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Andrew,
Is it possible that a carburetor piston is sticking in the up position
off and on? This problem is exacerbated by a hot engine, and it is hard to
find after you stop driving because unless it gets stuck tight it will drop
back down with vibration.
Bob Kramer
On Fri, Aug 9, 2024 at 4:47=E2=80=AFPM Andrew Devenish via Fot <fot@autox.t=
eam.net>
wrote:
> Hi Mike,
> The first question is a good one. The car was built for
> autocross by a guy in Indiana who knew his stuff. However, I bought it fr=
om
> a guy who had bought it to run PIB, but knew nothing about race engines. =
He
> had run it lean and holed #4. He told me he had not changed anything, but
> that is turning out not to be the case. (I suspect it holed the piston
> because I found he had fitted gros jets with the float level way too low)=
.
> I rebuilt it to same mechanical spec. It ran great but a little
> lean on the AAU needles for road course, so I=E2=80=99m now on AAA. It st=
ill runs
> great, unless it doesn=E2=80=99t =F0=9F=98=81.
> The car has had this issue since I built it. At first I thought
> the obvious - float heights, needle/seat, regulator pressure etc etc but
> while it always runs great I have this issues after a few =E2=80=9Claps=
=E2=80=9D.
> 2) The car had a Summit racing 3136 pump which has around 90GPH
> and an internal blow off at 7PSI, my regulator is at 4 PSI. Today I had
> taken the pump apart and checked it but all looked OK. I fitted a cheap
> solenoid pump in its place. Issue still there.
> I had checked both the Summit and now the solenoid pump for flow, there i=
s
> plenty.
> As I noted the float bowls are full when it quits running.
> 3) Great point - could be what I have. I know the fuel level in the
> jets is fine when not running, but a poor flow from bowl to jet would
> change that when running. My O2 is in the collector, so I can=E2=80=99t b=
e sure if
> it=E2=80=99s both carbs or just one. All 4 plugs look very similar, but t=
hat is
> possible as this =E2=80=9Clean=E2=80=9D condition is only for a few cycle=
s before it stops
> - not enough to color the plug. Will check when I can ( unfortunately a
> busy weekend coming up as I race sailboats too ). I=E2=80=99ve been think=
ing it is
> heat related, but it could just as easily be time. When I tried to run
> autocross it started to play up after 10 or so seconds of full throttle
> (which I can=E2=80=99t do in my yard). On autocross it would pull like cr=
azy, then
> go very flat, and then come back on, repeat. Your idea would do just that=
!
> 4) always worth a check, but it would have to be something that shows
> up only when hot.
> 5) yes, compression good. Between 220 and 225 for all, measured on
> crank with throttles open.
>
>
> Thanks also to the other responses that I received, I didn=E2=80=
=99t cc all
> on my replies in order to reduce the clutter=E2=80=A6
>
> Thank you,
> Andrew Devenish
>
> Sent from my iPad
>
> On Aug 9, 2024, at 3:51=E2=80=AFPM, Mike Harmuth <ofracer@gmail.com> wrot=
e:
>
> =EF=BB=BF
> Hi Andrew, a couple of things to check.
> 1st, is this a new problem? if so, what did you touch last?
>
> 2d Verify fuel flow, not just pressure i.e Gallons per hour? Disconnect
> the fuel line at the carbs, and stick it into a 1 quart or one gallon
> clean/clear bottle/jug. Turn the fuel pump on and time how long it takes =
to
> fill (1 Qt/ 1Gal whatever size container you're using). If you're gettin=
g
> more than 20 gallons per hour, the flow is OK. Set the bottle aside and l=
et
> it settle out, look for particles, rubber, fuel cell foam, dirt. If so, s=
ee
> where that's coming from. For example, old fuel cell foam will break down
> and clog the intake. When the pump turns off, the fuel in the lines drops
> back flushing the intake clear until next time. Fuel filter clean? Fuel
> pressure reg OK? Not just holding pressure (I run 3.5 on my HS4s) but
> actually sending fuel down the line? The gallons per hour test will
> indicate if you need to look into any of these areas, if you're gelling
> enough fuel, more down the list for now.
> link to flow and fuel requirements chart
> https://historicracinggroup.com/resources/Reference_Material/Canton/Fuel%=
20Consumption%20and%20Flow%20Quick%20Ref%20by%20CM%20Filters.pdf
>
> 3. A problem I had with an identical set up, was rubber hose breaking dow=
n
> and settling into the little box shaped well in the carb bowl where the
> line to the jet connects. It's happened to me twice now, last time was in
> June with fairly new hose feeding the carbs. It restricted the flow to th=
e
> jet, even though the bowl was full. At high load, not enough fuel could g=
et
> past the blockage.
> <IMG_20240630_112925914.jpg>
>
> 4. Vacuum leak- Is there a crack or loose bolt on the intake manifold?
> With the engine running, spray carb cleaner around the manifold to block,
> carbs to manifold. A change in engine RPM means something was drawn in
> through a gap.
>
> 5. Compression check- Are all the cylinders within 5-10% of each other?
>
> Happy hunting
>
> mike h
>
> On Fri, Aug 9, 2024 at 3:03=E2=80=AFPM Andrew Devenish via Fot <fot@autox=
.team.net>
> wrote:
>
>> Guys,
>> My car ( 1300, 12.5:1 comp on Sunoco 110 race gas, dual HS4 )
>> is still giving me grief. I=E2=80=99ve chased all the things I can think=
of, but
>> still same problem. It starts and runs great, but after a few laps of th=
e
>> yard ( 5-6, only 1000ft or so per up/down lap, so quick accels then
>> braking to turn ) it goes very lean ( I have O2 sensor ) and stops. I=E2=
=80=99m
>> running it without the hood for these test runs. It always stops at the
>> entry to a turn.
>> I=E2=80=99ve been working on it a lot, so know it has fuel pres=
sure, and
>> the float bowls are full of fuel. All plugs look very similar. The needl=
es
>> (AAA) are the spring type, and the slides move freely. I use ATF as flui=
d,
>> but have tried 50 weight too.
>> After a minute or so it will fire back up, but only run enough t=
o
>> get back to the shop before going lean again. If I pull out the choke it
>> will run, but is unstable.
>> I have wrapped headers and a heat shield around the carbs but the=
y
>> do still get hot.
>>
>> Any ideas ? Thinking to try some less volatile fuel as it seems
>> heat related and the Sunoco evaporates so fast !
>>
>>
>> Thank you,
>> Andrew Devenish
>>
>> Sent from my iPad_______________________________________________
>> fot@autox.team.net
>>
>> http://www.fot-racing.com
>>
>> Donate: http://www.team.net/donate.html
>> Archive: http://autox.team.net/archive http://www.team.net/pipermail/fot
>> Unsubscribe/Manage <http://www.team.net/pipermail/fotUnsubscribe/Manage>=
:
>> http://autox.team.net/mailman/options/fot/ofracer@gmail.com
>>
>>
>> _______________________________________________
> fot@autox.team.net
>
> http://www.fot-racing.com
>
> Donate: http://www.team.net/donate.html
> Archive: http://autox.team.net/archive http://www.team.net/pipermail/fot
> Unsubscribe/Manage <http://www.team.net/pipermail/fotUnsubscribe/Manage>:
> http://autox.team.net/mailman/options/fot/rkramer56@gmail.com
>
>
>
--0000000000008dcc95061f485110
Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr">Andrew,<div><br></div><div>Is it possible that a carbureto=
r piston is sticking in the up position off=C2=A0and on?=C2=A0 This problem=
is exacerbated by a hot engine, and it is hard to find after you stop driv=
ing because unless it gets stuck tight it will drop back down with vibratio=
n.=C2=A0<div><br clear=3D"all"><div><div dir=3D"ltr" class=3D"gmail_signatu=
re" data-smartmail=3D"gmail_signature"><div dir=3D"ltr">Bob Kramer</div></d=
iv></div><br></div></div></div><br><div class=3D"gmail_quote"><div dir=3D"l=
tr" class=3D"gmail_attr">On Fri, Aug 9, 2024 at 4:47=E2=80=AFPM Andrew Deve=
nish via Fot <<a href=3D"mailto:fot@autox.team.net";>fot@autox.team.net</=
a>> wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0p=
x 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir=3D"auto">
Hi Mike,
<div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 The first question is a good one. T=
he car was built for autocross by a guy in Indiana who knew his stuff. Howe=
ver, I bought it from a guy who had bought it to run PIB, but knew nothing =
about race engines. He had run it lean and holed #4. He told
me he had not changed anything, but that is turning out not to be the case=
. (I suspect it holed the piston because I found he had fitted gros jets wi=
th the float level way too low).=C2=A0</div>
<div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 I rebuilt it to same mechanical spec. It r=
an great but a little lean on the AAU needles for road course, so I=E2=80=
=99m now on AAA. It still runs great, unless it doesn=E2=80=99t =F0=9F=98=
=81.</div>
<div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 The car has had this issue since I built i=
t. At first I thought the obvious - float heights, needle/seat, regulator p=
ressure etc etc but while it always runs great I have this issues after a f=
ew =E2=80=9Claps=E2=80=9D.</div>
<div>=C2=A0 =C2=A0 =C2=A0 2) =C2=A0 The car had a Summit racing 3136 pump w=
hich has around 90GPH and an internal blow off at 7PSI, my regulator is at =
4 PSI. Today I had taken the pump apart and checked it but all looked OK. I=
fitted a cheap solenoid pump in its place. Issue still
there.</div>
<div>I had checked both the Summit and now the solenoid pump for flow, ther=
e is plenty.=C2=A0</div>
<div>=C2=A0 =C2=A0 =C2=A0 As I noted the float bowls are full when it quits=
running.</div>
<div>=C2=A0 =C2=A0 3) Great point - could be what I have. I know the fuel l=
evel in the jets is fine when not running, but a poor flow from bowl to jet=
would change that when running. My O2 is in the collector, so I can=E2=80=
=99t be sure if it=E2=80=99s both carbs or just one. All 4
plugs look very similar, but that is possible as this =E2=80=9Clean=E2=80=
=9D condition is only for a few cycles before it stops - not enough to colo=
r the plug. Will check when I can ( unfortunately a busy weekend coming up =
as I race sailboats too ). I=E2=80=99ve been thinking it
is heat related, but it could just as easily be time. When I tried to run =
autocross it started to play up after 10 or so seconds of full throttle (wh=
ich I can=E2=80=99t do in my yard). On autocross it would pull like crazy, =
then go very flat, and then come back on,
repeat. Your idea would do just that !=C2=A0</div>
<div>=C2=A0 =C2=A0 4) always worth a check, but it would have to be somethi=
ng that shows up only when hot.=C2=A0</div>
<div>=C2=A0 =C2=A0 5) yes, compression good. Between 220 and 225 for all, m=
easured on crank with throttles open.</div>
<div><br>
</div>
<div>=C2=A0 =C2=A0 =C2=A0</div>
<div>=C2=A0 =C2=A0 =C2=A0 =C2=A0Thanks also to the other responses that I r=
eceived, I didn=E2=80=99t cc all on my replies in order to reduce the clutt=
er=E2=80=A6</div>
<div><br id=3D"m_4627224738652001176lineBreakAtBeginningOfSignature">
<div dir=3D"ltr">Thank you,=C2=A0
<div>=C2=A0 =C2=A0 =C2=A0 Andrew Devenish</div>
<div>
<div><br>
</div>
<div>Sent from my iPad</div>
</div>
</div>
<div dir=3D"ltr"><br>
<blockquote type=3D"cite">On Aug 9, 2024, at 3:51=E2=80=AFPM, Mike Harmuth =
<<a href=3D"mailto:ofracer@gmail.com"; target=3D"_blank">ofracer@gmail.co=
m</a>> wrote:<br>
<br>
</blockquote>
</div>
<blockquote type=3D"cite">
<div dir=3D"ltr">=EF=BB=BF
<div dir=3D"ltr">Hi Andrew, a couple of things to check.
<div>1st, is this a new problem? if so, what did you touch last?</div>
<div><br>
</div>
<div>2d Verify fuel flow, not just pressure=C2=A0i.e Gallons per hour? Disc=
onnect the fuel line at the carbs, and stick it into a 1 quart or one gallo=
n clean/clear bottle/jug. Turn the fuel pump on and time how long it takes =
to fill (1 Qt/ 1Gal whatever size container
you're using).=C2=A0 If you're getting more than 20 gallons per ho=
ur, the flow is OK. Set the bottle aside and let it settle out, look for pa=
rticles, rubber, fuel cell foam, dirt. If so, see where that's coming f=
rom. For example, old fuel cell foam will break down
and clog the intake. When the pump turns off, the fuel in the lines drops =
back flushing the intake clear until next time. Fuel filter clean? Fuel pre=
ssure reg OK? Not just holding pressure (I run 3.5 on my HS4s) but actually=
sending fuel down the line? The
gallons per hour test will indicate if you need to look into any of these =
areas, if you're gelling enough fuel, more down the list for now.</div>
<div>link to flow and fuel requirements chart=C2=A0<a href=3D"https://histo=
ricracinggroup.com/resources/Reference_Material/Canton/Fuel%20Consumption%2=
0and%20Flow%20Quick%20Ref%20by%20CM%20Filters.pdf" target=3D"_blank">https:=
//historicracinggroup.com/resources/Reference_Material/Canton/Fuel%20Consum=
ption%20and%20Flow%20Quick%20Ref%20by%20CM%20Filters.pdf</a></div>
<div><br>
</div>
<div>3. A problem I had with an identical=C2=A0set up, was rubber hose brea=
king down and settling into the little box shaped=C2=A0well in the carb bow=
l where the line to the jet connects. It's happened=C2=A0to me twice no=
w, last time was in June with fairly new hose feeding
the carbs. It restricted the flow to the jet, even though the bowl was ful=
l. At high load, not enough fuel could get past the blockage.</div>
<div>
<div><IMG_20240630_112925914.jpg></div>
</div>
<div><br>
</div>
<div>4. Vacuum leak- Is there a crack or loose bolt on the intake manifold?=
With the engine running, spray carb cleaner around the manifold to block, =
carbs to manifold. A change in engine RPM means something was drawn in thro=
ugh a gap.<br>
</div>
<div><br>
</div>
<div>5. Compression check- Are all the cylinders within 5-10% of each other=
?</div>
<div><br>
</div>
<div>Happy hunting</div>
<div><br>
</div>
<div>mike h</div>
</div>
<br>
<div class=3D"gmail_quote">
<div dir=3D"ltr" class=3D"gmail_attr">On Fri, Aug 9, 2024 at 3:03=E2=80=AFP=
M Andrew Devenish via Fot <<a href=3D"mailto:fot@autox.team.net"; target=
=3D"_blank">fot@autox.team.net</a>> wrote:<br>
</div>
<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-=
left:1px solid rgb(204,204,204);padding-left:1ex">
Guys, <br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 My car ( 1300, 12.5:1 comp on Sunoco 110=
race gas, dual HS4 ) is still giving me grief. I=E2=80=99ve chased all the=
things I can think of, but still same problem. It starts and runs great, b=
ut after a few laps of the yard ( 5-6, only 1000ft=C2=A0 or so per up/down
lap, so quick accels then braking to turn ) it goes very lean ( I have O2 =
sensor ) and stops. I=E2=80=99m running it without the hood for these test =
runs. It always stops at the entry to a turn.
<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0I=E2=80=99ve been working on it a lot, so=
know it has fuel pressure, and the float bowls are full of fuel. All plugs=
look very similar. The needles (AAA) are the spring type, and the slides m=
ove freely. I use ATF as fluid, but have tried 50 weight too.<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 After a minute or so it will fire back up, but =
only run enough to get back to the shop before going lean again. If I pull =
out the choke it will run, but is unstable.
<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0I have wrapped headers and a heat shield around =
the carbs but they do still get hot.<br>
<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0Any ideas ?=C2=A0 Thinking to try some less vola=
tile fuel as it seems heat related and the Sunoco evaporates so fast !<br>
<br>
<br>
Thank you, <br>
=C2=A0 =C2=A0 =C2=A0 Andrew Devenish<br>
<br>
Sent from my iPad_______________________________________________<br>
<a href=3D"mailto:fot@autox.team.net"; target=3D"_blank">fot@autox.team.net<=
/a><br>
<br>
<a href=3D"http://www.fot-racing.com/"; rel=3D"noreferrer" target=3D"_blank"=
>http://www.fot-racing.com</a><br>
<br>
et=3D"_blank">
Archive: <a href=3D"http://autox.team.net/archive"; rel=3D"noreferrer" targe=
t=3D"_blank">
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fotUnsubscribe/Manage" rel=3D"noreferrer" target=3D"_blank">
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http://autox.team.net/mailman/options/fot/ofracer@gmail.com</a><br>
<br>
<br>
</blockquote>
</div>
</div>
</blockquote>
</div>
</div>
_______________________________________________<br>
<a href=3D"mailto:fot@autox.team.net"; target=3D"_blank">fot@autox.team.net<=
/a><br>
<br>
<a href=3D"http://www.fot-racing.com"; rel=3D"noreferrer" target=3D"_blank">=
http://www.fot-racing.com</a><br>
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et=3D"_blank">http://www.team.net/donate.html</a><br>
Archive: <a href=3D"http://autox.team.net/archive"; rel=3D"noreferrer" targe=
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</blockquote></div>
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