Tecumseh Lawn Boy Quits Running for No Apparent Reason

13 years ago

I'm messing with a Lawn Boy 10328 Silver Series mower with a Tecumseh 4.5 HP engine. The mower is about 10 years old and was serviced professionally two summers ago. Blade, air filter, and spark plug were all new that point, and oil is relatively clean. If the spark plug wire is any indication, it's probably had a new ignition module installed.

Since I got the mower, I've disassembled, cleaned, and reassembled the carb, replaced the fuel line, and flushed and refilled the gas tank. The mower starts on the first or second pull, but after about 10 minutes of use, the mower just dies as if fuel starved (except without the usual up and down surging one would expect with small amounts of remaining gas going from the tank into the carb). This SEEMS to happen most often (but not always) when the front of the mower has been tipped up for turning. If I wait a minute or so, reprime the engine, and then pull the cord, it'll start again.

Any thoughts on what might be causing this?

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Comments (6)

baymee
13 years ago
You don't mention anything about a possible blocked gas cap vent.
olddog2010
13 years ago
as it attempts to die press the primer button to see if you can keep it running.....if it remains running I think you low speed jet may have an obstruction that is intermittent....does it ever die when you are under a load?
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It could work out that way. For the blade adapter, put some penetrant on it and let it sit overnight. Strike the flat near the corner as if trying to spin it on the crank - it should come off. If not, take a propane torch and quickly heat the adapter but not the crank and hit it again. It's not an interference fit - it's just rusted on to the 45 degree bevel on the end of the crank. Then you can remove the muffler cover and baffle, followed by the muffler plate. This gives access to the lower seal. Before removing the old seal, take a strip of emery cloth and lightly shine up the crankshaft, removing the rust and buildup. Wipe it down with a clean oily cloth to remove any dirt or grit. Remove the old seal. Clean the seal area with a Q-Tip. Slide the new seal up the crank and press it into place. This might require the use of a piece of PVC pipe cut off square with a tubing cutter to slip over the crank and evenly seat the seal. To test lower bearing wear, grab the crankshaft and push/pull it to get a feel for the vertical play. Then, with the blade on tightly, push down on one end of the blade while pulling up on the other. Rock it back and forth to see how much side play there is in the bearing. There is always a little play because they are roller bearings, but you should see no more than about 1/16" at the blade end, and about the same vertical play. After thinking about it some more, I'm still not convinced that most of your trouble isn't with a dirty carb. From my experience and what I read here, most of them will run with a bad seal but just won't develop full power. Your symptoms sound like no gas getting through the carb.
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tomplum
13 years ago
A point to mention on the fuel line. Too much isn't a good thing on these. A slight bow in the line is ok- but too long of a line can create a situation similar to a vapor lock. Good advice above. If you can confirm it is a fuel problem- you are 1/2 way there. Also , if you had removed the main nozzel- it is best to replace the seals.
chesapeakebeach
Original Author
13 years ago
@tomplum -- thank you for mentioning that. When I replaced the fuel line, I just cut it to the same length as the old one. But then when looking at it after the reinstall, I realized it had a dip in it and wondered if that might cause difficulty. I'll go back a snip a bit more off so the fuel never has to run uphill.

This theory is actually pretty relevant, as the previous owner complained that the mower "wouldn't stay running" for her. I thought I'd found the problem when I removed the carb bowl and discovered a bunch of mushy crud in there, but maybe that wasn't what was really causing the stalling.
chesapeakebeach
Original Author
13 years ago
Well, I shortened the fuel line just slightly so it's running entirely downhill. Recleaned carburetor, this time with a WaterPick (the kind you use to clean your teeth that shoots little jets of water -- my new favorite carb cleaning method, because you don't have to fear spraying carb cleaner in your eye and can watch whether the water's come out well or not). Unbent a staple and recleaned the holes in the carb bolt.

In the process of disassembling and reassembling, I discovered that one of the screws holding the air filter housing had a flat tip, while the other had a cone-shaped tip. It struck me as odd that the flat-ended one was in the hole that had gas and air passing through it, so I reversed them and put the cone-shaped one in the hole that had gas and air going through it.

Somewhere along the line, I seem to have solved the problem, because I cut grass with the mower for about 20 minutes and it ran fine. So thanks for all the tips.

Now my only concerns are: 1) my ear senses that the mower seems to be running a bit fast, and 2) the mower is definitely very loud compared to other mowers (muffler dosen't have any obvious external defects or holes). For what it's worth, the exhaust air seems to be blowing out of the muffler with tremendous force -- none of my other mowers make flowers, etc. flap in the breeze like this one does. Thoughts?
baymee
13 years ago
maybe the internal baffle of the muffler let loose. i like the water pic idea though.

Tecumseh Lawn Boy Quits Running for No Apparent Reason

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baymee

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Tecumseh Lawn Boy Quits Running for No Apparent Reason

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