FE Timing

[Excaliber]

Well it SHOULD run poorly as you approach 'TDC and it's not surprising it doesn't even want to run at all at TDC. BIG cams, and there is NO DOUBT you got one, like a lot of advance. 22 BTDC isn't unreasonable for the best idle, power, etc. Yup, it's hell on the starter though.

Rule of thumb: Set the base timing as high as possible, 22 if that's what it takes, then back it down "just enough" to get the starter to spin OK. Finally, adjust the mechanical advance limit to give you a total of 32-35 and your timing is "done", move on to something else. That is NOT the problem.

Myself, I use my vacuum advance to direct manifold vacuum signal which gives me a "fast idle" speed when I hook it up. No problem, just adjust the carb throttle screw for a lower idle speed with the vac hooked up. Added benefit of this method is it helps or stops "run on" when you shut the hot engine off. It stops the run on because the carb throttle butterflies are pretty well closed up already. This in turn prevents the engine from drawing additional air/fuel into intake and the hot combustion chamber thus igniting the mixture. That's why some call run on, "dieseling".

I really like the vacuum advance unit for cruise rpm conditions. It add's another 10-15 degrees to your mechanical plus base timing for maximum mpg. Or in my case, for maximum CRUISE RANGE with a small gas tank! 32 total, plus 10-15 with vacuum advance and your looking at 45 to 50 total. Which is OK, maybe, how much you can get away with is dependant on the combustion chamber design, quench and other factors. MOST engine builders will NOT recommend a vacuum advance because it adds another level of potential for a "mistake" and a warranty problem.

Get it right and it's sweet! I'm getting 14 mpg with DUAL CARBS on my side oiler and thats without an overdrive! Just a top loader and 3:31 rear gears, cruise mpg about 70. NOTE: My forged pistons ARE custom designed specifically to add quench to the combustion chamber and my C.R. is 9.6 to 1 with iron heads.