Too fast!

PostPost by: Thornts » Fri Feb 18, 2005 5:57 pm

May I please pick the collective brains of the group? My twink, once warmed
up, holds onto revs for some time after you come off the throttle and even
at idle will not drop much bellow about 1,500 rpm. I have visually checked
the butterflies and they are fully closed so there does not seem to be much
mileage in adjusting the throttle stop screws. I suspect that the 'O' rings
may be past their best and unless anyone has a better idea I'll replace them
as a matter of course. Add the fact that coming right off the throttle from
high revs results in a lot of popping and banging and flames of unburnt fuel
from the exhaust, it seems there must be fuel finding its way into the
combustion chambers somehow. Idle jets? I'm blundering around here and would
welcome any suggestions.

Many thanks

Rob T

S3 SE
S2 7
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PostPost by: "e s" » Fri Feb 18, 2005 6:20 pm

vacuum leak
----- Original Message -----
From: "Rob Thornton" <***@***.***>
To: ***@***.***
Subject: [LotusElan.net] Too fast!
Date: Fri, 18 Feb 2005 18:17:04 -0000


--
_______________________________________________

"e s"
 

PostPost by: Esprit2 » Fri Feb 18, 2005 7:10 pm

From: "Rob Thornton" <***@***.***>

Sent: Friday, February 18, 2005 12:17 PM
Subject: [LotusElan.net] Too fast!


Rob.

Assuming the basic carbs and their settings are correct, there are a couple
of bolt-on items that can cause a rich condition if they fail.

On each carb, there's a bolt-on Throttle Bypass Valve on the front side,
near the mounting flange, low. That may be stuck open. It's normally
closed and vacuum controlled so it only opens on high-vacuum,
closed-throttle over-run. The idea is to allow a little mixture to do an
end-run around the closed throttle butterfly, feeding the engine just
enough to slow the rate at which the rpm bleeds off. This is done in order
to minimize the emissions spike that occurs on strong-vacuum over-run. If
the valve sticks open, the effect is similar to having the throttle stick
open a bit.

If the part is defective, it's normally considered not serviceable... just
replace it. However, it's worth a try to clean it out with carb cleaner
and lube it with a light oil like WD-40 or CRC 3.36... nothing viscous.

Or just blank it off with a hand-cut solid gasket. The engine will run
better and respond more crisply when the throttle is closed without the
valve.

An easy way to diagnose it is to blank it off with a solid gasket. If the
problem goes away and the engine generally runs better, then the Bypass
Valve on one or both carbs was bad. At least contributing to the problem.
Then the decision is whether to replace the valves or just stick with the
solid gaskets.


There's also a Temperature Compensator mounted on the front side of each
carb. Look for the sorta rectangular plastic cover that runs at an
angle... high near the airbox to low near the throttle. A bi-metallic
strip inside flexes with temperature changes, moving a plunger/ plug to
open and close an air passage. When warm, the plug opens the airway to
allow some un-metered, raw air to step around the air valve (piston),
leaning-out the mixture to it's normal running setting. The carb is jetted
to produce a proper running mixture with this air passage open.

When cold, the plug closes the passage and shuts off the extra air to
provide a slightly richer mixture... sort of an automatic, seasonal mixture
adjustment supplement to the cold start enrichment device (choke). The
temp at which the valve opens varies by engine application, is set at the
factory and is not published... but roughly, more-or-less generically
~140? F).

If the plug sticks and fails to open when warm, then the mixture will be
richer than normal.

This part is also considered to be not serviceable... just replace it.
However, it can respond very well to a gentle cleaning. The plug is a
sliding fit in a bore and gets dirty. Clean it with carb cleaner and
spritz it with a light lubricant until it moves freely. The trick is to do
that without removing the bi-metallic strip itself, disturbing it's setting
or bending it.

Do not turn the screw that retains the strip or the nut that adjusts it's
pre-load. If you do, or if you suspect someone has been in there before
you, then there is no official procedure for calibrating it. However it
can be done. There's a good article posted on the Vintage Triumph Registry
website at www.vtr.org.

You can also blank-off this device. Just turn the adjusting nut on the
bi-metallic strip... or bend the strip... so the plug is out so far it
will never close. That will solve the rich-when-warm failure mode, but
you give up the cold weather enrichment feature. But then, how often do
you drive the Elan in the Winter? In a northern climate, probably never.
But if you're in a more temperate southern climate where it gets cold but
not "wintry", then perhaps the Compensator is a feature you will want to
preserve.


Either device can result in properly tuned carbs suddenly running rich.
Together, they can really mess up the mixture. Neither device lasts
forever and given their age, they're due. The running problem you're
experiencing may be due to failure of one or both of these devices on one or
both carbs... four possibilities. I suggest you look at them all. And
whatever you do on one carb, do on the other carb as well.

Good luck,
Tim Engel
Lotus Owners Oftha North
Esprit2
Fourth Gear
Fourth Gear
 
Posts: 561
Joined: 02 Apr 2008

PostPost by: Thornts » Fri Feb 18, 2005 7:41 pm

Tim

That is fantastic; thanks for spending the time to take a novice thru it
all. More twiddling than I ever dreamed possible!

Its a daily driver so could be the cold weather has upset it.

Cheers

Rob

-----Original Message-----
From: Tim Engel [mailto:***@***.***
Sent: 18 February 2005 19:17
To: ***@***.***
Subject: Re: [LotusElan.net] Too fast!



From: "Rob Thornton" <***@***.***>

Sent: Friday, February 18, 2005 12:17 PM
Subject: [LotusElan.net] Too fast!


Rob.

Assuming the basic carbs and their settings are correct, there are a couple
of bolt-on items that can cause a rich condition if they fail.

On each carb, there's a bolt-on Throttle Bypass Valve on the front side,
near the mounting flange, low. That may be stuck open. It's normally
closed and vacuum controlled so it only opens on high-vacuum,
closed-throttle over-run. The idea is to allow a little mixture to do an
end-run around the closed throttle butterfly, feeding the engine just
enough to slow the rate at which the rpm bleeds off. This is done in order
to minimize the emissions spike that occurs on strong-vacuum over-run. If
the valve sticks open, the effect is similar to having the throttle stick
open a bit.

If the part is defective, it's normally considered not serviceable... just
replace it. However, it's worth a try to clean it out with carb cleaner
and lube it with a light oil like WD-40 or CRC 3.36... nothing viscous.

Or just blank it off with a hand-cut solid gasket. The engine will run
better and respond more crisply when the throttle is closed without the
valve.

An easy way to diagnose it is to blank it off with a solid gasket. If the
problem goes away and the engine generally runs better, then the Bypass
Valve on one or both carbs was bad. At least contributing to the problem.
Then the decision is whether to replace the valves or just stick with the
solid gaskets.


There's also a Temperature Compensator mounted on the front side of each
carb. Look for the sorta rectangular plastic cover that runs at an
angle... high near the airbox to low near the throttle. A bi-metallic
strip inside flexes with temperature changes, moving a plunger/ plug to
open and close an air passage. When warm, the plug opens the airway to
allow some un-metered, raw air to step around the air valve (piston),
leaning-out the mixture to it's normal running setting. The carb is jetted
to produce a proper running mixture with this air passage open.

When cold, the plug closes the passage and shuts off the extra air to
provide a slightly richer mixture... sort of an automatic, seasonal mixture
adjustment supplement to the cold start enrichment device (choke). The
temp at which the valve opens varies by engine application, is set at the
factory and is not published... but roughly, more-or-less generically
~140? F).

If the plug sticks and fails to open when warm, then the mixture will be
richer than normal.

This part is also considered to be not serviceable... just replace it.
However, it can respond very well to a gentle cleaning. The plug is a
sliding fit in a bore and gets dirty. Clean it with carb cleaner and
spritz it with a light lubricant until it moves freely. The trick is to do
that without removing the bi-metallic strip itself, disturbing it's setting
or bending it.

Do not turn the screw that retains the strip or the nut that adjusts it's
pre-load. If you do, or if you suspect someone has been in there before
you, then there is no official procedure for calibrating it. However it
can be done. There's a good article posted on the Vintage Triumph Registry
website at www.vtr.org.

You can also blank-off this device. Just turn the adjusting nut on the
bi-metallic strip... or bend the strip... so the plug is out so far it
will never close. That will solve the rich-when-warm failure mode, but
you give up the cold weather enrichment feature. But then, how often do
you drive the Elan in the Winter? In a northern climate, probably never.
But if you're in a more temperate southern climate where it gets cold but
not "wintry", then perhaps the Compensator is a feature you will want to
preserve.


Either device can result in properly tuned carbs suddenly running rich.
Together, they can really mess up the mixture. Neither device lasts
forever and given their age, they're due. The running problem you're
experiencing may be due to failure of one or both of these devices on one or
both carbs... four possibilities. I suggest you look at them all. And
whatever you do on one carb, do on the other carb as well.

Good luck,
Tim Engel
Lotus Owners Oftha North












Thornts
Second Gear
Second Gear
 
Posts: 130
Joined: 03 Mar 2011

PostPost by: Jon Eckman » Fri Feb 18, 2005 8:30 pm

Tim,

Does this info pertain to Webers?

Jon Eckman
66 S3 SE
















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Posts: 189
Joined: 23 Sep 2003

PostPost by: Esprit2 » Fri Feb 18, 2005 9:02 pm

From: "Jon Eckman" <***@***.***>

Sent: Friday, February 18, 2005 2:52 PM
Subject: Re: [LotusElan.net] Too fast!


Jon,

No, Zenith Strombergs. That's just where my mind jumped since ZS carbs
are more inclined to "do their own thing" than Webers are. But now that
I double check Rob's e-mail address I see that he's in the UK, so there's
probably a better than even chance he's dealing with Webers.

Oh well... gave me something to do.

Regards,
Tim
Esprit2
Fourth Gear
Fourth Gear
 
Posts: 561
Joined: 02 Apr 2008

PostPost by: Fred Talmadge » Fri Feb 18, 2005 9:35 pm

And it was such a good answer too....

Fred T. '65 S2

-----Original Message-----
From: Tim Engel [mailto:***@***.***
Sent: Friday, February 18, 2005 3:04 PM
To: ***@***.***
Subject: Re: [LotusElan.net] Too fast!

No, Zenith Strombergs. That's just where my mind jumped since ZS
carbs
are more inclined to "do their own thing" than Webers are. But now
that
I double check Rob's e-mail address I see that he's in the UK, so
there's
probably a better than even chance he's dealing with Webers.

Oh well... gave me something to do.

Regards,
Tim
User avatar
Fred Talmadge
Fourth Gear
Fourth Gear
 
Posts: 666
Joined: 24 Sep 2003

PostPost by: ElanontheWolds » Sat Feb 19, 2005 12:23 am

Better than even maybe but those of us in the UK with 1970 Elans do run ZS's
so your info is much appreciated

-----Original Message-----
From: Tim Engel [mailto:***@***.***
Sent: 18 February 2005 21:04
To: ***@***.***
Subject: Re: [LotusElan.net] Too fast!


From: "Jon Eckman" <***@***.***>

Sent: Friday, February 18, 2005 2:52 PM
Subject: Re: [LotusElan.net] Too fast!


Jon,

No, Zenith Strombergs. That's just where my mind jumped since ZS carbs
are more inclined to "do their own thing" than Webers are. But now that
I double check Rob's e-mail address I see that he's in the UK, so there's
probably a better than even chance he's dealing with Webers.

Oh well... gave me something to do.

Regards,
Tim










CopyrightC LotusElan.net and the author:

User avatar
ElanontheWolds
First Gear
First Gear
 
Posts: 25
Joined: 07 Oct 2008

PostPost by: Thornts » Sat Feb 19, 2005 1:32 am

Tim

Gave YOU something to do? I've just spent 4 hours looking for a Throttle
Bypass Valve on a Weber carb!

Seriously tho, a great and detailed answer to a question which didn't state
the basic info.

Hey, I'm going to go buy a Stromberg head and carbs just so I can use the
info you provided.

I'll try the O rings...

Thanks to all

Rob

-----Original Message-----
From: tim liggins [mailto:***@***.***
Sent: 19 February 2005 00:24
To: ***@***.***
Subject: RE: [LotusElan.net] Too fast!



Better than even maybe but those of us in the UK with 1970 Elans do run ZS's
so your info is much appreciated

-----Original Message-----
From: Tim Engel [mailto:***@***.***
Sent: 18 February 2005 21:04
To: ***@***.***
Subject: Re: [LotusElan.net] Too fast!


From: "Jon Eckman" <***@***.***>

Sent: Friday, February 18, 2005 2:52 PM
Subject: Re: [LotusElan.net] Too fast!


Jon,

No, Zenith Strombergs. That's just where my mind jumped since ZS carbs
are more inclined to "do their own thing" than Webers are. But now that
I double check Rob's e-mail address I see that he's in the UK, so there's
probably a better than even chance he's dealing with Webers.

Oh well... gave me something to do.

Regards,
Tim










CopyrightC LotusElan.net and the author:




















Thornts
Second Gear
Second Gear
 
Posts: 130
Joined: 03 Mar 2011

PostPost by: Elan45 » Sat Feb 19, 2005 3:26 am

Ron,

Get a small diameter tube, 12-18" long. Hold one end in one of your ears and move the other end around near the O ring seal between the carbs and head. Listen to the hiss inside the carb first, so you know what you're listening for, then listen around the O rings. Safe, cheap way of determining if the Orings are leaking.

Other than that, check the jets, both idle and the main circuit. Could be the emulsion tubes are not fully screwed down snug. Check that all the jets match the ones in the book, or know why they are not same.

Roger


Tim

Gave YOU something to do? I've just spent 4 hours looking for a Throttle
Bypass Valve on a Weber carb!

Seriously tho, a great and detailed answer to a question which didn't state
the basic info.

Hey, I'm going to go buy a Stromberg head and carbs just so I can use the
info you provided.

I'll try the O rings...

Thanks to all

Rob

-----Original Message-----
From: tim liggins [mailto:***@***.***
Sent: 19 February 2005 00:24
To: ***@***.***
Subject: RE: [LotusElan.net] Too fast!



Better than even maybe but those of us in the UK with 1970 Elans do run ZS's
so your info is much appreciated

-----Original Message-----
From: Tim Engel [mailto:***@***.***
Sent: 18 February 2005 21:04
To: ***@***.***
Subject: Re: [LotusElan.net] Too fast!


From: "Jon Eckman" <***@***.***>

Sent: Friday, February 18, 2005 2:52 PM
Subject: Re: [LotusElan.net] Too fast!


Jon,

No, Zenith Strombergs. That's just where my mind jumped since ZS carbs
are more inclined to "do their own thing" than Webers are. But now that
I double check Rob's e-mail address I see that he's in the UK, so there's
probably a better than even chance he's dealing with Webers.

Oh well... gave me something to do.

Regards,
Tim










CopyrightC LotusElan.net and the author:




















































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PostPost by: dlbarnes1 » Sat Feb 19, 2005 4:05 am

Thanks Tim, I appreciate this info on the Strombergs. It will be very helpful to me.
David -72 Sprint DHC (Federal)


----- Original Message -----
From: Tim Engel
To: ***@***.***
Sent: Friday, February 18, 2005 1:03 PM
Subject: Re: [LotusElan.net] Too fast!


From: "Jon Eckman" <***@***.***>

Sent: Friday, February 18, 2005 2:52 PM
Subject: Re: [LotusElan.net] Too fast!


Jon,

No, Zenith Strombergs. That's just where my mind jumped since ZS carbs
are more inclined to "do their own thing" than Webers are. But now that
I double check Rob's e-mail address I see that he's in the UK, so there's
probably a better than even chance he's dealing with Webers.

Oh well... gave me something to do.

Regards,
Tim














------------------------------------------------------------------------------






***@***.***

dlbarnes1
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Posts: 139
Joined: 22 Sep 2003

PostPost by: ericsalomon » Sat Feb 19, 2005 9:08 am

Great bit of correspondence! Good for a laugh.

Love this group!

Regards

Eric

-----Original Message-----
From: Rob Thornton [mailto:***@***.***
Sent: 2005-02-19 03:53
To: ***@***.***
Subject: RE: [LotusElan.net] Too fast!


Tim

Gave YOU something to do? I've just spent 4 hours looking for a Throttle
Bypass Valve on a Weber carb!

Seriously tho, a great and detailed answer to a question which didn't state
the basic info.

Hey, I'm going to go buy a Stromberg head and carbs just so I can use the
info you provided.

I'll try the O rings...

Thanks to all

Rob

-----Original Message-----
From: tim liggins [mailto:***@***.***
Sent: 19 February 2005 00:24
To: ***@***.***
Subject: RE: [LotusElan.net] Too fast!



Better than even maybe but those of us in the UK with 1970 Elans do run ZS's
so your info is much appreciated

-----Original Message-----
From: Tim Engel [mailto:***@***.***
Sent: 18 February 2005 21:04
To: ***@***.***
Subject: Re: [LotusElan.net] Too fast!


From: "Jon Eckman" <***@***.***>

Sent: Friday, February 18, 2005 2:52 PM
Subject: Re: [LotusElan.net] Too fast!


Jon,

No, Zenith Strombergs. That's just where my mind jumped since ZS carbs
are more inclined to "do their own thing" than Webers are. But now that
I double check Rob's e-mail address I see that he's in the UK, so there's
probably a better than even chance he's dealing with Webers.

Oh well... gave me something to do.

Regards,
Tim










CopyrightC LotusElan.net and the author:

ericsalomon
First Gear
First Gear
 
Posts: 22
Joined: 08 May 2004

PostPost by: lotuselanman » Sat Feb 19, 2005 9:24 am

Gidday,
Check it or have it checked for twisted butterfly shaft usaually caused by not have an effective throttle stop.
See ya, Les
----- Original Message -----
From: Rob Thornton
To: ***@***.***
Sent: Saturday, February 19, 2005 4:17 AM
Subject: [LotusElan.net] Too fast!




May I please pick the collective brains of the group? My twink, once warmed
up, holds onto revs for some time after you come off the throttle and even
at idle will not drop much bellow about 1,500 rpm. I have visually checked
the butterflies and they are fully closed so there does not seem to be much
mileage in adjusting the throttle stop screws. I suspect that the 'O' rings
may be past their best and unless anyone has a better idea I'll replace them
as a matter of course. Add the fact that coming right off the throttle from
high revs results in a lot of popping and banging and flames of unburnt fuel
from the exhaust, it seems there must be fuel finding its way into the
combustion chambers somehow. Idle jets? I'm blundering around here and would
welcome any suggestions.

Many thanks

Rob T

S3 SE
S2 7















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