Six8 x 43

Hi Guys,

Once upon a time I had an account and was a small contributor here, but after 5 years and a lot of life happening the email associated with it, as well as username/password are lost to the ether. So I made another one.

Here's my issue: the car idles like crap and part-throttle response is a joke, and it's gag-a-maggot rich at idle and part-throttle/cruise. My fuel economy is pretty much abysmal, too. No nozzle drip (first thing I checked) and holds a steady 11ish" vacuum at idle. Runs like a top at WFO.

Basic setup:

- 1969 Cutlass Supreme
- 350 block, J heads, Edelbrock Performer manifold
- Cam...God only knows. The guy I bought the car from 10 years ago said it was "one over stock"
- Coil-in-cal HEI unit from who knows what. at least it turns the right way for an Olds
- '68 Qjet, freshly rebuilt after fuel started flying out of the acl. pump hole. Thank you, Ethanol!

The original 350 block had been rebuilt with the above components by the guy I bought the car from. It only had 8k miles on it at the time and ran well, so I never pulled it apart to find out what all had been truly done to it.

After more or less ruling out the carb and or a vacuum leak as the culprit I turned my attention to the distributor. After tearing into it I found: 361 center plate w/ 139 weights, stock springs. Should be about 24* mechanical advance with that combo (thank you Google-fu). Vacuum advance unit is a factory one stamped XXX 30, which should mean 30* max vacuum advance. In other words, we're already at 54* total timing with 0* initial!!! I know for a fact the car has 12* initial because I set that myself when I got the car, and double checked it with my timing light and vac advance disconnected this morning. So I'm at 66* advance with everything, and, theoretically, it should be 3-rocks-in-a-can level detonation...but it doesn't detonate.

I also checked mechanical advance with the vacuum adv disconnected and hose plugged with my timing light, and it's roughly 23* all in around 4,500 RPMs (stock springs). It also didn't smell nearly as rich when the vac adv wasn't hooked up. When I plugged the vacuum advance back in it immediately started smelling rich and... got wonky. My idle timing bounces between 2* ATDC and 12* BTDC with vac adv connected. Bring the RPMs up a bit and it stabilizes (which may be from the mechanical kicking in), but I'm not getting anywhere near 15* additional timing from the vacuum advance, let alone the 30* it should be giving me. I should also mention I'm using manifold vacuum, not ported.

Thoughts? I'm assuming my vac adv can is shot, but why is it retarding the timing at idle? I need a sanity check here. Thanks, Guys.

joe_padavano

Wow, combining the benefits of a really low compression ratio with the only BBO heads that probably flow worse than SBO heads. Can't say that this is a great place to be starting from.

Octania

head choice aside for now...

You know how to test if a vacuum canister is leaky, right? holds suction....

I suggest getting an adjustable vacuum can and setting it for minimal travel, 10-11 degrees.

That was part of my 403's conversion to pre-computer HEI
It had symptoms similar to yours at first, though I have more like 9.7:1 compresson and comp cams cam for high compression engines.

It was hard to get it to idle right, initially had ridiculously rich burn your eyes exhaust. I had the write up with photos on line but a crash at ROP lost all that and I am not willing to go get all the photobucket links and re-write it again, for fear it might disappear again.

I did also run thru the carb according to the two famous common QJet books, and all that. Pretty sure the timing curve adjustments and using manifold vacuum made the most best difference.

joe_padavano

Lesson-learned for lengthy writeups:

Write the material in MS Word first, save locally, THEN copy paste to a forum.

oldcutlass

Welcome back. First off I would disconnect and plug the vacuum advance line. Then setup your timing for 34-36 deg btdc at 2800 rpm. Any advance after that needs to be limited. Then advance the rpm to ensure it does not creep any higher to 4500. Lock the distributor down and note your initial for future reference. Then set your carb a/f mixture screws to what the engine likes at the lowest stable idle speed you can get. Your engine will like the initial somewhere between 18-21. Hopefully your vacuum will come back up. After that I would concentrate on getting the vacuum advance setup, no higher than 50.

Six8 x 43

Thanks for the replies, guys. I've got a crane adjustable vacuum advance kit w/ different springs for the mechanical advance on the way - hoping it will be here tomorrow so I can play around this weekend. In the meantime I switched over to ported vacuum for the Vacuum advance, and it now holds steady at idle instead of bouncing over. It's a little better, but I'll need to tweak the curve and amount of advance before it'll really be dialed in.

As for the J heads... They came on the car. I knew I was in for some surprises when I got the above response from the previous owner about the cam that was put in it. I do have a set of Cs that have been fully worked over (port/polish, big valves, hardened seats, etc) that are slated for a 455 I'm hoping to get finished up and installed over the coming winter, and it's crossed my mind to swap them out with the Js in the meantime...

I'll post up sometime this weekend how the crane kit worked out.

Six8 x 43

Thanks for the replies, guys. The Crane kit came in over the weekend, and I finally had some time to install and tweak it last night. Here's where I ended up:

Initial Timing: 13* btdc
Mechanical: 24* btdc, all in at 2700 RPM (blue/blue springs)
Vacuum adv.: 15* btdc, all in at 13" Hg
Idle Manifold Vac.: 15", rock steady
Idle RPM: 750
RPM in gear: 600 w/ no drama whatsoever

My exhaust has gone from burning your nostrils/eyes, to regular 'ol "muscle car exhaust" smelling. The only minor tweaks that needed to be made after the changes were to the secondary air valve opening rate (was getting a short-lived bog off idle when I stabbed the throttle), and the idle mixture screws (they were about 1/4 turn too lean afterwards). Other than that, it's almost like a new car.

oldcutlass

I personally like a bit more initial with an aftermarket cam, but that's up to you. I also try to keep my total timing with vacuum advance below 50. Sounds like your getting close.