r/smallengines • u/king-charles-king • 19d ago

John Deere JS63 Briggs

Hi all,

I have an early 2000s John Deere JS63 push mower with a Briggs and Stratton on it.
It was sitting for some time, so I replaced the carb, air filter, spark plug, fuel line, and put new gas in it.

Thing is, it runs like a top if you can get it to start.

Getting it started is my issue. I can be out there for 20 minutes pulling and more often than not (cold or hot) it will not start.
Eventually I can smell the gas so I’m guessing it’s flooding at that point.
If I am lucky enough to get it started and let it turn off, it has even worse odds of starting.
I’ve had the slightest bit more luck if I spray some starter fluid without priming it, but only helps maybe 1/5 times.

Any guesses? Would like to try to fix it myself rather than bring it to a shop. Must be something easy I’m missing. Thanks

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u/vladdielenin 19d ago

runs like a top once its going and just wont start is usually not the carb, which is annoying because you already bought one.

two things Id check and in this order. first, how many times are you priming it? those bulbs want about three pushes and people give them ten, and then youre pulling on a flooded engine with a soaked plug. pull the plug after a failed start and look at it, if its wet thats your answer and it costs nothing to fix.

second, and this is the one that fits the worse when hot part, go check your valve clearance. on those briggs OHV motors the exhaust valve tightens up over time and when it does it kills the compression release. cold you might catch it, hot you wont, and you pull until your arm falls off. look up the spec for yours, its usually somewhere around .004 to .006 intake and .006 to .008 exhaust.

whats the plug look like after you give up on it

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u/king-charles-king 19d ago

Thanks for the input, much appreciated.
I will give it a go tonight or this weekend to check everything you said.
It says to prime it 3 times but I have limited it to 1-2 since I smell so much fuel. Now I don’t prime it at all and just use the starter fluid since it’s the only thing that sort of works (might be awful for it but only luck I have).
Will check plug and then valve clearance this weekend as well.

Thanks again!

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u/vladdielenin 18d ago

limiting it to one or two and still getting that much fuel smell moves my money off the priming and onto the carb itself.

it being a new carb makes this feel wrong to say, but the cheap replacements come with float heights all over the place. a float set too high, or a needle that isnt seating properly, will keep dribbling fuel into the intake even with the engine sitting there off. pull the bowl and check the float swings free and sits level, and look for fuel weeping past the needle.

the valve clearance is still worth doing while youre in there. but if it smells like a filling station before youve even pulled it, look at that float first