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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 12822
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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I'm attempting to repair and Briggs 6.75 HP on a Craftsman

Customer Question

I'm attempting to repair and Briggs 6.75 HP on a Craftsman push mower. The owner reported that it was running and just sputtered out. He also mentioned that it has been losing power over the last year or so. I checked for spark. It sparked but looked weak. I replaced the plug with a new one. Still no start. Checked the new plug for spark. The spark looked erratic like it wasn't sparking in the middle of the gap. I tried "priming" the engine by pouring a small amount of gas in the spark plug hole to see if it could be a fuel problem. Didn't fire. I checked and cleaned the carb. It does not seem to be a fuel problem. I suspect the ignition coil might be the problem by not providing enough current. Your thoughts?
Submitted: 1 year ago.
Category: Small Engine
Expert:  Vince O. replied 1 year ago.
Hello, have you checked the compression?
Customer: replied 1 year ago.

I did by holding my thumb over the spark plug hole. It felt as though there was sufficient suction.

Expert:  Vince O. replied 1 year ago.
Was the plug saturated? Does it have a primer or auto choke?
Customer: replied 1 year ago.

The plug was only saturated when I primed it. It has a primer.

Customer: replied 1 year ago.

I forgot to mention that on one start attempt there was a "chiff" through the carburetor with some gas vapor.

Customer: replied 1 year ago.

What I meant by primed it that was when I poured gas into the plug hole. sorry for the confusion.

Customer: replied 1 year ago.

Are we still connected?

Expert:  Vince O. replied 1 year ago.
But does the engine have a primer or is it the auto choke style.The thermostat for the auto choke has been known to stick and stay in the choke position
Customer: replied 1 year ago.

It has a primer - a red button and the air cleaner assembly that you push 5 times before starting.

Expert:  Vince O. replied 1 year ago.
Remove the air filter and spray some carb caner directly into the carb to see if it fires.
Customer: replied 1 year ago.

I tried that already. It simply won't fire. I've never had an engine behave like that before. I still think it's a matter of inadequate spark due to a problem with the ignition system since nothing I've used to prime the engine (gas in spark plug hole and carburetor throat) has any results..

Expert:  Vince O. replied 1 year ago.
The reason I asked about the compression is as long as there's a spark it should have least fired. You should have at least 70 psi
Customer: replied 1 year ago.

I don't have a compression tester. It seems it should have fired at least once, even without enough compression. There's gas and spark in the same place. The spark may be too weak to ignite the fuel. Are you ruling out an ignition problem?

Expert:  Vince O. replied 1 year ago.
Leave the plug in the motor and install another plug in the wire and have someone pull the rope while you check for spark under a load.If the coil is going bad or a weak spark as you say it probably won't spark then
Customer: replied 1 year ago.

Thanks. I'll give that a try. I won't be able to do it until tomorrow. I'll try to get back to you then.

Expert:  Vince O. replied 1 year ago.