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Hi Mike,
If you have removed the springs for the pistons, reinstall them. If you sti=
ll have the springs purchase some heavier ones or stretch the ones you have=
1" at a time and test. The pistons are most likely up all the way and they=
need to be closed more to pull a better signal on the needle jet.=C2=A0
Just like pressing the easy button!=20
On Monday, November 28, 2016 4:57 PM, Mike Harmuth <ofracer@gmail.com> =
wrote:
=20
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 a=
s per Kas's book). Rebuilt European SU HS4 carb setup with AAA needles (man=
ifold 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 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 to ge=
t over 6K, no matter how long the straight. Just before the last race of th=
e season, I installed an air fuel ratio gauge on the header (stahl) and fou=
nd out I'm running (progressively)=C2=A0 very lean (19:1) in 4th over 5K. A=
t 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 f=
ull over 5K, I get a good ratio again, 13.5- 14%.=20
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 f=
ilters 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 ov=
erlap 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 e=
ngine 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
_______________________________________________
fot@autox.team.net
http://www.fot-racing.com
Archive: http://www.team.net/archive
tt.net
=20
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<html><head></head><body><div style=3D"color:#000; background-color:#fff; f=
ont-family:HelveticaNeue-Light, Helvetica Neue Light, Helvetica Neue, Helve=
tica, Arial, Lucida Grande, sans-serif;font-size:13px"><div id=3D"yui_3_16_=
0_1_1480371071095_21108"><span id=3D"yui_3_16_0_1_1480371071095_21292">Hi M=
ike,</span></div><div id=3D"yui_3_16_0_1_1480371071095_21108"><span><br></s=
pan></div><div id=3D"yui_3_16_0_1_1480371071095_21108" dir=3D"ltr"><span id=
=3D"yui_3_16_0_1_1480371071095_21293">If you have removed the springs for t=
he pistons, reinstall them. If you still have the springs purchase some hea=
vier ones or stretch the ones you have 1" at a time and test. The pistons a=
re most likely up all the way and they need to be closed more to pull a bet=
ter signal on the needle jet. </span></div><div id=3D"yui_3_16_0_1_148=
0371071095_21108" dir=3D"ltr"><span><br></span></div><div id=3D"yui_3_16_0_=
1_1480371071095_21108" dir=3D"ltr"><span id=3D"yui_3_16_0_1_1480371071095_2=
1524">Just like pressing the easy button!</span></div> <div class=3D"qtdSep=
arateBR"><br><br></div><div class=3D"yahoo_quoted" style=3D"display: block;=
"> <div style=3D"font-family: HelveticaNeue-Light, Helvetica Neue Light, He=
lvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 13px;=
"> <div style=3D"font-family: HelveticaNeue, Helvetica Neue, Helvetica, Ari=
al, Lucida Grande, sans-serif; font-size: 16px;"> <div dir=3D"ltr"><font si=
ze=3D"2" face=3D"Arial"> On Monday, November 28, 2016 4:57 PM, Mike Harmuth=
<ofracer@gmail.com> wrote:<br></font></div> <br><br> <div class=3D"=
y_msg_container"><div id=3D"yiv1750785075"><div dir=3D"ltr"><div><div><div>=
<div><div><div>I'm tracking down a problem with the Spit race car (1296 Sma=
ll 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 AA=
A needles (manifold and carbs checked for vacuum leaks), Advanced Distribut=
or 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 Spitfir=
e case, 4th gear is 1;1, 4:11 locked diff ) gears. In 4th I'm struggl=
ing to get over 6K, no matter how long the straight. Just before the last r=
ace 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 o=
ver 5K. At 2K I adjusted it rich, to 12;1 and it keeps in the 13.5- 14.5 ra=
nge 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 th=
at 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 6=
K, ~20 Inches but would jump to ~28 briefly as the revs dropped if I blippe=
d the throttle. Under 6K, it was in the 15 inch range. Normal air filters a=
re 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 t=
he ratio "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 hav=
e 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><br>_______________________________________________<br><a ym=
ailto=3D"mailto:fot@autox.team.net"; href=3D"mailto:fot@autox.team.net";>fot@=
autox.team.net</a><br><br><a href=3D"http://www.fot-racing.com/"; target=3D"=
_blank">http://www.fot-racing.com</a><br><br>Donate: <a href=3D"http://www.=
team.net/donate.html" target=3D"_blank">http://www.team.net/donate.html</a>=
<br>Archive: <a href=3D"http://www.team.net/archive"; target=3D"_blank">http=
://www.team.net/archive</a><br>Forums: <a href=3D"http://www.team.net/forum=
s" target=3D"_blank">http://www.team.net/forums</a><br>Unsubscribe/Manage: =
<a href=3D"http://autox.team.net/mailman/options/fot/rick.parent@att.net"; t=
arget=3D"_blank">http://autox.team.net/mailman/options/fot/rick.parent@att.=
net</a><br><br><br><br><br></div> </div> </div> </div></div></body></html=
>
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_______________________________________________
fot@autox.team.net
http://www.fot-racing.com
Archive: http://www.team.net/archive
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