Thread: Any Holley experts out there.

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Hello all. Jst want to thank you in advance for any input you may have as everyone on here is so helpful when I have a question.

Anyway, here it is.The Car.
69 Camaro
355 sb
64 cc Aluminum head
flat tops.about 10:1
Comp Cam #12-225-4
.555 lift and 262 duration @ .050
lobe sep 110
cenetr line 106
roller rockers
Msd ignition
Dual plane intake w/ 1 inch spacer
Holley 750 dp hp series
turbo 350 w/2600 stall
3.73 rear using 275/50/15 tires M/T street slicks

Car runs great. Get in, pump the gas 2-3 times starts perfect and runs like hell.
No stumbles, boggs, missing, nothing. BUT it is running too rich and the gas mileage is about 5mpg on the street which is TOO poor.
I don't drive it much and to honest really haven't done much in the way of adjusting anything but now is time.
The other day I punched it from a stop sign(being a little kid) and took notice to a cloud of black smoke in my mirror. (could be my gas milage problem.) And it just plain runs rich at a idle for sure. Now I did do some adjusting with the vacuum guage and the idle screws, but I am thinking it has a power valve issue. ( I would think a 2.5 valve) would be ideal for my application but wanted other opinions. ALSO...This is important. I noticed my oil presure isn't as high anymore as it use to be. It is about 40psi when first started, but after a few minutes it drops to about 9psi at idle idle is @ 900rpms. Now it goes up about 10pse per 1000 rpms, but I am thinking my rich mixture is blowing feul by the rings and into the crankcase and thinning the oil. NO, I didn't check the dipstick yet or smell it, but will this weekend and change the oil.
My main concern was about the powervalve, and also, do they have 2 power valves in the double pumpers? I only rebuilt 600's before. I would assume there is a power valve in the rear metering block, but haven't look into it yet. Info is welcomed.

Again, car runs great. BUT the gas milage is WAY to poor for what it is and it has a RICH mixture problem. thanks guys.

If this is primarily a street car, IMO you have a bit too much carb for the engine and I've personally always preferred a vacuum secondary on a street car with an automatic trans. I think you'd be a lot happier with a 600 or 650 vacuum secondary carb. The oil pressure loss could also be carb related, if it's running that fat you might have pumped a bunch of that excess fuel into the crankcase where it's mixing with your oil!!!! I'd check to see if the oil smells like it has gas in it.

The 750 DP is a great carb, but probably not ideal for your application!

double pumper s have two power valves you did not say what you have for vacuum in gear at idle .but you should be about right with 2.5 power valves. i have pluged the back pv and jump up 10 on jet size and just use a power valve up front

The problem arises when you mention "HP" carb. A few years ago a trend was started with the custom carburetors where billet blocks were the rage and all the metering passages in the carb block got "special tuning" by adding more emulsion holes. Holley started losing sales and had to jump on the bandwagon. Long story short, what it all boils down to is the "new" style carbs have been altered in a way that will make them run rich and have every problem you are having. Don't get me wrong, they run great at WOT and such. But, cruising is not their strong point. They will turn you plugs black and gas will eat your lunch. If you want some milage and a cleaner running carb, search ebay and find a used, good condition, 3310 750 vacuum secondary. With very little tuning you can get that carb to run very well on your combo and run much cleaner. Save the HP for the track.....even though there won't be much difference between the two if tuned right.

Yes, double pumpers have two(2) power valves and you have to change both. I went through that years ago and got no answers from all the geniuses I knew. Then, I ran into a guy at the Holley display at the World of Wheels show in Chicago trying to hide all of their big, fat catalogs from me as I walk towards him. I don't know who he was saving them for but I got one from him anyway. Get your hands on one of those. There is more info written in plain English than you will ever find in all the how-to hot car mags combined. You need a vacuum guage. Put it in drive and stand on the brakes and read the guage. You need a power valve lower than your vacuum reading. Depending on the source of your advice, it's either half(1/2) the reading or 1.5-2 lower than same reading. Either way, you will get the result you want. I was going through the same thing. Raw gas was just washing down the cylinders and puking up the oil in no time. I finally installed an old 600 with vacuum secondaries that I just happened to already have and a 2.5 power valve just to see if that would work. It worked. Clean oil. No problems. Now, I run a an old 3310 750 vacuum secondary carb with a 4.5 power valve. No problems. I did pull the motor after that. The bearings were junk. I could see the copper in one of them. Luckily, the crank was still OK. I had it looked at for assurance anyway. I installed new bearings and used the same rings. Motor runs great and doesn't consume any oil. I wouldn't junk the double pumper yet. Just because the 'experts' recommend vacuum secondaries for automatics, it all depends on your car. Get your power valves changed and go from there. Holley has an installation DVD that comes with their carbs now, I think. I got one at a parts expo last year. See if you can get your hands on one. I think you can view the same on their website. And, get their catalog if you can. There is a wealth of info in there. You'll make it work. By the way, I just ordered an HP. Can't wait.