Duh, of course. I forgot about fuel delivery, even though it's bitten me
in the ass so many times I've got a callus. It's such a tricky thing, it's
amazing that Carbs work at all. If you get the needle and seat too big,
then even light fuel pressure overcomes the float, and you'll have surging
in the level because the float can't shut the valve quickly enough. Too
small and it's your new main jet. I presume you're running a couple of
hunky electric fuel pumps and a pressure regulator. I run two in parallel
and turn them both on, but that's just me.
Getting the level to remain generally constant is a tricky combination of
fuel pressure and needle and seat size. I increase pressure until the car
runs a little rich at low RPM but cleans out at high revs. Then back it
off a little. Not very scientific, but it seems to work.
As far as choosing a needle and seat go, if your plugs read lean from a
clean chop at full load, and going up on the main jet doesn't change much,
then try the needle and seat. If that helps then go up one more size and
start all over on getting your emulsion tube and main jet right, 'cause
what you have was arrived at while running on low bowl levels.
I speak from painful experience. Last spring Peyote was giving me fits,
running lean and missing, until I did as Kas suggested below and looked
into the float bowls. Nearly dry. A full day of testing, tweaking, and
wrench throwing wasted. Where was you when I needed you Kas?
Bill
-----Original Message-----
From: Kas Kastner [mailto:kaskas@earthlink.net]
Sent: Monday, February 04, 2002 5:45 PM
To: Bill Babcock; BillDentin@aol.com
Cc: fot@autox.team.net
Subject: Re: tolerable DRIVE SHAFT run out?
Bill's got the answer as far as the driveshaft is concerned. You can't do
it yourself for or as well as the pros do and it's generally peretty
cheap.
Frankly I've never had any problem and .020" dosen't sound like a lot to
me
, depending on length of the driveshaft. As Bill has already stated the
demand at full song in top is REALLY high and you must make certain all
the
electrics are putting out their fair share and a little more. We did have
this kind of thing with the TR-6 when the alternator (Lucas) would die
but
when we fitted the Motorola that all went away forever. Another thing of
course is the fuel demand. Is the needle and seat big enough to supply
the
demand at the speed? Most stock carbs do NOT have a big enough needle and
seata when the engine is highly modified and you'll run out in top when
running hard. Sometimes you can shut the engine down clean when at the
high
revs and the missing going on , then check to see if the float chambers
are
at the proper height. ( of course pull the lid and check the fuel height
before you start this manuver) If the engine is hot from several runs the
S.U.'s will perk over a bit and this won't work but the Webers should give
you a clue. At the same time I've had fuel pumps that just did not deliver
enoguh fuel for the power requirment and you need at least 15 gals per
hour.
Test with a quart can and a stop watch. I don't know anything about the
engine you are talking about so without some more detail I guess my guess
is
just another guess.(hah!).
----- Original Message -----
From: "Bill Babcock" <BillB@bnj.com>
To: <BillDentin@aol.com>; <Kaskas@earthlink.net>
Cc: <fot@autox.team.net>
Sent: Monday, February 04, 2002 3:37 PM
Subject: RE: tolerable DRIVE SHAFT run out?
> There are lots of driveshaft shops that will check and dynamically
balance
> your driveshaft.
> I've had several made from bits and pieces. When the pros finish with
them
> they are pretty, straight, and perfectly balanced. Don't even mess with
> measurements, it's cheap to get it done.
>
>
> By the way, unless you have true overdrive, I doubt your driveshaft is
> getting to 13K.
>
> In my humble experience, high end miss is usually caused by the familiar
> old bugaboos--fuel or spark, most likely spark. Even if it doesn't
happen
> in the lower gears. High gear, high RPM is the highest load your engine
> sees, which means highest combustion chamber pressure and highest
voltage
> required for the spark. It's also frequently caused by too lean a
> mixture--same root cause. I'd try closing the plug gap to .010" and see
if
> that has any effect. If it does, it's your sparks--and it doesn't matter
> what kind of system you have, you can have something truly bodacious and
a
> weak coil at high RPM will let you down.
>
> The second thing to try is going up big on the main jet. I don't know
> whether you have SUs or Webers. If it's webers, go up four or five
steps,
> and see what happens. It won't be optimal, but it'll tell you what's
going
> on.
>
>
> -----Original Message-----
> From: BillDentin@aol.com [mailto:BillDentin@aol.com]
> Sent: Monday, February 04, 2002 3:15 PM
> To: Kaskas@earthlink.net
> Cc: fot@autox.team.net
> Subject: tolerable DRIVE SHAFT run out?
>
>
> Hi Kas:
>
> Hope you are well!
>
> We are still working on 'high end break up', and John Reimer, a very
> successful local ROAD/ROUNDY ROUND/DRAG racer friend (from the old days)
> something to the effect of, "If you don't have similar symptoms in other
> gears (at top RPMs)", he would be looking at something spinning that is
> out
> of round, and at top speed perhaps we have past the tolerable limits.
He
> said he would look first at the drive shaft. the Thunder Bolt has a one
> off
> drive shaft. Using less than laboratory equipment in our own shop, we
> suspect we have 20,000ths out of round at one end. Is that too much
when
> we
> get to 13,000 rpms (read 6,500 actual)? Any idea what tolerable limits
> might be?
>
> Appreciate any thoughts.
>
> Bill Dentinger
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