Looking for help??? In all my years rebuildin and running Holley carbs, this article(s) was the most helpful in the world, This will be the last time I post to you unless you can prove that you followed the basic principles.

Start over from the beginning!!!!!!!!!!

Put the carb back to stock, set your timing, set idle to stock, i.e 1 1/2 turns out. set the float level. Put car in gear, then get your manifold vacuum reading. I it's lower then 7" you need a 5" power valve. (example)The specs of your engine must be completely known before carb tuning actually works, no vacuum leaks, no exhaust leaks,
timing dead on, e.t.c You are beating yourself up without even attempting to solve the problem.

you can run a holley carb with 90/100 jets and it will still run, you need to run the leanest size jets to achieve the best power in a mechanicAL CARB.
Read this article, then come back to us after you did the steps....Good Luck.

ACCELERATOR PUMP SYSTEM

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.


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.


Holley accelerator pump nozzles are stamped with a number which
indicates the drilled pump hole size. For example, a pump nozzle
stamped "35" is drilled .035". Pump nozzle sizes are available from
.025" to .052". Please note that whenever a .040" or larger accelerator
pump nozzle is installed the "hollow" pump nozzle screw, P/N 26-12,
should also be used. This screw will allow more fuel to flow to the
pump nozzle, assuring that the pump nozzle itself will be the limiting
restriction in the accelerator pump fuel supply system.

NOTE: When changing the pump nozzle it's best to jump three sizes. For
example if there's currently a off-line hesitation with #28 (.028")
pump nozzle, try a #31(.031") pump nozzle. If you must use a #37 (.037")
or larger pump nozzle, then also use a 50cc pump.


The same applies to the accelerator pump cams. Once a pump nozzle size
selection has been made the accelerator pump system can be further
tailored with the pump cam. Holley offers an assortment of different
pump cams, each with uniquely different lift and duration profiles,
that are available under Holley P/N 20-12. Switching cams will directly
affect the movement of the accelerator pump lever and, subsequently,
the amount of fuel available at the pump nozzle. Lay out the pump cams
side by side and note the profile differences. This little exercise may
help to better explain the differences between the cams and their
effect on pump action.


Installing a pump cam is straighfforward. It's a simple matter of
loosening one screw, placing the new pump cam next to the throttle
lever and tightening it up. There are two and sometimes three holes
in each pump cam, numbered 1, 2 and 3. Placing the screw in position
#1 activates the accelerator pump a little early, allowing full use
of the pump's capacity. Generally, vehicles which normally run at
lower idle speeds (600 or 700 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:


Lastly, a 50cc accelerator pump conversion kit is available under
Holley P/N 20-11 when maximum pump capacity is desired.

POWER ENRICHMENT SYSTEM

The power enrichment system supplies additional fuel to the main system
during heavy load or full power situations. Holley carburetors utilize a vacuum
operated power enrichment system and a selection of power valves is
available to "time" this system's operation to your specific needs. Each
Holley power valve is stamped with a number to indicate the vacuum opening
point. For example, the number "65" indicates that the power valve will open
when the engine vacuum drops to 6.5" or below. An accurate vacuum gauge,
such as Holley P/N 26-501, should be used when determining the correct
power valve to use. A competition or race engine which has a long duration
high overlap camshaft will have low manifold vacuum at idle speeds. If the
vehicle has a manual transmission, take the vacuum reading with the engine
thoroughly warmed up and at idle. If the vehicle is equipped with an automatic
transmission, take the vacuum reading with the engine thoroughly warmed up and
idling in gear. In either case, the power valve selected should have a vacuum
opening point about 2" Hg below the intake manifold vacuum reading taken.


A stock engine, or one that is only mildly built for street use, will have high
manifold vacuum at idle speeds. To determine the correct power valve the
vehicle should be driven at various steady speeds and vacuum readings
taken. The power valve selected should have an opening point about 2" Hg
below the lowest steady speed engine vacuum observed.

POWER VALVES

The power valve is a key component of the power enrichment system of Holley
performance carburetors. The power enrichment system supplies additional
fuel to the main system during heavy load or full power situations. Holley
utilizes a vacuum operated power enrichment system and a selection of power
valves is available to "time" this system's operation to your
specific requirements.


Each Holley power valve is stamped with a number to indicate its vacuum
opening point. For example, the number "65" indicates that the power valve
will open when the engine vacuum drops to 6.5" Hg, or below.


An accurate vacuum gauge, such as Holley P/N 26-501, should be used when
determining the correct power valve to use.


A competition or race engine which has installed a long duration, high overlap
cam will have low manifold vacuum at idle speeds. If the vehicle has a
manual transmission, take the vacuum reading with the engine thoroughly
warmed up and at idle. If the vehicle is equipped with an automatic
transmission, take the vacuum reading with the engine thoroughly warmed
up and idling in gear. In either case, the power valve selected should have
a vacuum opening point about 2" Hg below the intake manifold
vacuum reading taken.


A stock engine, or one that is only mildly built for street use, will have high
manifold vacuum (17" to 21" Hg) at idle speeds. To determine the correct
power valve, the vehicle should be driven at various steady speeds and
vacuum readings taken. The power valve selected should have an opening
point about 2" Hg below the lowest steady speed engine vacuum observed.
Holley has a 6.5" Hg power valve, P/N 125-65, which usually works out
well for most driving situations.

 

Believe me, I have triple checked all the basic stuff and I have already tried everything suggested. I checked the manifold vaccum with it in gear and it was bouncing between 7 and 8 so I installed a 5.5 power valve. I have always had my timing set at 38 degrees and I have tried 36 and 40 with very little differences and I don't have any vaccum leaks. I tried several different pumps and the stock size seems to work just fine, I don't have any throttle response issues or hesitation or bogging off the line. I have my fuel pressure set at 7 psi. I have torn down my carb and cleaned/rebuilt it and so have others that know more about holley carbs than I do, nobody has been able to figure out why it runs this way. I have tried different air bleed screws on the proform main body and nothing changes. I have sight plugs on the float bowls so I can see that the float level is set right. I have tried all stock settings and my car won't even drive without backfiring and sputtering if I have the stock jets in it, I have tried 68/78, 70/80, 74/84, 76/86, 80/90, 82/92, 84/94, 86/96, 88/98. It ran the exact same times at the track from 84/94 to 88/98 jetting. I have borrowed and tried different squirters, etc. I am at my wits end and I think I am going to just part out the proform main body, the only thing I can think is that it flows too much for my engine or that fuel pressure drops too low but that wouldn't explain why it runs fine at launch and while cruising. I had a friend who is good with carbs look at it and he couldn't find what is wrong, when I had 80/90 jets in it he drove it around then shut it down right away and we removed all the plugs and the plugs showed we were running lean. I thought that with jets that were so much larger than stock that it atleast wouldn't run lean.

 

timing set at 38 degrees, what is the initial? try 12 advanced initial, I found that my 750 proform loved 76/81, I also ran no vacuum advance, you are probobly running into a big timing issue more then carb. Actually what type of cam is it, the lift, the duration, what type of heads, the flow numbers, what type of intake, single plane or dual, what type of stall if your an auto, what type of motor, bore, e.t.c.... what type of distributor, what type of plugs, what type of headers, factor these in for me and I can get it running..

 

Initial timing is at 17 degrees with 21 degrees mechanical advance, I changed the springs and it reaches total advance at 2500 rpm. It is a MSD distributor with 6AL box. As for the engine it is a 350 ZZ4 shortblock, heads are new trickflow (I'll have to look up the flow numbers), cam is a Comp cam extreme energy hydraulic roller with 236/242 @.50, lift is .520/.540. 110 degree lobe separation. Intake is a gasket matched Edelbrock performer RPM dual plane. Hedman 1 5/8 long tube headers, dual 2.5" pipes with hooker aero chamber mufflers. B&M TC that only stalls at 1500 rpm but it is the high rpm power that I lost from the edelbrock 650 carb to this holley DP. AC-delco plugs gapped at .050
I am going to try and rig a fuel pressure guage to my hood temporarily so I can see if my fuel pressure drops off too much when I get on the throttle.

 

TOO MUCH TIMING!!! You have too much initial timing. The more advance, the less higher RPM's, the less, the more RPM's. That is why you are hitting a brick wall up high and surging at cruise RPM's. Start the carb back to stock, set the timing to 10 degrees and bolt it down, take a ride. If there is pinging or it doesn't have power, set the timing up 2 degrees in 2 degree increments. I guarantee once you have the timing dead on, that carb is gonna be like playing pocket pool.. When I had timing issues I blamed the carb as well, once I set my timing correctly there was a huge gain and change.. It's going to take up a lot of time and gas to get right, but devote one day to it and let us know how it worked out

Also the intake is killing you as well, Mechanical carb and the lift/LSA/duration needs more of a single plane. You also need a 2800 stall to get you into the traps faster.
Trade someone for the Edelbrock torker2 or a team G and right there you will feel a big change. I tied the performer RPM and hated it, I lost 35 horses switching from the team G.

 

frist guys you should check your fuel flow the guy said he went to bigger carb he has a 12sec car on a 12sec car the fuel pump should flow a gallon of gas in about 35 seconds this is the frist thing you check if its ok then start tunning the carb i had the same problem got the fuel flow right the car went from 12sec to 11.40et-(388LT1 750dp gm dual plain intake)

 

First I'd like to thank everyone for their input and advice. Second I want to kick myself for trying too many things. I played with my timing until I came to the conclusion (seat of the pants feeling only, not at the track) that timing was best at 13 initial and 35 total timing. I bumped up the fuel pressure at the same time to 8.5 psi. Then the car ran pig rich so I re-jetted it to 76-81 and it cruised fine and ran well except under wide open throttle so eventually from playing with the jets again I have come to the conclusion that the 76-86 combo seems to work well. Again, I haven't been to the track to verify this but my car wouldn't even cruise with 76-86 jets before I retarded the timing and increased the fuel pressure. Now the car cruises great and accelerates pretty hard. I don't have any driveability issues (except a vibration which I hope to solve with a new trans yoke). I'll have to wait until I get to the track to verify if this helps my times because I don't think I can feel the difference between 1/2 a second or not on the street.
Thanks guys.

 

Told you it was the timing

I'm glad you found the problem, good luck at the track

 

Thanks for the help.

 

Interesting thread and results.

Nice to see it drives better for now. If you can't drive it..ya might as well get rid of it.