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MG Midget and Sprite Technical - Vaporisation ??

Having had a hot idle, stall and no restart issue for some time, I've chased it through the ignition system swapping out all the ignition components. I finally swapped out the carbs, and heh presto it appears I've found the root cause.

There's little difference between the two sets of carbs, both are a pair HS2's. The pair giving the diffeculty have been polished and the throttle shafts have been cut down, there is also a large cut out in the heat shield to clear a tubular LCB manifold, and a further corner has been trimmed at some stage to clear some thing else.

I had sprayed some easy start fluid onto the carbs prior to there removal and identified that the throttle shafts are worn. I then had started doing some rebuild research with the Moss videos on YouTube and come up on the idea it might be vapourisation.

The behaviour of the car appears to fit the vaporisation issue. Once it has stalled it will not restart for about 10 minutes, there is a spark and there is fuel in both the float bowls. So could it be vaporisation, caused by the big hole cut in the heat shield? Has any one else had a similar issue?

My car has a steel fuel pipe running along the inside of the chassis leg, so quite near to the exhaust, my planned fix was to insulate this pipe, and close of the hole in the shield with some material.

Background - I'm running a 1380 on a 288 deg cam, mod'd head, LCB, Aprilla motor cycle rear box, electronic ignition, electric fan, I guess it's putting out 90 bhp.
James Eastwood

Likely the heat-shield; try 'old' carbs with 'new' heat-shield.

Actually - try an HS6(!)

A
Anthony Cutler

James,
My old midget sounds similar to yours. I had twin hs4s and an LCB manifold with a cut out in the middle of the standard heat shield to clear the exhaust. It was a 1400 Oselli built engine putting out about 105 BHP and it never suffered from the symptoms you quote.
I did have a Facet fuel pump and Filter King pressure regulator. I was never that impressed with the twin hs4s. I have put an HIF44 on my current Midget (mildly tuned at present) and am impressed with that.
Dave
Dave Brown

I had the same issue with my B it plagued me for years when the car got hot it would randomly stop and refuse to start as it cooled down it would restart had various people look at it but nobody could sort it out changed everything insulated the fuel system would still give trouble then one day it wouldn't restart turned out to be rotor arm replaced with new rotor arm same problem it seems new rotor arms are rubbish my local mg specialist won't sell rotor arms because they are useless I went to a motor factors and dug through his old spares box and found a lucas one which worked fine but apparently the distributor doctor sells good ones so give him a try.


Gary
G.J. Puxty

You can get good rotor arms from the Dizzy Doctor.
http://www.distributordoctor.com/rotor_arms.html

Dave
Dave Brown

The car is fitted with a Facet pump without a regulator. There is also a clear plastic in-line filter just upstream of the first carb, there's no sign of bubbles, but then this is under pressure, so it's possible that the fuel picks up heat in the metal pipe running through the engine bay, which then evaporates once at atmospheric pressure in the float bowls??

I could try old carbs with new heat shield, but with these intermitant problems a clear "X is better than Y" test is some times diffecult especaily as we're going into winter. Hence I was looking for anyone who recognised teh issue. I do have some heat insulation material though to experiment with.
James Eastwood

On subject of distributer arms, bear in mind I have changed the whole ignition system for my spare unit, (this included leads, cap, rotor, dizzy, coil and trading electronic ignition for points type in the process).

But thanks for link for future reference, v. helpful.

James Eastwood

This thread was discussed between 21/11/2011 and 22/11/2011

MG Midget and Sprite Technical index

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