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MG MGB Technical - Tuning New Zenith

Hi hows it going,
I have a 79b I bought a new zenith on ebay(Now when I mean new, it was sitting on a shelf in a box for a long time(you can see them on ebay all the time)). The only difference is that there is no coarse idle/fine idle mix screw(can I put mine on from my old zenith?), other than that, hose's are just in a different place. I have the needle from my old zenith carb which is still new on the ebay carb(had a weber dgv on after the old zenith) Wondering if anyone else has bought these carbs off of ebay. Now the thing is that using the zenith carb tool, I have it all the way screwed clockwise, and it gives it the most vacuum, and the only setting it will idle at. Is that normal at all ? Also I had it idling fine for about 5 minutes and then she stalled out. Is it ok that the carb doesnt have the coarse/fine idle adjustment ? Am I going to have to mess with the timing again to get a good idle without it stalling out? its set to about 14btc. I think I should check it again as well, car really wasnt warmed up last time. Was just trying to get it in the ball park. Any help will be great.

Thanks,
James

JRB Mr

oh yea also I dont have the air filter on the car either.
James

James,

From John Twist's article in the Moss catalog:

"The Stromberg carburetted MGB will not run with
the air cleaner removed, nor with a filter which replaces the original assembly."

Hope this helps.

John
John English

yea, I actually checked out his article after I posted this. Ill give it a try, hopefully tommorow. Any other input on the carb would be great too, expecially the part about it not having the coarse/fine idle mix. Ill try to get a digital pic but I guess I would have to email it to someone. You should be able to go to ebay and search zenith and see the carbs being sold so you know what Im talking about.
james

I assume you're talking about the ones they say came from a TR8.

On my Zenith with the fine idle screw, I've got it completely closed. I would think you could leave it off. Everybody has told me that without the pollution equipmentit doesn't do much of anything, anyway.

I think your problem is probably going to be the air filter. I'd really like to know what you find.

John
John English

This carb does have a idle air adjustment, remove the white cover on the side where the idle adj would normally be and you will see a screw in apiece of spring wire, by turning this screw in small amounts,yo u will make the adj you want.
Rick Hughes

Great thanks,
Rick Ill check that out on thursday afternoon. Ill tell you guys how its going. Thanks a lot.
james

Rick,
Is it definetly a screw ? Looking at it, it goes diagonally down left to right. The screw should be on the left side right ? Then there is a nut, then on the right side is some sort of round thing. Also I didnt have the crank case beather hooked up to the carb. Im sure that would have a difference in the tunning of the carb. Because I put the original air cleaner back on with the same needle adjustement(all the way turned to the right) and it idled great. But when I messed with the needle adjustment it ran rougher. Anway dont have any time for the next couple days. But would like to know about the idle adj scew Rick. How do you tune yours ? I take it use the idle scew and set to 1500 rpm and then use the other screw you were talking about to bring it down to about 800 ? like John Twist says ? Would like to know your guys input.

THanks,
James
james

James,

I don't think I'm going to be much help since I don't have your exact carb, but I'll tell you how I set my idle.

I have my fine idle adjustment completely closed - basically, I don't use it. I just use the coarse idle adjustment screw, and turn it down to about 800-900 rpms, while its warm. The tool you're using is for mixture - rich or lean - which will affect the idle, but isn't the way you adjust it. Your mixture needs to be right, and then set your idle. John Twist explains the mixture adjustment. But you probably already knew that, since you had an old Zenith. Forgive me if I'm telling you something you already know.

I think there must be a coarse idle adjustment screw somewhere on your carb. Is there any way you could post or e-mail some pictures? I've got a Zenith workshop manual - maybe I could help you identify it that way.

John

John English

This thread was discussed between 08/05/2006 and 16/05/2006

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