[Mgs] question on mga carb tuning

Clayton Kirkwood crk at godblessthe.us
Sun Nov 13 19:41:40 MST 2016

> -----Original Message-----
> From: Eric J Russell [mailto:ejrussell at mebtel.net]
> Sent: Sunday, November 13, 2016 1:20 PM
> To: mgs at autox.team.net
> Cc: crk at godblessthe.us
> Subject: Re: [Mgs] question on mga carb tuning
> > I am in the process of trying to reset my 1622 carbs. The manual
> > speaks of backing the idle screw all the way and then adding a
> > rotation back in for fast idle. I couldn't get anywhere until I turned
it in about
> four turns.
> > Is
> > there a problem? Also, pushing the lifter didn't do anything, but
> > lifting the piston caused the engine to die. Problem?
> I the suggestion is to back out the idle stop screw only until the
> is fully closed & then turn it in one turn. If you back out the screw 'all
the way'
> then the throttle stop screw is way more than one turn past throttle fully
> closed.
> How far are you lifting the piston? If you lift it a very small amount (~
> 1/32") the mixture goes slightly leaner. If you lift it a little more the
> goes way leaner and the engine would die. Ideally, lifting the piston
> causes the engine to speed up for a moment then drop down. If it
> dies then it is too lean. If engine speed increases and stays (and
increases more
> if you raise the piston ~ 1/16") then it is too rich.

Since it is difficult at best to know when the idle screw is all the way,
other than by feeling for a scrap where the end of the screw is, that is
what I did. Then I advanced one turn, but it took several more so that I was
getting enough  gas flow to light up the engine. That was about 1300rpm.
Raising the finger plunger on the side of the carb did nothing across the
band of adjustment for the jet. I couldn't find worse or better across a
wide band of the jet nut and ensuring the jet itself was held close to the
nut. This is all on the rear.

> Link to the MGA Guru's page on carbs:
> http://www.mgaguru.com/mgtech/carbs/carb.htm
> and tuning the carbs: http://www.mgaguru.com/mgtech/carbs/cb130.htm
> > Moved to the front carb. My piston lifter popped out and now I have
> > significant sucking going on there. I presume that this will keep me
> > from properly tuning the front?
> The lifting pin has to be in place. It should be held in by a tiny circlip
with a
> spring behind it.

Yeah, I remember the set up. Apparently, I didn't catch the c-clip in the
groove well enough. I remember at the time thinking the groove on the pin
was rather shallow.

> > Is there a simple way to lock down the cable to the throttle; it seems
> > tenuous at best?
> The cable passes through a hole in the cable stop and should be firmly
> by tightening the stop nut.
> See: http://www.mgaguru.com/mgtech/carbs/cb114a.htm
> > I presume my float bowls need to be mostly full so as to have enough
> > for hard acceleration? Mine have the top of the bloat about an inch
> When full the float should be near the top of the float bowl. If you then
> remove the float the fuel will be lower (because the float's volume has
> removed) The MGA Guru's page about tuning shows how to measure/adjust the
> float. Be sure the special washer on the central bolt of the float chamber
> is present. The fibre washer #72 shown here:
> http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29218#t
> op must
> be in place above the lid and below the banjo fitting of the overflow
> That washer allows the float chamber to be vented. Otherwise, if not
> then fuel can't enter.

All there. I will re-read Barney's page on that. I do know that if the lever
goes too low, the shut-off gets stuck open and gas flows out the jet:<)

> > I could never get the jet nut to make any difference either.
> Jet bearing securing nut #15 (in the above link) must be tight to hold the
> jet bearing assembly secure. Otherwise turning the jet adjusting nut can
> allow the entire assembly to turn but not adjust the jet position to
> mixture change.

Yep, it is on tight. I guess I could take the pots off the top and ensure
the jets are actually moving. I get tired of taking things off and on again.
I feel I've rebuilt 4 or 5 A's.

> Eric Russell
> Mebane, NC

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