I HAVE A 406 SB THAT LIKES TO MAKE THE HEADERS GLOW. I KNOW TIMING IS CORRECT. I HAVE REJETTED MY CARB FROM 74 TO 68 JETS, THINKING IT WAS TOO RICH. THE GLOW INTENSITY IS LESS, BUT IS STILL PRESENT. ANY HELP WOULD BE APPRECIATED.TY.

 

Need more information on your motor,,,like what Modifications you have done,,,like for instance ,,if you have ported and polished the heads,,or if they were done in the past then the unburned fuel will travel to the headers quicker,,making them red hot.
Also if you are running your carb mixture too lean this will also cause your exhaust to run hotter,,gasoline also cools remember.

 

You said that " the timing is right " and what I know from experience is that glowing headers usually indicate a lean condition ( cylinder getting too hot from lack of fuel or pre ignition ) If It has gotten better with a smaller jet then I would lean toward too much ignition lead ( timing ). Try retarding the timing 2 degrees at a time and see if the glowing gets better. If the engine is modified, the factory settings go out the window. 400 engines ( and all with a 3.75" stroke do not need as much timing as a 350 or engines with a 3.48" stroke ). I found more power running a 3.75 stroke engine on the dyno with as little as 28 degrees total timing whereas a 3.48 stroke might like as much as 8 degrees more. Thanks for listening.

 

^^^^ +1. Also, tune that thing on a good dyno to maximize the A/F mixture and give you all the HP you can get!