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Re: [Fot] Intake manifold vacuum and no high RPM

To: Mike Harmuth <ofracer@gmail.com>
Subject: Re: [Fot] Intake manifold vacuum and no high RPM
From: chasgee22@gmail.com
Date: Mon, 28 Nov 2016 17:43:57 -0800
Cc: FoTTriumph <fot@autox.team.net>
Delivered-to: mharc@autox.team.net
Delivered-to: fot@autox.team.net
References: <CAO0FjVY_SEB=Lz59oxNe_BeGN3A8Z4Bg0P7pJDJ7M4aRyiYqnA@mail.gmail.com> <MWHPR13MB1648B4280618359FD0A4324DF98A0@MWHPR13MB1648.namprd13.prod.outlook.com> <CAO0FjVbgLjm3ugN9fvbn5ZRLosMQtjO+UAstyKcHH2sofA+MrA@mail.gmail.com>
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Make sure the bowl vents are clear and working properly.  I don't know much a=
bout SUs, but how about float level?  Is it simply running out of gas the lo=
nger you drive it?

I've also seen this happen when a coil goes bad.  You might just switch out t=
he coil first to see if things improve.

Good Luck!

Chuck

> On Nov 28, 2016, at 3:58 PM, Mike Harmuth <ofracer@gmail.com> wrote:
>=20
> Thanks for the replies, here are the answers to some of the questions:
>=20
> Valve springs, - Dual springs with alloy retainers. The engine builder tes=
ted and shimmed them to a uniform pressure but I don't know the number off t=
he top of my head. I'll ask him tomorrow
>=20
> Silver springs in the carbs, the lightest they make I believe. I have a se=
t 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.
>=20
> The fuel pump, Holley red, all the lines, micron filter before the pump an=
d the regulator were changed last winter because I didn't know how old they w=
ere. I had the problem then as well, before and after the replacement. I ope=
ned the cell up two weeks ago. The foam is in great shape, the pickups and i=
ntake line look to be solid as well. The ATL cell is 6 years old.
>=20
> Fuel pressure is measured by a gauge at the regulator 2 feet from the carb=
s.
>=20
> I'm not sure that the problem isn't electrical but the car runs with a alt=
ernator (confirmed working). The distributor was built with a profile to mat=
ch my engine by Jeff at Advanced Distributors. I've changed the points (usin=
g 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.
>=20
> thanks for all the info.
>=20
> mike h
>=20
>> On Mon, Nov 28, 2016 at 5:05 PM, Sam Halkias <atr6racer@hotmail.com> wrot=
e:
>> What are you running for valve springs? Sounds like valve float to me.
>>=20
>> Sam
>>=20
>> Sent from my Verizon Wireless 4G LTE DROID
>>=20
>>=20
>> Mike Harmuth <ofracer@gmail.com> wrote:
>>=20
>> I'm tracking down a problem with the Spit race car (1296 Small Journal, 1=
2;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 (mani=
fold and carbs checked for vacuum leaks), Advanced Distributor for spark (34=
 degrees at full, mechanical only, advance @ 3.5K RPM)
>>=20
>> The problem I have has followed me on two different short blocks, I can e=
asily pull 7500RPM in 1st-3rd ( Close ratio TR7 gearing in a Spitfire case, 4=
th 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 seaso=
n, 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 adjuste=
d it rich, to 12;1 and it keeps in the 13.5- 14.5 range until I get over 5K w=
hen it really leans out. If I pull the choke to 1/2  full over 5K, I get a g=
ood ratio again, 13.5- 14%.=20
>>=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 l=
ow at 6K, ~20 Inches but would jump to ~28 briefly as the revs dropped if I b=
lipped the throttle. Under 6K, it was in the 15 inch range. Normal air filte=
rs are K&N with stub stacks but I get the same results with open carbs.
>>=20
>> Am I correct in assuming that the vacuum is too low or is it that due to o=
verlap 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 en=
gine compartment and steady through all revs.
>>=20
>> I have dyno time scheduled in a few weeks but I'd like to use that time t=
o tune not debug things.
>>=20
>> thanks
>> mike h
>> 63 spitfire
>=20
> _______________________________________________
> fot@autox.team.net
>=20
> http://www.fot-racing.com
>=20
> Donate: http://www.team.net/donate.html
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ail.com
>=20
>=20

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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; charset=3D=
utf-8"></head><body dir=3D"auto"><div>Make sure the bowl vents are clear and=
 working properly. &nbsp;I don't know much about SUs, but how about float le=
vel? &nbsp;Is it simply running out of gas the longer you drive it?</div><di=
v id=3D"AppleMailSignature"><br></div><div id=3D"AppleMailSignature">I've al=
so seen this happen when a coil goes bad. &nbsp;You might just switch out th=
e coil first to see if things improve.</div><div id=3D"AppleMailSignature"><=
br></div><div id=3D"AppleMailSignature">Good Luck!<br><br>Chuck</div><div><b=
r>On Nov 28, 2016, at 3:58 PM, Mike Harmuth &lt;<a href=3D"mailto:ofracer@gm=
ail.com">ofracer@gmail.com</a>&gt; wrote:<br><br></div><blockquote type=3D"c=
ite"><div><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 s=
prings, - Dual springs with alloy retainers. The engine builder tested and s=
himmed 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, th=
e lightest they make I believe. I have a set of heaver ones (red I believe) t=
hat I can try. The pistons are filled ~ 3/4 of the way,&nbsp; up with SU bra=
nded oil and the dampers are in place.<br><br></div>The fuel pump, Holley re=
d, all the lines, micron filter before the pump and the regulator were chang=
ed last winter because I didn't know how old they were. I had the problem th=
en 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 sol=
id as well. The ATL cell is 6 years old.<br><br></div>Fuel pressure is measu=
red by a gauge at the regulator 2 feet from the carbs.<br><br></div>I'm not s=
ure that the problem isn't electrical but the car runs with a alternator (co=
nfirmed working). The distributor was built with a profile to match my engin=
e by Jeff at Advanced Distributors. I've changed the points (using his high s=
peed set), rotor, cap, wires and capacitor over the summer, just in case, bu=
t with no affect. Timing is steady, double row timing chain.<br><br></div>th=
anks for all the info.<br><br></div>mike h<br></div><div class=3D"gmail_extr=
a"><br><div class=3D"gmail_quote">On Mon, Nov 28, 2016 at 5:05 PM, Sam Halki=
as <span dir=3D"ltr">&lt;<a href=3D"mailto:atr6racer@hotmail.com"; target=3D"=
_blank">atr6racer@hotmail.com</a>&gt;</span> wrote:<br><blockquote class=3D"=
gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-l=
eft: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 D=
ROID</i></font></div>
</div><div><div class=3D"h5">
<br>
<br>
Mike Harmuth &lt;<a href=3D"mailto:ofracer@gmail.com"; target=3D"_blank">ofra=
cer@gmail.com</a>&gt; 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 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 (ma=
nifold and carbs checked for
 vacuum leaks), Advanced Distributor for spark (34 degrees at full, mechanic=
al only, advance @ 3.5K RPM)<br>
<br>
</div>
The problem I have has followed me on two different short blocks, I can easi=
ly pull 7500RPM in 1st-3rd ( Close ratio TR7 gearing in a Spitfire case, 4th=
 gear is 1;1,&nbsp; 4:11 locked diff ) gears. In 4th I'm struggling to get o=
ver 6K, no matter how long the straight.
 Just before the last race of the season, I installed an air fuel ratio gaug=
e on the header (stahl) and found out I'm running (progressively)&nbsp; very=
 lean (19:1) in 4th over 5K. At 2K I adjusted it rich, to 12;1 and it keeps i=
n the 13.5- 14.5 range until I get
 over 5K when it really leans out. If I pull the choke to 1/2&nbsp; full ove=
r 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 d=
rilled and tapped the manifold to get a vacuum reading. It was steady but lo=
w at 6K, ~20 Inches but would jump to ~28 briefly as the revs dropped if I b=
lipped the throttle. Under 6K,
 it was in the 15 inch range. Normal air filters are K&amp;N with stub stack=
s 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 ove=
rlap with a performance cam? Any ideas on where to look to get the ratio "no=
rmal" at higher revs? Fuel pump is Holley Red, adjusted to 3 PSI at the engi=
ne 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 t=
une 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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y></html>=

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