MG Car Repair/75 MG Midget starts then stalls
I have a 75 MG Midget that sat in a barn for 17 years when I got it. When I try to start it the engine will fire but almost immediately stalls. I can 'kind of' get it to run by working the gas pedal vigorously, but as soon as the RPM drops to about 2000 the RPM immediately drops to zero and the engine dies. I have the same results with the choke in or out with my foot off the throttle or with the throttle pushed in half or all the way in. The choke and throttle seem to make no difference except to run the RPM up if the throttle is in.
I had the engine rebuilt to factory specs. I have checked the compression and all is okay. I have not checked the vacuum (don't know how), but the entire exhaust from the manifold to tail pipe is new and clear. I have installed a new fuel pump with new plumbing to the carburetor. I checked the gas flow and then checked the gas pressure at 3.5 lbs. I installed a new coil and checked that there is fire at each of the spark plugs. The gas tank and line are new, the originals having been torn off before parking in the barn, but I am using a small aux hand tank next to the engine to bypass that system. The air pump is presently disconnected and the pipe to the manifold is plugged. The hose from the rocker cover to the charcoal filter is also plugged. All the rest of the hoses and tubes are installed.
As Penelope Pit Stop says, "Healp, healp, healp." Any help is greatly appreciated.
You have done a lot not to have received good results. Working in dealerships most of my life I have a clear procedure to correct a bad running engine.
I have received cars where much was done before it was brought to me. And it just so happens that a close friend today asked for my help on an MG show car of his today. He restores British cars and is very well experienced but is story to me was almost the same as yours.
He just rebuilt his engine and it has been running great untill he removed the distributor and sent it off to a company that rebuilds distributors and he installed it and it only ran for about ten minutes and started running bad again.
I explained that my dealership experience required that I fix the cars as quickly as possible because I was always paid on commission so my income depended on a set procedure to correct engine problems.
My procedure must be done in order and nothing skipped for any reason. It does not matter if an item was ok an hour ago it must be tested and receive the correct result.
The very first test is a compression test and I don't care if it was ok an hour ago it still needs to be tested now and give me the results. All plugs out and at least 5 or mor revolutions of the engine WITH THE THROTTLE WIDE OPEN!
To prevent any spark jumping first remove the white wire/s off of the coil. After the compression test then and only then can you proceed. You should see from 150 PSI up to 170 PSI on all cylinders with little difference between cylinders.
Only if you have that can you proceed to Ignition. A scope would tell you in a few seconds if there is any problems in Ignition but most people don't have a scope avaiable to them. It can be tested with out a scope though.
First set the ignition timing very accurately then confirm that # 1 is indexed correctly. This is easy to do by pluging the white wire/s on to the coil again and connect all the spark plugs to their wires and lay them on a metal part of the engine so you can watch the sparks at the plugs and put your thumb over the number one plug hole and have someone spin the engine over.
As #1 piston comes up on compression it will blow your thumb off of the hole with a "Pop" sound and watch the #1 plug and you should see that the "Pop" seems to be causing the spark (a
"click") sound. If it seems to be a "Pop-Click" or a "Click-Pop" you didn't get the timing correct.
Now go down the line and do each plug hole the same way and you should see the same thing. Even if you checked the ordeer in the cap of the firing order this is a physical test that you did it correctly.
The sparks at the plugs MUST be blue in color and as thick as a pencil lead. If any are orange or yellow colored and thin as a hair, that is a weak spark. (not done in bright sun light)
Don't skip any of this thinking something is ok so you don't need to check it. Leave NO stone unturned and you can't fail to fix it.
Only at this point can you even think of looking at fuel. The order of testing is very important.
Your engine is a 1500 Triumph Spitfire engine and came with a Stromberg carburetor. Your fuel pressure of 3.5 PSI is a little high but all it would do is cause flooding and when you pulled the spark plugs if you noted a flat black powder on them this could be caused by the fuel pressure causing a flooding condition.
First check to see that the float chamber vent hose is pulled off of the carburetor. Then besure the air filter is on and no air leaks. (the carburetor is set so lean that it depends on the added vacuum produced by the air filter.)Also unplug the hose from the valve cover and let it vent to outside air.
Now confirm that the choke is OFF. Take a spray can of starting fluid and spray into the intake while someone tries to start the engine. The engine will fire off but not keep running unless you keep giving it a few shots of spray. This is normal and the reason we are not using the choke is because the Stromberg choke system is noted for failures and we are supplying the extra fuel via the spray can to take the place of the choke.
You should quickly be able to hold a steady throttle without spraying.
If at thie time it will not keep running on it's own and will run with the spray you need to get a vacuum gauge and remove the carburetor and check the float level and check the top diaphragm for any holes.
The intake manifold vacuum should be always well above 5 in hg and if you see it steadyily drop with the RPM up above idle you need to open the exhaust up and test run the engine with the exhaust open. (Even if it is new)
Let me know,