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MG Midget and Sprite Technical - PRIMARY CHARCOAL ADSORPTION CANISTER

First time on this midget link. My experience is on prewar, T Type and MGA SU carburetors. A neighbor asked for some help on his Rubber Bumper Midget. My experience with Zenith carbs is zero. The front charcoal canister is leaking liquid fuel along with fuel being sucked from the canister in to the carb with fuel accumulating in the air filter housing. What would be your best guess on the primary problem. Is there any good web sites for this Zenith carb?

Thanks for any help.
Gary 1933 MGJ2
gl krukoski

I can answer that one definitely, having dealt with the identical issue myself.

The float chamber on his Zenith is overfilling and dumping through the float chamber vent. Either it's got a standard-type float valve with crud in it or a bad float - or somebody's replaced the original float valve with a Grose Jet (as did I) only to start having flooding issues.

He'll need to change his oil, by the way. When the engine ingests that much raw fuel, it blows past the rings and right into the sump. I'll bet if he checks his oil, it will be over the mark and watery thin.

Let us know... we can help.

-:G:-
Gryf Ketcherside

Thanks for the quick response on the fuel problem. Will he need to replace the canister? I will order a kit for the Carb.

Gary
gl krukoski

Canisters can be disassembled, cleaned, and charcoal replaced (can be purchased from a pet store, used in tank filters).
You might hear from some who would recommend removal.
A S Kravchuck

I would think that the charcoal could rebound from being soaked in fuel. The real question might be is charcoal able to absorb and then release vapors indefinitely or does it have a upper limit on it's capacity to do so?

Gryf might correct me if I'm wrong on this but I believe that one of the 3 screws holding the auto-choke unit on the side of the carb is shorter than the others and if installed incorrectly the longer screw will interfere with the floats ability to drop, allowing the fuel to continue flowing unchecked.
Richard Reeves

Hi Rich
I do not think this carb has been apart for many years. There is more to this story then just the over flow of the carb. Last fall he started the car and let it idle, for how long I do not know. He returned to see that the exhaust manifold was red red glowing hot. I assumed, when I herd the story the thermostat had stuck closed. He replaced the thermostat the car would not start. That is when I was called. There may be other damage to the engine.

Thanks Guys for your input

Gary
gl krukoski

>>> Gryf might correct me if I'm wrong on this but I believe that one of the 3 screws holding the auto-choke unit on the side of the carb is shorter than the others and if installed incorrectly the longer screw will interfere with the floats ability to drop, allowing the fuel to continue flowing unchecked. <<<

You're absolutely right, Richard, although technically the float is prevented from RISING all the way, so it can't apply pressure to the float valve. Been there, too! Yes, the screws need to be oriented in such a way that the float can swing up and down throughout its entire travel.

As for the glowing manifold, I used to see my catalytic converter glowing when the car was running too rich thanks to the issues mentioned above. Needless to say, I was concerned! But I suspect that if the owner can correct the float chamber overflow, (new float valve) that fix will take care of the rest. In fact, my Midget used to run richest at idle while I had the Grose Jet in there, reason being that the engine wasn't using enough fuel then to drop the level in the chamber much, and the faulty valve would just let the chamber fill more and more. In the meantime, the high fuel level would result in excess fuel being drawn off at the jet, until the charcoal canister became completely blocked by fuel overflow - at which time, with venting prevented, fuel would simply squirt up through the jet and be swallowed by the engine. Bad... but yeah, I remember the idle steadily deteriorating while sitting at stoplights, until I had to give it some throttle to keep it running at all. That was the float chamber gradually overfilling. If unchecked, the engine would then flood out and stall.

Cheers,

-:G:-
Gryf Ketcherside

Oh yes, as for the canister - As Mr. Kravchuk suggested, you can refill them using aquarium charcoal. The bottom of the canister simply screws off, you remove a filter screen, and dump the stuff out. They're pretty simple, really.

Having said that, when I found out how much that charcoal cost, I just let mine air-dry for a while, and then I put it back in.

-:G:-
Gryf Ketcherside

Activated charcoal is about $10 / quart at most pet stores that sell aquarium supplies.

Because it is also used medicinally (for treating poison victims), there may be other ways to buy it that have higher prices, but fish tank stuff will be more than good enough for our application.

Activated charcoal is a form of carbon that has been processed with oxygen to make it extremely porous, one gram of the stuff has the surface area of a tenth of a football field (US).

Because of that micro-porosity, it can be difficult to re-activate the stuff once it has been saturated (industrially, they use temperatures of 100C ~ 800C to do it). For our use, it is easier to simply throw away and replace with fresh.


Norm
Norm Kerr

There is or was a very good webpage on the ZS choke - The Zenith Stromberg Water Choke
Rick Jaskowiak

but I can't find it anymore. I have the text but not the excellent pictures.
Rick still has a page of cars up, but no email or tech articles. http://www.paulbunyan.net/~jasko/

And there is also a good writeup by John Twist in the Moss MGB catalogue.

I can send you the text(s) if you email me, or somebody may have better copies. We discussed this a lot over a few years, and all of this was posted, along with orher comments and info. Search Spridget and MGB tech archives for "ZS choke" or similar.

The choke screws are a very strange & unique configuration, of unknown thread with taper seat heads, in two different lengths. They are avail;able from Moss. Simply having those screws loose or missing will cause this problem, and if wrongly installed they will interfere with the float.

FRM
Fletcher R Millmore

red glowing exhaust manifolds can come from extreemly bad timing of the ignition.
i would change the points and condenser while your at it and time the ignition using a strobe.

J2's are realy nice love the sound and feel of those ohc engine's (i keep dreaming of an L, once.....)
Onno Könemann

Thanks to all that responded to my call for help. I think we should be able to get this little MG back on the road now.

Onno Here is a photo of my J2 that I completer the restoration my self last fall. It is a very fun car to drive. The photo was taken on the Road America Race Track.

Gary


gl krukoski

lovely car!
Onno Könemann

Gary and Fletcher,

The choke article link I had is dead, too.
However, I've found it here:

http://www.sterlingbritishmotoringsociety.org/files/choke.pdf

It might be a good idea to save this pdf to your hard drive in case it decides to disappear again.

This is a very good article and makes me glad I ditched the ZS for SUs. Victoria British sells a manual choke conversion kit, #3-493 on page 73 of the catalog. Kinda pricey at $119.95US.

John Twist has some really good videos, too.
Go to:

http://www.youtube.com/user/Universitymotorsltd#p/u/95/L5GveCj3Hck

and watch videos #11, #12, and #13. Then again, why not watch all of them.

Lee
Lee Fox

A PO put a cheap-and-cheerful manual choke conversion on my Zenith years ago, and it works great. Once I learned the finer points of sorting these carbs, I'm okay with it. Took a while, though...

-:G:-
Gryf Ketcherside

Lee -
Thanks for this - it is a very important article.

"Then again, why not watch all of them."
Well, it seems it is going to take me upwards of an hour to download the .pdf. Further, somewhere along the line something changed in my computer and now it does not ask me what to do with a .pdf before I download it - it just opens. Then I have to tell it to save the file, and instead of taking the one it already has, it downloads it again - make it two hours! GRRRR... I HATE F&^*%ING .pdf's! ... and videos take me 6-10 min/MB, IF nothing goes wrong!

FRM
Fletcher R Millmore

So I downloaded the article - took 1hr 30 min!

There is also the John Twist article on this site:
http://www.sterlingbritishmotoringsociety.org/files/zenith%20stromberg%20tech%20tips.pdf

The reader's comments part has apparently been lost, in which I and some others had pointed out a couple of additional points Rick had missed; I don't recall them now.

FRM
Fletcher R Millmore

That article Fletcher posted is very good, and like Rick Jaskowiak's site, has been printed and stuffed into my shop manual for years.

To get that link to work, however, you need to substitute a space for each "%20". As a web designer, I never use spaces in file names for stuff I'm posting on the web, but not everybody knows that trick. Some web servers don't handle spaces well, and convert them to %20. Yeah, it IS a pain, and one of many reasons I'd rather work on my Midget than on a computer...

By the way, I came across one statement in John's article that doesn't necessarily apply - that of excessive idle speed being a function of a failed overrun valve in the throttle plate. In my ZS, that task is handled by the Deceleration Bypass Valve, which is a separate little component that attaches to the forward face of the carb, and is adjustable via a small screw. So be advised, everything the article says may not apply. If you come across anything different, just ask here.

Cheers,

-:G:-
Gryf Ketcherside

This thread was discussed between 20/07/2010 and 30/07/2010

MG Midget and Sprite Technical index

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