Help!! Holley gurus

[Willowbilly3]

What power valves to use?
I have my buddys 69 Z/28 here. It has been setting in a garage for 2-3 years and I told him I'd get it running. The carb had been leaking so I said I would take care of that. Well, it turns out to be a stock Holley for a 375 HP 396 or 425 HP 427 and it's on a 350 that I don't know anything about.
There is no quick kit so I end up ordering the big rebuild kit. Holy crap, there's enough stuff in there to rebuild half a dozen carbs, no wonder it was $100. Well, anyway there are no numbers on the old power valves or the inlet valves and I have maybe 8 sets of each in the kit. Also the kit gives very little pertinent info, it says to buy the book by some guy.

 

[Toad]

I'm not a big Holly fan but the new ones come with a 'tuning' CD. Maybe someone has one you can borrow. From what I remember, they're fairly good at tuning one up. I generally prefer a Edelbrock.

Toad

 

[Old Iron]

First off that carb is too big. A stock to mild 350 only requires a 600 to 650 cfm.
Holley power valves are set off the minimum manifold vacuum of the engine it's on.
You will need to know that before installing the correct one.
Just start with one in the carb, start the engine let it warm up, set the idle, put a vacuum gauge on the manifold, get a reading and put a power valve in that is 1.5 to 2 numbers lower.
If the reading, at idle, is 10 in. then install a 8.5 if it's 8 in. of vacuum then install a 6.5 in etc.
The correct valve will make a big difference on the responsiveness of the engine.

 

[26Troadster]

First off that carb is too big. A stock to mild 350 only requires a 600 to 650 cfm.
Holley power valves are set off the minimum manifold vacuum of the engine it's on.
You will need to know that before installing the correct one.
Just start with one in the carb, start the engine let it warm up, set the idle, put a vacuum gauge on the manifold, get a reading and put a power valve in that is 1.5 to 2 numbers lower.
If the reading, at idle, is 10 in. then install a 8.5 if it's 8 in. of vacuum then install a 6.5 in etc.
The correct valve will make a big difference on the responsiveness of the engine.

they always had to big of carb on them, even with the quadrajet (spelling) was a 750 on a small block and 850 on big block, and if i remember right the dz 302 had a 700 to 750 double pumper.

 

[Willowbilly3]

First off that carb is too big. A stock to mild 350 only requires a 600 to 650 cfm.
Holley power valves are set off the minimum manifold vacuum of the engine it's on.
You will need to know that before installing the correct one.
Just start with one in the carb, start the engine let it warm up, set the idle, put a vacuum gauge on the manifold, get a reading and put a power valve in that is 1.5 to 2 numbers lower.
If the reading, at idle, is 10 in. then install a 8.5 if it's 8 in. of vacuum then install a 6.5 in etc.
The correct valve will make a big difference on the responsiveness of the engine.

I found other information on another forum (since I started this thread) that said to half the vacuum reading. Since the biggest one in the kit is a 10.5 and a healthy mild engine might pull 18 or better, that makes sense.

 

[26Troadster]

i have a 6.5 if i remember right as my 350 with a comp. cams 292 hyd. only has about 12 inches of vac.

 

[Willowbilly3]

Thanks for the help guys. I am going to make a guess on them and hope I don't have to take it back apart. Since it's most likely stock and should pull 17 inches or so, I'm going to start with the 8.5s

 

[440shorty]

Late to the party

Sorry that I'm late, as I expect you have already reassembled the Holley. I always use vasoline or transmission assembly lube on the blue metering block and fuel bowl gaskets so they don't stick. That way one can disassemble for tuning and reuse the gaskets.
As for the power valve, stock is usually 6.5. If the engine idles in gear (automatic) at or below 6.5" vacuum, the power valve will begin to open and dribble fuel, causing a rich condition. You know, the blubbering, eye-burning idle that eventually fouls the plugs. In those cases, you would put in a lower power valve, but not too low, because sometimes at wide open throttle under load, engine vacuum can actually rise at higher RPM. If the power valve opened at that vacuum (like 2-3") it could actually close again, causing a high speed leanout - bad.
On the other hand, 10.5 power valve might open too soon and run rich at cruise, like a long uphill pull.
This stuff is paraphrased from the book Super Tuning and Modifying Holley Carburetors by Dave Emanuel, published by Cartech.
Since you've already finished the job, you might want to road test the car with a vacuum gauge just to verify that the engine vacuum doesn't drop below 8.5 under load.
440shorty

 

[gold03]

For the gaskets I use chap stick... not your wife's lip gloss. The old wax type. You can use the gaskets over and over.

gold03

 

[Ezheimers]

Are you 'Lubing up' all the carb gaskets? -EZ