Need tuning help on 340 (Part II)

I wanted to update on my progress.

First I re-checked everything ...cylinder pressure, fuel supply, no vacuum leaks, checked the 0* on balancer with a piston stop, made sure there were no air leaks ahead of my O2 sensor, etc. I also got a second timing light to make sure my readings were accurate. Then I made some changes.

Following suggestions from AJ/FormS, I changed the bushing in the MSD distributor to 14* (from 10*) mechanical advance, and used the heavier silver springs which slow the curve to all in at 3000 rpm. (I am currently set at 18*/32* for timing.) This seems to have been one main part of the problem …too fast a curve in the distributor. I was simply getting too much advance too soon. The other part is fuel, and fighting a lean condition.

As for fuel, my sense at this time is that it is pretty tough to get the Edelbrock carbs to move to a richer setting if you really need it. I am jetted three steps richer in front than what comes in the 650 AVS, and SIX steps richer in the secondaries. And I am still playing with rods, but finally the plugs are looking better!!

The spreadsheet from crackedback has been tremendously helpful in making jetting and rod changes. Thanks for that!!!

I did a 60 mile test run a couple of days ago, along with shorter drives and I'm no longer getting signs of detonation. Have held off on full WOT runs, but short full throttle blasts give me A/F of 12-12.5 so think I'm close there.

On the open road the timing felt a bit slow but it ran cool. I have the vacuum advance limited to 10* and I think I can either run more timing now, or add in more vacuum advance.

I am heading out Thursday for a 1500 mile round trip to Southern Colorado. I'll play with timing as I go, and I probably do have room to advance more than the 32* total I'm now running. (…certainly will as I gain elevation.)

I've really worked on the idle circuit tuning with vacuum gauge, this and running more initial than I was, have really cleaned up the overly rich smell I've had at idle, the 340 starts really good, runs cool, the motor sounds better, throttle response is really crisp, etc.

As summer progresses I'll be able to get to the strip and dial in the timing.

Thanks to all of you for your help!!!! Really appreciate this forum.