Subject: Re: [TR] Issues with Temp. compensators on a ZS CD 175

From: Jeff Scarbrough <[email-masked]>
Date: Wed, 19 Jan 2022 12:06:25 -0500

As I understand it, they also bypass air around the throttle plate.
But I'm not sure...

This guy has a pretty good video on 175 carb operation in general, and
toward the end of this one he shows how to check the operation of the
TC.

https://www.youtube.com/watch?v=g0UseZTKaO8&ab_channel=MidwestMotoring

Some diagrams in this thread too
https://forum.etypeuk.com/viewtopic.php?t=16206

On Tue, Jan 18, 2022 at 12:20 PM Sujit Roy <[email-masked]> wrote:
>
> I've been running into issues with my ZS carbs. The problem is as the car gets to operating conditions, the RPMs goes up from about 800 rpm  to about 1000.
> I have carbs with by-pass valves, but they are blocked off.
> Folk have said it's the temp. compensators. I rebuilt the carbs and have adjusted the compensators according to an article on Buckeye Triumph. Suggestions have been to tighten the adjustment screw so they don't open.
>
> So I have just read the Dealer Training on the subject of Carburetion. I see how the compensators work and make the fuel mixture leaner when at operating temperature. The doc says when they open, it weakens the depression which allows the piston to fall slightly thereby cutting the available fuel and creating a leaner mixture. This I get, but with the throttle plate in the idle position, and the volume of air passing the throttle plate can't change, then why does the engine speed increase?
>
>
> Regards, Sujit
>
> --
> Sujit Roy
> Cupertino, California
>
> https://triumphstagblog.wordpress.com/
>
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---

From: Bud <[email-masked]>
Date: Wed, 19 Jan 2022 13:45:07 -0700

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Sujit,
Having boiled my temperature compensators and trying to get them perfect I w=
ent down that rabbit hole for quite some time.=20
I found that the same problem you have actually was caused by too high fuel p=
ressure.=20
My problem went away when I installed a fuel pressure regulator in the gas l=
ine between the fuel pump and the carbs . I hooked up a vacuum/ fuel pressur=
e gage simultaneously and set the fuel pressure to 1.5-2 psi. Basically ZS c=
arbs will flood just a wee bit by the float valve not being able to hold bac=
k fuel any higher pressure  than that. Hence higher RPMs once warm with the e=
xtra fuel.
One indicator of this is a Triumph that needs little or no choke to start up=
 when cold. These cars were designed to be choked on most.

Bud

Sent from my Commadore 64

> On Jan 18, 2022, at 10:20 AM, Sujit Roy <[email-masked]> wrote:
>=20
> =EF=BB=BF
> I've been running into issues with my ZS carbs. The problem is as the car g=
ets to operating conditions, the RPMs goes up from about 800 rpm  to about 1=
000.=20
> Folk have said it's the temp. compensators. I rebuilt the carbs and have a=
djusted the compensators according to an article on Buckeye Triumph. Suggest=
ions have been to tighten the adjustment screw so they don't open.=20
>=20
> So I have just read the Dealer Training on the subject of Carburetion. I s=
ee how the compensators work and make the fuel mixture leaner when at operat=
ing temperature. The doc says when they open, it weakens the depression whic=
h allows the piston to fall slightly thereby cutting the available fuel and c=
reating a leaner mixture. This I get, but with the throttle plate in the idl=
e position, and the volume of air passing the throttle plate can't change, t=
hen why does the engine speed increase?
>=20
>=20
>=20
> --=20
>=20
>=20
>=20
> Archive: http://www.team.net/pipermail/triumphs  http://www.team.net/archi=
ve
>=20
> Unsubscribe/Manage: http://autox.team.net/mailman/options/triumphs/levilev=
[email-masked]

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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">Sujit,<div>Having boiled my temperature com=
pensators and trying to get them perfect I went down that rabbit hole for qu=
ite some time.&nbsp;</div><div>I found that the same problem you have actual=
ly was caused by too high fuel pressure.&nbsp;</div><div>My problem went awa=
y when I installed a fuel pressure regulator in the gas line between the fue=
l pump and the carbs . I hooked up a vacuum/ fuel pressure gage simultaneous=
ly and set the fuel pressure to 1.5-2 psi. Basically ZS carbs will flood jus=
t a wee bit by the float valve not being able to hold back fuel any higher p=
ressure &nbsp;than that. Hence higher RPMs once warm with the extra fuel.</d=
iv><div>One indicator of this is a Triumph that needs little or no choke to s=
tart up when cold. These cars were designed to be choked on most.</div><div>=
<br></div><div>Bud<br><br><div dir=3D"ltr">Sent from my Commadore 64</div><d=
iv dir=3D"ltr"><br><blockquote type=3D"cite">On Jan 18, 2022, at 10:20 AM, S=
ujit Roy &lt;[email-masked]&gt; wrote:<br><br></blockquote></div><blo=
ckquote type=3D"cite"><div dir=3D"ltr">=EF=BB=BF<div dir=3D"ltr">I've been r=
unning&nbsp;into issues with my ZS carbs. The problem is as the car gets to o=
perating conditions, the&nbsp;RPMs goes up from about 800 rpm&nbsp; to about=
 1000.&nbsp;<div>I have carbs with by-pass valves, but they are blocked off.=
</div><div>Folk have said it's the temp. compensators. I rebuilt the carbs a=
nd have adjusted the&nbsp;compensators according&nbsp;to an article on Bucke=
ye Triumph. Suggestions have been to tighten the adjustment screw so they do=
n't&nbsp;open.&nbsp;</div><div><br></div><div>So <span style=3D"color:rgb(17=
,17,17);font-family:Arial,Helvetica,Verdana,sans-serif;font-size:12px">I hav=
e just read the Dealer Training on the subject of Carburetion. I see how the=
 </span>compensators work<span style=3D"color:rgb(17,17,17);font-family:Aria=
l,Helvetica,Verdana,sans-serif;font-size:12px"> and make the fuel mixture le=
aner when at operating temperature. The doc says when they open, it weakens t=
he depression which allows the piston to fall slightly thereby cutting the a=
vailable fuel and creating a leaner mixture. This I get, but with the thrott=
le plate in the idle position, and the volume of air passing the throttle pl=
ate can't change, then why does the engine speed increase?</span></div><div>=
<span style=3D"color:rgb(17,17,17);font-family:Arial,Helvetica,Verdana,sans-=
serif;font-size:12px"><br></span></div><div><br></div><div><font color=3D"#1=
11111" face=3D"Arial, Helvetica, Verdana, sans-serif"><span style=3D"font-si=
ze:12px">Regards, Sujit</span></font></div><div><font color=3D"#111111" face=
=3D"Arial, Helvetica, Verdana, sans-serif"><span style=3D"font-size:12px"><b=
r></span></font><div>-- <br><div dir=3D"ltr" class=3D"gmail_signature" data-=
smartmail=3D"gmail_signature"><div dir=3D"ltr"><div>Sujit Roy<br>Cupertino, C=
alifornia</div><div><br><a href=3D"https://triumphstagblog.wordpress.com/" t=
arget=3D"_blank">https://triumphstagblog.wordpress.com/</a><br><br></div></d=
iv></div></div></div></div>
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hs/[email-masked]</span><br></div></blockquote></div></body></html>=

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