Thread: vacuum advance question

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Hey guys, new to the forum and to street rodding. My wife and I had her grandpa's old 1950 Studebaker pick up built into a mild street rod. We put a Chevy 350/290 HP crate engine with a 650 Holley. The guy that built it put on a used Eldebrock intake he had instead of the intake that came with the engine. I've got about 50 miles on the engine.
I was messing around with my timing light today, its digital with a tachometer, anyhow with the vacuum disconnected it runs about 860 rpm when I hook up the vacuum it jumps up to 1200 rpm, is that normal? Like I said I'm new to this, the reason I'm messing with it is it stutters and hesitates when I accelerate and I'm trying to figure out whats going on. A friend of mine set the carb with my vacuum gauge, but I think it idles too fast too. Any help guys? Ideas?
Thanks
Kenny

Yes, that's normal. When you supply vacuum to the can it pulls the advance plate forward / moves the timing.
If the carb was adjusted with a vacuum guage , but, the idle was to fast, then it will need to be re-done with the idle adjusted at a lower speed.

The stumble / stumbling could be as simple as an accelerator pump adjustment. What carb is on it?

Which edelbrock?

If it is the air gap, change to a performer.

Make sure the accel pump has a good seal on the plunger. Set the actuator rod to the hole nearest the end of the arm, that will give the biggest squirt.

Oh, I see it now, 650 Holley with an edelbrock intake. Let me see if I have a sheet on holley accelerator pump adjusting. There's probably 6 vids on youtube to do it as well. Let me look..

Here's 1 of them... https://www.youtube.com/watch?v=k-Nx5HEzvlY

and

Here's another https://www.youtube.com/watch?v=tMKxD_OFuCA

and here's one that helps select the cam https://www.youtube.com/watch?v=k2-RY2JqWek

Please do not take my comments as being argumentative. I destroyed an engine with constant flooding from adjustments on the Holley Avenger I have which is a 650 CFM on the exact same power plant. I have a mild flat tappet cam with a .280 lift at 050. I struggled for a while with whether to go from the mechanical advance to a vacuum advance. There are endless opinions so it comes down to a matter of what you feel best with. Let me list the things I found wrong with my setup and you can do a mental checklist.

1. I found several gaskets in the carburator had been compromised, it had set up for a period and they were dried out rupturring when I put the gas to them.
2. The floats had been in the car for some time and were compromised, I eventually replaced them
3. The float bowl setting was up halfway in the glass window. For my mild setup I needed the fuel set to the bottom of the bowl
4. Because of the above issues fuel was blowing out the air horn, flooding the engine and washing the cylinder walls free of oil
5. The jetting was too large
6. The idle circuit slots were not adjusted correctly and the car was idling off the transition slots resulting in a stumble when accelerating
7. The accelerator pump was not properly adjusted, too much slack between the arm and the pump rod
8. A good test was wether the idle adjust ment screws actually adjusted the AFR or Vaccum
9. I went a while thinking the carburator was the problem, it wasn't completely the problem
10. My MSD ignition curve came in with the initial timing set to 16 degrees and the advance stop and spring setting I had brought me to 36 degrees by 3000 rpm
11. The car was basically starving for timing at lower rpm. you dont have that problem with the vaccum advance if it is setup right. The issue is how much the distributor will advance mechanically
12. With the vacuum advance, it doesn't alter the timenig under WOT (check me out on that)
13. The advance springsets were too light and the weights were bouncing around inconsistently
14. There is a lot more but these are starts. I got a lot of help from Tuning MSD Distributors Call em, they advocate vacuum advance