Argh! Lawnmower issues!!! HELP?!?

I've got a Sears 5.5 horsepower gas mower. It's got a Tecumseh engine - (Sears model 143-985508, Tecumseh model TVS115-62118C). Date code is 8135, which should mean 1998, day 135.
Today I pulled the mower out and it started fine. I got most of my large back yard cut and stopped for a break. About 45 minutes later I go out and yank the pull cord and it doesn't fire at all. I press the priming bulb a couple times and try again. It starts and then immediately cuts out. If I yank again, nothing happens.
If I let it sit for a minute or so and try to start it, it fires up and then cuts out. If I spray starting fluid into the air intake and yank, the mower starts and runs a bit longer, but still stalls out.
The tank is full. The gas is fresh. The mower had NO issues an hour ago.
What's going on here? I wanna cut my grass!!! :(
A bit more history...
A couple weeks back, I had problems starting up the mower. I drained the plastic gas tank, and the fuel out of the gas line and carb bown. I put in fresh gas and the mower started up. It still acted odd, running at normal speed as long as I was cutting grass. If I stopped cutting, or passed through a thin area, the mower would start to cut out, then rev back up... repeating the process roughly every 8 seconds.
So, I figured that the carb was plugged up, or something similar. I know that the fuel bowl gasket and and the fuel bown nut gasket were pretty worn out... I assume that this could mess up the float/needle spec so I went out and picked up some parts.
I ended up with a spark plug, air filter, and the two gaskets mentioned above.
I pulled the carb off the mower and disassembled it. The innards were clean as a whistle. No gunge or varnish to be found. I blew everything out with a bit of carb cleaner to be thorough and reassembled everthing.
The mower fired up and ran great! All fixed I though...
Diagrams and specs can be found here:
http://members.shaw.ca/linkto/mower
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Caleb, could you be sitting it in the sun and it needing to cool down in the shade?
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Possible, but could that really make a difference? Would this be "vapour lock"?
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"Calab" wrote

Dunno, just experinece here that some have to cool off in the shade to work right.
Back in 1972 or so had to use a push mower (not powered at all) to 'bushhog' down grass taller than me. I was 5ft then (still am darn it!). Mower would overheat and i'd have to take it to the shade for an hour or more then get my brother to start it for me.
Grin, forgive me but I'm a 'bitty' sized girl. I'd always *try* to start it myself a few times but seldom could 'rip the cord' strong enough to get it going.
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On Wed, 18 Jun 2008 20:44:19 +0000, Calab wrote:

Not rocket science here. Gas is siphoned out of the bowl up through a jet into the venturi by the air rushing past jet passage. Pressing on the primer forces air into the bowl and causes gas to be pushed up usually through the same venturi. It's hard to tell from your story but is the motor running now or not?
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Nope... runs for a couple seconds. Sometimes hardly sputters at all, sometimes runs for about four seconds. Once it's sputtered, it won't fire at all unless I use starting fluid or let it sit for a few minutes.
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I didn't believe till it happened to me, but sometimes old or cheap motor oil makes a mower run wrong. Try an oil change, and use Castrol 10w30. Castrol was the only brand that quieted the rod knock on my last truck, which is why I say that brand.
Some Tecumseh engines, they had a run of bad ignition coils. Champion had a run of bad CJ8 spark plugs. New spark plug is cheap enough to try.
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Caleb,
As the gas leaves the gastank air must enter, usually through a reed valve. The reed valve may be located in the gas cap or be pressed into the gastank wall At 10 yrs that valve may be rotted. It's cheap and will cause the symptoms you describe. Check that valve
Dave M.
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I'm sure that it's in the cap... Will check it out. I assume that a cheap test is to run the mower with no gas cap?
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Calab,
Running without the cap for a short period of time will test the "reed valve hypothesis".
Dave M.
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The vibration will shower gasoline all over.
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If the mower runs with the gas cap loose a half turn or so, you need a new gas cap.
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On Thu, 19 Jun 2008 09:12:35 -0400, "Stormin Mormon"

Or, clear the gas cap vent hole with a paper clip.
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Thanks, MacGuyver. The rapid, simple, inexpensive solution to 61.42% of life's problems. Stick a paper clip in a couple times.
Works on vent holes, testing electric sockets, and anything that ails you. Did you know that 91.06% of statistics are made up on the spot?
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It is definitely a fuel related problem. I don't subscribe to the voodoo method of letting it sit in the shade. Did you remove and clean the float and float needle? (be very careful, some needles have a neoprene tip, some seats have an oring seat, usually red) Did you clear the hole in the bolt that holds the sediment bowl on? (crucial on Tecumseh) Did you inspect the gasket where the carb tubing attaches to the block? (needs good vacuum)
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Gasket between the carb plumbing and block was good.
When I had it apart, I didn't replace the needle or seat. Everything looks pretty much "brand new" in there. No sludge or varnish, etc.
I'm thinking that something must be clogging the needle/seat somehow.
Guess it comes apart again. :(
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What is part 416. Didn't see it named on the list. Some engines have a spark arrester for the exhaust and that filter can clog up (I've read) .. clean/replace.
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So... I had a chance to pull the carb off the mower today. Disassembled it and didn't see anything wrong. Blew a bit of air through the jet (Blech!) and it made kinda a small "pop" sound. Reassembled and all is good! Looks like something had plugged up the jet.
Going to need to get a gas filter on the line I guess. Going to add a draincock at the same time so I can empty the tank easily at the end of the year.
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