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Thanks for the replies, here are the answers to some of the questions:
Valve springs, - Dual springs with alloy retainers. The engine builder
tested and shimmed them to a uniform pressure but I don't know the number
off the top of my head. I'll ask him tomorrow
Silver springs in the carbs, the lightest they make I believe. I have a set
of heaver ones (red I believe) that I can try. The pistons are filled ~ 3/4
of the way, up with SU branded oil and the dampers are in place.
The fuel pump, Holley red, all the lines, micron filter before the pump and
the regulator were changed last winter because I didn't know how old they
were. I had the problem then as well, before and after the replacement. I
opened the cell up two weeks ago. The foam is in great shape, the pickups
and intake line look to be solid as well. The ATL cell is 6 years old.
Fuel pressure is measured by a gauge at the regulator 2 feet from the carbs.
I'm not sure that the problem isn't electrical but the car runs with a
alternator (confirmed working). The distributor was built with a profile to
match my engine by Jeff at Advanced Distributors. I've changed the points
(using his high speed set), rotor, cap, wires and capacitor over the
summer, just in case, but with no affect. Timing is steady, double row
timing chain.
thanks for all the info.
mike h
On Mon, Nov 28, 2016 at 5:05 PM, Sam Halkias <atr6racer@hotmail.com> wrote:
> What are you running for valve springs? Sounds like valve float to me.
>
> Sam
>
> *Sent from my Verizon Wireless 4G LTE DROID*
>
>
> Mike Harmuth <ofracer@gmail.com> wrote:
>
> I'm tracking down a problem with the Spit race car (1296 Small Journal,
> 12;1 compression, APT TR74 cam 295 duration and 0.324 lob lift, head ported
> as per Kas's book). Rebuilt European SU HS4 carb setup with AAA needles
> (manifold and carbs checked for vacuum leaks), Advanced Distributor for
> spark (34 degrees at full, mechanical only, advance @ 3.5K RPM)
>
> The problem I have has followed me on two different short blocks, I can
> easily pull 7500RPM in 1st-3rd ( Close ratio TR7 gearing in a Spitfire
> case, 4th gear is 1;1, 4:11 locked diff ) gears. In 4th I'm struggling to
> get over 6K, no matter how long the straight. Just before the last race of
> the season, I installed an air fuel ratio gauge on the header (stahl) and
> found out I'm running (progressively) very lean (19:1) in 4th over 5K. At
> 2K I adjusted it rich, to 12;1 and it keeps in the 13.5- 14.5 range until I
> get over 5K when it really leans out. If I pull the choke to 1/2 full over
> 5K, I get a good ratio again, 13.5- 14%.
>
> To me that seemed like the carb pistons aren't pulling all the way up so I
> drilled and tapped the manifold to get a vacuum reading. It was steady but
> low at 6K, ~20 Inches but would jump to ~28 briefly as the revs dropped if
> I blipped the throttle. Under 6K, it was in the 15 inch range. Normal air
> filters are K&N with stub stacks but I get the same results with open carbs.
>
> Am I correct in assuming that the vacuum is too low or is it that due to
> overlap with a performance cam? Any ideas on where to look to get the ratio
> "normal" at higher revs? Fuel pump is Holley Red, adjusted to 3 PSI at the
> engine compartment and steady through all revs.
>
> I have dyno time scheduled in a few weeks but I'd like to use that time to
> tune not debug things.
>
> thanks
> mike h
> 63 spitfire
>
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Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr"><div><div><div><div><div><div><div>Thanks for the replies,=
here are the answers to some of the questions:<br><br></div>Valve springs,=
- Dual springs with alloy retainers. The engine builder tested and shimmed=
them to a uniform pressure but I don't know the number off the top of =
my head. I'll ask him tomorrow<br><br></div>Silver springs in the carbs=
, the lightest they make I believe. I have a set of heaver ones (red I beli=
eve) that I can try. The pistons are filled ~ 3/4 of the way,=C2=A0 up with=
SU branded oil and the dampers are in place.<br><br></div>The fuel pump, H=
olley red, all the lines, micron filter before the pump and the regulator w=
ere changed last winter because I didn't know how old they were. I had =
the problem then as well, before and after the replacement. I opened the ce=
ll up two weeks ago. The foam is in great shape, the pickups and intake lin=
e look to be solid as well. The ATL cell is 6 years old.<br><br></div>Fuel =
pressure is measured by a gauge at the regulator 2 feet from the carbs.<br>=
<br></div>I'm not sure that the problem isn't electrical but the ca=
r runs with a alternator (confirmed working). The distributor was built wit=
h a profile to match my engine by Jeff at Advanced Distributors. I've c=
hanged the points (using his high speed set), rotor, cap, wires and capacit=
or over the summer, just in case, but with no affect. Timing is steady, dou=
ble row timing chain.<br><br></div>thanks for all the info.<br><br></div>mi=
ke h<br></div><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">On =
Mon, Nov 28, 2016 at 5:05 PM, Sam Halkias <span dir=3D"ltr"><<a href=3D"=
mailto:atr6racer@hotmail.com"; target=3D"_blank">atr6racer@hotmail.com</a>&g=
t;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0=
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div>
<div>What are you running for valve springs? Sounds like valve float to me.=
</div>
<div><br>
</div>
<div>Sam</div>
<div><br>
</div>
<div><font style=3D"color:#333333"><i>Sent from my Verizon Wireless 4G LTE =
DROID</i></font></div>
</div><div><div class=3D"h5">
<br>
<br>
Mike Harmuth <<a href=3D"mailto:ofracer@gmail.com"; target=3D"_blank">ofr=
acer@gmail.com</a>> wrote:<br>
<br>
<div>
<div dir=3D"ltr">
<div>
<div>
<div>
<div>
<div>
<div>I'm tracking down a problem with the Spit race car (1296 Small Jou=
rnal, 12;1 compression, APT TR74 cam 295 duration and 0.324 lob lift, head =
ported as per Kas's book). Rebuilt European SU HS4 carb setup with AAA =
needles (manifold and carbs checked for
vacuum leaks), Advanced Distributor for spark (34 degrees at full, mechani=
cal only, advance @ 3.5K RPM)<br>
<br>
</div>
The problem I have has followed me on two different short blocks, I can eas=
ily pull 7500RPM in 1st-3rd ( Close ratio TR7 gearing in a Spitfire case, 4=
th gear is 1;1,=C2=A0 4:11 locked diff ) gears. In 4th I'm struggling t=
o get over 6K, no matter how long the straight.
Just before the last race of the season, I installed an air fuel ratio gau=
ge on the header (stahl) and found out I'm running (progressively)=C2=
=A0 very lean (19:1) in 4th over 5K. At 2K I adjusted it rich, to 12;1 and =
it keeps in the 13.5- 14.5 range until I get
over 5K when it really leans out. If I pull the choke to 1/2=C2=A0 full ov=
er 5K, I get a good ratio again, 13.5- 14%.
<br>
<br>
To me that seemed like the carb pistons aren't pulling all the way up s=
o I drilled and tapped the manifold to get a vacuum reading. It was steady =
but low at 6K, ~20 Inches but would jump to ~28 briefly as the revs dropped=
if I blipped the throttle. Under 6K,
it was in the 15 inch range. Normal air filters are K&N with stub stac=
ks but I get the same results with open carbs.<br>
<br>
</div>
Am I correct in assuming that the vacuum is too low or is it that due to ov=
erlap with a performance cam? Any ideas on where to look to get the ratio &=
quot;normal" at higher revs? Fuel pump is Holley Red, adjusted to 3 PS=
I at the engine compartment and steady through
all revs.<br>
<br>
</div>
I have dyno time scheduled in a few weeks but I'd like to use that time=
to tune not debug things.<br>
<br>
</div>
thanks<br>
</div>
mike h<br>
</div>
63 spitfire<br>
</div>
</div>
</div></div></div>
</blockquote></div><br></div>
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