New problem... wtf?

[Phoenyx]

So been driving the Malibu a bit lately. But it had been using so much gas, you would think it had a 1000 HP big block. Then a week or two ago I happened to run into threetwentyseven and was showing it to him. He did two things. Moved my vacuum line (HEI) from the lower port to the higher port. And he also noticed the choke was out of whack. After that my mileage was WAY better (Thanks a lot threetwentyseven).

But today I decided to check the timing and play with the idle mixture screws a bit. So I unhooked the HEI line, plugged the carb port, set the idle at 800 and put the timing to 12 degrees. Adjusted the mixture scres to get as much vacuum as I can (about 10-12). Then tightened everything back up, re checked the timing. When I put the HEI line back on, the idle went up about 300-400 RPMs (is this normal?). Now the weird thing. I set the idle to about 900 RPMs, but when I put it into gear, it drops to 300-400. Put it into neutral, and now it jumps to 1000.

So I went and rechecked everything, and can't see anything wrong. And I tried plaing with the idle, but it seems to jump around about 200 RPMs.

Anyone have a clue what could be causing this?

 

[DoubleV]

Your idle went up when you hooked your vacuum advance back up because you have it plugged into a manifold vacuum port. This is normal. In fact this is the biggest advantage to running manifold vacuum i.e. more vacuum advance at idle for a stronger idle.

Amongst other things, a big drop in RPM's when you put in gear, can mean maladjusted idle mixture or can be timing related. I would try fattening up the idle a bit and see if that helps. Your advance springs in your distributor could be too light too.

10-12 vacuum at idle is pretty damn low.

 

[GBODYLS3]

holley says you should have the car in gear when you adjust the mixture screws. you might try that.

 

[Phoenyx]

OK so here's an update.

-The idle goes up in either port when hooking the vacuum line back up (and I'm pretty sure it didn't do that before).

-Another weird thing, like I said the timing is at 12 degrees @ 800 RPM (vacuum like unplugged) but it seems to be 'dieseling' or 'running on' when I shut it off.

-I did mess with the mixture screws a bit, so hopefully that's all it is. (kinda got cut off so had to wrap it up quick)

-Yeah the vacuum is kinda low. I'm guessing it's because of the cam?


So here's an example of what happens:

Fire it up and it seems to idle just perfect (900ish). Then put it into gear and the idles drops to 300-400. After a few minutes I can put it into neutral at the idle will be at 1100-1200, but still only about 400 in drive. It almost seems like the idle drops when I'm holing the breaks. Because as i slow to a stop it is idling noticeably high, but the last 4-5 feet before I come to a dead stop it drops down.

Today I will have some more time to go and recheck and readjust everything. Wish me luck. 8)

 

[Longroof79]

Your advance springs in your distributor could be too light too.

I was thinking the same thing. Perhaps you might need the next heavier size advance springs.


Also with a higher stall convertor, I wouldn't think the idle should drop as much when the car is put in gear.

 

[pontiacgp]

did you get the carb off the guy I contacted for you?

 

[khan0165]

using vacuum advance, I believe you are getting an extra 12deg of advance. You have 12 at idle, then however many between your curve (degrees between idle and mechanical advance), then an extra 12 from vacuum

... you could be at 45 to 50 degrees without even knowing.

which explains why you are having dieseling/knocking problems, and your idle rpm is so high

try heavier springs
or try leaving the vacuum advance unhooked and set 18 to 20 deg advance at idle.

 

[Phoenyx]

did you get the carb off the guy I contacted for you?

Not yet, waiting on our tax money.

The weird thing is that it was idling perfect the day before. I tried readjusting the idle screws, but still the same. Was raining so I didn't spend to much time out there today. Gonna mess with it some more tonight if the weather allows.

Thanks for all the help.