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I totally agree with Kas that the S.U.'s are the simplest carbs around. But
there are ways to get around the short comings (I call it chasing the weak
link). I use to have the problems Kas noted but found a fix. To keep the engine
running properly at high revs on long straights (RA and MidO) I had to increase
static fuel pressure to 6 psi to maintain 2.5 psi on the straights. Then with
development I needed more air/fuel so I taper bored the throat of the S.U.'s
and opened the .090" jets to .096" so I could still use the large array of .090
needles. Plus a few other things to make it all work together.
Ron Krantz
ReK Racing
> On October 19, 2018 at 12:31 PM Kas Kastner via Fot <fot@autox.team.net>
> wrote:
>
> Lots of times at the higher revs the float bowls of the S.U.'s just run
> out of gas and they need an enlargment of the needle and seat.Many times the
> stock needle and seat j ust does not have enough capacity to flow the fuel
> needed for the much richer needles used and the revvs. The SU's are so simple
> minded and easy to work with I'd want to very certain that the was a BIG
> benifit before changing to jetted carbs that need a ton of parts of you are
> going to make use of the capacity of the units.
>
> If you do not tune for the day and the weather at that time what is the
> point in having all that adustment. With the SU a couple flats adjustment up
> or down and you are done the hour. Bigger machinery does not mean bigger
> power or even more useful power.
>
> BUT, if you are going for the expensive route, get the msot you can get.
> DCOE 45's are the ticket. Start with a small venturi and work up from there.
> Yes, you neeed to buy alterate venturies otherwise you have just wasted your
> money.These same carbs were used on the Sebring and Le Mans Spitfire coupes
> 1147 cc engines and proved 3% more power by tuning. To get the benifit you
> need to work at it.
>
> Never be beaten by equipment.
>
>
>
> On Fri, Oct 19, 2018 at 9:01 AM fubog1 via Fot < fot@autox.team.net
> mailto:fot@autox.team.net > wrote:
>
> > > Yes HS4 carbs.
> > Glen
> >
> >
> > -----Original Message-----
> > From: van.mulders.marcel < van.mulders.marcel@telenet.be
> > mailto:van.mulders.marcel@telenet.be >
> > To: fubog1 < fubog1@aol.com mailto:fubog1@aol.com >
> > Cc: fot < fot@autox.team.net mailto:fot@autox.team.net >
> > Sent: Thu, Oct 18, 2018 5:48 pm
> > Subject: Re: [Fot] Weber vs Mikuni
> >
> > Glen,
> > With 1 1/2s carburettors, I suppose you mean HS4? The SU logic is a
> > little weird. 1" + 1/2" = 6/8" so you would think it are HS6s, but when
> > talking about HS carburettors, 1 + 1/2 = 1 + 4/8 and they took the 4 to
> > name these carbs HS4...
> > Marcel
> >
> >
> > ---------------------------------------------
> > Van: "fubog1" < fubog1@aol.com mailto:fubog1@aol.com >
> > Aan: "van mulders marcel" < van.mulders.marcel@telenet.be
> > mailto:van.mulders.marcel@telenet.be >, "Mike Harmuth" < ofracer@gmail.com
> > mailto:ofracer@gmail.com >
> > Cc: "fot" < fot@autox.team.net mailto:fot@autox.team.net >
> > Verzonden: Donderdag 18 oktober 2018 22:39:39
> > Onderwerp: Re: [Fot] Weber vs Mikuni
> >
> > Well I won't speculate on the cause, but I doubt that it's the SUs.
> > My small crank 1300 w/1 1/2s on a eurospec manifold w/Stahls
> > header, "big" valve head, would buzz easily to 9k, still making power, if I
> > let it.
> > Normal shift point 7800-8000.
> > FWIW...
> > Glen
> >
> >
> > -----Original Message-----
> > From: van.mulders.marcel--- via Fot < fot@autox.team.net
> > mailto:fot@autox.team.net >
> > To: Mike Harmuth < ofracer@gmail.com mailto:ofracer@gmail.com >
> > Cc: fot < fot@autox.team.net mailto:fot@autox.team.net >
> > Sent: Thu, Oct 18, 2018 2:12 pm
> > Subject: Re: [Fot] Weber vs Mikuni
> >
> > -"...hitting a wall at that point..." : is it possible this is
> > rather pointing to the camshaft than to the SU's? If it are the
> > carburettors, maybe the power would decrease more gradually above 6500 rpm.
> > -In general one choke per cylinder is better, and 2 Webers 40 DCOE
> > isn't overkill I think
> > - what about trying HS6 SU's on your actual manifold?
> > At what maximum rpm is your engine still reliable?
> > Marcel
> >
> >
> > ---------------------------------------------
> > Van: "fot" < fot@autox.team.net mailto:fot@autox.team.net >
> > Aan: "fot" < fot@autox.team.net mailto:fot@autox.team.net >
> > Verzonden: Woensdag 17 oktober 2018 15:49:45
> > Onderwerp: [Fot] Weber vs Mikuni
> >
> > I'm looking into switching out my twin HS4s on the 1296 race engine
> > to either Weber or Mukinis. I know this has been done for years and I'd
> > like to get close the best set up out of the gate.
> >
> > I don't think the SUs are up to the task of moving enough air with
> > the new ported head and Stahl header. I've worked on the SUs and gotten
> > them to finally deliver a good AFR , 12.6, at 6500 RPM under load but I
> > seem to hit a wall (figuratively) at that point. I suspect that the
> > openings just aren't big enough to deliver the mass of air required.
> > (spreadsheet or other flow calculator link appreciated)
> > Biggest gate I suspect is the intake valve, 1 3/8" head (~35mm) HS4
> > is ~38mm at best.
> >
> > Recommendations? I've seen all these setups at the track, each with
> > pluses, minuses and overkill cause it looks cool.
> >
> > One weber DCOE 40 or 2? what jets, tubes etc for a starting point?
> > Best manifold?
> >
> > 2 or 4 Mikuni 40? jet size?
> >
> > thanks
> > mike
> >
> > _______________________________________________
> > fot@autox.team.net mailto:fot@autox.team.net
> >
> > http://www.fot-racing.com
> >
> > Donate: http://www.team.net/donate.html
> > Archive: http://www.team.net/pipermail/fot
> > Unsubscribe/Manage:
> > http://autox.team.net/mailman/options/fot/van.mulders.marcel@telenet.be
> > _______________________________________________
> > fot@autox.team.net
> >
> > http://www.fot-racing.com
> >
> > Donate: http://www.team.net/donate.html
> > Archive: http://www.team.net/pipermail/fot
> > Unsubscribe/Manage:
> > http://autox.team.net/mailman/options/fot/fubog1@aol.com
> >
> >
> >
> > _______________________________________________
> > fot@autox.team.net mailto:fot@autox.team.net
> >
> > http://www.fot-racing.com
> >
> > Donate: http://www.team.net/donate.html
> > Archive: http://www.team.net/pipermail/fot
> > Unsubscribe/Manage:
> > http://autox.team.net/mailman/options/fot/kaskastner@gmail.com
> >
> >
> >
> > > _______________________________________________
> fot@autox.team.net
>
> http://www.fot-racing.com
>
> Donate: http://www.team.net/donate.html
> Archive: http://www.team.net/pipermail/fot
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> http://autox.team.net/mailman/options/fot/rkrantz77@comcast.net
>
>
>
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<!DOCTYPE html>
<html><head>
<meta charset="UTF-8">
</head><body>I totally agree with Kas that the S.U.'s are the simplest
carbs around. But there are ways to get around the short comings (I call it
chasing the weak link). I use to have the problems Kas noted but found a fix.
To keep the engine running properly at high revs on long straights (RA and
MidO) I had to increase static fuel pressure to 6 psi to maintain 2.5 psi on
the straights. Then with development I needed more air/fuel so I taper bored
the throat of the S.U.'s and opened the .090" jets to .096" so I
could still use the large array of .090 needles. Plus a few other things to
make it all work together.<br>Ron Krantz<br>ReK Racing<br><br>
<blockquote type="cite">
On October 19, 2018 at 12:31 PM Kas Kastner via Fot
<fot@autox.team.net> wrote:
<br>
<br>
<div dir="ltr">
Lots of times at the higher revs the float bowls of the S.U.'s just run
out of gas and they need an enlargment of the needle and seat.Many times the
stock needle and seat j ust does not have enough capacity to flow the fuel
needed for the much richer needles used and the revvs. The SU's are so
simple minded and easy to work with I'd want to very certain that the was a
BIG benifit before changing to jetted carbs that need a ton of parts of you are
going to make use of the capacity of the units.
<div>
<br>
</div>
<div>
 If you do not tune for the day and the weather at that time what is
the point in having all that adustment. With the SU a couple flats adjustment
up or down and you are done the hour. Bigger machinery does not mean bigger
power or even more useful power.
<div>
<br>
</div>
<div>
BUT, if you are going for the expensive route, get the msot you can
get.  DCOE 45's are the ticket. Start with a small venturi and work up
from there. Yes, you neeed to buy  alterate venturies otherwise you have
just wasted your money.These same carbs were used on the Sebring and Le Mans
Spitfire coupes 1147 cc engines  and proved 3% more power by tuning. To
get the benifit you need to work at it.
<br clear="all">
<div>
<div dir="ltr" class="gmail_signature">
<p><strong><font color="#000099">Never be beaten by
equipment.</font></strong></p>
</div>
</div>
<br>
</div>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">
On Fri, Oct 19, 2018 at 9:01 AM fubog1 via Fot <
<a href="mailto:fot@autox.team.net";>fot@autox.team.net</a>> wrote:
<br>
</div>
<blockquote class="gmail_quote">
<font size="2" face="Arial, Helvetica, sans-serif" color="black">
<div>
<font size="2">Yes HS4 carbs.</font>
</div>
<div>
<font size="2">Glen</font>
<br>
</div>
<div>
<br>
</div>
<div>
<br>
</div>
<div style="font-family: arial,helvetica; font-size: 10pt; color: black;">
-----Original Message-----
<br> From: van.mulders.marcel <
<a href="mailto:van.mulders.marcel@telenet.be";
target="_blank">van.mulders.marcel@telenet.be</a>>
<br> To: fubog1 <
<a href="mailto:fubog1@aol.com"; target="_blank">fubog1@aol.com</a>>
<br> Cc: fot <
<a href="mailto:fot@autox.team.net";
target="_blank">fot@autox.team.net</a>>
<br> Sent: Thu, Oct 18, 2018 5:48 pm
<br> Subject: Re: [Fot] Weber vs Mikuni
<br>
<br>
<div id="m_-3204379643218842764yiv7557179423">
<div>
<div style="font-family: Verdana,Arial,Helvetica,sans-serif; font-size:
10pt; color: #000000;">
<div>
Glen,
</div>
<div>
With 1 1/2s carburettors, I suppose you mean HS4? The SU logic is a
little weird. 1" + 1/2" = 6/8" so you would think it are HS6s, but
when talking about HS carburettors, 1 + 1/2 = 1 + 4/8 and they took the 4 to
name these carbs HS4...
</div>
<div>
Marcel
</div>
<div>
<br clear="none">
</div>
<hr id="m_-3204379643218842764yiv7557179423zwchr">
<div class="m_-3204379643218842764yiv7557179423yqt0596148954"
id="m_-3204379643218842764yiv7557179423yqt61649">
<div>
<b>Van: </b>"fubog1" <
<a href="mailto:fubog1@aol.com";
target="_blank">fubog1@aol.com</a>>
<br clear="none">
<b>Aan: </b>"van mulders marcel" <
<a href="mailto:van.mulders.marcel@telenet.be";
target="_blank">van.mulders.marcel@telenet.be</a>>, "Mike Harmuth"
<
<a href="mailto:ofracer@gmail.com";
target="_blank">ofracer@gmail.com</a>>
<br clear="none">
<b>Cc: </b>"fot" <
<a href="mailto:fot@autox.team.net";
target="_blank">fot@autox.team.net</a>>
<br clear="none">
<b>Verzonden: </b>Donderdag 18 oktober 2018 22:39:39
<br clear="none">
<b>Onderwerp: </b>Re: [Fot] Weber vs Mikuni
<br clear="none">
</div>
<br clear="none">
<div>
<span style="color: black; font-family: Arial,Helvetica,sans-serif;
font-size: small;"> </span>
<div>
<span style="font-size: small;">Well I won't speculate on the
cause, but I doubt that it's the SUs.<br clear="none"> </span>
</div>
<div>
<span style="font-size: small;">My small crank 1300 w/1 1/2s on a
eurospec manifold w/Stahls header, "big" valve head, would buzz easily
to 9k, still making power, if I let it.</span>
</div>
<div>
<span style="font-size: small;">Normal shift point 7800-8000.</span>
</div>
<div>
<span style="font-size: small;">FWIW...<br clear="none"> </span>
</div>
<div>
<span style="font-size: small;">Glen</span>
<br clear="none">
</div>
<div>
<br clear="none">
</div>
<div>
<br clear="none">
</div>
<div style="font-family: arial,helvetica; font-size: 10pt; color:
black;">
-----Original Message-----
<br clear="none"> From: van.mulders.marcel--- via Fot <
<a href="mailto:fot@autox.team.net";
target="_blank">fot@autox.team.net</a>>
<br clear="none"> To: Mike Harmuth <
<a href="mailto:ofracer@gmail.com";
target="_blank">ofracer@gmail.com</a>>
<br clear="none"> Cc: fot <
<a href="mailto:fot@autox.team.net";
target="_blank">fot@autox.team.net</a>>
<br clear="none"> Sent: Thu, Oct 18, 2018 2:12 pm
<br clear="none"> Subject: Re: [Fot] Weber vs Mikuni
<br clear="none">
<br clear="none">
<div id="m_-3204379643218842764yiv7557179423">
<div>
<div style="font-family: Verdana,Arial,Helvetica,sans-serif;
font-size: 10pt; color: #000000;">
<div>
-"...hitting a wall at that point..." : is it possible
this is rather pointing to the camshaft than to the SU's? If it are the
carburettors, maybe the power would decrease more gradually above 6500 rpm.
</div>
<div>
-In general one choke per cylinder is better, and 2 Webers 40
DCOE isn't overkill I think
</div>
<div>
- what about trying HS6 SU's on your actual manifold?
</div>
<div>
At what maximum rpm is your engine still reliable?
</div>
<div>
Marcel
</div>
<div>
<br clear="none">
</div>
<hr id="m_-3204379643218842764yiv7557179423zwchr">
<div class="m_-3204379643218842764yiv7557179423yqt0105059393"
id="m_-3204379643218842764yiv7557179423yqt73080">
<div>
<b>Van: </b>"fot" <
<a href="mailto:fot@autox.team.net";
target="_blank">fot@autox.team.net</a>>
<br clear="none">
<b>Aan: </b>"fot" <
<a href="mailto:fot@autox.team.net";
target="_blank">fot@autox.team.net</a>>
<br clear="none">
<b>Verzonden: </b>Woensdag 17 oktober 2018 15:49:45
<br clear="none">
<b>Onderwerp: </b>[Fot] Weber vs Mikuni
<br clear="none">
</div>
<br clear="none">
<div>
<div dir="ltr">
<div>
I'm looking into switching out my twin HS4s on the 1296
race engine to either Weber or Mukinis. I know this has been done for years and
I'd like to get close the best set up out of the gate.
<br clear="none">
</div>
<br clear="none">
<div>
I don't think the SUs are up to the task of moving enough
air with the new ported head and Stahl header. I've worked on the SUs and
gotten them to finally deliver a good AFR , 12.6, at 6500 RPM under load but I
seem to hit a wall (figuratively) at that point. I suspect that the openings
just aren't big enough to deliver the mass of air required. (spreadsheet or
other flow calculator link appreciated)
<br clear="none">
</div>
<div>
Biggest gate I suspect is the intake valve, 1 3/8" head
(~35mm) HS4 is ~38mm at best.
<br clear="none">
</div>
<br clear="none">
<div>
Recommendations? I've seen all these setups at the track,
each with pluses, minuses and overkill cause it looks cool.
<br clear="none">
</div>
<br clear="none">
<div>
One weber DCOE 40 or 2? what jets, tubes etc for a starting
point? Best manifold?
<br clear="none">
</div>
<br clear="none">
<div>
2 or 4 Mikuni 40? jet size?
</div>
<br clear="none">
<div>
thanks
</div>
<div>
mike
<br clear="none">
</div>
</div>
<br clear="none">_______________________________________________
<br clear="none">
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target="_blank">fot@autox.team.net</a>
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target="_blank">http://www.fot-racing.com</a>
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</blockquote>
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