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<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=610360508-30112016>In 4th gear, the combustion chamber has more time to
get too hot. What about trying say 30° maximum advance to check
if detonation has something to do with it?</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT color=#0000ff size=2 face=Arial><SPAN
class=610360508-30112016>Marcel</SPAN></FONT></DIV><BR>
<DIV lang=nl class=OutlookMessageHeader dir=ltr align=left>
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<FONT size=2 face=Tahoma><B>Van:</B> Fot [mailto:fot-bounces@autox.team.net]
<B>Namens </B>John Styduhar<BR><B>Verzonden:</B> maandag 28 november 2016
23:04<BR><B>Aan:</B> Mike Harmuth<BR><B>CC:</B> FoTTriumph<BR><B>Onderwerp:</B>
Re: [Fot] Intake manifold vacuum and no high RPM<BR></FONT><BR></DIV>
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<DIV class=gmail_default style="FONT-SIZE: small">I had the same problem in my
TR3 racer. I corrected the lean condition by installing a stronger damper spring
in the carb and oil in the piston. This created more vacuum in the throat of the
carb at the higher revs and caused more fuel to be drawn through the jet via the
venturi effect. Choking the carb does basically the same
thing.</DIV></DIV>
<DIV class=gmail_extra><BR>
<DIV class=gmail_quote>On Mon, Nov 28, 2016 at 4:23 PM, Mike Harmuth <SPAN
dir=ltr><<A href="mailto:ofracer@gmail.com"
target=_blank>ofracer@gmail.com</A>></SPAN> wrote:<BR>
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<DIV>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)<BR><BR></DIV>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%. <BR><BR>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.<BR><BR></DIV>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.<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
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