BS 26HP motor won't run...need diagnostics help

Hay hay hay

Well-known Member
Need diagnostic help ZTM
2007 Bad Boy ZT 60” zero turn (bought new, 500 hours, now used as a backup, and rougher jobs)
Briggs and Stratton V Intek 26HP
Won’t run consistently. Has started and run, then the next day won’t start.
Sometimes it will start on the key, next day won’t turn over with the key, but will crank with jump to post.
I am beginning to think I have a combination of random, intermittent problems.
So here is what I have tried over the last few weeks.
It had been sitting so I squirted a little gas in the air intake and it fired up and ran until out of gas.
I thought the problem was fixed so I filled the tank…..no start…checked the fuel pump…working fine.
Smelled like it was flooding. (all the while sometimes it would crank with the key, sitting in the seat (but sometimes not)
Changed a couple relays…that helped a few times…then will crank with key/ won’t crank with key started again.
Intermittent problems.?????
I decided to put on a new carburetor…3 hours and 2 cans of wasp spray later new carb installed…turned the key, SUCCESS ! it fired right up a ran mid-throttle setting in the shed for about 5 minutes, but was beginning to miss and back fire slightly. I turned it off. When I tried to restart it….no key crank.
Today it won’t crank with the key, will crank with the jumper, but it won’t start.
Here is my list:
New carb works OK
Fuel pump OK
Battery OK
Starter OK
Problems:
Could the ignition be intermittently? (the miss and backfire makes me think I have a spark problem)
Could the relays be popping in and out, to make the key start work intermittently?
Could a safety switch or relay be turning off the ignition fire?
Should I change all the relays on a 13 year old machine?
I really need this machine for backup mower.
When it runs it is still a very strong engine.
Thanks for your ideas and suggestions
 
Some things I have run into on small engines.

The woodruff key that holds the flywheel from shifting around. Possible that the key is worn or loose allowing the flywheel to lose its exact orientation on the end of the crankshaft. This key can cause no start, poor running, loss of power, and if it is a bit loose, it can cause intermittent problems as it jiggles around as the engine runs.

There is a fuel shutoff solenoid on some carburetors. I have a lawn tractor that would intermittently just quit as I was mowing. It turned out to have a fuel shutoff solenoid mounted into the carburetor. The electrical connection had somehow lost its integrity. I disconnected it and cleaned up the terminals and connections 2 years ago, and it hasn't quit since.

Junk in the fuel tank can raise heck with fuel flow. A little piece of a leaf is all it takes. At some point, it can get pulled onto the fuel outlet inside the tank and shut off (or partially shut off) fuel flow. Many times it will restart because the little piece of debris can float away from the outlet when the engine stops drawing fuel when it stalls.

Just a couple of ideas. Hope it helps.
 
Turn the fuel off before you go to shut it down
leave it run for 15 sec then shut down
then turn fuel on rt before u start it
see if that helps
 
Yes on the Woodruff. I had one partially sheared after whacking something that killed the mower. Lengthy process but accidentally found it. Had no idea that timing was that critical but it is. If you hit something that killed the engine last time out, surely a place to look....just pull the flywheel nut and peer down on the flywheel...clearly visible....any distortion of the woodruff means replacing it.
While you are going through things, I'd pull the kill wire off the ignition coils or find a place where you can disconnect it as close to the coils as possible to ensure that there aren't any switches accidentally closed between you and the coils grounding them out. That would eliminate any safety switch or switch to wiring harness bad connections. Agree on ensuring the carb shutoff solenoid has voltage.....haven't checked a schematic on that engine, but you may only have one of the two listed shut off mechanisms, or may have both.
 

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