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MG MGB Technical - Auto ZS choke back together and now it won't run

I can't find the old thread so I thought I'd start a new one.

I put my auto ZS choke back together with components from the $10 gasket kit from Moss. Followed the YouTube videos (including calibrating the heat mass via boiling water).

Anyway, noticed that the cold idle pin was never even close to touching the pin, so that was probably a waste of time entirely. I knew it was rich because when it would start cold and stalled once warm, it wouldn't restart. Plus my plugs are black and the car doesn't smoke.

So I broke the warm idle screw and it won't start anyway now that the choke is back together.

I wish I were more experienced with carburated cars, but I really have no idea what I'm doing. I bought the fuel mixture adjustment tool (long handle allen wrench) and I can't even see where that would go to try and tweak things just to get it started, regardless of running properly. Without it starting I don't know what to do.

HIDDEN QUESTION: Does anyone know what exactly the manual choke conversion will replace? Does it retain ANY of the OE Auto Choke?
Jeff Grant

The manual choke conversion will replace the water choke on the "front" of the carb. It will be controlled by a cable, identical to the manual choked SU carbs. I've got one out in the barn that I will take a look at...but not until Wednesday (sorry).
rick ingram

Wednesday is just fine Rick.

I actually have a pair of twin SUs in my parts car, do you think I can steal the choke assembly off that?

Some would probably say I should just take the dual SUs off that motor and toss it on my '80 B, but I think that'd put me in even worse shape than I am right now.
Jeff Grant

I would use the dual SU's if I were you. I do not believe that the choe assemblies are the same between the aftermarket manual for the ZS175 and the SU's.

I'll snap a picture and post it as well.
rick ingram

Jeff I wonder if you have the air piston in properly. I made this mistake and put it in 180 degrees out and would not run. found out when I lifted the air piston it did run. Chicagoland mg group has an article on rebuilding the zs and it is vey good. Also showes proper way to install air piston.
kra Karl

Rick, I'd love to run the twin SUs, but it's on a '71 motor (OE higher compression than my '80 B motor) so I have a feeling a lot of tuning would be needed to get it running right. For this season, I'd rather just buy a manual choke conversion and toss it on. Maybe this winter I'll attempt to swap carb setups so I can get rid of that parts body that's killing a spot in my lawn. ;)

Kra, I've seen the webpage you mentioned but don't have the link handy anymore. Can you find it for me? Is the air kick piston the one that's behind the three screws? If so, I know that's in correctly because it goes in and out with the manual twisting of the choke cam while it's not attached to the carb.
Jeff Grant

Jeff...you may be pleasantly surprised.
rick ingram

jeff Its under the cover on top of the carb. Four screws. The rubber skirt is attached to it. Chicagoland link is www,chicagolandmgclub.com
kra Karl

Here you go...the manual choke as installed on a ZS175

rick ingram

Thanks Rick for the picture!

Looks like it just replaces the heat mass with it's housing, does that sound correct?

Do you know if the instructions give good tuning information to at least get the motor running again?
Jeff Grant

By the way kra, I never took the carb apart, just the auto choke assembly. So I don't think the air piston can be my issue.
Jeff Grant

Why don't you send the entire carb to me and I will rebuild it for you the proper way.
Jim Pelletterie

Jim,
I've got a ZS I might be interested in having you do some work on. Please contact me. Thanks.
Al Wrisley

This thread was discussed between 20/05/2008 and 25/05/2008

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