--===============7821739705781597827==
boundary="_7588037D-D836-460A-877A-520C10CDDB11_"
--_7588037D-D836-460A-877A-520C10CDDB11_
Content-Transfer-Encoding: quoted-printable
Simon=20
I thought I had written to you about the =E2=80=9Cshoulder=E2=80=9D issue p=
reviously but I don=E2=80=99t see it in my mailbox.=20
The =E2=80=9Cshoulder=E2=80=9D is really where the dash pot vent is located=
. Some SU=E2=80=99s have none, but have a vented cap, some have one intern=
al vent and some have two. Since this vent is a connection to suction chamb=
er for the small chamber above the oil damper just under the cap, it would =
appear that the use of more than one vent has a bearing on the efficient op=
eration of the SU on that engine or application. =20
When the engine is cranking or running, the flow of air through the SU carb=
body reduces the pressure (lower than atmospheric, suction) in the suction=
chamber or dash pot. On most SU=E2=80=99s there is a set of holes above wh=
ere the carb and air cleaner are joined. Those holes ultimately connect to=
the inside of the suction chamber. That reduced pressure slightly raises t=
he piston and richens the air fuel mixture. Much like our 100 starts much e=
asier when cold by not only pulling the choke by lightly pressing on the ga=
s pedal.
I have searched through many SU manuals and various write-ups on SU carbs =
and this particular aspect of the SU=E2=80=99s does not seem to be a topic =
of concern or discussion. Suspect that the vents, both size and number, ha=
ve a lot to do with meeting the design specs for the application. The pisto=
n drop is one that comes to mind. How fast does the piston fall to idle whe=
n the driver is off the throttle? The spring size probably is the biggest =
factor but pressures inside and outside the carb has some bearing. =20
The Engineer in me wants to know the answers but the retired guy in me says=
I don=E2=80=99t need to know. What I do need to adhere to is the original =
design of the parts. IE: If there is a gasket on the air cleaner /carb int=
erface originally, is it there and fit correctly? If there are holes on th=
e carb body, either for fuel or air flow are they clean/unobstructed.=20
Whether your HD6=E2=80=99s had a single or double suction chamber vent, I h=
ave yet to find the answer. I do suspect that if they are supposed to have =
single vents but now has double vents, something may not work as designed.=
=20
Perry
Sent from Mail for Windows 10
From: simon.lachlan@alexarevel.plus.com
Sent: Sunday, October 6, 2019 1:33 PM
To: 'Healeys'
Subject: [Healeys] SU Dashpot puzzle
Here=E2=80=99s one for the technoctats:-
You may have noticed my posts about swapping from two-shouldered to single-=
shouldered dashpots. I did it because having two of one and one of the othe=
r was irritating, not because I thought there=E2=80=99d be any changes.
So, I swapped the offending two and that gave me three HD6s, all with one s=
houlder.
Car started on the choke, same as normal. Seemingly!
However, doing the garden hose in one ear trick revealed that the rear carb=
, always single shouldered, was making less intake hiss than the other rece=
ntly added pair. Easily rectified.
I took the car out this afternoon. Started fine and ran well. But, if I eas=
ed off, the revs dropped and the engine cut out. Also, there was quite a lo=
t of popping and f**ting on the overrun.
So, on my return, I gave the front two carbs about half a turn up on the sl=
ow idle screws. This, quite small adjustment really, seemed to cure it and =
even to raise the idle rather higher than I like.=20
Adjusted down quarter of a turn and all seems well.
Questions:- beyond the obvious =E2=80=93 ie that changing dashpots does mak=
e a difference after all =E2=80=93 what is going on? Why was there a change=
?
(Plainly, I swapped needles and springs when I swapped dashpots so I=E2=80=
=99ve got all the same in the carbs=E2=80=A6.the ones that I had all along)=
.
Any ideas?
Simon
--_7588037D-D836-460A-877A-520C10CDDB11_
Content-Transfer-Encoding: quoted-printable
<html xmlns:o=3D"urn:schemas-microsoft-com:office:office" xmlns:w=3D"urn:sc=
hemas-microsoft-com:office:word" xmlns:m=3D"http://schemas.microsoft.com/of=
fice/2004/12/omml" xmlns=3D"http://www.w3.org/TR/REC-html40";><head><meta ht=
tp-equiv=3DContent-Type content=3D"text/html; charset=3Dutf-8"><meta name=
=3DGenerator content=3D"Microsoft Word 15 (filtered medium)"><style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
.MsoChpDefault
{mso-style-type:export-only;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style></head><body lang=3DEN-US link=3Dblue vlink=3D"#954F72"><div cla=
ss=3DWordSection1><p class=3DMsoNormal>Simon </p><p class=3DMsoNormal>I tho=
ught I had written to you about the =E2=80=9Cshoulder=E2=80=9D issue previo=
usly but I don=E2=80=99t see it in my mailbox. </p><p class=3DMsoNormal><o:=
p> </o:p></p><p class=3DMsoNormal>The =E2=80=9Cshoulder=E2=80=9D is re=
ally where the dash pot vent is located.=C2=A0 Some SU=E2=80=99s have none,=
but have a vented cap, some have one internal vent and some have two. Sinc=
e this vent is a connection to suction chamber for the small chamber above =
the oil damper just under the cap, it would appear that the use of more tha=
n one vent has a bearing on the efficient operation of the SU on that engin=
e or application.=C2=A0 </p><p class=3DMsoNormal><o:p> </o:p></p><p cl=
ass=3DMsoNormal>When the engine is cranking or running, the flow of air thr=
ough the SU carb body reduces the pressure (lower than atmospheric, suction=
) in the suction chamber or dash pot. On most SU=E2=80=99s there is a set o=
f holes above where the carb and air cleaner are joined. =C2=A0Those holes =
ultimately connect to the inside of the suction chamber. That reduced press=
ure slightly raises the piston and richens the air fuel mixture. Much like =
our 100 starts much easier when cold by not only pulling the choke by light=
ly pressing on the gas pedal.</p><p class=3DMsoNormal><o:p> </o:p></p>=
<p class=3DMsoNormal>I have searched through many SU manuals and various wr=
ite-ups =C2=A0on SU carbs and this particular aspect of the SU=E2=80=99s do=
es not seem to be a topic of concern or discussion.=C2=A0 Suspect that the =
vents, both size and number, have a lot to do with meeting the design specs=
for the application. The piston drop is one that comes to mind. How fast d=
oes the piston fall to idle when the driver is off the throttle? =C2=A0The =
spring size probably is the biggest factor but pressures inside and outside=
the carb has some bearing. =C2=A0</p><p class=3DMsoNormal><o:p> </o:p=
></p><p class=3DMsoNormal>The Engineer in me wants to know the answers but =
the retired guy in me says I don=E2=80=99t need to know. What I do need to =
adhere to is the original design of the parts.=C2=A0 IE: If there is a gask=
et on the air cleaner /carb interface originally, is it there and fit corre=
ctly?=C2=A0 If there are holes on the carb body, either for fuel or air flo=
w are they clean/unobstructed. </p><p class=3DMsoNormal><o:p> </o:p></=
p><p class=3DMsoNormal>Whether your HD6=E2=80=99s had a single or double su=
ction chamber vent, I have yet to find the answer. I do suspect that if the=
y are supposed to have single vents but now has double vents, something may=
not work as designed. </p><p class=3DMsoNormal>Perry</p><p class=3DMsoNorm=
al><o:p> </o:p></p><p class=3DMsoNormal>Sent from <a href=3D"https://g=
o.microsoft.com/fwlink/?LinkId=3D550986">Mail</a> for Windows 10</p><p clas=
s=3DMsoNormal><o:p> </o:p></p><div style=3D'mso-element:para-border-di=
v;border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p =
class=3DMsoNormal style=3D'border:none;padding:0in'><b>From: </b><a href=3D=
"mailto:simon.lachlan@alexarevel.plus.com";>simon.lachlan@alexarevel.plus.co=
m</a><br><b>Sent: </b>Sunday, October 6, 2019 1:33 PM<br><b>To: </b><a href=
=3D"mailto:healeys@autox.team.net";>'Healeys'</a><br><b>Subject: </b>[Healey=
s] SU Dashpot puzzle</p></div><p class=3DMsoNormal><o:p> </o:p></p><p =
class=3DMsoNormal><span lang=3DEN-GB>Here=E2=80=99s one for the technoctats=
:-<o:p></o:p></span></p><p class=3DMsoNormal><span lang=3DEN-GB>You may hav=
e noticed my posts about swapping from two-shouldered to single-shouldered =
dashpots. I did it because having two of one and one of the other was irrit=
ating, not because I thought there=E2=80=99d be any changes.<o:p></o:p></sp=
an></p><p class=3DMsoNormal><span lang=3DEN-GB>So, I swapped the offending =
two and that gave me three HD6s, all with one shoulder.<o:p></o:p></span></=
p><p class=3DMsoNormal><span lang=3DEN-GB>Car started on the choke, same as=
normal. Seemingly!<o:p></o:p></span></p><p class=3DMsoNormal><span lang=3D=
EN-GB>However, doing the garden hose in one ear trick revealed that the rea=
r carb, always single shouldered, was making less intake hiss than the othe=
r recently added pair. Easily rectified.<o:p></o:p></span></p><p class=3DMs=
oNormal><span lang=3DEN-GB><o:p> </o:p></span></p><p class=3DMsoNormal=
><span lang=3DEN-GB>I took the car out this afternoon. Started fine and ran=
well. But, if I eased off, the revs dropped and the engine cut out. Also, =
there was quite a lot of popping and f**ting on the overrun.<o:p></o:p></sp=
an></p><p class=3DMsoNormal><span lang=3DEN-GB>So, on my return, I gave the=
front two carbs about half a turn up on the slow idle screws. This, quite =
small adjustment really, seemed to cure it and even to raise the idle rathe=
r higher than I like. <o:p></o:p></span></p><p class=3DMsoNormal><span lang=
=3DEN-GB>Adjusted down quarter of a turn and all seems well.<o:p></o:p></sp=
an></p><p class=3DMsoNormal><span lang=3DEN-GB>Questions:- beyond the obvio=
us =E2=80=93 ie that changing dashpots does make a difference after all =E2=
=80=93 what is going on? Why was there a change?<o:p></o:p></span></p><p cl=
ass=3DMsoNormal><span lang=3DEN-GB>(Plainly, I swapped needles and springs =
when I swapped dashpots so I=E2=80=99ve got all the same in the carbs=E2=80=
=A6.the ones that I had all along).<o:p></o:p></span></p><p class=3DMsoNorm=
al><span lang=3DEN-GB>Any ideas?<o:p></o:p></span></p><p class=3DMsoNormal>=
<span lang=3DEN-GB>Simon<o:p></o:p></span></p><p class=3DMsoNormal><o:p>&nb=
sp;</o:p></p></div></body></html>=
--_7588037D-D836-460A-877A-520C10CDDB11_--
--===============7821739705781597827==
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
_______________________________________________
Archive: http://www.team.net/pipermail/healeys http://autox.team.net/archive
Healeys@autox.team.net
http://autox.team.net/mailman/listinfo/healeys
--===============7821739705781597827==--
|