Holley Power Valve, Selecting, Testing and Quality

[Argess]

I have a 2x4 Holley (4160s....600 cfm each) set-up on a 428, and I have two issues.

1/ Tuning Issue: Normally, when I roll on the throttle, I can feel the engine pick-up, and then suddenly more power comes on, and then again a bit after that. This has to do with ignition timing vs power valve selection, not vacuum secondary opening rate....at least assume so because the story leading up to this is very long......

2/ Intermittent Issue: Sometimes, when I accelerate, nothing happens, just burps and hesitates and nothing. Let off the gas, try again, and it seems OK. Sort of like misfiring, but I can rule out ignition as everything has been replaced.

So I tear down the carbs. Here's what I found:

1/ Primary float of second carb was adjusted for too high a fuel level. Also evidenced by fuel residue around external float bowl vent....one of those vents that opens when the throttle is opened. Had to turn down float level close to one turn to set float dry.

2/ Power valves from each car were not "blown". However, they had a microscopic stamp ( number about 1/32" high...very small) on the brass piece that holds the spring that said 5.5. Don't genuine Holley Power Valves have the number on the aluminum part you put the wrench on?

3/ Testing with a Mighty Vac showed operation around 3 in Hg for both valves. Mighty vac was checked against another guage and shown to be accurate.

Now, for a light car that has a 290 adv Cam, and I am getting close to 16 in Hg with my current intial ignition timing at idle. According to what I read, shouldn't 8.5 Power Valves be a better choice? According to my 1966 Ford Manual, the twin Holley set-up used #85 PVs.

So...here's some questions:

1/ If my current PV arn't genuine Holleys parts, could they leak, even when closed and cause flooding which may be the cause of my "sometimes" hesitation/misfire?

2/ If I purchase replacements, wouldn't 8.5s be a better choice?

3/ Do you think the one float level set as bit too high may have caused any issues?

By the way, these carbs came from a respectable carb company. They also used to work satisfactorily, but my ignition was very far advanced at that time, and I didn't know it.

Thank-you.

[Frank Messina]

You've probably got a couple things going on there as far as your tuneup is concerned but I'll just address your PV questions. First if the power valve is leaking, the backside of the metering block will be wet from gasoline when you pull it away from the body.
Next there are a number of simple formulas in use to help decide which power valve to use. Everybody's got their favorite. One is take to take your highest steady state vacuum reading at idle and divide by two. So with 16" at idle, using this formula you'd want an 8. Another method says to divide by two and add two. So 16" divided by two plus two is 10". This means when engine vacuum drops below 10" the power valve opens and adds more fuel. Likewise the 8" PV won't open until vacuum drops below 8". This gets you smoothly up over that long hill when your cruisng along. When you mash the throttle though it doesn't matter what you have in there because vacuum goes to zero and the power valve opens. What you have to be careful of though is if you have too low a number PV in there, as the engine vacuum begins to recover, the PV can close and cause the engine to go lean. The car will feel like it's nosing over. Not good. Take your pick though, both methods will work, just give the motor what it wants.
As far as your no power hesitation is concerned, you've got some other tuning issues to address. HTH
Frank

PS: The only thing a high float level will do is cause a rich/poor idle. Set the floats with the engine running so that fuel just dribbles out (not shakes out) of the sight plug holes.

[vector1]

drive around with your vacuum gauge hooked up to the manifold, you can decide when you want the pv to open. these light cars don't pull a lot of vacuum to accelerate. wbo2 helps tremendously in tuning.

[zrayr]

Originally Posted by Argess

2/ Power valves from each car were not "blown". However, they had a microscopic stamp ( number about 1/32" high...very small) on the brass piece that holds the spring that said 5.5. Don't genuine Holley Power Valves have the number on the aluminum part you put the wrench on?

no. the only number is on the back & very tiny

Originally Posted by Argess

3/ Testing with a Mighty Vac showed operation around 3 in Hg for both valves. Mighty vac was checked against another guage and shown to be accurate.
Thank-you.

a mitty vac is not an accurate way to check. the power valve.

Originally Posted by Argess

Now, for a light car that has a 290 adv Cam, and I am getting close to 16 in Hg with my current intial ignition timing at idle. According to what I read, shouldn't 8.5 Power Valves be a better choice? According to my 1966 Ford Manual, the twin Holley set-up used #85 PVs.

2/ If I purchase replacements, wouldn't 8.5s be a better choice?

Thank-you.

your idle vacuum is not the number to go by. What is the vacuum at cruising with a very light load, like up a slight grade ? For example, if that number is 9, then a 6.5 is what you want for a power valve rating.

also, your float level is very important. Too high can cause a multitude of problems. Be sure all the floats are set the same. A little low is much better than a little high. Unless you are on the Bonneville Salt Flats

Z. Ray

[Argess]

You know, I'm sure there's nothing wrong with the carbs. They have worked great for 10 years. They sat around all winter while I rebuilt engine. It was all that was left for me to check with troubleshooting the hesitation/boggin/misfire/burping thing that happens....sometimes...other times it works fine, and sometimes, it comes on reasonably well, then suddenly a burst of power from no-where, then another. Bizarre.

I was just grasping at straws. I'll get some carb gaskets and clean and re-install, and after that? Already did all the ignition, fuel quality, fuel pump, fuel filter tests. I'm not sure what else to test or check.

Maybe percolation.... I really have no idea.

[Tom Kirkham]

Originally Posted by vector1

wbo2 helps tremendously in tuning.

This is so true. Without a wide band O2 sensor your are really fighting an uphill battle.

Are you running vacuum advance? vacuum secondary carbs? Big cam? What is your initial and total timing? Progressive linkage? Does your linkage bind? Can you post a picture of your engine? How is your fuel pressure?

If your carb is adjusted correctly, you should not be able to feel the transitions...

[Argess]

Not a big cam...a Crane Fireball 290...about 227 @ 0.05 I think.

no carb linkage binding, and it is progressive

fuel pressure is 7 psi

vacuum secondaries are connected carb to carb

timing 20 intial, 38 max. Problems are worse the lower the intial advance

@28 intial, I get detonation...I think...you can feel the engine fighting a bit.



Anyway, dont' forget, none of the problems are consistent, although they do repeat and generally fall into 3 categories:

1/ Works fine more or less. A bit more ignition tweaking, etc as it is close to working fine.

2/ power comes on in stages under acceleration, such as giving it 1/3 to 1/2 throttle. This is the most common scenario. Probably can be cured by tuning, yet sometimes it's as above (fine)....but may go away if #3 is cured

3/ completely loses its ability to get out of its own way when accelerating as above. Full 8 cylinders gone screwy. Not just 1 cylinder. Let off the gas, and try again and it seems fine. This one does seem to rear its ugly head after car is driven for 1/2 hour or more.

Arghhh...........