Vacuum Advance problem?

[Redog]

OK I've been pulling my hair out about this for a few months now and I'm no closer than I was back then.

I think I narrowed this down to Vacuum Advance on the dis, but I need some calarifaction. I read that if the advacne isn't working right, the RPMs will run a bit high.

Here's the problem:

I switched to HEI from the points on my Delta project. The RPM's were right on the money with the 3.42's in the rear end. (eg 2500 RPM @ 55 miles per hour and 3000 RPM's @ 70 MPH)

After the HEi was put in, the RPM's are off by about 15 miles per hour, the car is revving at 3000 RPMs when only going 55, and 3500 RPMs at 70. I think the vacuum advance thingy on the dis is messed up, and I'm thinking of replaceing it. The vacuum advance thing was replaced on the points ign before dropping the motor into the car.

Is this the problem? will this fix the problem I'm having?

[Olds64]

You can get an adjustable vacuum advance modulator for your distributor. This would be a good investment for your car. Then you can play with your total vacuum advance. You can also buy different springs for your mechanical advance so it kicks in at different rpms.

I would suggest taking the mechanical advance springs and the vacuum advance module off of your points distributor and putting them on your new distributor. They should fit. Then you would be at a zero point and you can tune from there.

[Jerry Weitz]

Originally Posted by Redog

OK I've been pulling my hair out about this for a few months now and I'm no closer than I was back then.

I think I narrowed this down to Vacuum Advance on the dis, but I need some calarifaction. I read that if the advacne isn't working right, the RPMs will run a bit high.

Here's the problem:

I switched to HEI from the points on my Delta project. The RPM's were right on the money with the 3.42's in the rear end. (eg 2500 RPM @ 55 miles per hour and 3000 RPM's @ 70 MPH)

After the HEi was put in, the RPM's are off by about 15 miles per hour, the car is revving at 3000 RPMs when only going 55, and 3500 RPMs at 70. I think the vacuum advance thingy on the dis is messed up, and I'm thinking of replaceing it. The vacuum advance thing was replaced on the points ign before dropping the motor into the car.

Is this the problem? will this fix the problem I'm having?

You can check you timing with and without the vacuum advance for one thing. Also you might use another tach to see if your in car tach is the same. Sounds like you might have a false tachometer reading after switching to HEI

[88 coupe]

Originally Posted by Redog

........I read that if the advance isn't working right, the RPMs will run a bit high .........

Advance (mechanical or vacuum) has nothing to do with the signal to the tach.

Assuming clean/tight power and ground connections:
The pulses from the points would have been under 12V and from the HEI, over 12V. If that makes a difference in the readings, I would suspect a faulty tach.

Norm

[kevinkpk]

I had to replace my distributor due to the advance worn out, I'd have to reset it after a couple weeks of driving as it would be to far advanced, and hard to start, try this for some good reading..

Vacuum Advance Tech - Setting the Timing Curve and Tuning - High Performance P

[Redog]

I know the tach is good. I can hear the car revving 500 RPM's higher.

At the track the car used to cross the finsih line at 4100 RPM's now it's at 4600

[Jim's rare 80]

Just a thought. Were did you hook your line fron the dist. advance to?

[texasred]

"True" RPM (actual engine revolutions per minute) at any given miles per hour is a function of differential gearing, tire size, traction and transmission slippage (auto or clutch). Don't confuse a measurement of revolutions with actual revolutions.

The signal from the tach, wiring, or tach may be going bad or need to be recal'ed, but you didn't change the "true" RPM with a different distributor.

C.J.

[Redog]

Originally Posted by Jim's rare 80

Just a thought. Were did you hook your line fron the dist. advance to?

The carb, could this be it?

[Jim's rare 80]

The vac. line from the dist. should go to a "TVS", thermal vacuum switch, then to ported vacuum on the carb. The tvs just stops vacuum to the dist. when cold. If you are going straight to the carb, then make sure you are plugged into ported vacuum. These are the ones coming out of the bowl area of the carb. The ones coming out of the bottom throttle plate are manifold vacuum. Check to see for sure.
Hope this helps.

[Redog]

^^ OK I think I understand a little bit better now.

I have 2 vacuum ports on the front of the carb. (It's an Edelbrock model number 1806)

(Looking at the carb head on) The port on the left (electric choke plug side) is a "timed Vacuum port" and has 3/16" vacuum off idle, I have the tranny pluged in here, and on the right side I have the vacuum advance pluged in there and it is a "manifold vacuum port" and 3/16" vacuum at idle.

So I guess I just have to switch them, is this right?

[67olds]

Redog,

Dealing with similar issue now on Chevy small block in 67 cutlass (wish it was an Olds 330). If your timing is already set using manifold vacuum connection, expect your timing to change significantly after switching the vac line to timed port. The (hopefully) 16-18" of idle vacuum present on the manifold port won't be there on the timed port.

Obviously, its no big deal, but expect to re-adjust timing. Going to switch mine this coming weekend. Tranny should be happy on manifold vac port.

Good luck,
jeff
67 cutlass supreme convertible

[Redog]

IDK.

My buddy pulled the advance off at the track and the RPM hit the same exact point.

I'll try it though

[Jim's rare 80]

Yes. Put the tranny line to manifold port, then before you connect the vac line up, plug it, and set your timing with vac line to the dist. plugged., then re-connect it to the timed side. let us know how it goes.

[Redog]

^^ Will do, but it will still be 2 weeks before I can drive a car again.

Broke my right foot 3 weeks ago today

[Jim's rare 80]

WHAT??? Tuck your right foot back, and drive with the left. What a new experience that woud be.

[J-(Chicago)]

Redog......
I believe Oldsmobile started putting automatic transmissions in their cars for the sole purpose of giving our 1 legged war veterans the joys of driving again

[Redog]

Originally Posted by Jim's rare 80

WHAT??? Tuck your right foot back, and drive with the left. What a new experience that woud be.

HA HA HA My wife told me to do the same thing.

Could probably do it with the Delta, but no way with the Alero. I can't even get my boot between the brake pedal and the center consol LOL

[88 coupe]

Originally Posted by kevinkpk

........Vacuum Advance Tech - Setting the Timing Curve and Tuning - High Performance ........

Could be an interesting discussion if one wanted to start a new thread.

Norm

[88 coupe]

Originally Posted by Jim's rare 80

........ The tvs just stops vacuum to the dist. when cold ........

Just?

Or, in addition to, the switch to manifold vacuum if/when the engine overheats?

Does it have a second valve I am not aware of?

Norm

[Redog]

I switcthe lines today but didn't drive it too much. I did manage to put the car sideways in my parking lot. It was fun, until it started to get away from me.

Anyway, The idle has dropped from 800 to 600 while stopped in gear and from 900 to 750 while in park. I'm going to bump up the idle a bit over the weekend, but it seems to be running a bit better (except for the bit of a rough idle and being 600 to 550 while stopped)

I still don't have a speedo, but I'm going to try using the wife's GPS and cruise down the road, It reads about 3 miles per hour too fast, but that's cool.

I did notice my tranny slipped a bit after the switch. It has a pretty bad leak and I put in a pint on fliud today, I'm thinking it was just a bit low (looked low on the stick) Plus is wasn't much above 30* here today. My Alero's tranny slips if the car isn't fully warmed up when it's under 20* The Delta's tranny didn't slip after the car was warmed up and it was spinning the wheels with no problems

[88 coupe]

Originally Posted by Redog

........ I did notice my tranny ........

I still don't do trannys. http://www.urbandictionary.com/define.php?term=tranny

Originally Posted by Redog

........ slipped a bit after the switch ........

Following is from post #8.

Originally Posted by texasred

........ RPM ........ at any given miles per hour is a function of differential gearing, tire size, traction and transmission slippage ........

A slipping trans would explain your RPM/speed discrepancy.

Norm

[J-(Chicago)]

Redog do you have that 200c metric behind your 350? If so, your problem is right there. I thought you put a 400 in though...

[88 coupe]

Although highly unlikely, at your power level, a "ballooned" converter is another possibility.

Norm