Author Topic: Power Valves  (Read 12840 times)

Henry Cloutier

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Re: Power Valves
« Reply #30 on: October 27, 2020, 08:44:16 PM »

Hi Kelley,
Somewhere in my now vacuum of a brain I had thought to do just that. Unfortunately I didn't have a new gasket to re-install the old one. I ordered a bunch of those along with the new PV all of which arrived yesterday. I elected to go with the new PV as apposed to the old one only because it was new (full well knowing new doesn't necessarily guarantee success). Admittedly I have been a little overwhelmed with all this so far. The carb is old, has been into before and I haven't done any of this for many years. All of that together probably equals something could go of the rails. I will fix it and I'm learning a ton along the way. That can't be a bad thing although frustrating at times.
 
Thanks for the input!     

PHAT69AMX

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Re: Power Valves
« Reply #31 on: October 28, 2020, 08:10:38 AM »
You're Welcome.
Be sure to lubricate the Needle Assy O-Rings with chapstick or something before screwing it into the bowl.
When reattaching the front and rear fuel bowls, 1st overly shorten the Accelerator Pump Arm Screw with the spring on it.  This prevents the Pump Arm from 'displacing' the Bowl downward when mounting the Bowl and Metering Block to the Main Body.  I stand the Holley vertical up on end when installing fuel bowls.  Install the 4 Bowl Screws but do not fully tighten.  The Bowl & Block assy can be 'wiggled around' in place with the screws almost tight.  "Centralize" this "slop", "midrange it" before then tightening the Bowl Mounting screws evenly in an "X" Pattern, Firm Hand Tight with a NutDriver.  Beforehand for the gaskets I get chapstick on my finger tips and liquefy it between the fingers and then apply it to the gaskets as only a thin film, avoiding any amount in the gasket holes.  "Midranged" Bowl mounting location promotes proper Accelerator pump geometry.  The bowl can be "mis-mounted" a considerable amount up, down, or sideways, due to the "slop" which adversely affects resulting Accelerator Pump geometry.

Imho the Secondary Idle Opening is whatever it want's to be.
The driving factor is the Primary Idle throttle opening must be correct relative to the transfer slots.
Primary is set on the bench, then not changed, unless closed further, which is unlikely.
Then once on the car all idle speed adjustments are made by way of the secondary idle speed screw.
Valve Adjustment, Initial Timing Advance, and Advance Curve must all be set 1st and not changed,
as changes to any of those will change the carb idle settings.
The Vacuum Secondary will also operate considerably better with sufficient secondary Idle opening.
The Vacuum secondary diaphragm is acted on by Venturi Vacuum, not manifold or ported.
Venturi Vacuum pick up ports are high up in the main body venturi bore just below the pinch point
and it has an opening to both the Primary and Secondary Bore on the passenger side.
So airflow on the primary side creates a venturi vacuum signal, BUT it must 1st overcome the "leak"
of the same common passage opening also on the Secondary side which has minimal to no air flow
creating basically no secondary Venturi Vacuum signal IF the secondary butterflies are almost or basically closed at "idle"...
Cracking the Secondaries more at idle increase "idle" air flow through the Secondaries,
which increases secondary Venturi Vacuum Signal, which reduces the "leak" the Primary has to overcome,
therefore resulting in a "better" more positive Vacuum Secondary actuation.

Put this is all just opinion, discussion, & bench racin', not at all intended as "gospel", or "the only way".

Henry Cloutier

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Re: Power Valves
« Reply #32 on: October 28, 2020, 09:08:52 PM »

Hello,
Very good information and this helps me understand the workings of the carb. Many people have jumped on this thread to assist me with the troubleshooting and possible avenues of repair. It's up to me disseminate all this info in order to get the Z running properly again. I very much appreciate all the help and guidance provided! I'm almost ready to start her up and check for leaks, course now the weather has changed for the worse. I did install the  missing choke bimetallic spring assy. during the carb re-installation and now I need to figure out what the engine needs for the start sequence. Seems like I remember needing from previous experience to pump the gas 2-3 times before turning the key in this now cold weather pattern. More to come as I work thru this troubleshooting process.

Best regards,

Henry Cloutier

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Re: Power Valves
« Reply #33 on: November 01, 2020, 09:49:40 PM »

Hello everyone,
Happy November 1st! The Z is back up and running. The replacement of the PV appears to have cured the stumble.  The throttle response is clean and the engine accelerates smoothly thru the gears. I also finally was able to get to the initial timing setting. It was sitting at 8 degrees and I bumped it to 10 degrees. The engine liked the new setting, so much so I'll try bumping it to 12 degrees next time I'm under the hood. Thank you all for the valuable info and insight during this process. For sure I made some rookie mistakes during this carb rebuild/troubleshooting scenario which I will not let happen again.

Best regards,

Hank

Kelley W King

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Re: Power Valves
« Reply #34 on: November 02, 2020, 01:25:19 PM »
It is possible that your cam is not exactly a 302 spec cam or your carb has a port partially clogged. The different PV makes up for the situation. But when I have a Holley that runs well and does not leak I call that good.


















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Henry Cloutier

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Re: Power Valves
« Reply #35 on: November 03, 2020, 12:47:58 AM »

Hi Kelley,

Agreed everything is possible and I don't have any previous maintenance records, My best guess is the cam is still OEM issue for the vehicle. All indications are this car had two owners last changing ownership in 1985. At that time the mileage was not quite 14k and I bought it with 31,832 showing. Numbers match on the motor and all appearances are the car car sat for extended periods of time, I'll never be sure. It is possible there is a plugged or clogged passage in the Holley...I cleaned everything as best I could using Gum out carb cleaner but for sure don't have the dip processes that would be available to those shops who do it for a living. She is running running better than when I started following the final changes so I am calling it good!

Best regards,

Hank

firstgenaddict

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Re: Power Valves
« Reply #36 on: November 24, 2020, 04:52:05 PM »

Hello,
Very good information and this helps me understand the workings of the carb. Many people have jumped on this thread to assist me with the troubleshooting and possible avenues of repair. It's up to me disseminate all this info in order to get the Z running properly again. I very much appreciate all the help and guidance provided! I'm almost ready to start her up and check for leaks, course now the weather has changed for the worse. I did install the  missing choke bimetallic spring assy. during the carb re-installation and now I need to figure out what the engine needs for the start sequence. Seems like I remember needing from previous experience to pump the gas 2-3 times before turning the key in this now cold weather pattern. More to come as I work thru this troubleshooting process.

Best regards,
Did you see how to set the choke correctly - adjust by bending the dogleg in the arm coming up to the carb from the bi metallic spring?

When you depress the accelerator it will set the choke HOWEVER if you hit the gas pedal at all after the car starts it will come down off the fast idle.
So I don't have to crank and crank and crank - If my car sits a week or longer I fill the fuel bowls and give a squirt down the primaries... press the accelerator once and fire it off.

FWIW The worst problems I have had ARE when I do not let the car fully warm up, it spits and sputters because of the long aluminum runners on the intake and fuel falling out in liquid form on the intake floor.
James
Collectin' Camaro's since "Only Rednecks drove them"
Current caretaker of 1971 LT1's - 11130 and 21783 Check out the Black 69 RS/Z28 45k mile Survivor and the Lemans Blue 69 Z 10D frame off...
https://plus.google.com/photos/112392262205377424364/albums?banner=pwa

Henry Cloutier

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Re: Power Valves
« Reply #37 on: November 24, 2020, 11:37:57 PM »

Hi and the arm came with a bend in it from the kit. I needed to bend the fast idle arm to engage the fast idle cam. Choke plate closes to about a 1/4 "from fully closed and the idle speed comes up to about 1100-1200 rpm before I kick it down some. I've seen data suggesting the fast idle speed should be up around 2200 rpm which seems really fast to me. I'll probably give the fast idle arm another bump to increase it slightly but otherwise it all seems to be working nicely. For sure she's a little cantankerous until wormed up. I figured out not to back out of the garage until the temp gage is up off the peg and then gentle on the throttle the first few minutes of driving.

best regards,

Hank

firstgenaddict

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Re: Power Valves
« Reply #38 on: November 25, 2020, 04:40:08 AM »
Sounds like you have the arm adjusted right, yes the fast idle should be more than 1100-1200 -I believe 2200 is correct, it does seem high to me as well, however mine is in that area as it will cost me points in NCRS judging.
FWIW if the intake is REALLY cold it needs the engine speed to keep the fuel in mixture- try driving one straight off start and they wheeze, pop, and snort.
James
Collectin' Camaro's since "Only Rednecks drove them"
Current caretaker of 1971 LT1's - 11130 and 21783 Check out the Black 69 RS/Z28 45k mile Survivor and the Lemans Blue 69 Z 10D frame off...
https://plus.google.com/photos/112392262205377424364/albums?banner=pwa