70newport

So I have a new holley street avenger 770 that I just put on my 383. The port on the side of my metering block that should be ported vacuum is giving full manifold vacuum. I backed the idle speed screw all the way out so I know the throttle blades aren't being held open from that..... Holley tech support says there could be a vacuum leak or the throttle blades are stuck open. How can I test for either?........

Thanks,

Gary

TVLynn

Re check your vacuum ports ??

RacerHog

That would be the right port.... You have the throttle plate open to wide... Or the carb has an internal problem, and that is very rare....But it happens...

Mr.4spd

I'm wondering if the throttle cable itself is holding the blades open, an adjustment issue. Try disconnecting the cable.

moe7404

if it is a 2 bbl to 4bbl conversion you might have other aliment issues. like the cable bracket. this conversion is common and missaliment is the way more common than it should.

TVLynn

Check the vacuum,, fitting on the metering block is for dist.. Often missed -- Also check the notes for Chrysler applications,

70newport

so I completely disconnected the throttle cable and it still has full vacuum.

I swapped the carb out for another of the exact same carb ( holley 670 street avenger) but new again and it is presenting the same issue.

I put on new carb gaskets above and below the 1" spacer just in case.

I backed the idle screw all the way out and still have the same issue and the car did not stall out.

Could this be caused by a intake manifold leak?

Thanks again everyone.

Mr.4spd

It's bizarre to me that it idles at all with the idle screw backed all the way off. There's got to be a leak somewhere, I've heard of using an unlit propane torch to find leaks (when the gas hits the leak you'll hear the rpms increase) but I've never tried it. Could be vacuum lines too. I'm not sure how a leak could cause your problem though.

TVLynn

i BELIEVE THERE ARE 3 VACUUM PORTS.. Only one ported vacuum source... Just do a search on deamon 770 and a set of instructions will come up...

RacerHog

What intake manifold do you have on the 383?

70newport

edelbrock performer intake manifold. I have the brake booster vacuum going directly to the intake manifold, pcv valve going to the back of the carb and nothing going to the front of the carb other than the metering block that currently has a vacuum guage on it. the other 2 ports are blocked off.

RacerHog

Here is my take..... The performer intake is a spread bore... If you are running the square flange carb and spacer? then you have left a ever so slight air gap at the spacer gasket and the intake manifold.... Give that a check....

70newport

I can't find a leak around there. I'm testing by spraying carb cleaner ..... If there is another way to test I'm open to suggestions.
I think my intake is square bore. http://www.edelbrock.com/automotive/...ormer-bb.shtml that's the one I have.... Let me know if I need something else in between.

RacerHog

Thats a spread bore intake....
What spacer did you use?


The one to your right will have a leak at the seconders on the choke thermostat side or passenger side.

If you can see the black line between the spacer and the intake. That is where the leak will be...

70newport

I currently have a normal square bore spacer but an not see any gap at all. I will get an adapter and try that in the next few days

RacerHog

If you say its good... I believe you... Just throwing out what has bit me in the past.....
The one on the left is the spread bore (intake) to square (Carb) Flange adapter. It will fix most 4150 or 4160 carb fitting issues.
Good luck.. Keep us posted..

70newport

So i tried a spread bore to square bore adapter plate and no change at all.

Could an intake manifold leak cause this at all ? If so is it possible that spraying carb cleaner around the intake would not change the idle at all. Im so confused with all of this.........

Mr.4spd

I'm confused too, and I'm not sure how a vacuum leak could cause the ported vacuum nipple to pick up manifold vacuum. I've drilled my own throttle body for ported spark hookup and the two don't cross paths anywhere. Are you having a drivability issue? The ported nipple "sees" trace amounts of vacuum while idling, this is why we disconnect the hose from the vacuum advance when setting initial timing. Is this perhaps what you're experiencing?

RacerHog

Ok... Don't get discouraged just yet....

Ok Lets got back a little further, from the beginning....
Did the car run good before you did the carb and intake swap?

If so... The intake could be leaking.... But I'm thinking you should plug all the ports so you can verify or isolate the leak. But is the carb a 770 or a 670?

Sangetsu

It is common for the port vacuum to have problems, in my experience I have seldom come across carbs where it works normally. Fortunately, it isn't particulalarly necessary, especially if you run an aftermarket distributor.

You need to make sure your carb is more or less set up properly, and to so so, you need a vacuum gauge and a timing light.

First, set the timing with the vacuum line to the distributer unplugged, and the vacuum port blocked.

Next, attach your vacuum gauge, and adjust the mixture screws to the get the highest vacuum reading, then adjust your idle screw until the engine is idling at the normal RPM. Then reconnect your distributor vacuum line. You can now check the port vacuum again.

If there is no change in engine RPM when you are adjusting the mixture screws, the carb will need a rebuild. The metering block gaskets are the Achille's Heel of the Holley carburetor, they can swell or distort enough to restrict the metering flow.

440roadrunner

I don't think anyone has addressed this!!!!

What are you running for a cam? Initial timing?

It is COMMON for an engine with a hot cam and NOT ENOUGH initial timing to "want" the throttle blades to be "too far" open

Sometimes, you have to adjust the REAR throttles open a bit

Mr.4spd

Nah, we've touched on this already. He's got the idle screw all the way out and the throttle cable disconnected.

TVLynn

The secondary throttle set screw miss adjusted ???? causing high idle !!!

70newport

sorry i have been away for a few days everyone.

So it is a 670 car on the car. My idle mixture was set using a vacuum guage and my initial timing is set at about 13* with no vacuum advance hooked up.

It is an aftermarket distributor but a factory replacement style with the points removed and "electronic ignition" replacement inside.

The car is actually running pretty good other then I have no ported vacuum.

The cam is a comp cams 268/268, 454/454 hydraulic flat tappett, hydraulic lifters, factory push rods and rocker arms with edelbrock 84cc e street heads and factory bottom end.

This intake was on the car before I did the engine build up with an old style 4150 carb and the car actually ran good.

Im almost to the point of giving up and just running with no vacuum advance........