[DeTomaso] Carb and fuel pump

[Daniel C Jones]

> I speculate at 130 MPH, I'm using up all the carb, or all the fuel pump.

Asa,

I ran into a similar problem while tuning the carb on my Triumph TR8 that
turned out to be a restrictive fuel filter.  I have O2 bungs in the exhaust
just aft of the header collector and was monitoring the air-fuel ratio with
a Innovate LM1 wide band oxygen sensor.  My neighbor was driving and in 2nd
and 3rd, WOT was rich through the RPM band but I noticed 4th would
eventually
go very lean at around 110 MPH (around 5500 RPM with my 205/50/15 tires and
3.45:1 final drive ratio) and it would stop accelerating.  Hmmm, not good.
I figured there were 4 possible causes:

 1. Fuel pump capacity insufficient
 2. Carb inlet needle and seat too small
 3. Fuel filter too restrictive or clogged
 4. Sock filter in tank clogged

I wasn't sure about #1 but I doubted it was #2 since past experience had
shown the stock needle and seat sufficient to support more HP than the
little 8:1 compression 215 cube V8 was making.  I didn't have a fuel
pressure
gauge or regulator hooked up so I went looking for a better fuel filter to
test.  I found a much larger diameter clear plastic fuel filter (Purolator
F21111) at a local auto parts store.  It was a bit shorter but had a much
larger filter area than the clear glass filter the previous owner had
spliced
in line.  Since the Purolator filter has a plastic body, I moved it to the
firewall to keep it away from direct engine heat.  The fuel filter
originally
on the car was maybe an inch diameter with a glass body, a metal mesh filter
element and 3/8" inlet and outlet.  I held it up to the light and could see
through the mesh so it didn't appear clogged.

After installing the filter, I made a few passes shifting out of 4th at
5500 RPM and it kept on pulling past 120 MPH in 5th with no signs of going
lean.  Apparently, the other filter was restricting the pump flow, causing
the bowls to drain.  With full bowls, I could run it through third before
they got too low to keep the mixture stable.

Before ditching the carb, I'd go looking for possible fuel or air
restrictions
(something like a clogged air filter should go rich).  Welding in an O2 bung
and borrowing a wide band O2 sensor will make the diagnostics much easier.
Also, some Holley carbs have a sintered bronze filter in the inlet

> The LIST 8414 carb I have on my Pantera, was originally released as a Ford
> OEM carb for 351's and 429's.

A vacuum gauge connected to a constant manifold vacuum source will tell you
if the airflow of the carb is too restrictive.  At the end of a high speed
WOT run, if reads more than an 1.0" to 1.5", the carb is restrictive.  1.0"
is good for a high performance street application and 0.7" for more race
oriented engines.

I'm not familiar with that particular carb but it possible that the carb is
emissions calibrated and is simply leaning out.  If it's a 4160, you'll want
to convert it to replaceable jets on the secondary side and see if richening
the mixture fixes the problem.

Dan Jones


On Sun, Dec 8, 2013 at 2:35 PM, Asa Jay Laughton <asajay at asajay.com> wrote:

>  Hi all,
>
> This year (2013) at the Silver State Classic Challenge, I recorded a top
> speed in the trap of 130.7 MPH.  When I reached the countdown to the trap I
> was already doing just shy of that to bank time before the Narrows.  I
> consciously pressed the accelerator a bit more to push her up to a goal 135
> MPH, but nothing happened.
>
> I speculate at 130 MPH, I'm using up all the carb, or all the fuel pump.
> One, the other, or both.
>
> The Carb is a Ford stamped Holley list with these numbers:
>
> D8PE-9510-KA
> LIST 8414
> 3113
>
> This link shows my email back in 1999 with info from Holley that I
> obtained.
> http://poca.com/detomaso/1999-09/329.html
> Apparently it's a 600 cfm.  it has vacuum secondaries and three-quarter
> turn emission lockouts on the mixture screws.  I've put a standard rebuilt
> kit through it once or twice.  It's been a really good carb, but I don't
> know it will pull more than 130 MPH.
>
> What to do.
> As always, money is a bit of an issue.  I'd like to install EFI but that's
> really expensive.
> I'd like to keep it responsive at low rpm like she is now, but still have
> the throughput needed at higher rpm at top speeds.  I think this leans me
> toward a vacuum secondary rather than mechanical.  I'm sure the cfm needs
> to be cranked up, but would 650 do it or should I head for 700 or higher?
>
> Does anyone have one they'd be willing to part with?
> Should I send mine into someone like Chuck Nuytten and have them do their
> magic on it, replacing metering blocks and other mods?
> Should I just buy a new one?
>
> The engine is a 351C bored .030 over, stock stroke.
> Heads are DOAE, quench chamber.
> Cam is a Crane hydraulic roller with these specs
>
> Intake is an FPP 4145
> Stock ZF transmission
>
> I've got some time so I'm looking for some informed/experienced opinions
> on what carb would be best.
>
> And since Professor Engles from the Midwest Division of the Pantera
> Research Institute is engaged with Fuel pump questions, I'll just follow
> his thread on that part. :)
>
> Thanks,
> Asa Jay
>
>
> --
> Asa Jay Laughton, MSgt, USAFR, Retired
> & Shelley Marie
> Spokane, WA
> ******************************     http://www.racingagainstautism.comhttp://www.teampanteraracing.comhttp://facebook.com/racingagainstautism
>
>
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