MG Car Repair: carb, charcoal canister, constant velocity

Question
We bought a 77 mg midget with a 150cd carb 91 cid it sat for 10 years so we put a new float in it because it would idle great but when we tried to speed up it would die or get very sluggish so we cleaned out the holes we could find and blew them out put it back together and now we get good rpms but it won't idle we put our hand in the carb and hold up the diapram and can get rpms?

Answer
Hi Christy,
When any engine sits for 10 years you need to do several things. Change all fluids and adjust the valves and run a compression test on the engine and drain and clean the fuel tank, lines, fuel pump and clean the carb. As gas evaporates, it leaves a residue. Set the ignition timing and check to see that the vacuum advance is working.
Many rubber components will deteriorate in ten years like the fuel pump diaphragm, the main diaphragm in the carburetor and the decel diaphragm (on the right side of the carb) also the EGR valve. If the car still has the emission equipment, you need to check the charcoal canister to see that it is clear.

As you say, you have done some of this but you can't leave any stone unturned. It sounds like you may still have a problem with the carburetor but all of the other items need to be done before you can blame the carb.
Even though is sounds like you have a carb problem now, you have to know that everything else is correct before proceeding.

What did you set the float level at? Also, did you adjust the fuel mixture? and did you clean all of the dried residue out of the main jet and off of the needle. Did you inspect the main large diaphragm for holes?
The carburetor is a Stromberg constant velocity carburetor. The speed that air goes across the jet is the same from idle all the way up to full throttle. This is done by the diaphragm lifting the piston to keep that air flow constant. As the piston raises as more air enters the carb, it pulls the metering needle out of the main jet thus allowing more fuel to enter. When YOU lifted the piston you allowed the air flow to slow down thus making it run lean. Even though you also lifted the needle out of the jet more it still leans out because of the slower air speed that can not pull as much fuel out of the jet. If the RPM raises when you lift the piston, then you either have the float level set too high and/or you have the needle adjusted too rich.
You should do all the other items first before further work on the carb.
Howard