[DeTomaso] WARNING: .050 may be the wrong kind of Bomb

Fri May 29 13:48:50 EDT 2009

Dan,

Is the carb on the engine one that has been jetted for your engine or 
one exactly like it over a variety of throttle openings?
If not I think it increases the odds that it is running too lean.

-----Original Message-----
From: pantdino at aol.com
To: detomaso at realbig.com
Sent: Thu, 28 May 2009 8:51 pm
Subject: Re: [DeTomaso] WARNING: .050 may be the wrong kind of Bomb

Dan, I would think you've found your problem.
If the secondary butterflies are not opening you will not be getting
any fuel from those barrels-- it is the airflow thru them that creates
the low pressure in the throat that sucks fuel in.

So all the air will be coming in thru the primary bores.  The fuel
circuit in them was not designed to be feeding an engine of that size
with those bores alone and will not be able to move enough fuel per
second to maintain the mixture at the proper ratio of air to fuel.
The mixture will go lean and the engine will be limited in power output.

The primary bores are offset from the midline of the carb, so as the
air goes thru it and the intake manifold some cylinders will get more
fuel and air than others, which would explain why some plugs were
cooked and others looked fine.

I'm not a carb expert but the above makes sense to me.

Jack?

I know from experience that if a piston hits a spark plug it smashes
the ground electrode against the center electrode, or at least moves it
closer.  There is no way it could knock the insulator off without
hitting the ground (side) electrode.

Jim

-----Original Message-----
From: Dave Londry <davel at emspace.com>
To: Dan Courtney <dfcex at excaliburre.com>
Cc: Jack DeRyke <JDeRyke at aol.com>; detomaso at realbig.com
Sent: Thu, 28 May 2009 1:22 pm
Subject: Re: [DeTomaso] WARNING: .050 may be the wrong kind of Bomb

Dan,
If your secondaries don't open, you'll be running more air through the
primaries than was ever intended.
I think that could well go lean.
I'll be interested in what the guys-who-know-carbs have to say.
dave

Dan Courtney wrote:
> I haven't picked up a borescope yet but I ran a compression test
tonight and
> all 8 cylinders were consistent around 150 psi. Haven't done a
leak-down
> test yet.
> There were no rings on these AP 25 plugs and I noticed #8 is gapped
at .045,
> pretty sure it was put in at .050. The other plugs are at .050.
> Could impact from the domed piston to the plug tip crack the
electrode
> without breaking the tip? Although #5 is missing 1/2 the tip, #6 has
an
> intact tip but not much electrode. The other 6 plugs all look brand
new.
> I may convert to AP 32's, to lessen any potential detonation, and
hopefully
> they come with rings.
> I may check the intake gasket, to see if it shows sign of an intake
leak.
> The intake bolts at the end by #5 & #6 are studs with nuts (to hold
the
> throttle linkage I fabbed for the AirGap) and may have loosened.
> Otherwise I can't think what could be potentially causing detonation.
> I'm assuming the backfire I'm getting about 6 seconds after any
significant
> deceleration is being caused by the collector donuts, as those
locknuts keep
> getting loose, but maybe from an intake leak?
> The secondary butterflies do not appear to be opening, but it seems
like
> that would lead to a rich condition, rather than lean for detonation.
> I'll try and find a borescope tommorrow, to see if anything is
damaged.
> If it looks good I'll try for a dyno tune appointment.
>
> Dan
>
> Dan F. Courtney
>
> La Jolla, CA
>
> (858) 551-5455 Phone
> (858) 551-5456 Fax
> ----- Original Message -----
> From: "P. Rimov" <rimov at charter.net>
> To: "Dan Courtney" <dfcex at excaliburre.com>
> Sent: Sunday, May 24, 2009 7:45 M
> Subject: Re: [DeTomaso] WARNING: .050 may be the wrong kind of Bomb
>
>
>
>> Dan are you running domed pistons or have you had the heads milled
to
>> increase the CR? If so you may need to add an extra ring or two on
the
>> plugs of the offending cylinders. It is possible the extra gap on
the plug
>> was just enough to result in contact with the piston. Plugs are
great for
>> heat but not so good when they are dropped or bumped by a piston.
It is
>> possible the spark plug wire was loose or popped off at some time to
cause
>> the #? to foul. I would not start worrying about pulling the heads
just
>> yet. What ever pieces broke off in the cylinder are long gone
through the
>> exhaust. I would be more concerned about any valve damage from the
plug
>> remnants before or while they exited the exhaust valve. Valve damage
can
>> easily be ruled out through a compression check and lead down check,
but
>> again I don't think you have to start worrying just yet. One last
thing I
>> would change your oil and make sure to filter it and check for any
foreign
>> material.
>>
>> Cheers my friend
>>
>> Paul
>> ----- Original Message -----
>> From: "Dan Courtney" <dfcex at pacbell.net>
>> To: <JDeRyke at aol.com>
>> Cc: <detomaso at realbig.com>
>> Sent: Sunday, May 24, 2009 7:12 AM
>> Subject: Re: [DeTomaso] WARNING: .050 may be the wrong kind of Bomb
>>
>>
>>
>>> Jack,
>>>
>>> I timed it at 12 deg @ idle, 32 deg total in around 2,800 rpms.
>>> Fuel pressure is from an electric pump internally regulated at 6.5
psi.
>>> The plugs in the same cylinders looked OK before switiching out
after 600
>>> miles of highway and desert driving.
>>> It's not just the ceramic part missing, also the electrode and, on
#5,
>>> 1/2 the top of the tip.
>>> It's seems strange that the other 5 plugs (except #2 / fouled) look
new.
>>> Where would I find this scope? I really don't want to pull the head.
>>>
>>> Thank You,
>>> Dan
>>> Dan F. Courtney
>>>
>>> La Jolla, CA
>>>
>>> (858) 551-5455 Phone
>>> (858) 551-5456 Fax
>>>  ----- Original Message -----
>>>  From: JDeRyke at aol.com
>>>  To: dfcex at pacbell.net ; detomaso at realbig.com
>>>  Sent: Sunday, May 24, 2009 12:27 AM
>>>  Subject: Re: [DeTomaso] WARNING: .050 may be the wrong kind of Bomb
>>>
>>>
>>>  In a message dated 5/24/09 12:10:59 AM, dfcex at pacbell.net writes:
>>>
>>>
>>>    What worries me more is, where are the tips of the plugs? Are
they
>>> sitting in the cylinders, about to punch through my brand new
pistons? Or
>>> has that already happened?
>>>    I'm also wondering if detonation could have played a role.
>>>
>>>
>>>  Thats a sign of detonation. Check your total ignition advance and
your
>>> fuel pressures. Normally, a plug gap will either fire, or not, so
thats
>>> not the cause of your detonation. The piston crowns likely look
>>> shot-blasted but unless they made really deep pits, the pistons
will be
>>> OK. Any extra pieces of ceramic are long gone out the tailpipe. A
fiber
>>> optic borescope can look thru the plug hole and inspect the piston
tops
>>> without pulling the heads. My best guess- J Deryke
>>>
>>>
>>>  **************
>>>

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