Initial timing question

[PhilB]

Concobra – thanks for all the effort you put into analyzing my problem. I took some measurements over the weekend and have more data. I apologize for relying on my failing memory to supply the original info.

Cylinder pressures measured with the engine cold were all above 150 psi. Manifold vacuum at 900 rpm was 19 in-Hg. Initial timing was 23 deg. The engine will run at 14 deg, but is rough. I’m using ported vacuum advance. As initial timing is advanced to 23 deg, rpm increases and idle smoothes out. The engine actually runs fairly well; it accelerates nicely under heavy throttle (feels like the front tires are coming off the ground), but bogs under wide-open throttle. I’ve tweeked the carb about every way imaginable but can’t seem the fix the WOT problem. The best jetting I’ve found is about 3 stages rich (over factory settings) on both primary and secondary. I backed off to 1 stage rich, which caused partial throttle as well as WOT problems. Another bit of the puzzle is that during shifts, the exhaust pops fairly consistently on one side. I’m using Shell Valley’s less than elegant RTV-sealed header-to-side pipe joints with exhaust over wrap. I read somewhere that upstream exhaust leaks can cause this problem. I’d like to weld flanges on the headers and pipes and bolt the joint, but I like the flexibility that SV’s design gives. Hope I’m not imposing on you too much, but any further thoughts you have will be greatly appreciated.