My holley is pulling vacuum at idle from timed port and I have changed the metering block gasket and still does this. It's a 3310 750 cfm. Anybody know what's going on?

 

One guess would be that your butterflies are open too far and the carb isnt in its idle circuit to begin with?

 

That is what I thought also but I have adjusted the butterflies and it still does this. I can idle it down until it dies and still pulls vacuum.

 

Just because it dies doesn't mean the butterflies are closed enough to block the timed port.

Sounds like your idle circuit is messed up, either adjustment or physically. The gasket may keep the timed port from getting vacuum, but it can't be involved with it having vacuum when it shouldn't.

Take the carb off, turn it over, and look at the butterflies. The timed port shouldn't be uncovered, and the transition slot should be uncovered only about its width. My bet would be you'll find exactly what 88IROC350TPI suggested - butterflies open well beyond that.

 

The short-term cure is to open the secondary throttles up a bit using their throttle stop screw (small allen-head set screw in bottom of base, only visible from underneath carb). Best way I know to get it set right is to take the carb off and observe how far the primary throttles are open; back the primary idle screw off until the primaries are just barely cracked open, i.e. almost to the point where they sit against the bores and the idle screw no longer has any effect; adjust the sec idle screw to where the sec throttles are open the same amoutn the pri ones used to be; put the carb back on, and check the idle speed; keep doing this until you get an idle speed fo around 500 RPM or so with the pri idle set to minimum. Then once you get that, adjust the primary idle screw to get your 800 RPM or whatever.

The long-term cure is to figure out why the primaries have to be so far open to get the idle speed you want in the first place. That carb should not have that problem on a properly tuned car with a reasonable cam and other parts for what the carb is intended for (basically it works well with nearly any streetable cam). The most usual cause is the timing WAY retarded from what the engine wants; usually from using the stock timing "spec" on a modded motor, which is totally inappropriate.

Once you get the idle speed issues worked out, tune the mixture screws for max idle vacuum. Then shut the engine off, count the number of turns out that they are, and set both of them to the average; and re-tune for max vacuum. You should be able to get the 2 screws to within 1/8 turn of each other at optimum idle mixture in just a couple of iterations of this procedure.

So, what cam do you have? what intake? how much idle vacuum? what is your timing: initial, total, and what's the curve?

 

Thanks for the replies. I have taken the carb off and looked at it. The slot is only open enough to look like a perfect square. I'll take it back off tomorrow to look at the secondary side.