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post #1 of (permalink) Old 01-07-2002, 11:03 AM Thread Starter
 
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More Holley Carb Questions

I have a 1984 Scrambler with a freshly rebuilt 258 and it has problems (stalling when cold, hesitation, bogging after shifting[auto tranny])simmilar to the ones described in JoeyCJ55's post entitled "Holley Carb Problems," which I read entirely. I run a one year old Holley 2 barrel 350 cfm carb with manual choke (PN: 7448 or 7748, I can't remember). The engine has a mild cam and was bored 30 over with 10/10 bearings; it also has stock intake and exhaust and an HEI conversion. After reading some other posts, I may have found a few problems right off the bat (I use manifold vac. for the distributor advance and use the factory harness wire for the distributor). Regardless, my questions are concerned with the carburetor. How can you tell if the powervalve is blown? I have taken it out (it's an 8.5) and blown/sucked air with my mouth and all I found out was that gasoline tastes bad. Also, I get virtually no change in idle by adjusting the idle screws and was told that this indicates that I have the wrong carb for the application(I got this from BOB's scientific tuning site). I can't find a vacuum leak but my brand new engine only pulls 14.5 at idle (in park) and cruises around 9.5 but dives to 5 or less with any stress. It was running rich and fouling plugs so I changed jets from 61 (stock) to 55. That helped the engine run better overall, but increased the hesitation problems. I have a Dave Emanuel's book and have read it and have also tried BOB's scientific tuning methods but I get weird results (with new O2 sensor I get cruise readings of 0-100 mv but at idle and under stress I get readings of 700-900mv). Any Suggestions????

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post #2 of (permalink) Old 01-07-2002, 11:36 AM
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Re: More Holley Carb Questions

Your power valve is waaaaaay to big. I have the same carb on my Jeep and I only run a 4.5. I would like a 4, but I don't think they make them. I think I am running 57 jets, but can't remember. I started with a 6.5 pv and had the same problems. Trial and error got me to the 4.5. A 3.5 was too small. Now that it is set up, I think it is a very good carb. But now I'm going to fuel injection.

My girlfriend said if I spent one more dime on my Jeep she would leave. Man I'm going to miss her!
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post #3 of (permalink) Old 01-07-2002, 12:24 PM
 
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Re: More Holley Carb Questions

First of all, start using punctuation...
One long sentence is hard on us old, dyslexic bastards! [img]/wwwthreads_images/icons/mad.gif[/img]
<hr>

I have a 1984 Scrambler with a freshly rebuilt 258 and it has problems (stalling when cold, hesitation, bogging after
shifting[auto tranny])simmilar to the ones described in JoeyCJ55's post entitled "Holley Carb Problems," which I read entirely.
*I run a one year old Holley 2 barrel 350 cfm carb with manual choke (PN: 7448 or 7748, I can't remember).*

Need the List Number off the front of the choke air horn. (inside the air cleaner)
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*The engine has a mild cam and was bored 30 over with 10/10 bearings; it also has stock intake and exhaust and an HEI conversion.*

'Cammed' engines (more lift or duration than stock cam) will cause lower vacuum readings.
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*Afterreading some other posts, I may have found a few problems right off the bat (I use manifold vac. for the distributor advance and use the factory harness wire for the distributor).*

Don't pick and choose, fix the problems as they come up.
Plug the vacuum advance into the ported vacuum port on the Holley metering block, get a power relay and use at least 10 Ga. wire to supply the GM HEI.
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*Regardless, my questions are concerned with the carburetor. How can you tell if the powervalve is blown?
I have taken it out (it's an 8.5) and blown/sucked air with my mouth and all I found out was that gasoline tastes bad. *

Gasoline not only tastes bad, but is poisonous...
If the diaphragm didn't move when you sucked on the large side of the power valve, the valve is blown.
If the little brass valve on the 'screw' end closed when you sucked on the power valve, the valve is fine.

It's the 8.5 power valve that concerns me most... but we'll get to that later...
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*Also, I get virtually no change in idle by adjusting the idle screws and was told that this indicates that I have the wrong carb for the application(I got this from BOB's scientific tuning site). *

There are a lot of reasons for not changing idle when turning the screws...
Only ONE of them is the wrong carb.
You may have the 'Smog' version that controls the emulsion air and not the idle fuel control, ect...
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*I can't find a vacuum leak but my brand new engine only pulls 14.5 at idle (in park) and cruises around 9.5 but dives to 5 or less with any stress.*

Those numbers are pitiful. You should be pulling 18 to 22 at idle.
I'd bet your cam isn't degreed in correctly, or you are using a retarded timing set...
Or you have one HUGE vacuum leak somewhere....
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*It was running rich and fouling plugs so I changed jets from 61 (stock) to 55.*

Wrong move...
We'll cover that in a minute...
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*That helped the engine run better overall, but increased the hesitation problems.*

You leaned out the transition between idle circuit and main circuit...
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* I have a Dave Emanuel's book and have read it and have also tried BOB's scientific tuning methods*

Read Dave's book again, stay away from BOB's site...
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*but I get weird results (with new O2 sensor I get cruise readings of 0-100 mv but at idle and under stress I get readings of 700-900mv).*

Don't worry about the O2 sensor just yet, you aren't that close...
----------------

*Any Suggestions????*

Yes, now that you mention it...

1. Float bowl level.
It sounds like you are running rich, and it's probably as simple as the float level being too high.
You didn't mention float level, or fuel pressure regulator...

2. The rating on a power valve is in inches of vacuum it takes to CLOSE the valve!
You are not generating enough vacuum to close the valve a lot of the time!

If you have a 8.5 valve on an engine that normally does 9.5 down the road, every time you barely tip the throttle you are drowning the engine!
Drop down to a 4.5 or 5.5 until you have this sorted out...

3. Your jets don't take over fuel control until about 1,500 RPM (depending on carb cfm size for your application).
Smaller jets won't help you with low speed cruse, idle, or acceleration hesitation.

4. Do this tune up by the numbers... Don't consult 'Dr. BOB' or anyone else.
Dave Emanuel's book is a good reference, read it again.
<hr>

Engine stopped.
1. Throttle Opening. Throttle blades straight up and down (perpendicular) to throttle bore using the PEDAL.
Just throwing open the throttle linkage isn't good enough.

2. Smooth, steady accelerator pump shot. Smooth fuel flow into the Venturi bore that lasts until the throttle blades are fully open. Should start the instant the throttle linkage starts moving.
No bubbles, no sputtering, no starting late, no finishing early. Smooth and even delivery of fuel into the Venturi bores.

3. Check under the base plate, and on the sides of the carb for open vacuum ports that should be plugged.
Make sure nothing interferes with the movement of the linkages.
Check for DOUBLE return springs. A single spring isn't good enough! Use double springs. No exceptions.

4. Make sure your air cleaner or air cleaner housing isn't interfering with the carb. Keep all parts of the air cleaner and housing at least 3/4" away from float bowl vents.
Use the largest air cleaner you can fit under the hood.

5. Make sure you have at least two fuel filters, one hard case before the pump, and one before the carb.
I read no mention of a fuel filter of any kind.
----------------

Engine running.

1. USE COMMON SENSE!
Some of the adjustments you will have to do while the vehicle is running will cause fuel to spill, and fuel vapor to escape the fuel system.
Do these adjustments out doors, on flat land, away from structures, and keep a fire extinguisher handy!

2. Float level.
The single most common screw up any of the rookies make.
You are going to spill fuel on this one, so keep rags handy, and make sure the fire extinguisher is right there...

3. Clean up the fuel mess before you start a fire...

4. Idle mixture using a vacuum gauge, and keeping the screws turned out even...

5. Idle speed.

6. Vacuum leaks.

7. Set your accelerator pump clearances

Get back with me when you have done these things, and we'll go from there.





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post #4 of (permalink) Old 01-07-2002, 12:32 PM Thread Starter
 
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Re: More Holley Carb Questions

I forget to mention (because I knew that you would ask) that the float is set correctly. Also, my timing is set at 15 degrees BTDC (stock is 9-12) and I was under the impression that my cam did not need to be degreed since it is so mild. Is that not the case?

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post #5 of (permalink) Old 01-08-2002, 12:26 PM Thread Starter
 
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Re: More Holley Carb Questions

The carb part number is as follows: R7448

The float was and still is set correctly.

I have a fuel filter in my tank and one between the pump and carb. Also, I am using a stock mechanical fuel pump without a regulator.

I switched to 5.0 power valve and size 61 jets.

I rechecked the vacuum readings and found 17 mmhg at idle. Also, I switch the distributor to ported vacuum and spray-checked for leaks; I didn't find any.

I did not change the wire to the distributor because I really don't know what you are talking about concering the relay.

I attempted to set the idle with a gauge but didn't find much fluctuation. I did notice, however, that the engine idles much better (hot or cold) with the choke pulled slightly (the fast idle cam is not engaged). Too much air or not enough fuel?

I still have one question though: Why does my engine run like crap when it's cold and then run well when its warm?

With the changes so far, I have not noticed any significant changes.



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post #6 of (permalink) Old 01-08-2002, 01:22 PM
 
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Re: More Holley Carb Questions

Low vacuum, non responsive idle adjustment, lack of power, 'bogging' down....

This is sounding more and more like cam timing or distributor in 180 degrees out of time.

Check for TDC on the #1 cylinder...
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1. Find compression stroke on #1 by taking the spark plug out, and putting a cork, your finger, or a paint ball in the hole and waiting for it to blow out.

Once you find compression on #1 cylinder, Use a wooden dowel rod or chop stick to feel for the top of the piston.(NO METAL IN THE CYLINDER!)
Crank the engine over BY HAND WITH A SOCKET ON THE CRANKSHAFT CENTER BOLT.

Use the dowel rod to feel for the piston to reach Top Dead Center.

Check your balancer mark and the timing cover for '0' (Zero).
If your balancer doesn't show the mark at '0' (Zero), your balancer is bad.
----------------

2. Mark the tower where your #1 spark plug wire attaches to the distributor cap, mark the distributor base where the #1 tower is also.

Take the cap off, and see if the rotor lines up with the #1 tower (more or less, 1 rotor blade width before or after is acceptable).

If your rotor nose points anywhere but at #1 tower, you have a distributor timing problem.
Pull and reinsert the distributor until the rotor nose points at the mark you made on the housing for #1.
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If this is the problem, start over with the carb and timing adjustments.
Don't skip any of the steps I wrote before... This will put us at square 1 so we know what's going on...

So many cats, so few recipes...
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