Power Valve Issue?

[Bernica]

Originally Posted by pusherfans

which one do I plug, rear (secondary)?

Yes. The secondary....

[Bernica]

Also, what size are the air bleeds Holley shipped it with? They are the small jets located on top of the carb ust above the squirters. Again, just for reference, my Hi Air is 36 and Idle Air is a 76....

[pusherfans]

Okay, I finally had a minute and got some info and have a novice stupid question.

I pulled the TP and threw it across the room (not really)

now I can see and work on the carb. I hooked up my brand new Holley vacuum gauge. Warmed up the beast.

measured

7-8 inches of hg at 1000 RPM (what consider normal idle for that thing)

Current power valve: 8.5

conclusion: pip rich due to power valve being open most of the time, specially when I am just kissing it where it was already rich with the stock power valve.

Novice question: I am assuming that the vacuum reading is related to the mechanical components of the engine (cam, intake, carb, air cleaner, etc) and not matter what the mixture, rich or lean, at 1000 RPM, at a given throttle position, it will always read the same vacuum, assuming all mechanical pieces are constant and the mixture being the only variable. (yes, changing the mixture will change the idle speed, but then I would I would correct it by changing the butterfly to keep 1000 RPM. Is this a correct assumption?

why I ask is because, I want to know if I can use this reading to get my 3.5 power valves or if I need to get the stock power valves back on it, adjust the idle again and re take the vaccum reading to see what power valve I need.

This is just step one in my plans. I have all of your previous suggestions noted for the next steps, should my last attempt t make it run right fail.

[Excaliber]

With a cam profile like that, in my opinion your beating a dead horse expecting it to run worth 10 cents below 2,000 rpm. Don't care what kind of carb you got, aint gonna happen.

[zrayr]

Originally Posted by Excaliber

With a cam profile like that, in my opinion your beating a dead horse expecting it to run worth 10 cents below 2,000 rpm. Don't care what kind of carb you got, aint gonna happen.

so true. start with the right carb, or engine for that matter, for your application. Otherwise you will be in for endless aggrevation. Your engine would be more fun on a racetrack, or as dad used to say, "you can't make a silk purse out of a sows ear."

[pusherfans]

Okay, changed the power valves to 3.5. 100% better off the line. Right by 1800 no problem. night and day difference. However, yes, there is always a however. It stil does not like to cruise in that slightly open position.

I will put the vac gauge on it tomorrow and the O2 sensor and getting readings of both in all throttle positions (idle, cruising [cracked open], 1/4, 1/2, 3/4 and WOT) and send the carb and all the data to AED and hope for the best. I just don't think I know enough or have time to keep messing with it.

I understand my cam won't make it easy, but the car did not do this before, so I don't know what is going on.

thanks for all the help. once this is all resolved, I'll post back.

[RET_COP]

Be careful about putting a low number PV in without checking your total driving habits with a vacuum gauge hooked up. This could lead to a LEAN condition at higher RPMs while letting off on the throttle and getting back into it.
I had 9"Hg at idle and thought I needed a low PV. I assumed that when I opened the throttle the Vacuum would drop from 9"Hg and also my cruise vacuum would be low. I was dead wrong. I discovered different when I hooked up a vacuum gauge. I also found out that my BG 650 carb is a little on the small side for my 355 and it tends to create more of a vacuum (across the board) during driving.
From idle on light acceleration the vacuum went higher.
I cruise between 8 and 11 inches depending on load conditions ( headwind, hill)
When I got into the throttle vacuum dropped but not as fast as I thought.
So I ended up leaving the 6.5 PV in as it was closed during cruise condition and opened when I needed the fuel without the possibility of a lean condition.
I think there are too many variables to make off the cuff decisions and assumptions. ( carburation, cubic inches, car weight, driving habits, CAM, jets etc.)
Try it on your combination you may be surprised
Lou

[Bernica]

RET COP is right.
Check out this video from a while back when I was where you are, sort of...

http://www.youtube.com/watch?v=7sMKIQyCLSs

[pusherfans]

Originally Posted by RET_COP

Be careful about putting a low number PV in without checking your total driving habits with a vacuum gauge hooked up. This could lead to a LEAN condition at higher RPMs while letting off on the throttle and getting back into it.
I had 9"Hg at idle and thought I needed a low PV. I assumed that when I opened the throttle the Vacuum would drop from 9"Hg and also my cruise vacuum would be low. I was dead wrong. I discovered different when I hooked up a vacuum gauge. I also found out that my BG 650 carb is a little on the small side for my 355 and it tends to create more of a vacuum (across the board) during driving.
From idle on light acceleration the vacuum went higher.
I cruise between 8 and 11 inches depending on load conditions ( headwind, hill)
When I got into the throttle vacuum dropped but not as fast as I thought.
So I ended up leaving the 6.5 PV in as it was closed during cruise condition and opened when I needed the fuel without the possibility of a lean condition.
I think there are too many variables to make off the cuff decisions and assumptions. ( carburation, cubic inches, car weight, driving habits, CAM, jets etc.)
Try it on your combination you may be surprised
Lou

you are right on. I checked my driving with a vacuum gauge hooked up and found that my vacuum varies from 11 to 17 inches of Hg in normal driving. Off the line easy, it drops to about 5. 3/4 throttle drops to about 2 and WOT drops tp 0 for a second and then works it's way up. a 4.5 may have been okay for me , but a 6.5 seemed a little high for my case.

but I still have that funny cruise I am chasing.... i'm looking into the distributor that I now broke....

[pusherfans]

New distributor in place, no change. However, I think I now know how to fix my running problem.. . .

I put together what 3 folks told me:

1) Try 1.5 turns on the idle mixture rather than my one turn I currently have
2) My local mechanic tried 7/8 turn and it was a little better, but lean idle
3) AED said that if I have it out only ½ turn or so, I need bigger idle air bleeds, like 6 counts bigger

1.5 turns made it worse, so I tried 0.5 turn. And it ran waaayyyy better. Then I backed off another ¼ turn and it stalled. Then I went 1/2 turn minus 1/8 turn and cruised for a long while. Runs awesome from 1800-2500+ rpm. The cruise is near perfect. The chug is 99% gone. Off the line is not for the weak at heart, it’s so lean (18-20) it’s hard to get moving, but then it dives to 11.8-12.5.

That tells me that that is where my problem is. The transition. I will try to get 74 sized ait bleeds to replace my carb's 68, to follow what AED told me and readjust the idle mixture and see where it goes. If this does not fix it, I may sell this carb and buy the 4150 street version (with less aggressive fuel curve) or a Demon, or Quick Fuel or an AED custom built carb. I may even drop to an 830-850 rather then the 950…. That's where we are now.

[65hilly]

I had an experience with the engine in my Capri V8, that sounds like the exact same symptoms. Note sure what ignition system your using, mine was the standard dizzy and points. As I said same symptoms, just at a constant mid range miss / flutter. What it turned out to be, was the condenser in the distributor, as the vacuum advance rotated the plate inside the distributor, it pulled the wire out of the condenser!! found it by pure ass!

[pusherfans]

I changed the air bleeds from 68 to 74. helped a lot, now I will tweak with idle mixture and front and rear butterflies.

[vector1]

what you did was lower the fuel curve for that circuit, interesting to see how it runs where this circuit transitions to the next one.

[pusherfans]

Originally Posted by vector1

what you did was lower the fuel curve for that circuit, interesting to see how it runs where this circuit transitions to the next one.

I was able to add fuel by turning the idle mixture to 7/8 of one turn rather than 3/8 of a turn. (all estimated).

Runs well, cruises fine, but that's not the final answer. it's still way lean at idle for it to work right.

I ordered 78 size air bleeds and will try that. I have a feeling I am leaning it out and then adding more fuel and will keep chasing my tail. The main circuit just seems to come in too soon.

if the 78's don't fix it, I'll put the stock ones back on and sell the carb and buy another carb. This time one for the street. This one currently is awesome in all points except for cruising, but it is a drag race carb.....

[vector1]

that tells you right there the circiut is cannot provide enough fuel for the vacuum provided, pretty simple. enlarge the ifr restriction. and very little goes a long way, like one drill bit size at a time.

[cdnus]

If you are increasing the idle air bleed size you are leaning the idle & cruise.
I would first try opening the screws 1/8 turn @ a time till you get to 1 &1/2
if that doesn't fix the idle then mess with the bleeds.

JMO. Craig

[pusherfans]

Originally Posted by cdnus

If you are increasing the idle air bleed size you are leaning the idle & cruise.
I would first try opening the screws 1/8 turn @ a time till you get to 1 &1/2
if that doesn't fix the idle then mess with the bleeds.

JMO. Craig

I tried that and I tried everything else I could think of. If I turn it 1.5 turns, it bogs and sounds like a 2 cylinder tractor while cruising. . ..

The problem is that the cruise circuit comes in too soon, I think my engine has too much signal at cruise (12-17 "Hg) and the carb has an agressive fuel curve, great for drag racing, not so great for cruising.

it's worth a try with the bigger air bleeds, but I have a feeling, I will always need to keep the idle way lean to make up for the main circuit coming in too soon.

[vector1]

The test for IFR's / idle air bleed combo is adjust idle for best mixture, then turn up the idle speed to about 1200 - 1400, under where the main circuit begins feeding fuel. Turn the idle screw out to see if the idle speed increases with the additional enrichment. If the engine rpm increases, you probably need more IFR. You can also turn the idle speed screw in to see if it is too rich. If turning the mixture screw in increases engine rpm then the IFR is too rich. When the IFR is correct, the engine rpm should decrease an equal amount whether you are turning the mixture screw in or out.

quoted from troy patterson

[cdnus]

What do you call lean for idle?

Craig

[StanJ]

Originally Posted by vector1

The test for IFR's / idle air bleed combo is adjust idle for best mixture, then turn up the idle speed to about 1200 - 1400, under where the main circuit begins feeding fuel. Turn the idle screw out to see if the idle speed increases with the additional enrichment. If the engine rpm increases, you probably need more IFR. You can also turn the idle speed screw in to see if it is too rich. If turning the mixture screw in increases engine rpm then the IFR is too rich. When the IFR is correct, the engine rpm should decrease an equal amount whether you are turning the mixture screw in or out.

quoted from troy patterson

I was about to post this diagnostic but I see Vector has beaten me to it.

Regarding Pusherfan's issue with main circuit tip-in timing; it's actually a really easy, straightforward thing to adjust...but in this case, a picture would probably reduce the necessary amount of text necessary to describe it by a couple hundred words. I'll try to post a photo and explanation from my office computer later today.