You may need to run a little more total timing but it's not always best to increase initial timing to get it. Too much initial often results in difficult hot restarts. For most well thought out engine builds I like to use around 10-12 initial, 10-11 mechanical (20-22 at the crank), and 10-15 degrees from the VA. In most cases I use ported vacuum to the advance as my engines are higher compression wider LSA camshafts which promote good cylinder pressure at low RPM's so no need to run a butt-load of initial timing to make the engine happy.
When I custom tune engines brought here I use similar numbers unless they are lower compression with big cams or tight LSA. I always address idle fuel delivery as well and when I get that up to par it's still rare to need a lot of timing at idle speed for most engines.
Anyhow, it is best to make very small changes with total timing. Right now you have 26 degrees total timing at full load. Most engines I've tuned like closer to 30-34 degrees with some liking a bit more than that. Some engines like a tad less so be conservative when advancing the timing as detonation may occur and it will destroy the best prepared engine......
I tried just advancing the timing another 5 degrees, which didn't make much difference other than a bit harder to start.
So initial went back to 10 degrees, then I switched the vacuum advance from manifold vacuum to ported vacuum. At an idle, this didn't seem to affect it much, and I wasn't sure why. So I pulled the carb and checked the port I was using, it sits just above the throttle plate when it's closed.
To verify I was actually getting ported vacuum, and to what extent, I checked this port against the manifold vacuum port using a gage on each simultaneously.
So what I'm getting is basically the same from either port. Just minor differences at part throttle.
It feels like it runs better with ported vacuum, so that's where I'll leave it for now.
On another somewhat related issue, my lean condition at higher RPM's was being caused by the fuel shut-off solenoid I was using between the mechanical pump and the carb.
I could overcome this by engaging the electric pump, but even with that in this Arizona heat I would still get starvation issues.
After removing the solenoid and installing a couple of heat shields for the fuel lines, there were no more problems.
(This is a square body Suburban, just for reference).
Well, except one, my fuel tank was getting hot from the airflow from the engine and the exhaust pipes at each front corner of the tank.
To prevent this from continuing, I built a heat shield that sits in front of the tank just behind the axle, and then made a lower shield that resembles a skid plate, but it's purpose is to cause an airflow around the tank, drawing cooler air from above the tank between the floor and the frame, and the small gap between the shield and the frame.
Before I did this, when I would drive for an extended period, when I would remove the gas cap the pressure would blow the cap 6 feet away.
Took it on a 2 hour freeway trip today and checked the tank, absolutely no pressure whatsoever. I was worried that I might have done all that work for nothing or even made the problem worse, but it turned out great. Even with the A/C on at 75 MPH, no heat issues, and it's a 100°plus day in Tucson today.
