Initial jetting recommendations - O-3310S Holley 750

I would change the squirters to a 25 and the spring to the plain silver one.
The primary jets should be just about right as well as the secondaries.

That black spring will never fully open on a 351 unless you are turning 9,000rpm.

The 31 s are a big block squirter and tend to bog the engine off of idle a little.

Other then that you are close. I don't see a major problem with the carb numbers. Even the power valve ia about right.

Remember that if you are using the holley automatic choke thermostat that is a "universal" thermostat and will generally open too quickly.

I have found that the choke thermostat off of the 84 Mustang GT works very well. It is easy to get also as an aftermarket part.


And don't forget the fuel level settings. Too low and the carb leans out and too high and it floods. Don't take them for granted.

Remember the carb angle in the Pantera can be different and thus effect the correct fuel level setting.

Hope this all helps.

I would start at
68 jets in the primary 72 in the seondary ( 18 sound sligh for vacumn and usually the power valve is half the vacumn .. was it at the carb ..if so its 1/2) 31 squirter is fine I ave never changed pump cams in my life from stock ..I would make sure the play in the accelaertor pump lever jiggles about .015, I would use std 28cc accelerator pumps NOT 50cc should work.

Guys, thanks for the input on the carb. I pulled the 750 off the white
Pantera and temporarily installed the 735 that I used to run on the red
Pantera. While the 750 was off, I converted it to a 4150, installed the
plain spring and have set the accelerator pump and float levels.
Unfortunately, I've not had a chance to run it yet as it's been raining
and raining and raining some more. I had a problem with 735 Holley
metering block gaskets. Holley has different gaskets depending upon
whether or not the metering block is equipped with an accelerator pump
transfer tube:

http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars...ock_gaskets.jpg.html

The metering block on the left has an accelerator pump tranfer tube above
the power valve and uses a gasket with a semi-circular notch above the
power valve cut out hole while the one on the right has a small hole instead
of the transfer tube and uses the gasket without the notch. I pulled the
brown gasket out of my 735 Holley even though it does not have an accelerator
pump tranfer tube. I replaced it with a blue non-stick gasket of the same
style before I realized it was the wrong gasket. I've since replaced it with
the proper style. It is currently jetted with the stock 66 primary and 78
secondary jets and has the stock plain spring but a short (4.5") power valve.
The latter was on the recommendation of someone I know who has had a fair bit
of experience tuning the 735's.

> Remember that if you are using the holley automatic choke thermostat that is
> a "universal" thermostat and will generally open too quickly.

It's weird but that was never a problem on the red Pantera with that carb
but the white Pantera has a larger capacity radiator (and a milder engine)
and takes longer to warm up. In fact, the white Pantera has manual fans
and I generally never have to to turn them on, even in stop and go traffic.
In any event, it does seem like the choke is coming off early.

> I would change the squirters to a 25 and the spring to the plain silver one.

I've changed the springs but am holding off on the squirters until I run
it with the wide band for a while.

> I have found that the choke thermostat off of the 84 Mustang GT works very
> well. It is easy to get also as an aftermarket part.

Good tip, thanks. I've got a 4180 that supposedly came off an '84 or '85
Mustang 5.0L. I'll take a look at it's choke set-up.

> And don't forget the fuel level settings. Too low and the carb leans out
> and too high and it floods. Don't take them for granted. Remember the
> carb angle in the Pantera can be different and thus effect the correct
> fuel level setting.

Floats are set so that with the engine running, it just starts to dribble
out the sight holes when the car is rocked gently.

> 18 sound sligh for vacumn and usually the power valve is half the vacumn
> .. was it at the carb ..if so its 1/2

It was manifold vaccum. For a manual transmission vehicle, Holley suggests
a power valve opening point half the idle vacuum. Others suggest 2" below
the lowest reading you get at part throttle cruise vacuum. I'm going to
start with 4.5" which is lower than either of those methods would suggest.
Most Holleys have PVCR's that are just too large so delaying the power valve
opening might not be a bad idea (better would be to properly size the PVCR's).
I'm curious as to what effect it will have when I put the wide band on.
We'll see how lean it gets before the power valve opens. When I ran the
735 Holley on the red Pantera, it was really hard to get the vacuum to
drop much unless I went to WOT so I ran a power valve 2" below my cruise
vacuum but that car had a fairly different 351C (2+ points more compression,
more cam, single plane intake) than the one in the white Pantera. When
the rain stops, I need to drive the white Pantera around with the vacuum
gauge hooked up to see how it behaves, double check the ignition (still
points) and then hook up the wide band.

> I would make sure the play in the accelaertor pump lever jiggles about .015,

Currently, I've got the accelerator pump set at WOT with 0.020" clearance
when the accelerator pump is bottomed out though Holley recommends 0.015".
Some books say to simply take out all the slack in the accelerator pump
linkage when the throttle is closed but that yields much larger than 0.015"
clearance at WOT. That would delay pump action.

> I would use std 28cc accelerator pumps NOT 50cc should work.

Agreed, the 50cc pump is way too big for this engine.

Dan Jones

I would check the timing of the engine, not enough timing will also make the engine bog down low.
When my car came from Florida it was like that and I was able to put an extra 10 degrees in it which brought it back to life.

I realise this is easier said than done !

> I would check the timing of the engine, not enough timing will also make the
> engine bog down low. When my car came from Florida it was like that and I was
> able to put an extra 10 degrees in it which brought it back to life.

That's a good recommendation and is next on my list. This car has less than
17K miles from new and it's still a points distributor which may have never
been serviced. Plus, it's one of the the dual vacuum retard/advance
distributors. The previous owner capped off the retard port when the Holley
750 and Edelbrock Performer intake were installed. When I purchased my other
Pantera, also a very low mileage car, it didn't run well. The previous owner
had the carb rebuilt which had little effect. It turned out to be the original
points distributor. After installing a Mallory Speed-o-Lite kit in the
distributor, it ran well. I've still got that distributor and an MSD 6 AL
box around here. I may have to install them when I get a chance.

One trick, if you ever have the transaxle out, is to degree the flywheel
so timing can be set at the back of the engine (through the bellhousing
port). Just remember that the flywheel is 180 degrees out from the balancer.
I didn't and dutifully degreed my flywheel so I can now check up to 40
degrees retard through the bellhousing port :-)

BTW, I did get a chance to drive the Pantera with 735 Holley to work today.
Runs much improved but still not perfect.

Dan Jones

I got the chance to spend a few more hours tuning the 735 Holley on the
351C in my Pantera. As initially installed, it way very rich across the
board but would go lean under initial part throttle, as if the accelerator
pump was not working but a visual inspection showed that not to be the
case. Even so, I replaced the accelerator pump diaphragm as this engine
had been sitting on the shelf for several years. To lean out the carb and
make sure I had no vacuum or power valve leaks, I did a number of things:

replaced vacuum caps and the distributor vacuum line

tightened the 90 degree vacuum fitting on primary metering block

removed the metering blocks and squirted carb cleaner through passages,
blew dry with compressed air

replaced the inlet needles and seats, along with float adjusting nuts
and plastic sealing washer

replaced the idle mixture needles (large head style) and cork gaskets

leaned idle mixture screws from 1 1/2 turns out to 1/2 turn out

lowered the float levels on primary and secondary, the adjuster nut is
flush with the plastic top and bottom washers in place

reduced primary jets from #66 to #64

replaced the 4.5" power valve with an unmarked power valve (likely
a 6.5") from an AED rebuild kit, AED power valve is window style but
has fewer windows than previous power valve

bumped timing from 8 to 13 degrees BTDC to compensate for slower burn
of leaner mixture

These changes had the desired effect of leaning out the carb but I went
too far and ended up with the carb lean across the board and cruise
mixtures in the 16's. The previous owner installed a larger radiator
and fans which were wired up to a manual switch. With the carb
calibrated rich, there was never a need to turn the fans on, even idling
in traffic it would stay cool. With the very lean mixture, temperature
crept up in stop-and-go traffic and I could hear the coolant pulsing to
the overflow bottle when I turned the engine off. Also, with the extra
timing, it would kick back slightly on the stock starter when hot. With
the fans on, the engine stayed cool and no coolant noises were heard when
the engine was switched off.

For the next round of tuning, I went to 3/4 turn out on the idle mixture
screws and raised the primary float to richen the idle and primary
mixtures. That ended up a little richer than desired. Setting the idle
mixture screws back to 1/2 turn got me pretty close to where I want to
be. It's now at low to mid 15's cruising in 5th gear between 60 and 80
MPH and drops to mid 12's at WOT. Low speed cruise is in the high 14's,
low 15's and drops to low 12's WOT at low speed. Should yield good
fuel economy and WOT power.

To tune a Holley for best power and fuel economy, you usually have to
alter the power valve channel restrictors (PVCR's). The power valve
only determines the opening point when the additional fuel is added.
It's the PVCR's that how much fuel is added. In general, PVCR's should
be no larger than one half the diameter of your main jets. This ratio
of orifice size to jet size will give you a 25% increase in fuel flow,
approximately the difference in fuel flow required to make the difference
between a stochiometric (14.7:1) and a best power fuel air mixture.
Unfortunately, standard Holley carbs provide no easy way to change the
PVCR's so you have to modify the metering block, either drilling the
passages larger or epoxing them shut and re-drilling smaller. Many
performance Holleys have huge PVCR's which make it impossible to get
reasonable WOT mixtures on milder (and smaller displacement) engines
but the 735 Holley was set up by Ford with reasonably sized PVCR's.
Also, there are aftermarket metering blocks and carbs (QFT is one
example) that have replaceable PVCR's.

The mystery vacuum leak was traced to the PCV grommet in the Boss 351
style Ford Motorsport cast aluminum valve covers. The previous owner
installed the valve covers and used a push-in grommet that allowed the
PCV to pop out. The first couple of times it happened, it was just
partially out and I assumed I knocked it loose when I re-installed the
air cleaner. It finally popped all the way out which clued me in.
I replaced the grommet with the proper twist-in style (Ford part number
C7AZ-6A892-B for finned cast aluminum valve covers with 1 1/4" hole)
and now it stays put.

I had set the idle for maximum vacuum (1 1/2 turns out) which may be
okay for automatic transmissions (in gear with foot on brake) but is
not so good on an unloaded manual transmission. With the wide band
hooked up, I could see the idle was too rich. With the carb off the
car, I initially set the idle screws at the suggested 1 1/2 turns out.
In retrospect, it makes sense I would need to have the idle mixture
screws leaner. A low compression 351C would need less idle mixture
volume than the high compression 428CJ the carb was designed for.
This particular carb has a bulky 90 degree vacuum fitting directly
above the passenger idle mixture screw. That and the electric choke
make the mixture screw difficult to see which makes getting a screw
driver on the screw tricky. I discovered the best way is to set a
small flashlight to illuminate the screw head and look through the
tinted 1/4 window. That made it easy to change the idle mixture.

I had initially set the floats level with the carb off the engine.
When rocked, fuel would dribble out the sight hole as it's supposed
to but I believe that contributed to the initial rich mixture. The
Pantera bolts the transaxle directly to the engine and the assembly
is mounted level in the car. Most production cars have the engine
installed with the nose high, so most intake manifolds have a cant
angle that levels the carb out. In the Pantera that tilts the the
carb nose down which affects the float level. Lowering the float
level had the desired effect on the mixture but I still need to run
the car around to make sure the engine doesn't stall under hard
braking and cornering.

While setting the timing, I discovered a loose distributor wire.
Someone had simply taped a bare wire end to a connector blade.
I installed a matching connector on the bare end.

Given the idle vacuum, I could probably switch to a taller power
valve but what's in there now should work fine and be a bit better
for fuel economy. Next on the list is playing with the secondary
spring.

Dan Jones