Let me take a shot at this one...
I believe for a '79 you're running a Zenith Stromberg
carb right?
..if so....
As you face the engine, looking down the throat of the carb,
on your right hand side, is an adjustment screw that allows
you to control how much air is bled off to make the piston
rise as you mechanically open the butterfly in the main throat
of the carb.
This valve tend to express it's noticeable effect as ...controlling how
quickly the throttle will rise or fall when you abruptly hit or let off on
the peddle.
If this valve is too far 'screwed in' this makes the piston rise very
VERY easily, almost letting it float around.
Screwed all the way out counter-clockwise, compresses a light spring
that in turn closes off a small thin membrane valve.
The biggest problem here is people play with this adjustment screw
not knowing what it does. As they play with it they see no effects.
That's because they're not blipping the throttle as they play with the
setting.
So in the end it's usually really wacked out before you ever touched it.
If you screw it too far, you can run the internal
nut/spring-support off the end of the internal threads of the adjusting
screw.
FROM THEN ON IT BECOMES NON-ADJUSTABLE.
until you take it a part and put it back on the end of the screw.
The adjustment looks like a small cylindrical head screw with a captive
slip-over full circle cir-clip on it just before the screw enters the body
of the
carb. It sticks out at 90 degrees to the throat.
...one caveat. Some late models had a casting that shielded the screw
from being adjusted by the typical shadetree mechanic.
So you may not be able to touch it.
This is not the valve under the plastic cap on the side of the carb,
(no plastic cap? Alright.... a screw down the middle of a larger
nylon looking hex nut on the side of the carb the stick up toward the
bonnet.)
... sorry long winded, but I've been there... went crazy....
pissed me off when i realized the interactions.
good luck
Paul Tegler wizardz@toad.net http://www.teglerizer.com (new
format)
OBie - '73 BGT - daily driver
Punkin' - '78 Spitfire - corner ripping screamer
Lil' Greenee - '73 RWA Midget - lady killer
-----Original Message-----
From: Duinhoven_Hans@emc.com <Duinhoven_Hans@emc.com>
To: JPGarner@UCDavis.Edu <JPGarner@UCDavis.Edu>; Duinhoven_Hans@emc.com
<Duinhoven_Hans@emc.com>; mgs@autox.team.net <mgs@autox.team.net>
Date: Monday, May 15, 2000 5:05 PM
Subject: RE: Engine breathing & battery fit
>Thanks Joe,
>
>Mine is different a '71 B uses the old style dual HS4 SU carbs.
>Also my carbs have fully been overhauled, so leaks are not expected.
>The full engine is defederalised - ex Calif car...
>The only rare thing which is left is the butterflies still are original, so
>still equipped with an overrun valve.
>
>Any clue?
>
>Cheers,
>
>Hans
>
>-----Original Message-----
>From: Garner, Joseph P. [mailto:JPGarner@UCDavis.Edu]
>Sent: maandag 15 mei 2000 20:23
>To: 'Duinhoven_Hans@emc.com'; MG list (E-mail)
>Subject: RE: Engine breathing & battery fit
>
>
>Hans,
>
>>When driving with little throttle at an easy pace, the engine starts to
>>backfire a bit.
>
>I occasionally have the same problem, also like you it occasionally happens
>when i accelerate. I have identified the following circumstances:
>
>1. it only happens when i am going very slow (i.e. idling) in high gear,
say
>25mph in 4th.
>2. it only happens when the engine is cold
>
>I have put this down to the fact that my automatic choke is playing up. I
>recently cleaned up the whole of the carb unit as best i could without
>taking it off the engine (the idea of trying to tune my 79B to california
>regulations without a CO2 analyser, and with bugger all idea of what i was
>doing is a little bit too much to stomach). I used one of those
>degreaser/dirt shifting sprays on all the linkages, plates, springs and
>other moving parts on both the throttle side of the carb and the autochoke
>side. if you do this, be careful not to get any on the engine. and always
>wait for everything to be cold!
>
>At the same time i added a bottle of carb cleaner to the gas tank. Although
>this is no substitute for having the carb properly overhauled by someone
who
>knows what they are doing (my next big expense). It actually induced a
major
>noticeable improvement. The engine now idles at 1500 when warming up,
rather
>than about 2250 (that's a sticky choke). It hasn't back fired since, and
the
>ocassional "grabbing" sensation of the engine revs at low revs when cold
>(which is classic of a dirty carb) have cleaned up too.
>
>Nevertheless Humphrey (the car) is being booked in for a professional carb
>overhaul later in the month (my girlfriend is beginning to worry about this
>new competition for my meagre resources)
>
>cheers
>
>Joe.
>
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