[DeTomaso] New Pantera owner on Long Island

Tue Mar 24 20:03:07 EDT 2009

Sorry, long...

This is my favorite website for tuning Holleys.  http://www.bob2000.com/carb.htm

Here's what I do.  I'm not saying I'm an expert or anything, but it has worked well for me.

Start with a carburetor in good shape.  Old Holleys sometimes have tuning issues that are hard to diagnose.  At least it's hard for me.  Maybe it's leaking air.  Maybe it's dirty, I don't know.  I've had great luck with relatively new Holleys.  I've had bad luck with very old Holleys.

Hook the electric choke to the stud on the back of the alternator.  It's a small stud that only makes 12v when the alternator is turning.  That way, your choke won't open unless the engine is running.  You also aren't stealing electricity from your coil.  Be careful not to shock yourself.  Use a voltmeter to find the stud that only makes 12v when the engine is running - not key on, spinning.

Use an inline fuse.  If the wire shorts to a ground, it will turn into a red hot problem in about 10 seconds.  That's how I lost my tach wire.  (it wasn't me - it came that way)  Don't forget to use a fuse.

Rotate the choke (black plastic cylinder) until it barely closes.  Send 12V to the hot wire and wait for it to open all the way.  The engine doesn't have to be running.  You just need 12V to the electric choke.  You might want to time how long it takes to open.  If it takes 5 minutes, you're going to have a choke for 5 minutes once you start your car.  Make sense?  If it opens too fast, rotate the choke so it stays closed longer.  You should have an idea of how long you need your choke, based on how cold it is where you live.  It's about 2 minutes in Houston in the middle of winter.  The electric choke is a timer.  It isn't based on the engine temp or the outside temp - not very much anyway.

Adjust the floats.  I tried the Moroso clear site plugs, but I don't like them.  I switched to dominator fuel bowls (Summit/QFT). They have larger clear site windows.  You can easily see the fuel level w/out removing the plugs.  I really like these fuel bowls.  If you use the stock fuel bowls, you have plugs brass plugs.  Run the engine.  Shut it off.  Open the plugs and rock the engine from side to side.  Adjust the fuel level so it barely comes out when you rock the car from side to side.  If you have it set too high, it might stall under heavy braking.  If that happens, adjust the fuel level down a bit - until it doesn't stall under braking anymore.

Make sure the carburetor is level.  Most 351C intakes are slanted to the front.  If the carburetor isn't level, it might cause the engine to stall under braking.  This caused me fits until I made a slanted spacer to level the carb.  Once the carb was level, the problem went away.

Next, adjust the idle screws.  It sounds like what you are doing is correct.  I do it slightly different, but that's because I don't have a choke.  I adjust the idle screws so it runs w/out having to tap the gas pedal by the time I get to the first major road from my house.  It's a little too rich, but I don't want to deal with the driveability issues.

Next, use an A/F meter to set the jets.  You basically have 2 settings - cruising and full power.  The power valve only impacts the flow of fuel to the jets.  When the power valve opens, it's like you just added 6-10 jet sizes.  It doesn't do anything at idle.  It isn't 100% open and 100% closed, but it's easier to think of it that way.

I try to set the jets so the A/F is at slightly rich under full power.  You make more power by going lean, but if you go too lean, you start burning parts.  It also causes pre-ignition to happen earlier.  There's a phrase - lean-is-mean.  Most Holleys are jetted slightly rich.  It's safer that way.

I also try to set the jets to be at max lean (but not too lean) during cruising.  It keeps the plugs cleaner, plus you get better gas mileage.

I'm not any good at reading plugs.  I'm an old timer, but not that old.

You can fiddle with power valve restrictors if you have a billet metering block, but I haven't found the need.  A good Holley gives great power and great mileage if it is adjusted properly.

You can also fiddle with air bleeds.  My carburetor has changeable air bleeds, but I haven't messed with them.

Don't forget to use a vacuum advance distributor.  Lean mixes burn slower, so you need more advance.  It's worth 2-3 mpg, plus it runs cooler, and it's quieter.  As soon as you mash on the pedal, the vacuum goes away, and you're back to where you would have been w/out a vacuum advance distributor.

Hook the vacuum line to the port on the metering block - not the intake manifold vacuum (on the baseplate of the carb).

I think that proper timing impacts the smell too.  If your timing is retarded too much, it's probably sending more gas out the exhaust and maybe changing the chemistry - i.e. temps for the combustion.  I'm just guessing on this one.

Your gas smell might be coming from your charcoal cannister.  It vents the fumes from the gas tank.  It is located behind the low-pressure water bottle.  It is most likely 36 years old, so it's probably soaked with fuel by now.  I removed mine.  It smelled like the inside of a gas tank.  You can replace it, but I don't think there is a direct replacement.  I'm sure there is an equivalent part somewhere, but I've never looked.

If you really want it to run good, take it to a dyno.  If its a decent dyno, they'll help you with the carburetor.  Come prepared, though.  Bring jets, gaskets, tools, etc.

I've messed around with the accelerator pumps, but not enough to know what I'm doing.  I've been pretty happy with my Holley by following the steps listed.

Oh yeah, the power valve.  It opens when the vacuum drops below the rating.  A 7.5 power valve will open when the intake manifold vacuum drops below 7.5hg.  There are high-flow power valves that flow more fuel than normal power valves, but it is also restricted by the PV feeds (in the metering block near the pv threads).  You can drill them out to flow more fuel, but I wouldn't bother.  If you're going to go to that effort, buy a billet metering block. They have changeable PV feeds.  At any rate, use a PV that opens when you need power.  Simple enough, right?  Drive with a vacuum gauge and an a/f meter, cruise down the interstate, start pushing down the gas until it starts to stutter.  Watch the vacuum gauge.  When it hits the PV rating, you should see the a/f meter go rich, and you get more power.  Go to a larger rating to get it to open sooner.  The stock PV is normally pretty good, but you can either go to 1/2 the idle vacuum or 4-5HG below the cruising vacuum, whichever is smaller.

Order of tuning:
1. rebuild carb if possible or start with a new carb
2. adjust the choke
3. adjust the fuel level (if you change it later on, you'll impact everything else)
4. set the initial timing
5. adjust the idle screws
6. adjust the jets (most time consuming)
7. adjust power valve
8. use a vacuum advance distributor

My carburetor is a ProForm main body (you can also do a Holley part for this), dominator fuel bowls, Quick Fuel Technology metering blocks and base plate.  If I don't like the Webers, I'm going to switch back to the Holley.

Good luck.

-----Original Message-----
>From: "Mirril M. McMullen" <mirrilm at earthlink.net>
>Sent: Mar 24, 2009 5:25 PM
>To: LEVITT1946 at aol.com, detomaso at realbig.com
>Subject: Re: [DeTomaso] New Pantera owner on Long Island
>
>Robert,
>
>Seems to me you cant run the electric choke off the 12volt coil wire because
>of the ballast resistor.
>
>You need another 12 volt source.
>
>Someone will respond with the real reason you cant use that source.
>
>Mirril M. McMullen 
>Mobile: 917 295.9587 
>AIM:      MirrilM 
>email:   MirrilM at earthlink.net 
>
>
>-----Original Message-----
>From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
>Behalf Of LEVITT1946 at aol.com
>Sent: Tuesday, March 24, 2009 2:33 PM
>To: detomaso at realbig.com
>Subject: [DeTomaso] New Pantera owner on Long Island
>
>Hello All,
>I am the new owner of the 1972 Detomaso Pantera That Boyd was talking about
>
>yesterday. The holley 750 (3 yrs old) that is on the car had the choke wired
>
>open and held in place .The car has been running extremely rich since I  
>purchased the car. I went to my local speed shop and purchased a holley
>matching  
>electric choke. I wired the hot wire to a 12v ignition controlled wire.
>Ground  
>wire connected to the carb itself.At ice cold start I turn the key on 
>....pump  gas once and hear the choke engage.Then I turn the key and she
>starts up 
>....low  idle and will flutter out unless i control the gas peddle myself to
>
>keep her  running. I have also tried readjusting the four tiny screws at the
>four 
>corners  of fabulous holley carb.I have backed each screw all the way in and
>
>then back  out 1.5 turns .I have then adjusted each screw for highest RPM.
>The 
>car feels  like she is missing or tugging and I know its the carb. When i 
>shut her down she  sometimes blows a flame out the tailpipes. Any ideas?
>Blown or 
>wrong power  valves installed? Stuck float levels? 
>All of this seemed to start right after I installed the electric choke. Car
>
>was running rich before the choke by the way . Fuel pressure is at 7. vacuum
>
>approx 13. Mallory electronic ignition. Plugs are dark with less than 1000  
>miles on them  
>Robert    
>**************Feeling the pinch at the grocery store?  Make meals for Under 
>$10. (http://food.aol.com/frugal-feasts?ncid=emlcntusfood00000002)
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