Holley Acc Pump Adjustment - Team Camaro Tech
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post #1 of 19 (permalink) Old Oct 9th, 02, 03:40 PM Thread Starter
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I read the following quotation off the holley web site reguarding the accellerator pump adjustment.

"The first adjustment to check is the clearance between the pump operating
lever and the pump diaphragm cover's arm, at wide open throttle. This
clearance should be around .015". The purpose for this clearance is to
assure that the pump diaphragm is never stretched to its maximum limit
at wide open throttle. "

They are saying to make the adjustment at WOT. This sounds wrong. How can you make the adjustment at WOT without damaging the pump diaphram. Seems like it should be adjusted at closed throttle. Can anyone clarify the procedure.

-dnult
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post #2 of 19 (permalink) Old Oct 9th, 02, 03:49 PM
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It won't hurt to lightly bottom out the pump with a .015 feeler gauge.

If it had .015 at closed throttle, the travel would not be enough.

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post #3 of 19 (permalink) Old Oct 9th, 02, 04:05 PM
 
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No, its not wrong. Thats how it is done.
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post #4 of 19 (permalink) Old Oct 9th, 02, 05:15 PM Thread Starter
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<BLOCKQUOTE>quote:</font><HR>Originally posted by chacane67:
No, its not wrong. Thats how it is done.<HR></BLOCKQUOTE>

Ok, now for the clarification part.

Should I hold the throttle at WOT and press down on the pump lever while inserting a feeler guage? Should I stand on my head or hold my tounge a special way? The procedure says "...to ensure the diaphram is never streached...". Seems to me you would have to streach it to make the measurement. What am I missing?

-dnult

-dnult


[This message has been edited by dnult (edited 10-09-2002).]

[This message has been edited by dnult (edited 10-09-2002).]
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post #5 of 19 (permalink) Old Oct 9th, 02, 05:24 PM
 
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LOL, sorry bro.....

Yes you should do this at WOT, (on the arm) and the way I check it is to open to WOT, and then insert the feeler guage and make sure that the arm can still move that 0.015"-0.025" without compressing the spring on the adjuster arm.
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post #6 of 19 (permalink) Old Oct 11th, 02, 05:05 PM Thread Starter
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<BLOCKQUOTE>quote:</font><HR>Originally posted by chacane67:
LOL, sorry bro.....

Yes you should do this at WOT, (on the arm) and the way I check it is to open to WOT, and then insert the feeler guage and make sure that the arm can still move that 0.015"-0.025" without compressing the spring on the adjuster arm.
<HR></BLOCKQUOTE>

No way...for real? I just tried setting the spring-loaded bolt stop 0.015" from bottoming out the pump actuator lever. I had nearly 1/8" gap at closed throttle which ain't no good. In other words, I had no idle enrichment. The accellerator pump wouldn't actuate until nearly 1/4 throttle.

My carborator is a 4011 type (I think). It's got the one-piece cast bowl / base assembly with a key-whole style top plate.

I went back to my first thought of setting 0.015" gap between the lever and the arm at closed throttle. The spring does compress nearly 3/16" but the coils do not bind. What's up?

-dnult



[This message has been edited by dnult (edited 10-11-2002).]
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post #7 of 19 (permalink) Old Oct 11th, 02, 06:01 PM
 
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What position is your accelerator pump in? (also which color?)

Yours does sound a little weird.....1/8"?

[This message has been edited by chacane67 (edited 10-11-2002).]
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post #8 of 19 (permalink) Old Oct 11th, 02, 06:45 PM
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I always have problems with sticking the feeler in once the throttle is WOT. I question if the spring compresses or the pump arm moves...

Try my way... Loosen the top nut some, then put the .015" feeler between the pump arm and the hex head. Put an open end wrench on the lower hex head (right above the feeler gauge) and go to WOT. Now if the top nut is up off it's seat adjust it so it just makes contact.


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post #9 of 19 (permalink) Old Oct 12th, 02, 02:51 AM
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I had a slight hesitation upon getting into the throttle. What work for me was to adjust the arm so there was no play and the arm would immediately start to move when the throttle lingage moved. I had to slightly tighten it up one more time but all hesitation went away. In effect, you need to slightly preload the arm. I never bothered with the .015 measurement. This was a few years ago and all's been well.

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post #10 of 19 (permalink) Old Oct 12th, 02, 06:22 AM
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Rick is touching on something here... Pump movement should start right as the throttle does. You still don't want to bottom out the pump though. Some times it's necessary to bend the arm that extends to the plastic cam slightly to acomplish this...
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post #11 of 19 (permalink) Old Oct 13th, 02, 05:09 PM Thread Starter
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<BLOCKQUOTE>quote:</font><HR>Originally posted by DjD:
Some times it's necessary to bend the arm that extends to the plastic cam slightly to acomplish this...<HR></BLOCKQUOTE>

I just got back from the Oreilly fall nationals where I spoke with a Holley rep. He mentioned bending the arm. I'll have to give it a look some evening or next weekend. Sounds like that might be the key since I can't seem to find the middle ground.

BTW: The pump cam is brown. This is the biggest cam they make. I was trying to solve the hesitation problem. Maybe the real problem is the arm. It's installed in the standard position (can't recall the whole number).

-dnult
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post #12 of 19 (permalink) Old Oct 16th, 02, 06:03 PM Thread Starter
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I took some measurements off of three accellerator pump cams I had on had. Here are the results. The three cams I have on hand are a white cam (with two holes), a pink cam (with three holes), and a brown cam (with one hole). I clamped an old holley carb in the vise, installed a protractor on the throttle arm and measured the lift with a dial indicator.

I won't present the full result here, but rather will summarize my findings and ask for comments on a couple of observations I made. My nomenclature is P for pink, W for white, and B for brown. The letter is followed by two numbers separated by a colon. The first number is the hole number in the throttle lever (1 or 2) and the second number is the cam hole (1, 2, or 3).

The W2:2, W1:1, and B1:2 settings showed a similar result that was logrithmic. The lift was higher and more agressive at lower throttle angles and leveled off around 40 degrees. Full throttle was at 76 degrees.

The P2:3, and P1:1 settings were more linear throughout the range of settings, although the P1:1 setting provided nearly 0 lift below 5 degrees. I suspect an adjustment of the actuator lever might correct the problem. At low angles, the arm was contacting the clock spring on the throttle shaft.

I apparently had my carberator setup with the B2:2 setting which is impractical. It provided nearly zero lift at low angles and over 0.350" lift at 76 degrees. All other cams / settings topped out between 0.130 and 0.200" lift. This must be why I couldn't get the acc pump geometry set according to the procedure.

Now for the questions. There were two predominant profiles - logrithmic and linear. The logrithmic profiles were more agressive than the linear profiles below about 50 degrees. On the other hand, the linear profiles surpassed the logrithmic profiles above 50 degrees by about 0.050". Which of the two general profiles would be most desirable for a street engine.

My engine combo is a 350 +0.030 with an Edelbrock Performer RPM package (heads, cam, and intake) running 11:1 compression. The carb is a Holley 4011-3 (750CFM vac sec).

I am currently trying to fix an off-idle hesitation problem. Timing and jetting should be Ok now - I think the acc pump is the last issue before fine tuning the other things.

If anyone would like to see the results of my measurements, let me know and I'll send you an excel (or ascii) file. I currently don't have a web page set up - sorry.

-dnult
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post #13 of 19 (permalink) Old Oct 16th, 02, 07:20 PM
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"Somebody Stop Me!!!!!" LOL!! You've been busy. I have this little red Holley book and it has a page with a cam volume chart and lots of good info... The chart only shows the 1 & 2 positions and volume given is based on a high capacity pump not the stock one on most our carbs. Pump capacity is rated per 10 strokes of the pump with the proper .015" WOT clearence. The numbers given are greater than you will get with a stock pump but will be proportionate. Here's the cam colors stated,

Note: pos 1 refers to the mounting screw in hole 1 on the cam and hole 1 on the throttle lever and likewise pos 2 is both in hole 2.

White pos #1 17cc; pos #2 19.5cc
Pink pos #1 30cc; pos #2 37.5cc
Brown pos #1 36cc; pos #2 (not given)

The only time you would mis-match holes (screw in throttle lever hole 2 and cam hole 1 as an example) is for drag racing where you are trying to set the squirt to come on at staged rpm and is the only time you wouldn't want the squirt set in play as the throttle just cracks.

I recently went to a 28 squirter from the stock 25 which shortened the duration (let the shot out faster) and created a bigger off idle stumble than I started with. Switching from the white cam (pos 2 19.5cc) to the orange (pos 2 24.5cc) increased the volume enough to over come the larger squirter and resolved the flat spot.
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post #14 of 19 (permalink) Old Oct 16th, 02, 08:25 PM Thread Starter
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I guess I need to purchase a holley book. I'm going to have to take a second look at the cam I called white. It isn't pun-kin orange - I presumed it was fuel tarnished. Perhaps it is orange after all.

If I read your comments correctly, stepping up a cam actually increased your off-idle stumble. That doesn't seem obvious does it. I can only presume that the shot was too short or you might have had the problem I saw with a few cams. Three of the settings I tested didn't pump hardly anything below 10 degrees opening. What is your hunch?

I stuck the 'white' cam in on position 2. It flattens out around 50 degrees, but not as much as several other measurements I took. I also reanalyzed my data by taking the delta between degree settings and plotting it. This gave me a proportional value of the shot size per RPM. The W2:2 was a richer, more broad shot below 50 degrees. Above 50 it pumps very little and practically zero just short of WOT. Unfortunately I'd wake the dead at this hour if I were to start it up. Something for tomorrow. I just hope I don't lean out this 11:1 motor and fry a piston.

-dnult
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post #15 of 19 (permalink) Old Oct 17th, 02, 06:41 AM
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I guess I need to purchase a holley book. I'm going to have to take a second look at the cam I called white. It isn't pun-kin orange - I presumed it was fuel tarnished. Perhaps it is orange after all.
White might look grayish but I doubt orangeish.... I think the number 218 is stampped on the white. (I can verify tonight at home)

If I read your comments correctly, stepping up a cam actually increased your off-idle stumble.
Just the opposite, the larger nozzle reduced the duration of the shot causing the stumble and stepping up the cam (more volume) removed the stumble. The 2 changes in effect gave me more faster.

Three of the settings I tested didn't pump hardly anything below 10 degrees opening. What is your hunch? Mis-matched holes? You might have a staged idle of 3000rpm at the lights and want little or no pump until then. What was this carb off of before you got it?

I stuck the 'white' cam in on position 2. It flattens out around 50 degrees, but not as much as several other measurements I took. I also reanalyzed my data by taking the delta between degree settings and plotting it. This gave me a proportional value of the shot size per RPM. The W2:2 was a richer, more broad shot below 50 degrees. Above 50 it pumps very little and practically zero just short of WOT. Unfortunately I'd wake the dead at this hour if I were to start it up. Something for tomorrow. I just hope I don't lean out this 11:1 motor and fry a piston.
-dnult

I think the white is designed for street use where you want most of your shot off idle. As for leaning out your mill the pump shot is a helper to get the carb from one circuit to the next. It has nothing to do with the actually running rich or lean. Here's a direct quote from my book. (Holley Carburetor Handbook by Mike Urich)

<BLOCKQUOTE>quote:</font><HR>The accelerator pump has 2 functions:
1. To make up for the lag in fuel delivery when the throttle is opened and more air rushes in.

2. To make up for fuel condensing onto the manifold surface when the throttle opens suddenly at low engine speeds.

Because air is lighter - has less mass - than fuel, airflow responds much more rapidly than fuel flow to changes in throttle settings. Whenever the throttle is opened, the engine instantly receives more air through the larger throttle openings. But fuel flow in the man system doesn't respond as quickly to match this increased air flow.<HR></BLOCKQUOTE>


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