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It sounds as if your too large on the venturi. By making the venturi too large, it drops manifold vacuum enough to affect the carb's circuits. If vacuum is too low, it wont pull as much air, or fuel from the idle circuit, more off the main jet from all the freeflowing air coming across the stem. Here is a good recipe for what you have,,, its exactly the same carb set up I have on my M, and it works great,,,,, Start by cleaning the throttle body out once more. Every passage has a place to go when you inject compressed air into it to clean it out. The main thing is to trace every passage you clean, does the air come out of every place you pressureize?? If not keep trying, or boil the carb out to remove the debris. You should be able to place the tip of your finger, over the passage in the throat of the carb, (right beside the butterfly it looks like a slit in the side of the throat) blow air thru and get a strong stream of air out it. If it doesnt, that particular area of the idle passages is plugged. Either way you look at it, it has to be made sure that the passages are clear. If its clear, you might try to see if it works, but in my opinion, the venturi is still to large for what you have. Using a 6 cyl bowl, I did enlarge the jet size 5 sizes, since it had the big stem in it already, I only opened up the bottom 2 holes 2 sizes smaller than the new jet size. I use a #27 venturi, with the M throttle body. I use 89 octane pump gas in it, it does not need any thing more exotic than the 89octane. I have right at 165 psi of cranking pressure in my M, with a 8060 head. I recommend trying this setup with what you have,,, it will make some real good low end power, and still big enough to run up to 2100rpm. Check those passages really good, put in a new idle screw, that does help,,, Im assuminmg it has the large brass idle screw, VS the smaller 6cyl type adjuster right? Some MTA's had the new style idle circuits, thats about the time they swapped into the new carb designs,,, ChadS
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