MG Car Repair: Idle problem, carburetor linkage, vacuum lines

Question
QUESTION: Hi Howard,
I tried using propane around the intake manifold and carburetors,I removed and capped all vacuum lines at the intake manifold, I slowly restricted the air at each carburetor intake. I noted no change to my idle problem. Is there something else to try?
         Thanks Al

ANSWER: Al, I don't keep all the threads of conversations so either tell me what the original problem is or don't start a new thread so I can look back at what was done and tried.

Howard

---------- FOLLOW-UP ----------

QUESTION: Hi Howard, I was not sure how to add to my original question. I hope this will do the trick.
My problem is that the engine idle on my 1965 Sprite hunts up more then down approximately 600 rpm from a set base idle of 1000 rpm. More problematic is that the base idle from which it hunts changes automatically for no apparent reason. I can drive the car and it will hunt from a new base idle of around 1200 rpm at every stop I make the entire trip. The next time I drive the car the base idle may drop down around 600 rpm and I have to use the throttle cable to bring it up to  1000 rpm so the engine will not stall the rest of the trip.       
I replaced the throttle cable thinking that it my be sticking at times. This did not fix the problem. The gas peddle and linkage inside the car has been checked, cleaned and lubed. I tried pushing down on where the throttle cable attaches to the  carburetor linkage in the engine compartment, when the idle was around 1100 rpm ,to see if the carburetor linkage was sticking. The idle remained high. It did not drop down to the 600 rpm base idle it had reached before. I seem to be dealing with two problems. A hunting problem and a set idle problem. Except for the idle problems, the car runs great at road speed. It has good acceleration and power.

         Thanks Al

Answer
Al, there are some basic facts and one is that no engine can run at 1000 to 1200 RPM without sufficient air and fuel to do so. That means that air is going past your throttle plates or entering someplace else.

You need to confirm that the throttle plates (throttle butterflies) are closing all the way when you back off the adjusting screws.

When I build a set of SUs I can bolt them on and expect it to fire up and run almost correctly without making any additional adjustments.

With the carbs off, I back off the stop screws all the way so I can see the plates close all the way (fast idle screw also backed out) I then turn both stop screws in until they just touch but don't open the throttles at all and then I turn the adjusting stop screws in 9 flats (one and in half turns)I also turn the jet adjustment nut up until the jet is flush with the surface of the bridge. I then adjust the jet down about an eight of an inch for preliminary setting and i confirm that the shoulder of the needle is flush with the bottom of the piston and that the float level is to specs for the model car and type of float arm.

I then confirm that visually both throttles have free play when I pull the cable. And that when the little arms do contact each throttle to open it, they both make contact at the same time.

Then I warm up the engine and use a Uni-Syn gauge or you can use a hose in the ear method to set the idle of each carb down to about 700 to 900 RPM.

If the engine is hunting at that point you either have a vacuum leak or a distributor advance problem. Which you should not have because the ignition system MUST be done before any fuel related work is done.

The sequence of work must be, Compression first, Ignition second and Fuel is ALWAYS last.

Howard