Small engine won't start

[waterinthefuel]

Ok, this one has me perplexed. My grandfather recently passed, and I wound up with his old gas edger that his neighbor had given him. It always ran great, it has an old 2hp Briggs engine on it. Now, I was edging the driveway and it stopped like someone flipped a switch. I then tried to start it and it would pop over a few times but nothing. Then it would run for a few seconds but nothing. It had old gas in it and so I took off the tank and flushed it and put new gas in it. I took the plug out, cleaned it, gapped it and put it back in. It's got spark out the wazoo. I'm perplexed because I know its a fuel issue, but it has one of those carbs that's just a straight pipe. It has no bowl. I can inject fuel into the air cleaner intake and it still won't pop over. Not even a single pop, yet it has good clean spark. I am stuck, I just don't even know where to go now. I'm a licensed mechanic but airplanes all have carbs on them with bowls that I know how to clean, adjust, etc. A bowl-less carb has me scratching my head. I can't even access the inside of the carb, it's just a pipe with butterflies inside. Anyone have any ideas?

It's an old Gibsons, probably from the mid 70's. When it did run Ive never seen an engine that could run slower or smoother, but now its dead. And half of my driveway is edged and half isnt.

 

[Scott Danforth]

The crud in the tank is now in yhe carb. Clean the carb.

Never run anything on old gas

 

[Grub54891]

If it looks anything like this carb, it has a diaphragm pump.

 

[fhhuber]

If the diaphragm has a hole, its not going to operate the pump and the engine won't run. But if that's it, pouring a small amount of gas (less than 1/2 oz) in the intake should have the engine popping for a few seconds.

It failing to pop over when you put fuel directly down the intake means something else is going on. The carb might be just fine, or may ALSO be a problem.

Compression
Properly timed spark
Correct valve timing (*assuming its one of the 4-stroke Briggs engines, since the 2- strokes are REALLY rare.)
Correct fuel-air mix.

You have spark,
You FORCED it to have fuel-air mix.

Check if it spun the flywheel on the shaft and threw the spark timing out. It should be a tapered shaft with a "woodruff key" (not sure of the correct name... its what the old guy who taught me to fix em called it) to hold it in alignment. If it backfired it could snap the key and throw the spark out of timing. something like a $0.50 part for the key when I used to fix my own engines. Its a small partial circle ( a bit less than half) piece of metal that is harder than soda can metal but softer than mild steel.

Note: You can get away with making a new key from a softer metal and it will work until the engine backfires. If you use a harder metal, then it won't shear when its supposed to and you can break the crankshaft.

 

[waterinthefuel]

Yes it does kinda look like that carb in that pic. It has a very fine screen on the pickup tube so I doubt there is any crud at all in this carb. But I put fuel directly into the throat and it didn't pop, at that point I'm bypassing any crud in the carb.

It's a 4 stroke. What's weird is it did this yesterday and I read that I should just put fresh gas in it. I did and it started on the first pull and ran beautifully. I put it to the side, go eat lunch, and I come back out and it won't even pop over. Still has good strong spark and seemingly has good compression. I mean it's pretty stout to pull for a 2hp engine.

I thought about it being out of time. That will take a bit of checking to see if its right. It didn't backfire or do anything that I know of it was running beautifully and then stopped, but its well worth looking into at a later date. Right now I have to get some sleep, I'm a truck driver and I go out tomorrow.

 

[fhhuber]

When the flywheel spins on the crankshaft, it may line up for acceptable timing occasionally and run, then it will shift timing and stop. Anything that can make the flywheel shift can make it alter the spark timing. Since the pull cord acts on the flywheel, that can be shifting the timing as the engine enters compression stroke. Then you engage the edger or load the blade by starting to edge, or just change the throttle and shift the timing again.

 

[bigdee]

You ruled out spark and fuel. All that is left is timing.....check for a sheared woodruff key on flywheel.

 

[waterinthefuel]

In case anyone wants to know what it was, the carb was out of adjustment for some reason AND it needed a new spark plug. The plug would fire when you'd pull it out of the hole and check it but it became very hit or miss when you installed it to try to start it. The engine is over 40 years old and the plug was god knows how old. A new plug, and a little help adjusting the carb and it starts 1st or 2nd crank and runs so slow you can count the strokes.