Another timing curve question
I don't know of anyone running the Mini-Express that would idle anywhere near that low in a 440 or 451. Mine had a few degrees taken out during the regrind (original was 278, now 272). 107 centerline, in at 105.
Working on the carb too, although only one thing at a time ;) It's an old #4780 (800 DP). Eventually I'll get tired of screwing with it and get something more modern and adjustable!
Already have 3/32" holes in all four blades, the only way I could get enough air in and keep the transfer slots square on both the primary and secondary. If I could run more than 22 initial timing I could probably reduce or eliminate some of the holes - but I still need to keep the t-slots close to square.
Incidentally I know from watching the wideband gauge that the PV is opening way too late (I'd originally followed the common and stupidly wrong advice of half the idle vac). I just picked up an 8.5 and 9.5 at O'Reilly so will be putting one of those in for my next test run.
It's been said that 90% of carburetor problems are in the ignition. Or was that the other way around ;)
Ok, now we can talk about your carb. Nothing wrong with it, except it can be a bit tedious to adjust.
First things first, if you have a pin gauge set, pin gauge every hole in that thing. Write it down.
Emulsion of ~.028 is a great starting place, but I can't remember what the 4780 had. Also, somewhere around .031 on the idle feed restriction is a good start. You can drill all that stuff out and get yourself some 6/32, 8/32 and 10/32 brass set screws 3/16 long and some very small bits and a pin vise. You can drill out all those press in brass bits and use the set screws to make easy changes.
Also, you need to measure the T slot holes, both in the main body where the metering plate goes, and where the hole in the main body meets the base plate. I'm thinking you'll need to put restricters in there.
Once you clean up the idle and transition circuits, you can go to work on your power valve circuit along with the main jets. You can make the power valve channel restricters adjustable too. Set your cruise tune with the main jet and use the power valve to adjust WOT.
Once you get that, you may find your ignition timing requirements have changed.
