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Re: 58 MGA - Carb confusion

To: <mgs@autox.team.net>
Subject: Re: 58 MGA - Carb confusion
From: "Eric J Russell" <ejrussell@mebtel.net>
Date: Sat, 18 Oct 2003 20:16:44 -0400
----- Original Message ----- 

> Subject: 58 MGA - Carb confusion
>
> I just installed Carbs returned from rebuilding.... I believe I've
put back as they were originally.  My 1500 MGA started up first pull
and immediately went to high rpms..... I can't get to fall below
2500/3000 rpms regardless of what I do (except when I pull the choke
cable as far as I can pull, then it appears to starve the engine)...
>
> Car also is running very rich.......all idle screws are backed
off....if I replace needles with "lean" versions from Moss, will this
help.....that other suggestions might I learn from
>

First check the easy stuff.

Is the throttle cable too tight and thus not allowing the throttles to
return to idle? Anything binding or interfering with the throttle
cable or accelerator pedal & linkage?

Is the choke cable too tight and keeping the fast idle cams 'on'? Are
the choke 'fast idle' screws turned in too far? With the choke off
there should be some clearance between the ends of the screws and the
fast idle cams.

I doubt very much you would need to use 'lean' needles. Standard
needles should work fine unless you have made *major* internal
modifications to your motor. Make sure your rebuilder did indeed
install the correct needles. The shouldered portion of the needle's
shaft should be flush with the bottom of the air chamber's piston.
When you yank out the choke you are more than likely merely upsetting
the mixture so far toward rich that it is slowing down for that
reason.

When you say, "running very rich...all idle screws are backed off" do
you realize that the idle screws have nothing to do with the mixture?
You adjust the mixture by moving the jet adjusting nut underneath the
carb (up to lean, down to richen).

Next, you'll need to remove the carbs to make sure the throttle discs
are not installed 'backwards' (I think it is possible) and/or make
sure they were centered on installation. The throttle discs have
beveled edges that will (should) fit snugly against the walls of the
carb's bore. If the discs are not installed correctly (backwards or
not centered), they will not close enough to allow proper idle speed.

To center the throttle discs, you'll need to back out the idle speed
screws and then slightly loosen the two small screws holding the
throttle disc (they may be locked in place by spreading the split ends
of the screws). Next rotate the throttle shaft in the 'close'
direction. Adjust the position of the discs in the throttle shaft
until it will close tightly - i.e. fit tightly against the bore of the
carb's throat. Carefully tighten the screws then recheck the
operation. They should move smoothly - no binding and close tightly.

HTH,
Eric
1978 MGB
1960 MGA




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