Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Can anyone help me with my MG? PLEASE!

I have a 73 MGB that I am restoring with my dad and we have run into a glitch or problem of some sort with the fuel system. We changed Fuel tank, pump, filter and CARBURETOR (it has a brand new weber now), so we don’t THINK that’s the prob. It idles okay but when you give it the gas acts as if it is starving for fuel and dies out, UNLESS you hit the gas HARD and make it jump into high RPM’s FAST… I was wondering if you might be able to help me out on this (or know someone that can), we are frustrated beyond being frustrated with it… Thank you SO much, any help is appreciated!

Questions first.
Ignition timing correct?
Vacuum advance and weights working correctly?
Vacuum advance hose routed to where it should be?
Lastly, what kind of Weber? There’s downdrafts, sidedrafts, etc.

Why the switch to the Weber? Are you sure it the correct model? It’s easy to get too large of one (hoping for high performance) and find out it only runs well at wide open throttle. Do you still have the old carbs? What kind are they? Who did you buy the Weber from? Can they help make sure you have the correct model and jets? Correct initial Weber tuning often requires replacing jets and emulsion tubes, sometimes repeatedly, until the best combination is found. You may need to find an expert, or become one!

I had a friend with one of those and he had to adjust his timing about every 2 weeks, It was just a symptom widespread for those. While youre at it if you have a dwell meter check the points!

Sounds like it is over-carbed. You may have to talk to some people to find the right set-up for that carb. Or, return it for a smaller one. You may also have to re-jet the one you have. When you press the gas pedal, the accelerator pump squirts fuel into the intake to compensate until the venturi can catch up. I suspect yours is squirting too much in, and flooding the engine. Or, leaning out too much, because the venturi is too big, and the air flow cannot pull enough fuel, leaning it out too much. Either way, I believe your looking at problems with the carb.

You are correct except for the fact the problem existed before the weber and still continues, We won’t know until it is figured out, but my thought was a new carb, same problem, carb must be ok so look at something else.

What we really need is the OP to tell us more - did they replace a Weber witha Weber? Or what?

If the OP replaced a faulty, leaking carb with a carb too big, he’d have similar problems. Also, if it has a vacuum leak, that would also cause problems. Has a vacuum gauge ever been put on to check vacuum?

Is the hot air hose or pipe connected to the air filter? If your accelerator pump is not working it will cause this. If your float level is low it will cause this on some carburetors.

We thought our prob WAS the carbs. It had old twin SU carbs and we thought they were worn out and clogged and decided it would be easier to just replace them. But it didn’t help our prob… it was ONLY running with the choke pulled out and it would idle but not rev very well. We switched to Weber and now it idles fine, and it revs fine too ONCE we get into high RPM’s…

We replaced the old twin SU’s with a new weber from It is a common thing to do with a mg, or so we were told… they make carbs specifically for mg’s.

yes I still have the old carbs. They are the twin SU’s… I bought the new from and was told that it is a common thing for MG owners to replace their old SU’s with new webers and that it not only makes the car more reliable but also increases your MPG and helps other things also…

We thought the prob was in the carbs… I had old twin SU’s and we thought that they were just worn out and clogged and thought we might as well replace them… but that didn’t fix our prob… it helped sort of, because it WAS with the old carbs, not even idling without the choke pulled out and it wouldn’t rev up it just died, and now it’s idling and even revving smoothly ONCE you get into high RPM’s…We bought the carbs from, the weber is a carb made FOR a 1973 MGB like mine, EXCEPT, my MG is originally a manual choke, and the weber we bought is electric and so now it’s an automatic electric choke (we switched it over, we figured it would be easier). Could that cause problems???

True, it’s common, but those SUs were actually pretty good, once set up correctly. SUs are very simple, easy to work on and fix. Regardless, you need to find a Weber guru who can fully adjust your carbs, or google it and start working on it yourself. Here’s a discussion on Weber carb problems I found:

Join an MGB forum, there are fanatics out there very willing and able to help you. They are great, simple, fun cars.

One more option- are there any British car clubs in your area? You’ll find lots of local contacts there, and folks who can help with the carb. Brit car owners LOVE to join clubs!

The electric choke option is not the problem.

Since you have a new Weber specifically made for an MGB and the odds of carburetor jetting or accelerator pump problems are slim, you should go back and examine the ignition timing that I mentioned in my first post.

Sticking advance weights, faulty vacuum advance OR incorrectly routed vac. advance hose, timing that is retarded too much, etc. could cause the problem you have and as Oldschool correctly mentioned on another topic; ignition faults are often diagnosed as carburetor problems.

(The SU carbs are actually pretty good carburetors and downright simple.)

I agree with you, as stated previously.

Talking to folks who work on MGs the most common problem with Weber carbs is that they’re incorrectly adjusted. Look at the Weber web site - these are carbs for a number of models, not just this specific one. The MG folks say it’s very easy to overcarb with a Weber, takes work to get it right. All the other basics need to be checked, too, of course, but the Weber replacement is a red flag, from everything I’ve read.

And there are MG forums full of experts on the subject. I’m certainly not one.

I hope OP gets back to us with the final resolution, too many possibilities, roll of the dice so to speak.

I had an MG a long time ago and it was not the carburators or the fuel. It happened to be the timing points condenser that was shot. The engine would idle almost perfectly but would die as soon as you hit the gas. If I was able to get it going, it acted like it was out of gas and could not get over 25 mph.

If you do have the points and condenser in it, replace the condenser.