70sgeek

re: 17057253 carb


I installed a newly built Qjet tuned to my engine specs today and the rear base at bottom center has a threaded open vacuum port which is pulling strong vacuum when open with the engine on, but immediately causes the engine to choke off and shut down when I try to connect anything to it - I added a fitting to it and tried plugging my brake booster into it, then the pcv, then just capping it off completely - in each case, car simply wouldn't start or if it did, immediately shut down when foot came off the gas.


But if I leave it open, engine runs beautifully, even as the uncapped port is sucking vacuum. Is this port supposed to be left open like that?

olds 307 and 403

The threaded bottom port is always hooked to the brake booster. Does the booster work properly with manifold vacuum attached? I had a 76 Cutlass with a 350 Qjet, that port was not there and the booster was hooked up to a fitting on the manifold.

oldcutlass

Have you tried increasing your curb idle setting and then readjusting your a/f screws once that port is plugged or hooked to your power booster?

70sgeek

Brake booster is plugged into manifold fitting and works properly off that.


So far I've only had a chance to run it as originally set out of the box - have not touched anything but the idle screw, in attempt to lower the running idle - currently the lowest it goes before throttle arm bottoms out is 1000 and 800rpm respectively in Park and Drive.


With leaving the rear port open (uncapped), engine runs perfectly at idle or over the road - no stumble, no audible vacuum leak sounds, even idle, etc. Gauge idle vacuum looks to be around 17-18 as well out of the box. But I know the throttle arm shouldn't be sitting completely bottomed out.


I guess I need to try turning the idle up and cap the port off to see if I can then lower it back to a normal level. I'm thus far assuming no change to the engine timing should be necessary but I haven't yet had time to check it. In my road test tonight, no change in the engine's manners from before, but for a noticeable acceleration improvement in line with the modifications which were performed.


I last had the timing set at right around 17 degrees initial and approx. 34 degrees all in, running the Pertronix Flamethrower electronic ignition.

Fun71

With that port uncapped you have a huge vacuum leak, so you need to cap it and adjust the idle to compensate.

oldcutlass

This will also cause your idle to be high. Plug the port, reset your idle, and adjust your a/f mixture.

70sgeek

Agreed - should hopefully be a fairly simple Sunday project

olds 307 and 403

Who built your carb?

70sgeek

Dialed in the idle with rear port capped. Basically rendered the a/c solenoid unit useless though, because the throttle arm sits just far enough ahead of it to miss the fully extended solenoid arm. Idle settings are now 800 and 650 in park and drive respectively.


Ken from Everyday Performance in Connecticut built the carb - Well done in my opinion, I gave him my specs and he pre-set it just about right on out of the box. 17-18 lbs vacuum, decent idle and reasonably improved acceleration grunt off idle and above.


Will be road tripping to the beach today so hopefully all should be sorted out by end of day at latest

olds 307 and 403

Ken did mine as well, very happy with the price and the job done.

oldcutlass

Glad you got it lined out.

shiftbyear

Something doesn't seem right, if you have the idle speed screw cranked in where the a/c solenoid won't contact the linkage, something is wrong to me. But if it's running good, maybe just leave it. I've heard good things about Everyday Performance, but a few check you can look at are: 1. is fuel dripping from primary boosters at idle. 2. when you turn the carb upside down do the throttle plates look like the attached picture. If your carb has either of these issues even though it's running ok, I'd give Ken a call. Good luck with your Olds.