rebuilt with new O ring, metal diaphragm etc. I used carb cleaner and made sure everything was clean before reassembly.
Heating element resistance is within spec. The leak down test shows 25 psi at start dropping to 19 psi after just two mins and to zero within a couple of seconds.

I have checked the pressure regulator. O ring looks okay, but I have a new one on order just incase.

Is there anything else I have missed and should check, before I reluctantly take the WURs apart again?
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1984 MY 924 2.0 NA
1975 MG Midget

[Fasteddie313]

Doesn’t that late model 2.0 have that extra hot start valve or whatever all that is?

Post a diagram that matches your car..
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80 Turbo - Slightly Modified

[morghen]

The 85 model does. I was going to mention that if you want to try to replicate it on your car i’d offer the details.
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Supercharger and EFI kits
https://www.the924.com

[Fasteddie313]

I think that could possibly be leaking down if his car is equipped with that late model system..
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80 Turbo - Slightly Modified

[ChrisMadge]

Its a 1984 MY, build date is October 1983. It has one hot start solenoid.

System is:
Fuel tank - pump - accumulator - filter - metering head -
injectors
CSV
WUR
- hot start solenoid
- return line back to tank

I dont see how I attach pictures to my post, without using a url?

For one of the leakdown tests I bypassed the hot start solenoid, IE the small outlet from the WUR was connected directly to the return line to tank. The leak down test result was the same. I'm not sure this really proves anything. If fuel is passing through the WUR to the solenoid then the WUR is leaking?

During the WUR rebuild, I didnt 'resurface' the fuel cell. https://k-jet.biz/wp-content/uploads/2019/06/double_diaphragm_wur_rebuild.pdf
It looked fine to my, admittedly poor, eyesight. So last night I took the WUR apart again, removed the fuel cell, and using a small mirror with some 1200, 2000, 3000 grit wet and dry re-sufaced. I'll refit and try it again tonight.
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1984 MY 924 2.0 NA
1975 MG Midget

[jacobroufa]

[ChrisMadge]

WUR has been resurfaced, I used a small mirror with some very fine wet and dry. The cell is quite small in your hand and its easy to rock it from side to side if you are not careful. I found it better to use a twisting back and forth motion. 30 mins working through finer grades gave a nice smooth sinny surface from outside edge to centre.

To do this meant taking the fuel cell out of the casing, which meant spending some time reseting the fuel pressures by pushing in the cell for warm control pressure, and plug for cold control pressure. Its a bit of a faff trying to do it on the car, but I got there eventually.


Leakdown test is much better. Holds pressure for 20 mins. Car restarted perfectly after 5 and 30 mins. Ill need to try 45 and 60 mins next.

I'm guessing the central section of the fuel cell where the button presses against was worn, and resurfacing has solved the leakage problem. The WUR control pressure is constantly changing between vacuum and non vacuum which over time leads to wear?
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1984 MY 924 2.0 NA
1975 MG Midget