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  #46 (permalink)  
Old 08-25-2010, 11:44 AM
chevykid90's Avatar
454, what turns your crank?
 

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i think your right, i just put the old spring back in. and if memory serves me right it was the silver (just metal) one. what spring should i go to next?

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  #47 (permalink)  
Old 08-25-2010, 03:12 PM
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Quote:
Originally Posted by chevykid90
i think your right, i just put the old spring back in. and if memory serves me right it was the silver (just metal) one. what spring should i go to next?
Purple would be the next lighter one to try. You need to get the accelerator pump cam right first, as changing the spring to open earlier without enough pump shot now will just make it worse, a bigger lean hole. From your description of running it up the rpm scale slow in first gear avoids the backfire, you definately need more pump shot. giving the mixture screws 1/4 turn richer may help too, they may be too lean.

Was there a pump cam on the 8700 Holley you bought, from your other thread?? Color?? Might be better than what you have, Orange would be a good one to try.
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Old 08-25-2010, 11:38 PM
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454, what turns your crank?
 

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i thought of that already, but it came with a white one, which looks to be the same size very very similer. going to pick up a cam kit tomorrow, you think the best thing to do is just go one step higher in cam and repeat until no backfire? seems that would be the best way to go about it (like most anything with an engine). lol
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  #49 (permalink)  
Old 08-26-2010, 06:52 AM
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Holley's instructions are on page 6 and 7 HERE.

ACCELERATOR PUMP:
The accelerator pump's purpose is to make up for the lag in fuel delivery to enable the engine speed to increase in response to throttle opening. Differences in vehicle weight, transmissions, and rear axle ratios affect the amount of fuel and the delivery rate that should be provided by the accelerator pump. This may necessitate the customizing of your accelerator pump to your vehicle and its use.

NOTE: The old saying “if a little is good, a lot is better” does not apply to the proper tuning of the accelerator pump. Your car’s performance can be just as bad if it receives “too much fuel too soon” as if it receives “too little fuel too late”.

Two factors that affect the accelerator pump’s delivery is the pump cam and the pump shooter (discharge nozzle). The pump cam determines the total volume of fuel and affects delivery rate; the pump shooter diameter affects delivery rate and helps determine the duration of the shot.

The cams will have 2 (some 3) holes in them. Besides the change to the fuel delivery curve made by changing holes, position #1 is used when the throttle blades at idle are "normal", position #2 is when the tune of the car requires an idle speed of >1000 RPM or so. Position #2 makes up for the additional throttle shaft rotation that's required for the higher idle speed. Cams w/position #3 are usually used on REO 50 cc pumps. Generally, vehicles which normally run at lower idle speeds (600-800 RPM) find this position more useful because they can have a good pump shot available coming right off this relatively low idle. Positions #2 and #3 delay the pump action, relatively speaking. These two cam positions are good for engines that idle around 1000 RPM and above. Repositioning
the cam in this way makes allowance for the extra throttle rotation required to maintain the relatively higher idle setting.

Pump arm adjustment and clearance should be checked and verified each and every time the pump cam and/or pump cam position is changed.
A 50cc accelerator pump conversion kit is available under Holley P/N 20-11 when maximum pump capacity is desired.

Holley says: "If you need more pump shot sooner, then a larger pump nozzle size is required. During acceleration tests, if you notice that the car first hesitates and then picks up, it’s a sure bet that the pump nozzle size should be increased. A backfire (lean condition) on acceleration also calls for a step up in pump nozzle size. Conversely, if off-idle acceleration does not feel crisp or clean, then the pump nozzle size may already be too large. In this case a smaller size is required."

The pump shooters have a number stamped on their casting which designates the shooter size in thousandths of an inch, i.e., a #25 shooter has a .025” discharge orifice. The smaller diameter nozzles lengthen the pump shot duration and are used with heavier vehicles or with vehicles equipped with lower numerical rear axle ratios.

Larger diameter nozzles (.035” - .037”) shorten the pump shot duration, but deliver a greater initial volume of fuel. These sizes should be used on applications where engine speed will increase rapidly (vehicles with good power-to-weight ratios). Best acceleration is achieved when the accelerator pump delivers the lean best power air/fuel ratio to the engine; not when the maximum volume of fuel is supplied.

If a shooter size greater than 0.038”-0.040” is required, a “hollow” discharge nozzle screw is advised. Above a 0.037” squirter size, a 50 cc REO pump may also be required, available under Holley P/N 20-11. Make squirter changes in 3-step increments- if you have a 28, go to a 31, etc.

Be sure the squirter you are using hasn't been drilled oversize! If it has, the number on it obviously will no longer apply.

The smaller sized accelerator pump squirters will cause the duration of the pump shot to be longer. Because the fuel cannot be compressed, the spring in the acc. pump lever compresses then this spring pressure continues to supply fuel through the squirter until the spring has extended back to its original length.

An important point should be kept in mind when tuning a double pumper: The secondary accelerator pump must supply fuel for a sufficient time so that the secondary main nozzles can begin to flow fuel to the engine after the secondary throttles are opened. If the nozzles do not start by the time the pump shot expires, bogging will result.

Also check the accelerator pump nozzles closely to see if they've been drilled oversize. You may have a hard time telling, if they did a good job so a numbered drill set or a wire spark plug gap measuring feeler gage would help to determine the size.

Here are a couple links you might find useful:

INSTRUCTION MANUALS BY P/N- http://www.holley.com/TechService/Instructions.asp

Exploded View and Nomenclature
Manual for Models

2010, 2300, 4010, 4011, 4150,
4160, 4165, 4175, and 4500- http://www.holley.com/data/Products/.../199R10014.pdf

TECHNICAL LIBRARY-
http://www.holley.com/TechService/Library.asp

Last edited by cobalt327; 08-26-2010 at 06:57 AM.
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  #50 (permalink)  
Old 08-26-2010, 11:01 PM
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454, what turns your crank?
 

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ok after reading all that it makes a lot more sense to what everything actually does, and in relation to each other.

so should i then put in that smaller discharge nozzle you sent me and start tuning all over again with a new cam kit?

also it was stated about the number 2 hole being used with an idle >1000 RPM. my car does not like to idle at all below 1000, thats were she sits out of gear and when in gear will go down to about 700-800, i proly will know the answer to my question, but she really does not like the second hole so should i just stick with the first one? maybe i just didnt get the slack taken up enough on the pump arm?

i am almost thinking its going to be one of those things were you would actually have to be here in person to help adjust, seems like there are a lot of moving parts and they all must correspond with eachother just right to make it work well.
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Old 08-26-2010, 11:18 PM
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I would start w/the cluster that I sent, along w/a white cam to start. It's important to remove ALL slack between the linkage and the pump are at idle. There has to be at least 0.015" clearance at WOT so the diaphragm isn't damaged.

Then, using what you read above you can see what the cure is for whatever the problem you have w/an off-idle hesitation or whatever.

I don't recall how the timing curve is set up on your engine. You do need to be sure there isn't an excessive amount of transfer slot exposed at idle. This has been covered numerous times, but basically, it calls for the vacuum advance being hooked up to manifold vacuum so the idle speed is increased, this allows the curb idle screw adjustment to be used to lower the idle speed, this in turn lessens the transfer slot exposure.

If you have little control of the idle quality using the idle mixture screws, this is telling you the transfer slot is over-exposed. This will cause an off-idle stumble, too.
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Old 08-26-2010, 11:54 PM
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454, what turns your crank?
 

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honestly not sure what you mean by the control of idle. i know that when i have the vacuum gauge hooked up i can see the needle moving when i adjust the screws, but the idle doesnt really go up when i turn them out, only goes down when i turn them too far in.

and the term "transfer slot" kind of through me for a loop....i dont recall ever hearing that term before, maybe i just call it something else?
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  #53 (permalink)  
Old 08-27-2010, 02:30 PM
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If you recall how a Holly feeds fuel to the engine, you'll remember the transfer slot is where the fuel comes from when the carb is "transferring" from the idle circuit to the main circuit.

At idle, you want the fuel to be primarily coming from the idle mixture ports, not as much from the transfer slot. That's why the rule of thumb for the transfer slot has often been described as making the slot look "square" (i.e. as wide as it is tall). This is done by turning the curb idle screw in or out as needed to get the proper exposure to the slot- too much will have the engine feeding off of the transfer slot instead of the idle mixture ports, this causes the idle mixture screws to be non-responsive and the idle to be too rich.

To close this transfer slot exposure down, often what's done is the vacuum advance is connected to manifold vacuum. This causes the idle speed to increase. When the idle speed is lowered (by turning the curb idle screw out) this also lessens the slot exposure. Which in turn returns control of the idle to the idle mixture screws.

If you're unsure of what you have for transfer slot exposure, you can remove the carb and look to see what it is.


TRANSFER SLOT (shown over exposed)
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  #54 (permalink)  
Old 08-27-2010, 05:42 PM
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454, what turns your crank?
 

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ok now all of that makes sense. but i have my vacuum advance hooked up to manifold vacuum all the time? i dont have a port vacuum port. i have the the adjustable vacuum canister on my dis. and i set it to only start working after about 13-14 pounds of vacuum. not sure how to describe the tool i used but when you pumped the handle it sucks air in, also used it to check vacuum leaks in my tranny module and break booster.
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