[DeTomaso] No Idle Blues continued

charles buthala charlesbuthala at yahoo.com
Wed Jul 4 13:10:43 EDT 2007


All righty then, I plugged the brake vacuum and gave the secondary screw a 1/4 turn, rechecked TDC and location of rotor.  It fired right up and I could get it to feather down to 8 to 900 RPM with the timing somewhere between 10 and 15 degrees.  Any amount of gas would change the timing, is this normal?  I thought that the mechanical advance would not start under 2000 RPM.  
  Well anyway when I reved it up to run to the work bench and get a screwdriver it dropped RPM and stalled.  I could not get it to fire again.  I had this problem before, when it gets hot it will not fire.  I had the timing light hoked up and it was flashing, gas pressure was up and I could see pump shot.  I checked the #8 plug and it was not wet but was a little dark.  I turned in the 4 corner idle screws 1/4 turn to 1 turn out.  Hummmmmmm.

Will Kooiman <wkooiman at earthlink.net> wrote:
  I have the same intake.

I had similar problems with my 428 in my Mustang. I had the Shelby C7ZX 2x4
intake with 2 Holley 1850's. It wouldn't idle like I wanted. I could close
the idle screws all the way, and it wouldn't die. I could open them all the
way, and it wouldn't make a difference. I tried drilling holes in the
primary throttle blades. That helped a little.

I know I'm going to get slammed for this, but it turned out to be a problem
with the rings. It looked like it had standard rings in a .030 block. One
cylinder had a ring gap of .100 - more than a spark plug gap. The ring
tension was almost non existent. I bought the engine from a guy that had
rebuilt it. It sat in my dad's barn for about 8 years. I took it apart,
replaced the bearings, cleaned it up, and put it back together. The hone
was still on the cylinders. I didn't even look at the rings. This was a
rush job - moving, job issues, etc. - so I didn't spend the time I should
have. Once I noticed the rings, I bought new file-to-fit rings, and it made
a huge difference. It felt like it had 150hp more.

Another idea is to borrow a known-good carburetor. Even if the
jets/idle/etc. aren't optimized for your engine, it should be close enough.

Good luck.

-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of charles buthala
Sent: Wednesday, July 04, 2007 10:06 AM
To: detomaso at realbig.com
Subject: Re: [DeTomaso] No Idle Blues

Great information thanks. I will check for vacuum leaks, and plug off the
port that goes to the brakes. I am running a single plane Jack Rousch high
rise A331 intake manifold. I do not have the problem that Mike had, that
sounds like a float bowl problem. I was reading some of the comments on the
Network 54 Cleveland forum, and found that one person had a similar problem.
The fix was to turn the idle speed down all the way and on the bottom of the
main body of the carb there is an adjustment screw for the secondary
butterflies. It said to adjust the secondary flies to open up the idle
slots 0.020. If the idle circuit is not working then the 4 corner screws
will not work.
What is the stock fuel pump pressure, I can only get 6psi. 
My problem with setting the timing is that I have to keep it running, turn
the distributor, hold the light and think all at the same time. 

Will Kooiman wrote:
I have a Proform center section, QFT baseplate, QFT metering blocks, and
QFT
fuel bowls.

I'm not debating Mikie's experience. I'm just offering mine.

I couldn't be happier with my carburetor. I'm getting right at 20mpg, it
starts great once it warms up a little, and it runs great too. 2-3 years
ago it did 342HP at the wheels. I've fixed some stuff since then, so it's
probably around 370HP by now.

My 4-corner idle screws are out 1/2 of one turn. Any more than that and the
A/F gauge goes way rich all the way up to about 3000rpm.

It idles at 800rpm. I believe the idle vacuum is around 17 or 18.

If you have to open your screws that much to get it to idle, you probably
have a vacuum leak somewhere. The most common places are the intake
manifold and possibly missing ports on the carburetor. Also - there's the
vacuum line to the brakes, but I imagine you would have noticed that if you
drove it. Try plugging all vacuum lines (especially the PCV) and see if it
will idle.

It could maybe be the timing too, but it would have to be way retarded to
act like this. You said you had 30BTDC at 1450rpm. I'm not sure when the
advance starts kicking in, but I doubt it adds that much by 1450rpm - maybe
8-10 degrees. If that's so, your initial is around 20BTDC. We could debate
forever if that's "right", but it surely isn't retarded.

I don't know how retarding the cam affects all of this. I've never done it,
so someone else will need to chime in.

If your fuel lines are too small, you'll see it under load or at high rpm -
not at idle.

I started with a 650 dbl pumper. It ran fine. The only problem I had was
the manual choke closing on its own once. Not a big deal. Oh yeah, I also
got junk in the needle/seat once. The first change I made was the center
section. Just for grins. No problems there, but it didn't seem any better
either - maybe a little smoother, but not that big of a difference. The
next step was QFT billet metering blocks. They have changeable power valve
enrichment circuits, plus all the emulsion circuits can be changed. I was
running 1.5 turns out on the idle screws with the Holley metering blocks.
With the QFT blocks, I had to go to .5 turns. The last step was the billet
baseplate, plus the QFT fuel bowls. The QFT fuel bowls have a site window
that is easy to see through. The others are almost impossible for me. It's
a lot easier to set the floats with these fuel bowls.

By the way, I have A3 heads, a Mallory (with pertronix) distributor, stock
pistons - so about 10.5-1, slightly smaller cam - Comp 282S, and straight up
timing.

To reiterate, what you're describing sounds like a big vacuum leak. I had a
small one at cylinders 7 and 8. That's where I attached the carburetor
return spring. When I tightened the bolt, I didn't get it tight enough. It
kept pinging, when it shouldn't. I removed the intake and saw a black path
into the ports where it had been sucking oil.

What intake are you running?

Will.

-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of MikeLDrew at aol.com
Sent: Wednesday, July 04, 2007 1:08 AM
To: charlesbuthala at yahoo.com; detomaso at realbig.com
Subject: Re: [DeTomaso] No Idle Blues

Charles,

FWIW I had the same problem with my Cobra, which had a Holley 750 with a 
Proform center section. It turns out the Proform center was a complete and
total 
POS.

It was virtually impossible to start the car without without pumping the gas

and holding the throttle wide open, and it didn't idle properly. RIck 
Moseley came over to help troubleshoot it, and was horrified at the spray
pattern. 
At idle, the carburetor was literally POURING gas into the engine. The 
'spray' boosters weren't spraying at all--it was just running like a water 
fountain. There was no way to adjust it.

The solution was to throw the 'trick' Proform center section over the hedge 
and reinstall the stock Holley 750 center, which works flawlessly.

Be advised that efforts to start the car with the ProForm section often 
resulted in a fireball three feet high out the carburetor, something you can

ill-afford in a Pantera. You might not have the same problem, but just in
case, be 
prepared.

Mike


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