Subject: [Fot] SU carb smooth bore or leave rough?

From: Mike Harmuth via Fot <[email-masked]>
Date: Tue, 24 Nov 2020 15:41:55 -0500

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I was going over my race carbs (SU H4)and wondered if there's anything to
be gained  (or lost) by smoothing out the casting (before the jet)? I'm not
sure if it's designed (or left) that way to promote turbulence and better
mixing as the air flows over the jet or if polishing it down would help.

I'd hate to trash a pair of good carbs before I get some answers.

thanks
mike h

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<div dir=3D"ltr">I was going over my race carbs (SU H4)and wondered if ther=
e&#39;s anything to be gained=C2=A0 (or lost) by smoothing out the casting =
(before the jet)? I&#39;m not sure if it&#39;s designed (or left) that way =
to promote turbulence and better mixing as the air flows over the jet or if=
 polishing it down would help.<div><br></div><div>I&#39;d hate to trash a p=
air of good carbs before I get some answers.</div><div><br></div><div>thank=
s</div><div>mike h</div></div>

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From: Phil Gott via Fot <[email-masked]>
Date: Wed, 25 Nov 2020 12:44:10 -0500

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Still need the bridge!
We had a set of computune carbs with bridge removed on a 948 bug eye. It nee=
ded hand choking to start, wouldn=E2=80=99t run worth a darn below 3000 rpm.=
 And if it stalled in the grid, very likely, it needed a vigorous push start=
.
Post Mortem we learned that on these the float level needs to be set high en=
ough that the fuel literally dribbles out of the jet. That=E2=80=99s apparen=
tly the only way to get them to run at most any throttle setting and engine s=
peed other than wide open.
There are a lot of ways to improve these carbs, but removing the bridge isn=E2=
=80=99t one of them unless you after pure WOT horsepower.
Phil Gott

Sent from my iPhone

> On Nov 25, 2020, at 12:35 PM, Bruce Stutzman via Fot <[email-masked]> w=
rote:
>=20
> =EF=BB=BF
> Back in the day we thought we needed the bridge to help mix the incoming a=
ir with the fuel.
> Bruce
>=20
>> On Wed, Nov 25, 2020 at 12:04 PM David Gott via Fot <[email-masked]> w=
rote:
>> Hi Mike,
>>=20
>> My TR4 came with a pair of Computune set up HS6=E2=80=99s that have had t=
he damper removed, and the whole bridge at the jet removed.  The jet stands a=
lone on its own, sticking up the height of the former bridge.  Also, the thr=
ottle shafts are Steel, and very thin, only picking up the throttle plate on=
 one side.  Alas, the steel has worn out the aluminum body and needs bushing=
s badly.  I=E2=80=99m sure they flow great, but without the bridge, probably=
 tough to drive at anything other than WOT.   I bet part throttle modulation=
 is difficult, but good dyno numbers are sure to be there....  I will try th=
em some day!  Anyone have experience running the Computune carbs? =20
>>=20
>> Dave Gott
>>=20
>>=20
>> Sent from Yahoo Mail for iPhone
>>=20
>> On Wednesday, November 25, 2020, 11:34 AM, DAVE HOGYE via Fot <fot@autox.=
team.net> wrote:
>>=20
>> I know that Huffaker does this.  I believe they also remove the damper oi=
l and or the damper completely and shave down the throttle shaft to almost n=
othing.  So, I don't think you'd be trashing them, but I don't know what the=
 dyno results are either. As far as I know, they also replace head gaskets a=
nd engines quite regularly on their BMC builds. =20
>> Dave H.=20
>> =20
>> =20
>>> On 11/24/2020 12:41 PM Mike Harmuth via Fot <[email-masked]> wrote:
>>> =20
>>> =20
>>> I was going over my race carbs (SU H4)and wondered if there's anything t=
o be gained  (or lost) by smoothing out the casting (before the jet)? I'm no=
t sure if it's designed (or left) that way to promote turbulence and better m=
ixing as the air flows over the jet or if polishing it down would help.
>>> =20
>>> =20
>>> _______________________________________________=20
>>> [email-masked]=20
>>>=20
>>> http://www.fot-racing.com=20
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mcast.net=20
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>>>=20
>>=20
>>=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">Still need the bridge!<div>We had a set of c=
omputune carbs with bridge removed on a 948 bug eye. It needed hand choking t=
o start, wouldn=E2=80=99t run worth a darn below 3000 rpm. And if it stalled=
 in the grid, very likely, it needed a vigorous push start.</div><div>Post M=
ortem we learned that on these the float level needs to be set high enough t=
hat the fuel literally dribbles out of the jet. That=E2=80=99s apparently th=
e only way to get them to run at most any throttle setting and engine speed o=
ther than wide open.</div><div>There are a lot of ways to improve these carb=
s, but removing the bridge isn=E2=80=99t one of them unless you after pure W=
OT horsepower.</div><div>Phil Gott</div><div><br></div><div><br><br><div dir=
=3D"ltr">Sent from my iPhone</div><div dir=3D"ltr"><br><blockquote type=3D"c=
ite">On Nov 25, 2020, at 12:35 PM, Bruce Stutzman via Fot &lt;[email-masked]=
.net&gt; wrote:<br><br></blockquote></div><blockquote type=3D"cite"><div dir=
=3D"ltr">=EF=BB=BF<div dir=3D"ltr">Back in the day we thought we needed the b=
ridge to help mix the incoming air with the fuel.<div>Bruce</div></div><br><=
div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Wed, Nov 2=
5, 2020 at 12:04 PM David Gott via Fot &lt;<a href=3D"mailto:[email-masked].=
net">[email-masked]</a>&gt; wrote:<br></div><blockquote class=3D"gmail_q=
uote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,20=
4);padding-left:1ex"><div>
Hi Mike,<div><br></div><div>My TR4 came with a pair of Computune set up HS6=E2=
=80=99s that have had the damper removed, and the whole bridge at the jet re=
moved.&nbsp; The jet stands alone on its own, sticking up the height of the f=
ormer bridge.&nbsp; Also, the throttle shafts are Steel, and very thin, only=
 picking up the throttle plate on one side.&nbsp; Alas, the steel has worn o=
ut the aluminum body and needs bushings badly.&nbsp; I=E2=80=99m sure they f=
low great, but without the bridge, probably tough to drive at anything other=
 than WOT. &nbsp; I bet part throttle modulation is difficult, but good dyno=
 numbers are sure to be there....&nbsp; I will try them some day!&nbsp; Anyo=
ne have experience running the Computune carbs?&nbsp;&nbsp;</div><div><br></=
div><div>Dave Gott<br><br><br><a href=3D"https://overview.mail.yahoo.com/?.s=
rc=3DiOS" target=3D"_blank">Sent from Yahoo Mail for iPhone</a><br><br><p st=
yle=3D"font-size:15px;color:rgb(113,95,250);padding-top:15px;margin-top:0px"=
>On Wednesday, November 25, 2020, 11:34 AM, DAVE HOGYE via Fot &lt;<a href=3D=
"mailto:[email-masked]" target=3D"_blank">[email-masked]</a>&gt; wro=
te:</p><blockquote><div id=3D"gmail-m_4453025841764188289yiv4410313316"><div=
  <div style=3D"font-size:12pt;font-family:helvetica,arial,sans-serif;color:=
rgb(51,51,51)">
   <span style=3D"font-family:helvetica;font-size:12pt">I know that Huffaker=
 does this.&nbsp; I believe they also remove the damper oil and or the dampe=
r completely and shave down the throttle shaft to almost nothing.&nbsp; So, I=
 don't think you'd be trashing them, but I don't know what the dyno results a=
re either. As far as I know, they also replace head gaskets and engines quit=
e regularly on their BMC builds.&nbsp;&nbsp;</span>
  </div>=20
  <div style=3D"font-size:12pt;font-family:helvetica,arial,sans-serif;color:=
rgb(51,51,51)">
   <span style=3D"font-family:helvetica;font-size:12pt">Dave H.&nbsp;</span>=

  </div>=20
  <div style=3D"font-size:12pt;font-family:helvetica,arial,sans-serif;color:=
rgb(51,51,51)">
   &nbsp;
  </div>=20
  <div style=3D"font-size:12pt;font-family:helvetica,arial,sans-serif;color:=
rgb(51,51,51)">
   &nbsp;
  </div>=20
  <div id=3D"gmail-m_4453025841764188289yiv4410313316yqt59346"><div style=3D=
"font-size:12pt;font-family:helvetica,arial,sans-serif;color:rgb(51,51,51)">=

   On 11/24/2020 12:41 PM Mike Harmuth via Fot &lt;<a href=3D"mailto:fot@aut=
ox.team.net" target=3D"_blank">[email-masked]</a>&gt; wrote:
  </div>=20
  <blockquote type=3D"cite">=20
   <div>
    &nbsp;
   </div>=20
   <div>
    &nbsp;
   </div>=20
   <div dir=3D"ltr">
    I was going over my race carbs (SU H4)and wondered if there's anything t=
o be gained&nbsp; (or lost) by smoothing out the casting (before the jet)? I=
'm not sure if it's designed (or left) that way to promote turbulence and be=
tter mixing as the air flows over the jet or if polishing it down would help=
.=20
    <div>
     &nbsp;
    </div>=20
    <div>
     I'd hate to trash a pair of good carbs before I get some answers.
    </div>=20
    <div>
     &nbsp;
    </div>=20
    <div>
     thanks
    </div>=20
    <div>
     mike h
    </div>=20
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