QuestionQUESTION: I have a 1979 mg midget, I have a hard time starting it in the mornings, however, when it idles the rpm fluctuates up/down sometimes dies out when i come to a dead stop, although it starts up right away. Can you tell me what is going on with it? how can I fix this problem? also how can I tell if my carburetor has a manual or automatic choke on it? I read that if it has a catalytic converter it has an auto/choke if so then where is the catalytic converter located? your answers would be highly appreciated, thank you.
ANSWER: Hi Minnie,
The car did have an auto choke and the CAT (catalytic converter) is on the exhaust pipe up close to the front of the exhaust system.
Any time a car is brought in to me like yours I have to run tests. Compression test first, then Ignition (timing set and confirm fire at each plug.)(compression gauges are not expensive)
Only after these will I look at fuel as a possible fault. First test the fuel pressure at the carburetor and then I would look at the carburetor and auto choke system.
Hard to start cold is a common fault of a failed auto choke system and that is somewhat easy to test. When it is cold just spray "Starting Fluid" into the intake as someone tries to start it. Any auto parts store has "Starting Fluid". If that makes it start right away even if it don't keep running right. Most likely the choke is not working.
Howard
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QUESTION: Hi Howard,
Thank you for your quick response, I did as you said and sprayed some starting fluid in the carb.and it starts right up and it idles after it warms up. I also found a few vacuum leaks and fix those up however, now my engine is running rough, it sputters and makes a blup blup blup sound coming form the tail pipe I can feel it on my hand while it idles. I have a stromberg 150-CD4, I slowly restricted the air that goes into the carb. and the engine started to smooth out and rpm went up. I looked for intake manifold leaks by spraying carb. cleaner also on hoses, could not find any leaks. I checked the carb. diaphragm no tears on it, added oil to the dashpot. The compression on all four are 130-133. and just so I'll know what I have in my car, I replace the spark plugs @.025 (it had bosh) fuel filter and air filter. can you tell me why it is running like it is?Thank you so much.
Minnie
ANSWER: Hi Minnie,
Even though it is a constant velocity carburetor, the restricting of air does richen the mixture and the fact that the RPM raises is a clear indication that too much air is entering the intake. First close off ALL vacuum ports and try it again and if it still corrects the running by restriction the air check the float level, and put the 3mm Allen wrench down into the top and see if the needle is adjustable and turn the adjusting screw clockwise a half turn at a time to see if you can correct the problem. If not take a dry gas like propane and spray it up under the intake manifold to see if you can find a manifold leak as it is almost impossible to use a liquid to spray up from under it and hit all the places. I usually do it out side and with a cold engine so as to reduce the danger of the propane igniting. Dangerous but effective.
Howard
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spark plugs
QUESTION: Hi Howard,
as I mention before my engine is running really rough to where the engine and car shake. I did as you said, rev. the engine to look for black smoke out of the tail pipe and none appear even with engine warm to temp. I pulled the plugs and this is what I have as you can see. they are light brown on one side and clean on the other side. starting from left to right is #1 cylinder and so on. I have no adjustment on top of pot, the little hole on top does not go through it is solid. fail to mention that my muffler sounds loud too. what do I need to do to get my engine running right? your help is appreciated thank you.
Minnie.
AnswerThe top of the pot is a thumb screw cap and you need to unscrew it to put the Allen wrench down into the oil to get to the adjusting screw.
The plugs do not indicate a "Choke ON" problem but they do look lean meaning not enough fuel. Remove the plastic top cap and insert a 3mm Allen wrench down into the oil in the top and rotate the adjusting screw clockwise about a half turn.
Then while the plugs are out do a compression test (throttle open) You should see from 125 PSI to possibly 170 PSI. They should all four be close to each other (5 PSI).
Then set the ignition timing as to factory specs.
After all that see if it has improved any. Don't skip anything.
Let me know,
Howard
