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Carburetor Back Fire or Popping Sound

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bill_000

New member
"Have a 1997 Mercruier 5.7 LX

"Have a 1997 Mercruier 5.7 LX Thunderbolt 5 V8 & 4 barrel Carb-, The problem I am having is when I started the boat there is a loud popping sound coming from the carburetor. The boat runs fine doesn't stall, idles fine. When I throttle up fast I get a backfire. The sound does not go away after running engine over time. Changed plugs, some where good some where bad can't really read plugs. HELP!"
 
"I would start with a compress

"I would start with a compression check and check your timing.
It could be a hung valve, bad mixture, poor accelerator pump circuit, bad spark, etc.
Quadrajet carb, right?

Rod"
 
"What is the volt meter showin

"What is the volt meter showing when it backfires? If the voltage regulator has gone bad, high voltage will cause backfiring. JW in Dixie"
 
Worn and crossed plug wires wi

Worn and crossed plug wires will cause backfiring. Spark can jump from one wire to another under a load. Spray or mist the plug wires along the entire length with a bottle of water while idling and see if the engine stumbles. Yes? replace the wires.
 
Same as the Reverend Guy's

Same as the Reverend Guy's last post - but - under the distributor cap. I've seen this several times. Moisture under the cap causing cross fire.

cheers
 
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