I have been doing a little planning in terms of adding ignition control to the Megasquirt installation on my 1971 B20E. As part of this, I have been trolling the forums to try and get a sense of what people had been using for ignition control maps on the B20E. While doing this, I came across some posts that suggested that the B20E would run better without the vacuum retard function connected. Just run on pure mechanical advance with a range of about 8 deg to 32 deg (the mechanical advance on the B20E provides about 25 deg of advance on the crankshaft).

I decided to give this a try just because I was curious. I blocked off the vacuum retard line to the distributor and reset the idle down to around 900 RPM and confirmed the advance operation with a timing light. A little test driving with this arrangement showed no perceptible change in performance or drivability. I didn't do enough testing to determine whether there was any change in fuel efficiency with the resulting higher advance at low throttle openings. However, when I went to do a restart on the car with this arrangement I discovered that it had become very difficult to get started. The engine turned over without any problem and there were no misfires; however, I was having a problem getting successful sustained operation. Getting a start generally required wide open throttle like I was doing a flood clear. I reconnected the vacuum line to the distributor and the starting difficulty immediately went away. I repeated all of this twice to confirm that the starting problem was related to the disconnection of the vacuum line. With the current fuel set up that I have on Megasquirt combined with my Bosch SR437X starter motor, the engine is normally a very quick start up hot or cold.

I find all of this a little puzzling. Has anybody else experimented with disconnection of the vacuum retard on the B20E and did you experience similar results? Is the restart problem possibly caused by the fact that with the vacuum line blocked off, I had to really screw in the idle air screw to get the idle speed down to something around 900 RPM. I know that my idle MAP with the vacuum line blocked was much lower than it is without it blocked off. Is it possible that the starting problem was caused by a lack of idle air when hot rather than being directly related to the changed ignition timing?