74 mg back firing out exhaust

[Buick35]

All of a sudden my 74 mg started popping out of the exhaust and running poorly.I also noticed that it's idling lower than usual.I checked the points and somehow the gap had widened up.I reset them and it runs a little better but still popping but not as bad.I drained the old gas and am going to put fresh in tomorrow and check for vacuum leaks.It has a single down draft weber. Any other things to look for? It's got a new coil,condenser and points last summer.I did notice that the points aren't contacting quite squarley.Thanks.

[Mark Shaw]

It may be fuel starved.  Check your fuel filter.

[rocketraider]

Exhaust backfires generally trace back to ignition, specifically an interruption of ignition. Then when it fires again it ignites raw fuel that managed to pass into the exhaust system.

 

Condenser is suspect, as is the off-square points set. If correcting those doesn't help, you may have to go into the distributor and check for wear and slop.

 

Course it could just be Lucasifer having a little fun.

[demco32]

15 hours ago, Buick35 said:

All of a sudden my 74 mg started popping out of the exhaust and running poorly.I also noticed that it's idling lower than usual.I checked the points and somehow the gap had widened up.I reset them and it runs a little better but still popping but not as bad.I drained the old gas and am going to put fresh in tomorrow and check for vacuum leaks.It has a single down draft weber. Any other things to look for? It's got a new coil,condenser and points last summer.I did notice that the points aren't contacting quite squarley.Thanks.

An MG never had a Weber carburetor but it should have  an SU carburetor. ( assume it is a MGB car?)

Your car is running too rich and that is wat you hear in the exhaust.

If it is spitting  in the carburetor you hear , it is running too lean.

Adjusting with the weber carburetor is only possible with change jets.

The Su carburetor is a better carburetor for this car and you can adjust the mixture.

Needle deeper in the jest = leaner mixture

Needle higher in the jest is richer mixture.

  

 

[demco32]

sorry, should be 'jets'

 

[Restorer32]

Your problem is the "gulp valve".  Ex wife and I drove 2 MGBs as far as they would go before rusting to death and both required replacement of the gulp valve to cure pervasive back firing.

[Leif in Calif]

This Forum is a great source on most things and I bet your question was answered by the above replies, but you should be aware for this site:

https://www.mgexp.com/forum/

 

They are as committed as the folks here, but more focused. 

 

Leif

[Buick35]

6 hours ago, Restorer32 said:

Your problem is the "gulp valve".  Ex wife and I drove 2 MGBs as far as they would go before rusting to death and both required replacement of the gulp valve to cure pervasive back firing.

I think th PO removed the gulp valve along with all the rest of the emission stuff.

[Buick35]

57 minutes ago, Leif in Calif said:

This Forum is a great source on most things and I bet your question was answered by the above replies, but you should be aware for this site:

https://www.mgexp.com/forum/

 

They are as committed as the folks here, but more focused. 

 

Leif

Thanks,I've been in touch with them also but thought I'd try both sources.

[Digger914]

After you get past the language barrier where the hood is the bonnet, the top is the hood and you discover that the bent ring spanner that you can't special order from Snap-On is just an offset box end wrench, working on the MGB is almost easy. Maybe not as easy as it was before Radio Shack went away, but the internet still makes finding electrical parts easier than rebuilding melted switches.

 

For years MGB's came with twin SU's which were good and sporty, but meeting US emissions forced the change to the single Zenith which tended to get sticky inside. The simplest, almost too simple first step to fixing MGB single bucket side draft carb problems is pull the top and clean the sticky off the innards.

 

25 years ago replacement Zeniths were hard to find and this car is almost 50 years old. Replacing a flaky side draft with a working down draft was a non EPA authorized repair and before an old MG racer showed me how to rebuild a Zenith, I was considering the intake manifold and carb replacement option. Buick35 sees a single down draft Weber when he's looking under the hood / bonnet of his MGB and that negates most of my MGB experience, but I can suggest fresh gas with some Seafoam in the tank and down the carb followed by a good drive before taking things apart looking for bigger problems.

[Buick35]

18 hours ago, Digger914 said:

After you get past the language barrier where the hood is the bonnet, the top is the hood and you discover that the bent ring spanner that you can't special order from Snap-On is just an offset box end wrench, working on the MGB is almost easy. Maybe not as easy as it was before Radio Shack went away, but the internet still makes finding electrical parts easier than rebuilding melted switches.

 

For years MGB's came with twin SU's which were good and sporty, but meeting US emissions forced the change to the single Zenith which tended to get sticky inside. The simplest, almost too simple first step to fixing MGB single bucket side draft carb problems is pull the top and clean the sticky off the innards.

 

25 years ago replacement Zeniths were hard to find and this car is almost 50 years old. Replacing a flaky side draft with a working down draft was a non EPA authorized repair and before an old MG racer showed me how to rebuild a Zenith, I was considering the intake manifold and carb replacement option. Buick35 sees a single down draft Weber when he's looking under the hood / bonnet of his MGB and that negates most of my MGB experience, but I can suggest fresh gas with some Seafoam in the tank and down the carb followed by a good drive before taking things apart looking for bigger problems.

Thanks,I've done that.Someone said it's the condenser ,I'll try changing that but I don't think that's it.

[critterpainter]

As long as you are changing the condenser, give the vacuum advance a quick check and loosen the screw under the roter and drop a few drops of oil on it.  This will lubricate the mechanical advance and is mentioned in the service manual.  The las 3 MG distributors I workedon had stuck or gummy mechanical advances.

[Buick35]

I couldn't get the vacuum advance to move any by sucking on the tube so I'm thinking it's stuck.Thinking of just getting an other distributor.Wouldn't hurt to have a spare anyway.

[Buick35]

On 9/24/2023 at 1:44 AM, critterpainter said:

As long as you are changing the condenser, give the vacuum advance a quick check and loosen the screw under the roter and drop a few drops of oil on it.  This will lubricate the mechanical advance and is mentioned in the service manual.  The las 3 MG distributors I workedon had stuck or gummy mechanical advances.

I just changed the condenser and it seems better,I'll test drive it tomorrow.