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MG MGA - Engine dies without choke

Has been reliable on HIF SUs for some years. Recent short trip - warmed up and drivng normally suddenly stopped and would only move on the choke. Continued on the choke - making smoke.
Removed and checked the carbs - nothing obvious - but still won't run normally.
No obvious airleaks - about to start again with H4s and new gaskets but purplexed -

The motor is a 1500 - rebuilt as a 1600 with a 1622 leadfree head. The car is standard except negative earth + alternator.

Anyone been here before ?

Roger
Roger Walker

Sometimes with these odd occurrences you cannot see the wood for the trees. Suggest you go thru Barney’s “Tune up the casual way” steps. It doesn’t take long and covers all the possible causes.
http://mgaguru.com/mgtech/care/cf120.htm
Mike
Mike Ellsmore

Check to see if there is a large open hole on one end of the intake manifold round cross tube. Occasionally they lose the Welsh plug out of one end, after which it will only run with full choke and higher idle speed.

In general, look for a big vacuum leak, like loose nuts securing the carbs to the manifold.
Barney Gaylord

As Barney has noted, one of our guys at Phillip Island raceway lost this plug out of the inlet manifold so it does happen - it took awhile to locate, had the experts baffled!
Mike
Mike Ellsmore

Thanks - makes good sense - will be taking the carbs off again this weekend. More anon
Roger Walker

Its been hot in the UK recently. Fuel vaporisation causing engine to stop & then overcome by the use of the choke?

Richard
R A Evans

Halfway report - carbs off - manifold gasket discoloured around the central intake - can only be from airflow.

I was using an early MGB inlet manifold (with HIFs and a connection for the brake servo) with a flange which is marginally thinner than the standard MGA's exhaust manifold - it has meant that the exhaust manifold has been tightly secured to the cylinder head but the thinner inlet manifold less so -

The misfit has worked for five years since we fitted an OE exhaust manifold - but the bodge showed up in the end. Temperature may have had something to do with it.Final report next week.

Thanks for your help

Roger
Roger Walker

Roger. I had a similar problem (intake and exhaust manifold flanges of different thickness). To solve it, I measured each side of each flange, then either shimmed the less thick one or modified a set of the large, hardened washers that serve to hold the flanges to the cylinder head. The reason I say to measure each flange (both ends) is because one of the exhaust manifolds was a set of Peco headers which had a different thickness of flange on all three flanges. Thus, I had to make four custom spacers where the exhaust and intake manifolds shared a stud.

As most have noted, if not directly, a lean mixture will require the use of the choke on an otherwise well running engine. And, over time, having different thickness of manifold flanges bolted with the standard hard washer will allow a leak somewhere. It would seem to the intake manifold in your case.

Hope you get it sorted.

Les
Les Bengtson

Les - I thought I would return the car to its original state with H4 carbs on the original A manifold. Close inspection of the carbs has reminded me they need a major overhaul (and the main reasons for the change to HIFs) The mixture of brass and steel in the choke linkage was not designed to last sixty years.
If I can't get them to work properly - your solution to the mismatch will be my Plan B.

situation on-going.

Roger
Roger Walker

Refitted original H4 carbs with MGA manifold. Possibility of air leaks seemingly eliminated.
Compression on all four cylinders good. Ignition checked but she will only start on choke - runs for a couple of secs then dies - spits out a lot of smoke - plugs all oiled up.
I am comletely at a loss.
Roger Walker

Final report: Stale fuel - really stinks - produces a lot of smoke and is about as useful as paraffin (Kerosene - Don't ask me how I know - UK was still short of petrol in 1950).
Moral ? Don't get caught again. Drive it more - all year round.

Question - what to do with five gallons of stale gas.
Roger Walker

Rather than waste it, I used to use up all my spare racing fuel in my lawn mower, it was from my racing 2-stroke kart engine that ran on Petrol mixed with Castrol R40.
I have always loved the smell of Castrol R and I always made me think that I was back on the race track. (probably sped up my lawn mowing too)

I had a few "petrol-head" neighbours (mostly motor bikers) and they used to all wander outside as soon as the Castrol R aroma drifted into their gardens.

It used to make me smile, it reminded me of the old Bisto gravy ads :^)

Not sure who you will attract if you use your "stinky" old fuel in your lawn mower though!

Cheers
Colyn
Colyn Firth

Roger
Its good you have sorted it.
How old was the fuel? I have bought a fuel stabiliser for my lawnmower petrol, which they claim keeps the petrol fresh for 3 years and protects against the corrosion from ethanol.
Thinking I will also use it in the MGA even though I have ethanol free fuel (Esso)
Graham V

Graham. Interesting tip about stabilizer - must investigate. Not sure how old the (Shell premium) fuel is,probably at least part of it would have been from 2019.
Colyn - I ran a twincam on Castrol R and sympathize on the smell. I don't think this stuff will compete. There must be a silver lining somewhere though,
Roger Walker

This thread was discussed between 22/07/2021 and 17/11/2021

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