Question about timing?

[mjr45]

Walter, the dizzy is a 79 it appears to be in fairly good shape and it does have the vacuum advance which I disconnected to check timing, it "appears" to work in that with some suction the breaker plate will move.

[Zed Head]

NOT, took it out for short spin and sputtered and bucked anywhere above 3500 RPM, came back, re-adjusted the timing to 0°, took it out ran great with lost of zip right up to 4500 RPM and then the same thing.

Your timing changes are probably masking or confusing the real problem. Seems more like an air/fuel ratio issue. Fuel supply or AFM issues. Considering all, I would hook up a fuel pressure gauge, zip-tie it to where you can see it and go for a drive. Verify that you have 36 psi or greater when the problem happens.

If you want to check your mechanical and vacuum advances, just for peace of mind, hook up your timing light, set timing to zero (you'll have to adjust idle speed to keep it running) then disconnect the vacuum advance hose from the distributor. Rev the engine up until the mark stops moving. It should go to just about 20, the last mark, or ~22 degrees, depending on distributor weights. Then, at a low idle speed, connect the vacuum advance hose to an intake port that has full-time vacuum. The AC bottle port is a good one, although it's small so you'll need an adapter (tape works). Timing will jump to full vacuum advance. You might have to drop idle speed again to make sure you have no mechanical advance.

It's a little bit tedious, with lots of connecting and disconnecting and idle speed adjustments, but you'll know exactly what the distributor is doing while you're driving.

[mjr45]

Zed, I have a fuel pressure gauge up in the engine bay, so I'll get some more fuel line tomorrow and run it up to the wipers and see what is happening as I drive, good idea from you since I'm beginning to suspect something in A/F ratio. The AFM was calibrated per the Atlantic Z site. Yesterday when I had the timing set at 0° I got 13" and at 10° 14" of vacuum which is OK for 9000' (at least as far as I know) and the needle was steady, so that leads me to suspect that at 10° and lots of stumbling @ 3500 RPM and the tach bouncing all over the place that the mixture is rich and the fuel pump is not able to keep up, @ 0 ° it does it at 4-4500 RPM, so maybe the mixture is leaner at that setting allowing the pump to keep up at higher RPM, maybe, I don't know, I'm confused at this point.

I will try your work on the dizzy vacuum advance first, just to see and then hook up the fuel pressure gauge after I know all is right with the dizzy. Just as an FYI, the pump end of fuel delivery hasn't been touched, I know I should have done this in the "refresh" but somehow didn't. Thanks for the help.

Mike

Edited March 23, 2014 by mjr45