My 1960 190b drives smooth and strong on a highway drive. No problems until I come to a stop. Engine idle speed drops from the 800 I've set it to, down to about 550-600. Once or twice the engine has actually died.

Open the throttle a couple times, idle returns to 800 rpm.

Timing is per spec: starter speed 8 BTDC, 15 at 800, 30 at 3000. Points at 50 degree dwell. Solex PAJTA carb adjusted to lean best idle, idle speed 800 rpm warm. No hesitation, accelerates smooth and strong, cruises smooth. Engine starts immediately cold or warm. Plug gap set correctly, plug tips dry and light brown, compression 160 160 162 160 (wow!).

Is this idle speed drop a valve problem? fuel flow? fuel bowl? dirty headlights?

Thanks.
Tom

This is my belief, seems you already understand why. Check the obvious bits out and remove that tank screen to clean it or replace if needed.

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Id be checking the points cam rider to make sure it still has lots of material.
You are describing a very typical point gap closing issue or as Marrs pointed out, basic fuel issue.

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Thanks gentlemen. Cleared the problem by simply enriching the idle mixture. I had previously adjusted the carb with "lean best idle". When I backed the screw out another 1/4 turn this afternoon, the idle stays at 800 regardless of conditions. What an improvement!

Tom