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inneedofrepair

Mower only runs with air box removed

inneedofrepair
12 years ago

Craftsman 917.378770 self-propelled mower

Briggs 7.0 hp, OHV, serial 128602 0215 E1 020405 FA

carb: 214661, primer, no choke

I rebuilt the carb with Briggs OEM parts after soaking it for two days in carb cleaner then boiling it. I also sprayed it real good with aerosol carb cleaner. I adjusted valve lash. I replaced the spark plug. I replaced the fuel cap. I replaced the primer bulb. I removed the air filter while diagnosing. I flushed the fuel tank, fuel line and replaced the fuel filter.

With the air box installed, I can prime the engine and it will run for three seconds and die. If I remove the air box, it runs fine. Note: This is with no air filter or filter cover on the air box and without the air box breather line connected to the air box.

If the air box is removed and I place my finger over the prime hole in the carb, it still runs fine.

What gives?

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