I suspect that the problem is probably related to a vacuum leak if the carb you purchased was supposed to be set up for an MG or, as others have mentioned, it may simply be too big for the engine. I once replaced the ZS carb on my 1977 MGB with a Weber from Moss Motors and it ran perfectly right out of the box, at least after I plugged a couple of now unused vacuum ports on the manifold. By the way, this was a down draft carb. The side drafts are generally too big for a stock engine and will display similar problems as what you are experiencing. By the way, my son now owns the car and is doing a conversion to the dual SUs.
This could could just be a badly mounted carb, but I somehow doubt it.
If you are using the stock dizzy with the Weber carb, you either have the wrong carb or the wrong dizzy. It’s that simple. The advance profile of the stock dizzy is designed for the stock SU carb not a Weber.
The Weber won’t give you anything that the SU can’t deliver apart from tuning problems and your (probably) stock engine certainly won’t like a Weber, a certain degree of engine work such as porting is required before you will derive any real benefit.
I’d advise talking to Joe Curto, the SU specialist in NY, I highly recommend Joe, a very knowledgeable man who will doubtlessly put you straight and that is a high commendation coming from the man who designed the MG team SU jets, needle profiles and spring dynamics for MG cars during the 67 - 71 rally seasons.
Your other port of call would of course be Burlen engineering. But the bottom line is dump the Weber unless you have the equipment and knowhow to implement it.
That is pretty interesting Wizard. Perhaps the capacitor broke down past a higher voltage as the RPM’s increased.
I had just bought the blasted thing and installed it. The dealership gave me the new one just to see it was that. Took everybody for a ride.
What is the dizzy???
Sorry I didn’t get here sooner.
I agree that the Weber carb is not your problem. It is generally thought to be a great improvement over the standard SUs. Carburetion was NOT your problem right up front. '73 was right at the break between a points-and-condensor ignition system and the new fangled pointless ignition systems. I don’t know which one your “B” has. IF it is the earlier option, definitely check your point setting, preferably with a dwell meter. If you don’t have access to one (Who does these days?) you can set them with a feeler guage. IIRC it’s .015", but you may want to look that up. If you are this deep into MGs you surely have a good manual. Even the factory issed owner’s manual has that sort of info. If you pop the cap off of the distributor, you should be able to turn the rotor one direction but not the other. If you turn it one way and release it, it should spring back to its original position. If not, your mechanical advance mechanism is stuck, or its springs are bad. They were usually pretty hardy, but your car is 36 years old now. (It’s eligible for antique tags in most states.) Is the ignition timing set correctly? It will run if it’s out of time, but it won’t run right and may exhibit the symptoms you are describing. Finally, I think what you have is a vacuum leak. I don’t know where, but since you have changed the carb, I’m going to guess it’s where the manifold bolts to the head. Get a piece of rubber hose about two feet long. Use it as a stethoscope to find the leak. Leaks HISS. Hold one end near one ear, and move the other around the manifold/carb area to see if you can pick up on where the leak may be. If your car has power brakes, check the vacuum hose going to the brake booster and the booster itself. I forget just when PB began to be standard, but it was about then too.
Finally, you need to join this http://www.british-cars.co.uk/ forum. There are hundreds if not thousands of MG lovers all over the globe who regularly post there, including myself. If none of the suggestions given here work for you, someone there will have more to go on.
Good luck, you have a neat car there that deserves all the love and care that you and your dad are giving it. BRAVO to both of you, mgchick.
MG McAnick
It’s Brit slang for distributor.
I don’t necessarily agree. Cars I’ve put Webers on ran fine with a perceived increase in power, and much easier starting.
Hood = top
Bonnet = hood
boot = trunk
carburetter = carburetor
tyre = tire
The UK and America are two countries separated by a common language.
I’m also a slow typist.
That’s the same website I recommended below.
I’ll accept the disagreement, I have a 4.2 Jaguar with triple dual choke weber’s and they run fine now I have them jetted correctly and spent a day setting them up. But they don’t really give me that much more of anything without a change of cams and I did have to change the dizzy. Plus I have to balance them every few weeks & the weber’s fuel consumption is through the roof.
You can get the same performance (and fuel consumption) from SUs with valve, needle and spring adjustments. Admittedly they don’t look as good as the weber’s though.
Glad you popped in on this one. I was thinking the same thing myself but I have never worked on an MG. I have used Weber carbs in the past and I agree that it is not only not the problem, it was a wise choice to go with it.
I do have one modification to your suggestion on finding a vacuum leak. Get a can of spray carburetor cleaner or throttle body cleaner and spray it around all the gaskets on the intake manifold, both to the interface with the head and to the carburetor base and adapter base while the engine is idling. If you come across a leak, the idle will change. No leaks, no change.
I suspect that the problem is with the distributors vacuum advance, if it has one. If the mechanical advances are stuck, a little sewing machine oil will free them up, better than WD40 in the long run.
Start with scratch with the carbs and go with what is statated above 1st reaponse. Stay with SU carbs properly rebuilt. Cam shaft could be worn. What kind of shape is the engine is. Forget the Weber carbs. Make sure the valves, compression, etc. in the engine is correct, then go to the carbs.
Not true.
This is not true. Something else is wrong with that car.
Thanks… We have checked the obvious places a vaccum leak would be but we’ll check some more. Also I will check the condenser and distributer. When we first began restoring this car it had sat for 15 years and so we replaced, points, condenser, spark plugs wires, fuel filter, etc… did all the little things, and it ran great, started right up, ran very well. We didn’t however change the fuel tank at the begginning, we just ran it off a portable tank of gas so we could set the carbs and just work on it… Well we cleaned the tank by running gas thru it and started running it off the old tank, thinking it seemed pretty clean, we were wrong apparently cauze that’s when all our problems started and it hasn’t run right since… At first it just started dying after we’d drive it a certain distance, then it would only idle with the choke pulled so we assumed that we must’ve ruined our carbs, so we replaced them and you know the rest… just thought I’d give you that little bit of info…
Well…now you’ve let us know lots of info that can help. Sounds like you have dirt in the fuel system. Have you taken the tank off and had it cleaned?
It has a brand new tank on it now… but we’re not even running it off the tank at the moment because there is a leak in the lines between the BRAND NEW fuel pump and tank. So we’re just running it off a portable fuel canister.
would a faulty condenser or a vaccuum leak cause the car to sometimes not start??? It won’t start today, only cranks…
At least you can start to pinpoint the problem, something has failed, my first guess the coil. Assuming of course the points and timing are good and plug wires are attached correctly. Do you see spark at the plugs? does starting fluid give it a kick? Intermittent problems are the worst so tou are well on the road to recovery, I so wanted to buy my bosses mgc gt and looked today for a good deal on an MG I envy you!
I’m also of the opinion that the problem is not carb related.
Have you taken a look at the ignition system yet? What about something simple like contact points being closed up? (not rare on an old car)
If it cranks over without starting then the first thing should be to inspect the plug wires for a spark. No spark means:
No power to coil. (fuse, ignition switch)
Bad coil.
Bad condenser.
Closed up ignition points.
Distributor not turning. (not likely)
This is an extremely simple car to diagnose and repair.