Help with new Holley 3310

Hi all-
Looking for some of you experts to help me out here.
My '68 GTX, as some may recall, was bought last year with a "mystery" motor in it - I simply have no information whatsoever on the engine.

I was told by the seller that it was a fresh rebuild by a now-deceased Dodge dealer lifetime mechanic and that he wanted to build a "beast".

Here's a video of it running:
http://www.youtube.com/watch?v=NSbOtCBqIZU&feature=g-upl&context=G2abe6b6AUAAAAAAADAA
There's another video in my youtube account of it as well.

Now to my problem:
I put a brand new Holley 3310 on it (750 vac. sec.).
Trivia: the one Holley developed for the '69 Road Runner originally.
I've used this carb on several 440s over the decades and it's always been a right-out-of-the-box sort of thing; just set mix and throttle and go.

Not this time. This rascal loads up just idling, despite my dialing in for best vacuum and rpm, so much so that it runs you out of the garage.
If you look closely in the video, from what I can tell it has around 6 psi vacuum @ idle.
The rest of the tuneup is fresh and it has the Mopar electronic ignition on it.
I have replaced the fuel tank, lines, pump and fuel filter as a course of going over the whole car.

Questions:
1. Am I right to suspect the power valve is open at idle, due to the relatively low vacuum? If so, what power valve should I swap in?
2. Can anyone take a wild-arsed guess as to what cam is in this thing by sound alone?

I wish I could tell you anything more about the engine, but I got nothing.
P.S. Yes, I'm aware that's an old small block radiator in it - I'm on the lookout for the proper one.

Thanks in advance!

Sounds like my 340. I have a 286 cam and 8in vac. Tried tuning my 3310 just didn't like it. Much easier with a 750DP and 4 corner idle. I'd say you have a .509 in that thing. Just my opinion of course!

Belvedere said:

Sounds like my 340. I have a 286 cam and 8in vac. Tried tuning my 3310 just didn't like it. Much easier with a 750DP and 4 corner idle. I'd say you have a .509 in that thing. Just my opinion of course!

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Thanks for replying.
For some reason, I was thinking it might be even more than that, but I guess the 3" duals all the way back barking at me makes it sound meaner than it is?

Anyone else have any help, especially on the power valve/Holley thing?

I had an engine backfire with a 3310 and it blew the power valve.

Symptoms were that it would run way rich and not idle at all but at full song it was fine.

I love that carb and run it on all my street 440's and my 360 in the truck.

Dodge 330 said:

I had an engine backfire with a 3310 and it blew the power valve.

Symptoms were that it would run way rich and not idle at all but at full song it was fine.

I love that carb and run it on all my street 440's and my 360 in the truck.

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Yep, the older ones were susceptible to that, but Holley has been using a "backfire-proof" power valve for some years now that supposedly prevents that now.

If someone would chime in here with which power valve I should be using, I'll find out either way when I go to replace it.

the power valve that holley puts in them out of the box is a 6.5" vac, with a cam as large as yours sounds you may want to run with a 2.5. it has been my experience that they do not like to idle with the 6.5"s you can get the 2.5 at most good speed shops. or maybe summit, jegs ect. best of luck!

arizona satellite said:

the power valve that holley puts in them out of the box is a 6.5" vac, with a cam as large as yours sounds you may want to run with a 2.5. it has been my experience that they do not like to idle with the 6.5"s you can get the 2.5 at most good speed shops. or maybe summit, jegs ect. best of luck!

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Thanks much!
That's exactly what I want to know.

2.5 is probably the right answer but just to make sure check your idle vac in gear if you have an auto tranny.

Is your initial timing correct? It's my experience with big cams and not enough compression to back them up the timing wants to be off scale (15+ deg) at idle. It's almost like you can't give it enough initial.

Meep-Meep said:

2.5 is probably the right answer but just to make sure check your idle vac in gear if you have an auto tranny.

Is your initial timing correct? It's my experience with big cams and not enough compression to back them up the timing wants to be off scale (15+ deg) at idle. It's almost like you can't give it enough initial.

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Yeah, I noticed that also - the more initial I gave it, the more it liked it.
Dunno if this one has "enough compression" or not (mystery motor, remember) but it sure seems like it, though - standing behind the car, the exhaust pulses are very forceful, like it's trying to blow you over.

It's a 4 speed btw.
Thanks!