Today while driving home i started hearing a rattle, so when I got home i got to tinkering around, and I ended up finding the rattle, by holding the break and bringing up the rpms a little by pre-loading the engine. Turns our the rattle was loose exhaust hanger. But in the process of finding this, I encountered this:

Car is a 72 Cutlass, stock 350, th350 trans. edelbrock 1405 carb with electric choke.

In the process of doing so, I noticed, not matter how far I come down on the gas, the car never tried really hard to lurch forward. And this was on dirt. Even almost WOT it just shakes and seems to have no power. Almost like some of the newer cars that don't let you apply the breaks and the gas at the same time. If I let off quick, the car dies. Everytime. If I slowly ramp down, it stays running. No visible black smoke that I could see. This is when it was fully warmed up after the drive home.

Not the car runs okay on the road. It's not perfect, and I feel like the car is "slow" to jump off the line. On the other hand, I may be expecting a lot, afterall it is a 72 motor. Is this leaning toward some massive vacuum leak in the booster? I don't even know what to start looking for. If I remember right, when I had my 1406 carb on the car, I had similar issues, but again, only when I was too heavy on the gas going up a small garage ramp etc, and when I let off too quick.

This may be related, may not be, but I've also recently noticed the car seems to run great and have better response right when you start it. after two or three minutes it seems to become less responsive. This is all before the car comes up to full operating temp. The responsiveness goes away so to speak before I'm up to 160* on the temp gauge.

 

It is very easy to check for a leak at the booster. Simply disconnect the vacuum hose from the check valve in the booster and plug the hose. NOTE that this means you will NOT have power brakes, so be careful if driving this way.

If the engine runs better now, you've found the leak. If it's the same, the booster isn't the problem.

 

You may be running lean if it runs better with the choke on. What is your timing set at? How come so many lousy running Olds on here always have an Edelbrock carb?

 

Fan hitting shroud at the bottom?

 

With an Edelbrock, I usually find a lean fuel mixture to be a float height issue. Adjust the float height and drop. They NEVER come correct when new and need to be adjusted for proper operation, despite what the instructions say.
It does sound like you are running lean, so also verify the vac unit on your distributor is not leaking along with the brake booster.

 

Thanks. I plugged the line from the intake to the booster, no real change. :/.

Kind of a bummer, the booster/MC looks a bit crappy, so this would have been "good" if it was the problem.



I took a plug out, after 5 seconds of "preloading" it and the plug looks pretty black.

IMG_4255_zpsx8upyuay.jpg


Did you post in the wrong thread?

 

I actually checked the float height and drop 2 weeks ago. I adjusted them, and they are within a 1/32 of the spec. It was as close as I could.


I guess, the ultimate problem, the car running rich at idle, or if I pre-load it(like as if I was going to do a break stand burnout), isn't a big deal, but fixing it would probably make the car overall run better. Like if I rev the car quick in drive, and let off, like to torque the motor, it'll rev, and then stall as the rpms fall.

 

I dont think so you heard a rattle stepping on the gas, thats a relatively vague description that covers a lot of ground I was just trying to help you cover your bases. your description fits well w the fan starting to hit the shroud? I didnt realise you were hearing engine knock or ping if thats the case its might be timing related, did you ever change the original chain ?

 

Looks like your mixture is so rich that you're hearing solid fuel rattling in the cylinders. That starts around 10.5:1 AFR. Lean out the idle mixture screws for starters!!!
Also Ohm out your plug wires - you need them to be less than 5000 Ohms each or you'll start having this type of issue.
Then buy the jet kit for your Edelbrock and start experimenting! This took several bad things to happen to get to this stage.

 

I must have been too wordy in my original description. The rattling had nothing to do with the drivetrain. It was actually one of the exhuast hangers, one of the bolts was a little loose and it was vibrating. I noticed this problem while pre-loading the engine while troubleshooting trying to find the rattle.

Again, I must have not been clear in my OP.

I'll try leaning out the idle mixture anyway, i had it 1/2 turn out more than baseline because I was trying to correct a popping at WOT. It seemed to help with that.

 

I'd like to see what your plugs look like after a run at speed, when it pops. At that point cut the ignition while at speed and pull a plug. Your descriptions are lacking descriptors, so yes we have to make assumptions.

 

Okay. I'll have to try and figure out how to do that. There really isn't a safe place near me to wind out first and second and then shut the car off and pull over safety. I'll report back when I've done this.

 

Someone asked about my timing, and I had an hour, so I went out and measured it.

Base timing at ~700rpms is 18* with the vacuum advance disconnected. It's 20* with the advance connected. Rpms based off craftsman dialback timing light.

Vacuum Advance Disconnected, a 2250/2300 rpms AT 30*. 34* at 2800, 36* at 3100 38* at 3500, 40/41* at 4000rpm


With vacuum advance connected I'm at 49* at 2200, 55* at 3000, 58* at 3500 and 58* at 4000.

So this is sort of unrelated, or maybe not, but It looks like I should have my timing come in a bit sooner?

I did replace the factory springs with those out of the mr. gasket kit, I used one of the kits light, and one medium spring per advice here. Maybe I should use both light springs?

These connected vacuum advance number are connected to ported vacuum. As my 3-2 and 2-1 downshifts are much improved on ported as opposed to manifold. For whatever reason?!

 

Test again without the vac unit hooked up. You're convoluting the numbers by adding in vacuum, which is NOT part of the all-in timing measurement. It looks good to me, although the vac unit may not be the best one for the job. I'd speculate that 40-45 degrees of mechanical advance plus up to 20 of vac is tolerable in a 350. Higher compression will need less overall mechanical advance.

 

I tried to seperate them, both rpms with and without vacuum connected, so I could give everyone the big picture.

The vacuum canister does not appear to be adjustable. Should I be starting to look for one that is? Or should I look into one of the cheap TSP distributors, that come with an adjustable can already? Like $70 on ebay.

 

No, you need to fix your transmission kickdown problems and do more basic tuning first.

 

Your transmission vacuum modulator needs to be connected to manifold vacuum or it will not shift correctly. If its shifting gears when connected to ported you have something wrong, probably a bad modulator.

Your timing numbers are confusing, please note your timing settings at the same rpms accurately for both the with and without vacuum advance readings all the way until it stops advancing.

 

Okay. I'll go back and re-read the thread on adjusting the kickdown cable.

I didn't change the transmission modulator. My downshifts are noticeably improved when I changed my vacuum advance canister on the distributor from the manifold port to the ported port.

How does one test the th350 vacuum canister?


And okay, you want timing numbers for both vacuum connected, and disconnected at the same rpms. Got it.

 

Pull and hold the vacuum on the TH350 modulator and make sure it can hold vacuum indefinitely - the same way you test the distributor vac module. A Mity-Vac hand pump works great so you can watch the gauge. I think Autozone carries them now.