QuestionQUESTION: Hi, I have had some carburator work done on my 77 mgb and it was runnning. The car had sat for several years and there was sediment in the tank. So I replaced the tank and now it dosnt want to run. I always had trouble with the carburator for years. Now I dont know if I should rebuild or replace the carb. with a totly new one or a different one altogether. Can you give me direction?
ANSWER: Hi Marcia,
There is no reason to replace a carburetor unless you have hit it with a hammer.
Mechanics had a saying, "The easiest car in the world to fix is a car that doesn't run and the hardest car in the world to fix is a car that don't run on occasions.
Since your car does not run it falls into the category of "easily fixed"
All gas engines only require 3 items to run, Compression, fire and fuel with conditions on each.
Compression --- needs to be high enough. 125 PSI to 180 PSI on a compression test.
Fire --- Needs a thick blue spark at the correct time. Remove the spark plugs and attach the wires to the plugs and lay the plugs on a metal part of the engine and spin the starter over and watch the sparks. (thick blue spark)(not in bright sun light) Then set the timing to specs.
Fuel ---- Needs a combustible fuel available to the combustion chamber. Replace all plugs and spin the starter and spray starter fluid into the intake. If it starts, it is the fuel or fuel supply that is at fault.
Do these three tests and if you have not found the problem let me know the results of each test.
Howard
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QUESTION: The car will run but it is very rough and then it will stall. It will not stay running. we know the fuel line is ok and the spark is fine. we are pretty sure it is in the carb.
AnswerThere is not much in a Stromberg carburetor so you can remove it and open it up. Under the top cover is a diaphragm and it must be checked for holes or cracks. Note that there is a "tooth" in the outer rim that fits in a grove in the carb when you install it. The piston must slide up and down on the shaft freely. Be careful not to bend the metering needle.
Remove the bottom float chamber and clean the float chamber out and clean or replace the needle and seat and reset the float level. (17mm from the base of the carb to the bottom of the float when held up vertical with the float hanging down with just light pressure on the needle and seat. The decel valve on the side of the carb has a diaphragm that gets so stiff it does not operate so it either needs to be replaced or adjusted so it is closed off completely. The temperature compensating valve on the same side should be cleaned but is just a mild adjustment to mixture. Don't bend the bimetal plate.
The large brass screw on the side must be turned all the way in and is not used.
The coolant operated choke on the left side fails very often so it needs to be checked by removing the three screws on the edge of the coolant unit. (do not remove the center bolt and mark how it is in place so when you replace it, you can get it where it was) Pull the unit out away from the carb and you will see a small lever. You should be able to move the lever back and forth freely. This is the choke and is moved by a bimetal spring in the coolant chamber. when the carb is back on the car you can move this lever to manually operate the choke to see if that is a problem.
Let me know,
Howard
