Briggs and Stratton, PowerBuild 12.5hp not working

[Dimbiss]

This engine powers a Murry 125/95 ride on mower, similar to a Craftsman. Long story short:
Unit has clean fresh fuel. Fuel flows to carbon without problem. Healthy spark from sparkplug. Starter motor turning her over, but not powering up.
My only other observation is that the turnover from the starter slows with the sparkplug attached.

Any ideas or suggestions appreciated. Thanks in advance.

 

[NibbanaBanana]

Fuel, spark, compression, timing.

 

[Snagglefoot]

Take off the air filter and give it a shot of carb cleaner to see if it catches. If it does you may have crud in the bowl or jets.

 

[Lubener]

Make sure the flywheel key is not partially or completely sheared. Either way it can throw off the ignition timing where the engine won't start...

Try using starting fluid either in the plug hole or down the air intake and see if the engine tries to start momentarily. It does sound like your battery needs to be charged or replaced. It may not spin the engine fast enough for it to start.

 

[fantastic]

Starter motor turning her over, but not powering up.
My only other observation is that the turnover from the starter slows with the sparkplug attached.

Any ideas or suggestions appreciated. Thanks in advance.

Take off the valve cover & check the valve lash. Put them in spec. Do you have some feeler gauges?

 

[Nukeman7]

Take off the valve cover & check the valve lash. Put them in spec. Do you have some feeler gauges?

^^^^This right here! The slow cranking with the spark plug installed is due to excessive compression because the valves are too tight (i.e., not enough clearance).

 

[TnT_M]

IMO, Check the battery before anything else. Slow cranking leans me that way. How old is your battery?

 

[The_Eric]

Have you been mowing with it all season and it suddenly won't start or has it been sitting for a decade and it won't start?

 

[Dimbiss]

Hi guys, many thanks for the suggestions. Have had the unit for approx 20 years and work it like a dog. Even fitted a ball hitch to tow a trailer to move anything up to a ton in weight. It does need a new battery, but am jumpstarting it off a Solis20 tractor as I needed to find out if the alternator is goosed. Then this happens. I will try the starter fluid first. I do have feeler guages, but any idea what the valve clearance should be. I can also clean up the carb at the same time. Then I will be able to check the o/p voltage from the alternator. If Nukeman7 and Fantastic could met me know the valve clearances should be, it would be appreciated. Thanks in advance.

 

[MParr]

You will need the engine model number and serial number for the correct value clearance values.