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Discussion Starter · #1 ·
I bought a Craftsman FWD self propelled push mower with Briggs 6.5 engine. The gentleman I bought it from said he had just mowed with it a week earlier but it wouldn't start when I got there. The gas smells fresh and the primer bulb is definitely moving gas into the carb. The mower still won't start. No sputtering, popping, backfiring, nothing. It pulls good and feels like its getting plenty of compression. Here's what I've tried so far: Checked the sparkplug for spark, it's getting spark, the spark looks strong and the plug looks good. Took off the air cleaner and sprayed carb cleaner / starting fluid directly into the carb and pulled it, no love. Made sure the throttle linkage was working and was set on start. Checked to make sure the kill switch linkage was working. Made sure the self propelled wasn't engaged.
Anyone have any suggestions? Thanks!
 

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Try replacing the Spark plug, Sometimes the Plug will spark outside of the engine but when you put in in, The force of the compression stops the spark from jumping.

That or maybe take the spark plug out and spin the engine a few times to clear any gas out of the cylinder.. It may be flooded.

Cheers
-Capstan
 

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Yeah, definitely try a new plug and go from there.
 

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The guys are right, try that. Then maybe look into a blown keyway. Might be so far out that spark is at wrong time?
 
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Discussion Starter · #7 ·
Alright, I'll try replacing the plug first and then report back.
OK so here's an update. Put in new spark plug properly gapped. Still won't start. Drained gas (just in case). Visual inspection of carb and bowl. Looks ok, and getting gas. Sprayed carb cleaner into the carb and pulled, no start. Sprayed carb cleaner into the spark plug chamber, replaced plug and pulled, no start. Removed gas tank and engine cover. There was a LOT of old grass under the engine cover. Removed excess grass and cleaned things up. Visually confirmed that engine brake assembly was working properly. Haven't checked the flywheel key yet, that's next. Thanks again for your help... any new suggestions?
 

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OK so here's an update. Put in new spark plug properly gapped. Still won't start. Drained gas (just in case). Visual inspection of carb and bowl. Looks ok, and getting gas. Sprayed carb cleaner into the carb and pulled, no start. Sprayed carb cleaner into the spark plug chamber, replaced plug and pulled, no start. Removed gas tank and engine cover. There was a LOT of old grass under the engine cover. Removed excess grass and cleaned things up. Visually confirmed that engine brake assembly was working properly. Haven't checked the flywheel key yet, that's next. Thanks again for your help... any new suggestions?
Have you done a compression test?

I'm thinking it may have overheated.. Sometimes the piston will get scored causing Something called "Blow By" Which is where the air/fuel literally Blows By the piston into the crankcase..

A Quick test of this is:

Remove the dipstick, then set the dipstick in the dipstick tube but don't screw it back in.. So it's just sitting on top of the tube.

Then, Pull the engine over quickly. The dipstick should barely move.. If it jumps up.. or worse, Oil comes out.. You have bad Blow by and subsequently.. No Compression


-Stan
 

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Well, it depends on the engine. Some engines spin with enough pressure in the case to throw oil up the tube anyway, even it there is no blow by. However, I do agree with Stan that the problem may be due to engine damage from overheating. A little grass can cause havoc for and air-cooled engine. :(
 

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Discussion Starter · #10 ·
Have you done a compression test?

I'm thinking it may have overheated.. Sometimes the piston will get scored causing Something called "Blow By" Which is where the air/fuel literally Blows By the piston into the crankcase..

A Quick test of this is:

Remove the dipstick, then set the dipstick in the dipstick tube but don't screw it back in.. So it's just sitting on top of the tube.

Then, Pull the engine over quickly. The dipstick should barely move.. If it jumps up.. or worse, Oil comes out.. You have bad Blow by and subsequently.. No Compression

-Stan
I don't have a compression tester, so no. I think if the flywheel key is intact, I'll just junk the mower. It doesn't seem to be a simple fix.
 

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Simple test of compression is to pull the spark plug and move the spark plug wire well out of the way. Put a finger or your thumb over the spark plug hole and spin the mower engine over. If it's the kind of mower you have to stand behind and depress a lever in order to pull the starter rope, you might need someone to help do that while you hold your finger over the spark plug hole. If there is compression, you will feel it pushing against your finger. In fact, it should push your finger completely off of the spark plug hole.
 

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Check if any fuel or oil is coming from the muffler, you should have some liquid escaping if its not burning.
tighten the head bolts.
Some times you can look at the blade and see if it has had a recent hard lick that may have sheered the flywheel key.
 

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If you are 100% sure you have good fuel and NO water in the tank OR float bowl, I think you have an intermittent problem with the kill switch, weak spark, low compression or a partially sheared flywheel key. The machine is worth saving and consider it a great challenge to get it going.
 
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