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Old 07-17-2003, 11:14 PM
87 350monteSS's Avatar
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holley accelerator pump

Can somebody tell me how i should have my accelerator pump set up on my 750 cfm with vacuum secondaries it has a bog when i step into it too quick, like is the stock pump big enough, and what accelerator cam should i use? maybe some of you have worked with or had a setup close to mine.



Specs of my motor are stock 1996 350ci block with old style pocket ported and polished heads holley 750cfm vacuum secondaries with holley street dominator intake hydrolic 488 lift cam with 1.6 roller tip rockers accel coil headders to dual 2 1/2" with flowmaster mufflers





Thanks in advance you guys are the best, you've turned my vehicle from a car into a street machine

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Last edited by 87 350monteSS; 07-17-2003 at 11:19 PM.
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Old 07-18-2003, 07:08 AM
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Sounds more like someone has done some other work to the carb...? If it bone stock and never been apart it should work with most street cams and setups... If the transition is not smooth it possibly has to light of a spring in the dash pot...? Or possibly the power valve is not right...?
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Old 07-18-2003, 09:11 AM
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This is your second post on the subject, one must help ones self.
This information is located in the Knowledge base, plus I sent you a email on the subject along with Holly's site for trouble shooting.
What don't you understand? The spring is wrong for the secondary opening timing, the accelerator pump and pump cam are wrong. Please read the info on the site for trouble shooting.
Each motor is different YOU must tune in your carb, no one can tell you how to do it exactly because of different set-ups.
http://www.holley.com/HiOctn/TechSer...o/FMCTech.html
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Old 07-18-2003, 09:25 AM
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try unscrewing the nut on the arm half turn at a time to see if that helps i set mine with 000.00 lash
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Old 07-18-2003, 09:38 AM
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The pump MUST be adjusted at WOT. This is why everyone complains about Holly carbs because there not adjusting the carb properly.
Heres from Hollys site.
The accelerator pump system consists of three main components: the pump diaphragm, the pump cam and the pump nozzle. This is the carburetor system that is most responsible for having good, crisp, off-idle throttle response. Its purpose is to inject a certain amount of fuel down the throttle bores when the throttle is opened. By accomplishing this purpose it acts to smooth the transition between the idle and main circuits so that no stumble,
hesitation or sluggishness will be evident during this transition phase.

READ HERE for the proper way to adjust the pump arm.

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. This will cause premature pump failure. Once this clearance has been set take a good look at the pump linkage and work the throttle. Make sure that the accelerator pump arm is being activated
the moment that the throttle begins to move. This will assure that pump response will be instantaneous to the movement of the throttle. These adjustments can be made by turning the accelerator pump adjusting screw that is located on the accelerator pump arm together with the pump override spring and lock nut.

The amount of fuel that can be delivered by one accelerator pump stroke is determined by the pump's capacity and the profile of the pump cam. The period of time that it will take for this pre-determined amount of fuel to be delivered is affected by the pump nozzle size.

A larger pump nozzle will allow this fuel to be delivered much sooner than a smaller pump nozzle. 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.

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Old 07-18-2003, 11:12 AM
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sorry 1bad80 iam not trying to upset anybody but before i was adjusting the spring in the secondaries which went very well and helped a bunch now iam trying to adjust the accelerator pump
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Old 07-18-2003, 11:37 AM
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Sorry If I came on strong, I did not mean to. You were given some incorrect advice, I wanted you to go to the site and read the trouble shooters guide first before touching your carb. It can cause you more problems and not know what to fix or change back to. Dont touch the power valve, if your driving at a constant speed (55) and the car seems to sputter or act funny thats when you should change to a lower power valve.
You probably have a Holly #3310- 750 carb.
If there is no backfire when the throttle is put down all the way the nozzle is OK, Its the spring for the secondaries. A quick change spring cover would help you quite a bit for tuning it in, it sounds like the rear are opening to soon causing the lag, a heaver spring would help. I advise on getting the trick kit, it has most of the parts that you need. Please email me if you have any other problems or questions and I'll do my best to help you.
George
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Old 07-18-2003, 01:37 PM
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i got and installed the quick change kit last week and have tryed all of the springs i found the lightest spring to seem to work the best since i have so little vacuum from the big cam, its seems now that when i mash the pedel to quick it bogs, i adjusted the accelerator arm and lever to .015 and that helped, the guy that organially built the car said it never had a bog when he had it, the second owner tryed to tweek every thing and screwed a lot of it up
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Old 07-18-2003, 07:51 PM
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If you don't have any luck messing around with pump,cam,nozzle size....then do this......get your hands on a vacuum gauge...connect it to a full manifold vacuum supply and start the car....note the vacuum you have at idle.....you will divide this by 2 to get the size power valve you need........next remove fuel lines,drain the bowl,remove bowl,now...be careful when removing the metering plate.....look behind it to see if fuel made its way behind the power valve.....if it's wet back there then the power valve is blown out.......if not check the #'s to see if they match your cars divided by 2 vacuum.....change accordingly........clean everything carefully, pay attention to air bleeds.......assemble and fire it up........hope this helps........dig through the Holley tech site like suggested also....very good info there.....
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