Well, if I run my vacuum advance (full), then it "lopes" really bad (I do have a cam though) and it surges in gear so bad that I have to put it in neutral when I stop or it will lope itself/surge until it dies.

if I run my vacuum advance (timed port) then it has a stumble in it just a little above idle until about 1700 to 1800. I still think that it "lopes"/surges too.

If I run no vacuum advance, then I can keep it in gear when I stop and it doesn't lope nearly as much.

Q: What exactly is the vacuum advance for? I know that as it draws more vacuum that it advances it, but do I really need to run it considering it is almost d@mn near unbearable.

What are the advantages of running or not running?

 

OK, if I run it off of a timed port, it has a stumble right at 1500, but everything else is fine. What could I do about this?

 

that "stumble" is actually detenation. your timing is too far advanced. Either you have your initial set too high, or the vacuum canister is giving the engine too much advance(it's probably a little of both.)

From what i see on your website the cam you have isn't too big, you should want your initial timing probably around 10*-18*. whatever it likes, then buy a crane adjustable vacuum advance can(about $22) and limit the amount of vacuum advance until that stumble goes away.

and you want to run vacuum advance, on a street car, i see no reason not to. It will help gas mileage quite a bit.

 

What's the rest of the motor?

The purpose of vac advance is to add advance when both the engine speed and engine vacuum are high, i.e. cruising, to give leaner mixtures more time to burn. It's for gas mileage and driveability. There's no reason NOT to run it on a street-driven car.

Under no circumstances should it add a "stumble". Sounds to me like your carb is adjusted wrong, such that you have the idle speed screw turned in too far, which uncovers the idle transfer slot, and creates the little off-idle transition "stumble".

 

here is my setup.

- '67 327 +.040 over (about 20k on rebuild)
- flattop pistons
- HEI ignition (non-ECC)
- 750 edelbrock (new)
- aluminum intake
- edelbrock aluminum 64cc 2.02/1.60s
- PAW cam 282* advertised (224* @ .500") w/ .465" lift
- Hedmen headers
- Hedmen Y
- Hooker 3" catback


he way my curve is set up, it starts at 1500 and that is when it wants to stumble. If I pull my vacuum advance off, then it doesn't stumble which rulls out the carb. I just don't know why it stumbles when it starts to advance timing, because when it starts to advance it only advances a degree or two and still stumbles regardless. I had my initial timing set at 12*. If I ease into it, then it does it real bad, but if I just mash it, all it does is spin, but it's too quick for me to tell if it stumbles when I mash it.