Hello I have what may be a stupid question but I have no clue what the correct answer is so here it goes…. What type of gasket do you use to mount the carb to the intake (dual plane)? The 4 hole or the open center style? The reason I am asking is because I pulled my carb off and when I pulled it off I noticed the divider on my dual plane had raw fuel collecting on it…I was using an open center gasket and not the 4 hole….I think using the open center gasket leaves a gap between the carb base and the divider because there is no gasket there to seal the base to that part of the manifold. I have been trying to hunt down my overly rich idle for some time and I figured I'd pull of the carb to adjust the secondarys some more to make sure correct amount of my transition slots were exposed. My mixture needles do work, I can have them turned all the way in and have the car almost die and the idle is still way too rich, I am running out of ideas at this point. I'm running a Holley 3310 with a 6.5 PV with stock jetting, GMPP dual plane vortec intake, and XR276 Cam. Thanks for the help!

That gap is nothing to worry about w/ an open gasket. You don't want to use a 4 holer on a dual plane intake, because the gasket will sag over time and hang down obstructing the throttle blades.

Holleys are calibrated to be intentionally over rich out of the box, because it's a lot harder for someone to burn an engine up being over-rich, than over-lean (piston melting time). It's not just the jetting that makes them this way, the non adjustable air bleeds are a major contributor. I'm guessing the car runs fine but smells too rich. I am actually running that exact same cam, but on a 112 centerline, w/ fuel injection. It is a very rich smelling exhaust even playing w/ tuning the EFI. When you start getting big w/ overlap it's going to be hard to get it to smell clean.

Yea the car runs fine but it smells too rich, I come inside after playing with the car and I can smell it in my clothes long after I come in.

Actually I am running the 112 centerline also...I got a good deal and couldn't pass it up.

I assume your XR276 is the hydraulic roller version? If it is flat tappet, there is nothing you can do about the idle richness, the flat tappet will be even dirtier than the roller. Mine is the roller version, and it still leaves the smell on your clothes. Just the way it's going to be unless you have a cat.

Yes it is, I guess it's the nature of the beast. I do plan on putting cats on the car a little ways down the road, so until then I'll live with it. Thanks for the help!

lean out the mixture screws a tad then to clean up the smell.

The idle mixture screws won't affect the fact that the idle air bleeds are still set up to give you a very fat idle mixture. I had a Holley 600 DP on a 327 and it idled stinking rich even w/ the idle screws almost completely seated. Some guys get crazy and start hanging pieces of wire into the bleeds to modify their size.

Ok....I went to put the carb on the car again same story. I adjusted the secondaries and primaries exposing the correct amount of the transition slots. Put the carb on the car and the idle is around 1500 and I can't adjust down.

I did notice one thing though, the primary butterflies each have about an 1/8" hole in them. Are they supposed to have holes in them? Comparing them to my buddies 650 DP his do not have these in either sets of butterflies, so I don't believe they are supposed to be there. Can anyone confirm? Once again the carb is question is a 3310. Thanks again for the help

No those holes were drilled to lean out the mixture. If you're not trying to get an idle above 1000rpm, you can close the secondaries completely typically.

You want the secondaries almost closed. If you let the blades 100% snap shut they will bind. 99.9% closed makes them easier to open

Those holes in the primary blades are a crutch for a high overlap cam.

For a mild set-up, you need blades with no holes.

well yes holley spec for closed is "1/2 turn off completely bottomed out" Sorry I didn't clarify that.

Would you guys recommend soldering up the holes in the primary butterflies since my cam doesn't have a real aggressive idle? Or should I be just fine with what I have? Thanks again.

Update, I switched out the primary butterflys for ones that are undrilled. The original set were drilled horrible by the previous owner and doing so also warped the butterflys. After installing the new ones and exposing the correct amount of the transition slots I bolted the carb on the car, adjusted the idle mixture and viola the rich idle is gone and it idles much better now. Thanks for help!