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MG MGB Technical - Replacing Zenith Stromberg

Hi Folks,
I am having problems with the inital startup of my MGB after being shut down over night for example.
I know its that *&^%$ water choke that's causing it. I have tried adjusting it but to no avail.
After it starts it will restart the first turn of the key if only stopped for a hour or two and it works fine. My question is: Would it be better to do a carb conversion to a webber or SU or convert the Choke to manuel. I know the cost difference for sure but if I don't do something I will soon need a new Starting Motor.
Since the season will soon be over her for Convertibles I will have all winter to fix it.


Cec
Cec Fry

If your emissions testing does not require the
original Zenith carb, you're probably better off
changing to twin SUs (stock on late UK Bs) or
a Weber. The major advantage of this change is
that it gets rid of the restrictive manifold.

I'm still using the Zenith on my 79, and use
a combination of new autochoke body (minus heat
mass and water connection) available from
Moss or Burlen, with the manual choke conversion.

The autochoke can be rebuilt (see Rick
Jaskowiak's superb web site.)

http://personalpages.tds.net/~jasko/choke/ZSchoke.htm

But in my case, the plastic cam and pin were so
worn that a new choke body was the best choice.
Ronald

Another option is the HIF44 carb. Its a pretty straight forward replacement for the ZS. The note in the VB catalog says you'll have to plug the water choke holes and remove the air filter and air box.
william fox

The weber will be the cheapest and easiest conversion. As a bonus, it will free up a bit more performance. The SUs are great, but you will spend more time getting to know them and setting up for your car. They tend to be a few hundreddollars more than the Weber conversion from what I have found. However you do get two carbs for your money! Buy the carb(s) from one of the US vendors, the Canadian guys want way too much.

Pete
Pete

Cec. I have replaced the Z-S with a Weber DGV on both of my RB cars. Most of the information in the above postings is correct, but, since we have answered this question many times before, we tend to give abriviated answers. First, you are correct that the choke is the must likely problem. If the carb is in otherwise good condition, you might well consider going to a manual choke. Many of the Z-S carbs, however, are getting old and, to the best of my knowledge, brand new units, to NA spec, are not being made. But, a Z-S in good condition is not a bad carb. The SU HIF-44 is supposed to be a direct, bolt on swap, but I have only read about it, not done it.

Changing to a set of SUs or a Weber DGV is a more difficult and costly process. The original intake manifold will not work and a new one must be obtained. The original set up was a one piece intake/exhaust manifold. You can cut the intake portion away and weld up the one hole remaining in the exhaust manifold and continue to use it with the cat attached. I did this for several years. But, many of these manifolds have cracked over the years, most frequently at the radical bend at the front where the cat is attached. Look carefully at the inside of this bend for cracking. Also look for loose studs which make for a poor seal between the cat and manifold. Deterioration in this area lead me to replace the system with a set of headers and go with an inline, aftermarket, cat to meet emissions testing requirements. If you have no testing, a good header system or use of a used, early style exhaust manifold and exhaust system is advisable. A good used exhaust manifold and a new exhaust sytem is slightly less expensive than a new header and exhaust system.

The cost of a pair of SU carbs, to 68 specification, and a good, used intake manifold, is very similar to the cost of the Weber DGV and intake manifold. The SUs have two throttle plates of 1 1/2" (about 38mm) which operate simultaneously. The Weber DGV 32/36 (most commonly used) has a progressive linkage similar to a four barrelled carb. The 32 mm throttle plate opens first and the 36 mm begins to open when the accelerator pedal is something more than half way to the floor. Both throttle plates are fully open in the "pedal to the metal" mode. My personal car is somewhat anemic until the pedal is floored and both barrels are open. With the opening of the second barrel, you feel a definite "kick" and the car performs more like my SU equipped car does on a regular basis. Ecomomy is slightly better with the Weber than the SUs, but not much as I find myself having to go pedal to the metal more frequently with the Weber to accelerate quickly.

So, I have found best replacing the Z-S choke for an inexpensive cure, using SUs for performance and a Weber to meet emissions testing requirements (and slightly easier set up and tuning). Decide what you can afford and what you want to achieve, then go for it. Les
Les Bengtson

A new emission accepted ZS carb is available from The Proper MG (http://propermg.com/Default.htm). Not cheap at $479 though.

Mike
'79B
Mike Janacek

And only at that price for ONE MORE DAY. I was almost going to order one myself. I think I will hold off. As if I can make it thru two more years of emissions, I will be able to get the exemption. Then, I will probably go to either the Weber or the Dual SU's.
John
John F

The first year I had my 76B I changed out my auto-choke for the manual conversion kit. I think it's like 70 bucks US. Then this year I went the next step and got rid of the ZS all together for the twin SU's Cost me about 1000 parts and everything. Night and Day difference though and well worth the money. I couldn't be happier with this daily driver and I can easily do 85 and the engine doesn't even strain. When I had my ZS 75 was pushing it.

Josh
Josh

Thanks Guys I have ordered the choke conversion and will try that first. I have no proplem with this car as I am not looking for power just nice unhesitating starts and stops and I have that now. I can easily Cruise at 110KMs with this car.

Thanks again
Cec
Cec

This thread was discussed between 29/09/2002 and 30/09/2002

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