4410 artical

They leave a lot of the details out of a lot of the articles to save space, I think. I suggest writing in to request clarification. Who knows, your question might even make it to print.

I'll admit to being unfamiliar with that carb. On a Holley, the condition is consistent with a lean condition. It may be setter addressed increasing the shooter size, rather than messing up your cruise mixture ratio.

According to this article, by Holley, the power valve opens at the manifold vacuum referenced by the valve size....

http://www.holley.com/data/Tec...cal/power_valves.pdf

So:

65 = Opens at 6.5" or below
85 = Opens at 8.5" or below

Therefore the 85 power valve is actually opening at a higher manifold vacuum (earlier) than the 65 valve.

The Power Valve is SIZED by using the max vacuum at idle, then dividing by 2. That value is a "rule of thumb", not when the valve opens (as far as I understand it).

If this is the same article I saw, he also opened the PCVR (Power Channel Valve Restrictors) and increased the size of the squirter orifice. All these would tend to dump more fuel into the engine more rapidly when the accelerator is depressed...

I would hope he checked his manifold vacuum...

Rocky

quote:

According to this article, by Holley, the power valve opens at the manifold vacuum referenced by the valve size....

http://www.holley.com/data/Tec...cal/power_valves.pdf

So:

65 = Opens at 6.5" or below
85 = Opens at 8.5" or below

Therefore the 85 power valve is actually opening at a higher manifold vacuum (earlier) than the 65 valve.

The Power Valve is SIZED by using the max vacuum at idle, then dividing by 2. That value is a "rule of thumb", not when the valve opens (as far as I understand it).

Rocky, you're right. Chris, the 2x8.5=17 is not the correct way of looking at this. In short, if your engine idles as X, get a PV named X divided by 2.

I doubt any carb has ever backfired from being too rich when floored. When opening the throttles quickly you create a need for a lot more gas, which the carb desperately tries to cover with acc-pump and power-valve. Looking at a Air/Fuel ratio gauge, any engine goes leaner just when floored. Backfires in the exhaust on the other hand can happen from too rich, but usually when letting go of the throttle.

Normally backfires in carbs (not exhaust) are due to too late timing. So set the timing first.

In all humbleness, I'd suggest reading my book, it deals with tuning the ign/carb and the symptoms of when your engine needs adjustment. Or let me know directly of any questions?

Just ordered your book, the power valve is open until the vacuum reaches in this example 18"
of vacuum, so it is open most of the time I am guessing ( no information on vacuum at Idell )
If this P.V. was in my car it would be adding fuel all the time, unless I was going down the Baker grade in 4th gear at 100 and took my foot off the gas, waaaaaaaaaaaaaaaaaaaaaahhhhhhhhh
18" of vacuum.Tuning corroborators is becoming a lost art!

quote:

the power valve is open until the vacuum reaches in this example 18"

Chris, sorry to say, but that's not correct, then the PV is hardened beyond use...

The power valve is designed to supliment the main jets when the vacume is lost on acceleration, when the engine is at idle the power valve is not open as the vacume at idle keeps it closed, when the engine is accelerated the following thing take affect in the carb, 1 the accelerator pump depresses the diaphragm in the pump and through the squarters delivers a shot of fuel above or at the boosters, number2 and at the same time the power valve opens and also provides additional fuel, as you reach a cruising speed and you engine rpm decrease the vacume returns and the power valve is closed, now the engine will run on just the jets.This is repeated every time you accelerate. When I referred to the 18 pounds of vacume in the article I was trying to illustrate that my engine that only develops 13 inches of vacume would never actuate the valve it would be open continually. By the way a 6.5 power vale would be for 13 inches of vacume , 6.5 X 2 = 13 .

quote:

Originally posted by No Quarter:

quote:

the power valve is open until the vacuum reaches in this example 18"

Chris, sorry to say, but that's not correct, then the PV is hardened beyond use...

Here's Holley's view:
If the vehicle has a manual transmission, take
the vacuum reading with the engine thoroughly warmed up and
at idle. If the vehicle is equipped with an automatic transmission,
take the vacuum reading with the engine thoroughly
warmed up and idling in gear. In either case, the power valve
selected should be 1/2 the intake manifold vacuum reading
taken. EXAMPLE: 13” Hg vacuum reading divided by 2 = 6.5
power valve. If your reading divided by 2 lands on an even
number you should select the next lowest power valve. EXAMPLE:
8” Hg vacuum reading divided by 2 = 4 power valve.
Since there is no #4 power valve you should use a 3.5.

--
A few comments:
-Your PV would not be continually open if you had a 6.5 and a 13 idle, it opens when the engine produces less than 6.5
-Acc pump works on throttle position only, PV on vacuum only. So going up a long steep hill could mean no acc pump help but PV constantly adding fuel (as it should be)
-It's rare the engine runs only on the jets, because up to approx 60 mph the idle circuit still contributes

Just my $0.02

Actually, the PV is held CLOSED by vacuum, so when the vacuum DROPS (as it does when you open the throttle butterflys), the loss of vacuum opens the valve - that's when the PV circuit adds more gas.

By the way, my car, I mean the guy who wrote the article... pulls 16-17" of vacuum at idle...

Rocky

PS> Chris - nice car - I saw your slideshow in the gallery - couldn't figure out how to post there.