[Mgs] question on mga carb tuning

Eric J Russell ejrussell at mebtel.net
Sun Nov 13 14:20:02 MST 2016

> 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 believe the suggestion is to back out the idle stop screw only until the 
throttle 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 
mixture goes way leaner and the engine would die. Ideally, lifting the 
piston 1/32" causes the engine to speed up for a moment then drop down. If 
it immediately 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.

Link to the MGA Guru's page on carbs: 
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.

> 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 held 
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 fuel
> for hard acceleration? Mine have the top of the bloat about an inch down.

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 been 
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#top must 
be in place above the lid and below the banjo fitting of the overflow pipe. 
That washer allows the float chamber to be vented. Otherwise, if not vented 
then fuel can't enter.

> 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 affect 
mixture change.

Eric Russell
Mebane, NC 

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