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MG Midget and Sprite Technical - Fuelaholic 1500 midget

Hi everyone,

I hope someone may have some idea's on this, basically my 76 mg midget 1500 uses a lot more fuel than my previous one and when i pull it out the garage it likes to put black muck all over anything in its way.

What i've tried:

Replaced point's, Leads, plugs, float needles

Modified the waxstat jets with coins to make them fixed jets

Tested that the carb pistons drop equal times and are taking about 7ish seconds to drop with hole plugged.

Re designed the fuel linkage for the twin su's so a pipe with t-piece goes in the middle giving equal fueling rather then standard setup with fuel going direct to left carb then fed to right one. As the left carb in my opinion seems to be the rich one as i end up with the jet right up when trying to set them up.

The engine appears to be a newish one with stanpart stamped on the block and a warranty sticker with a thermostat. i have the reciept for fitting so looks like it's only done 13,000 miles on this engine.

I've also stuck about 6 or 7 layers of card gaskets on the fuel pump to try lower the pressure a bit haha

I hope someone has some other idea's to try

C Rich

Hi, Chris -

The fuel pump on the 1500 is calibrated to deliver the correct pressure. The spring under the diaphragm is what does the actual pumping, and maintains pressure once the float valves shut, at which time the diaphragm is prevented from pumping until fuel is drawn off from the float chambers. So decreasing the pump pressure isn't really a solution in this case.

My car's got the demon Zenith carb, but I do know that you can test for this condition with SUs by running the car until you know it's overrich, then removing a float bowl cap and seeing how much fuel is in there. If it's brimming, your float valve setup is suspect. Others can give more details than I when it comes to SUs.

You mentioned that you replaced the float valves, and I assume you used the needle types from what you wrote in your post. Good on ya... Grose Jets (the ones that seal with a couple of steel ball bearings) caused severe flooding for me, and I've heard others report the same problems. So avoid those.

Do you know for sure that the floats are good? If they've gone leaky, and are filling with fuel, they won't shut off flow as designed, and can flood things out big time.

Let us know!

Gryf Ketcherside

Where in humberside are you Rich? I could have a look for you if you are anywhere near me in sunny scunny?
Bob Turbo Midget England

Hi Gryf,

Thanks for your reply :-)
The worry with the fuel pump is that apparantly there is two different one's fitted to the 1500, but do you think excess pressure wouldn't be the issue?

Theres no ajustment on the floats and I can't see any fuel in them or any sign of holes, damage etc.. i do wounder what kind of level the fuel should be at in the bowls? as that could be checked easyly. A thing i thought of was the breather above float bowl been blocked but thats also all clear.

They are the needle types valves they don't look as good as what i bought for my old midget that had neoprane rubbery tipped ones.

Hope I can solve it soon petrol is an arm and a leg price at the minute :-(

Hi Bob i live in Hull so we are separated by the bridge toll i think based on it's current mpg it would probably cost about 30 to get there and back maybe 20 if you find the fault haha Thanks for the offer I might take you up on the offer if im really stuck and it's nice to meet other owners.


C Rich

I think there maybe some mis communication between gryf and C rich

gryf has the USA zenith carbs (makers of my TV also?) and C richard has the duel HS4s Su carbs

if the pressure is to high why not a aftermarket fuel pressure mr gasket or hayes, Im guessing several 1000 of em on ebay

Prop... "what we have here is the failure to cummincate" said the white southern sheriff to sidney portyah


I doubt that it is a fuel pressure problem.

You don't mention the plug colour? Are they getting black and sooty?
You also don't mention any attempt to simply adjust the mixture strength with the adjusting nuts on the bottom of the carbs. I would try turning these both upwards by an equal amount - maybe 3 flats to start with.

And have you checked that the chokes are both fully returning when you push in the choke control knob? Maybe the return spring is missing off the bottom of the linkage.

Guy Weller

The plugs where rather sooty when i changed them and i did mention the fact i moved the left carbs jet right up when i take the piston and needle out the jet protrudes out.

I always start with the jets flat then two turns down with the nuts and look at them to see there equal then run the car and test each with a screw driver raising the piston one at a time. It seems if i raise the right piston the engine stalls and if i rase the left it it momenterally speeds up even the the jets right up?

The chokes are working fine i spent allot of time making sure they dont get stuck

C Rich

Obvious question but no fuel leaks anywhere else to mess with the pressure in the gas lines? no way for air to get in? that would seem like it would throw off your gas pump.
Seth Brecklin

Are you still using the standard 1500 air filters? dirty filter perhaps although you sound as if you have been pretty methodical and would have checked that.

Piston drop times are the same, but do they have the same springs in each?

Air leakage on the throttle spindles would make them difficult to set up. Have you tried spraying WD40 or similar onto the spindle bushes to check for leaks?

Worn jets / needles perhaps? The carbs that use a bias spring in the needle do tend to wear the jets oval which would cause rich running.

Guy Weller

This thread was discussed between 07/06/2010 and 08/06/2010

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