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74 mg popping coming from carburetor

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74 mg popping coming from carburetor #1
GREG WALSH Cocoa, FL, USA Sign in to contact	Topic Creator (OP) Apr 6, 2026 01:55 PM Joined 8 years ago 734 Posts

My MG started popping or backfiring bad through the carburetor(Webber)upon acceleration but idles fine. My mechanic said I need a new condensor,could that be the cause? It only happens under a load. And how do I test my old one?Thanks

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Re: 74 mg popping coming from carburetor #2
Sjmckean70 Shayne Mckean Suffolk, VA, USA Sign in to contact	Apr 6, 2026 02:08 PM Joined 2 years ago 213 Posts

It sounds like you’re running too lean or you have an ignition timing problem. The popping might be early combustion in the intake manifold, rather than in the cylinder. If you are lean, look for vacuum leaks or dirty jet in the carb. If it’s a timing issue, that’s an easier fix once you confirm timing with a gun. And yes, a bad condenser can give you timing issues.

Shayne

1977 MGB (White)
1977 MGB (Blue)

Edited 1 time(s). Last edit at 2026-04-06 02:10 PM by Sjmckean70.

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Re: 74 mg popping coming from carburetor #3
B-racer Jeff Schlemmer Shakopee, MN, USA Sign in to contact 1950 Willys Jeep Pickup "Ratrod" 1964 Land Rover Series IIA 1971 MG MGB	Apr 6, 2026 02:36 PM Top Contributor Joined 19 years ago 20,900 Posts

It could be the float level is too low (low fuel for the emulsion tubes), idle jets too lean, vacuum leak, or any number of ignition issues such as a weak condenser, early timing, seized centrifugal advance, etc....

Is there anything that happened to the car preceding this problem starting? Take it out of storage and its full of old fuel??? Carb setup new?

jeff@advanceddistributors.com

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Re: 74 mg popping coming from carburetor #4
GREG WALSH Cocoa, FL, USA Sign in to contact	Topic Creator (OP) Apr 6, 2026 04:19 PM Joined 8 years ago 734 Posts

I took it to an MG mechanic a couple of weeks ago to have the clutch master cylinder replaced and while it was there he did some carb. adjustments.He said the choke( electric type) was set for cold weather and I'm in Florida.It ran o.k. on the way home about 15 miles, other than the speedometer quit.When in the shop he said I needed a condensor.I installed a new one about two years ago along with a new distributor.Yesterday I put a new fuel filter on and a bottle of sea foam. I haven't driven it since.

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Re: 74 mg popping coming from carburetor #5
GREG WALSH Cocoa, FL, USA Sign in to contact	Topic Creator (OP) Apr 6, 2026 06:04 PM Joined 8 years ago 734 Posts

I just started it and it was still popping when I gunned the throttle.I noticed that the electric choke was open and while running I manually closed the choke butterfly and opened the throttle again and no popping. Is there a way to adjust the mixture other than changing the jets? I think it's too lean, and how do I adjust the choke on my webber?Thanks.

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Re: 74 mg popping coming from carburetor #6
Sjmckean70 Shayne Mckean Suffolk, VA, USA Sign in to contact	Apr 6, 2026 07:24 PM Joined 2 years ago 213 Posts

I would take it back to the mechanic, tell him to reset the choke. If it ran fine, he should have left it alone. Choke setting for cold weather means you get a little more fuel on startup. Nothing wrong with that. Changing it to warm, it gets less fuel on startup, because presumably, it takes less time to warm up. How does it run once it has warmed up? By then, the choke has been deenergized and has no effect on the carb.

Shayne

1977 MGB (White)
1977 MGB (Blue)

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Re: 74 mg popping coming from carburetor #7
GREG WALSH Cocoa, FL, USA Sign in to contact	Topic Creator (OP) Apr 7, 2026 07:56 AM Joined 8 years ago 734 Posts

Thanks, I just checked the choke position after I got up this morning and it's in the closed position and the fast idle screw is against its stop so that looks o.k. I'll try cleaning the idle mixture port and adjusting it because I still think it's running too lean.I can't find a filter on the carb.itself,I don't think it has one but I could be wrong..

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