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MG MGB Technical - ZS Problem - Not getting fuel??

Hello ,

I have been having ongoing, and ongoing and ongoing problems with my 79 B and the ZS carb.

It just does not want to start easily or run well.
After some fiddling around we found that with the air filter off and raising the piston about 1/8 - 1/4 inch, the car starts with no problem and runs better while holding it there. To bad we can't do this when driving huh!

Can anyone tell me what this indicates and what I need to do or adjust?
I'm ready to scrap ths ZS for a weber as I have stated in the past, but am finding the ZS hard to give up on and to purchase a new unit.


P.s.
Someone asked me (or stated), maybe it's the manifold rather than the carb, could this be and how can I tell ?


Thx - Elizabeth
Elizabeth

just dropped in --- maybe....some loose nuts or a bad gasket seal from carb to mainfold to head. Easy way to check is to carefully spray some gas, or carb cleaner stuff at the connections -- a rise in idle will indiicate untight seals.

(best I can offer -- I'm an SU aspirator)
glg

If this is a dupe, sorry I lost my connection.

When spraying engine starter on the intake manifold the idle drops.

This means leak right, but the idle dropped rather than going up??


Thx- Elizabeth

Elizabeth

Elizabeth,

Have you checked the rubber diaphragm situated below the top lid. When bad the car does not respond that well when the accelerator is applied. Ie, there will be no internal vacuum to raise the piston.

Hope this will help.
Erik
Erik

I have already replaced it once a few months ago. How long do they take to wear out?

The previous one was quite stretched, for a better lack of term.

Can I buy these without buying the whole carb rebuild kit?





Elizabeth

Elizabeth

Elizabeth - Like glg, I am more familiar withthe SU carburetors, but your statement that "raising the piston about 1/8 - 1/4 inch, the car starts with no problem and runs better while holding it there" sounds like you have the float level misadjusted and are runing quite rich.
Good luck - Dave
David DuBois

We did find the bolts to the manifold a little loose and tightening them but that did not seem to make much difference.

We will try the flaot valve next.


Thx - Elizabeth
Pushing on........and on......
Elizabeth

I agree with David that the mixture must be
too rich. Raising the piston decreases the
venturi effect at fixed throttle so less fuel
entering.

The autochoke is often the culprit in rich running.
Check out

http://www.paulbunyan.net/~jasko/choke/

Once you're sure the autochoke is off when
warmed up, you will need to adjust the mixture
with the special Z-S adjusting tool. (Available
from Moss and VB.) The official way to adjust
the mixture is with a CO meter. Unfortunately,
the gunson meter has become very expensive in the
U.S. (about $250.) Alternatively, you can
use the lift the piston test. Here's an
excellent Chicago MG club article on tuning the
Z-S carb. Note that rotating the needle
clockwise richens the carb, anticlockwise leans
the mixture. If you turn the needle too far
anticlockwise, it will fall out of the holder
and the air piston will have to be removed to
replace it.

http://www.chicagolandmgclub.com/techtips/general/559.html
Ronald

We previously went to a manual choke so I think that is out unless it is hanging up and we have tried adjusting with the carb tool starting out with the needle flush with the piston.
I think we will start from scratch with the tuning but check the float bowl first.


Thx- Elizabeth



EA Martin

Elizabeth,

Having changed the diaphragm a few mounths ago, should not neccesiate it beeing done again. You could check if the rubber notch on the downward side of the diaphragm is properly seated in the recess of the carb body.
Over here you can buy the rubber in any gas station since it is a Volvo and SAAB part. I guess you would be able to find them separatly in any Volvo or SAAB dealer quite inexpensively.

Erik
Erik

http://www.buckeyetriumphs.org/technical/Carbs/CarbsI/CarbsI.htm

Great series of articles about the ZS from our relatives over at Buckeye Triumphs. Consider a rebuild. The parts kit isn't too much and it will eliminate all the guess work, unless you put it all back together and have the same problem.
Brad Batchelor

I have a 77b with the ZS carb, I had a running rich problem that took me months to sort out. I feel your pain…..

Mine had a few associated problems, it wasn't just the carb. Things to look for and check:

Does the cat glow red? If so, you are running way to rich and it is very dangerous. From what I have read, many b's suffered fires from this, and that can cause bodily harm! Not to mention the loss of your b……. Not sure which I‘d choose LOL.

You'll want to check the basics, i.e. timing, plugs, rotor, cap etc… I ended up replacing all tune up parts. Make sure everything is set to spec, a manual is a must. You’ll also need to check the pickup (mines a petronics and it was set to far out) in the distributor and make sure it is serviceable and set to spec.

Check the evaporative loss control system, particularly the return line that runs back to the truck canister/tank into the tank. Typical symptoms include gas smell in the trunk and cockpit while driving. Mine was fouled by a miss installation of the canister/tank, causing the canister/tank to fill up with fuel, I have also heard that the line itself is susceptible to plugging up, I used a vacuum gage to test after fixing the fitment of the canister/tank. This will cause it to run rich if plugged.

Check the anti run on valve, if it’s not opening and closing it will also cause problems.
Check the charcoal canister, if it’s been running rich this will also fill up with gas, new ones over 100 bucks, I got a used one at the wrecking yard for 20 and I’ve heard you can rebuild them using fish tank charcoal filter (larger chunks) and paper filter cut to fit.
(twist to open)

Also need to check all the hoses going to and from the carb, replace if worn or cracked. Check the air pump and air rail, the air rail tends to carbon up, if no air is pumping in, it will run poorly.

The carb itself has a myriad of problems where rich running is concerned, at least mine did!

I rebuilt mine using the moss kit, about 23 bucks. Replaced the needle and still had problems. There are a couple key area’s, piston shaft must be free (no sticking), the jet (needle seat) is susceptible to wear, hard to find and must be professionally replaced (press fit, I found one in England, could not find in US). Check float height setting, if incorrect it will run rich and I’ve heard there is a vibration problem is some cases causing gas to bypass the float chamber, make sure the float shaft and floats are not to loose, it should be smooth without to much play.

Check the idle valve on the side of the carb, make sure this is not plugged up with carbon, and there are two set screws, brass screw screws into the white nylon screw, ones for fine tuning (brass) and the other is for large adjustments (nylon), mine was screwed so tightly I thought it was one adjustment screw.

The water auto choke, this is probably the trickiest part of the whole thing. Even when installing a manual choke, most of it still remains. Essentially you’re just bypassing the water and spring component. The actual choke mechanism is still the same, there is a secondary needle (the choke needle, not sold separately at moss, they want you to buy the whole choke assembly) that has a habit of bending and spinning and popping out of position. So all of this needs to be checked along with replacing the o’rings that hold it into position. You’ll also need to check the choke/idle adjustments and set screws, these to must be set to spec. I found a serviceable choke needle at the wrecking yard for about 25 bucks. Once it was installed correctly it helped a great deal.

Hope this helps!

If I can be of further assistance email me and I’ll do my best. This plagued me for months, I’m sure I have a few more grey hairs because of it!

kb.

p.s. If you’re not in a smog controlled area, a Weber might be the best way to go, at least I know the second I do my last smog in Feb., I’m definitely dropping my ZS!
Kevin Boldin

Thank you for all of the tips, It seems I will be very busy after work and on the weekend.

Note: I am in an emmissions free zone so the smog stuff was previously removed. The catalytic converter does not get red even though the car gets plenty hot.


Another thing - I did find the choke to be sticking a bit and cleaned that up. What is used to lubricate it? Anything special?

I've also ordered the carb rebuild kit and extra diaphrams for later use.


Thx - Elizabeth




EA Martin

I usually use white lithium grease for cables and pivit points, internally (inside the housing) a very light coat of wd40, the little spring and cam can clog up with to much lube.

kb.
Kevin Boldin

If you are unwilling to convert to twin SU's (I don't like the Weber and it is more expensive, anyway) then you can get a conversion kit from Burlen Fuel Systems for a single HIF44 to directly replace the Zenith-Stromberg.

Mike!
mike!

As a matter of fact, I planned on ordering the Weber tomorrow from Brit-tek. With the Single HIF44 there is no manifold change correct?
And is the performance much better than the weber?


Elizabeth

EA Martin

Hello Elizabeth, I'm sure you have heard this before but honestly the best money I ever spent was converting over to a weber carb and cannon header. I also switched to pertronix ignition. Getting rid of that God awlful intake/exhaust header makes a ton of difference.
FWIW
Dan H.
Dan Hanson

I ordered the Weber/Cannon set up from Brit-Tek this morning.
The last one they had due to a Weber strike I am told.
WOO HOO!!!
I am on my way at last!
Elizabeth

Elizabeth, good luck with the install. Pretty straight forward. You will be very pleased.
Dan H.
Dan Hanson

This thread was discussed between 08/08/2004 and 12/08/2004

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