Lawnmower gets hot and quits

On Wed, 20 Jul 2005 14:36:14 -0500, Duane Bozarth

You are right. The vent is plugged.
The cap is hard rubber with a rubber washer that has 2 small holes in it. Behind the 2 holes is another flat thin rubber washer that has deterioated and the deteriorated rubber is actually protruding partially thru the tiny holes. I suspect it completely stopped up the vent holes.
I tried removing the deteriorated rubber, but can't really get to it. If she comes in bitching about the mower dying again, I'll add a new vent hole thru the cap.
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replying to Sherman, Matty wrote: This info may be old but it is the funniest string I have ever read. It is 12 years later now and I hope that "she" is OK and that "he" is happy with his new wife.
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Sounds like a valve clearance problem to me. Either that, or the fuel line is too close to the engine. But more likely valve clearance.
I took a small engine repair course years ago. To fix this, you have to take off the motor cover, the cylinder head, and then remove both valves. Grind a little off the bottom, ch eck the clearance, and put it back together. Requires some specialized tools, and some replacment gaskets.
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Christopher A. Young
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Stormin Mormon wrote:

.....
That sure wouldn't be the first place I'd look....more likely electrical as someone else noted w/ thermal expansion...besides the magneto, it could also be the plug ceramic...(look, look)...oh, I see he did change the plug so it's upstream of there...
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I may well be misaken. But I've seen valve clearance problems several times before. Though, coil problem is a bit easier to fix. How about find another coil to try for awhile?
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Stormin Mormon wrote:

How about checking for spark when hot first, as has already been suggested (several times)????
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What makes for less clearance after 4 years of running? I'd have thought the opposite would happen. Or is it worn on the stem and not contacting properly so relieving the valve seat brings it back?
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wrote in message

have to

valves. Grind

together.
thought
contacting
No, the valve seat sinks into the block. There's supposed to be a little clearance between the lifter and the tip of the stem, so you grind the end off. That's for the more common valves in block type., not on an OHV..
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wrote in

Or the seat and the valve face wear. In that case, seat and valve regrind or replacement....
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Have you tried cleaning or replacing the air filter?
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Larry Wasserman Baltimore, Maryland
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wrote:

This is a push mower Craftsman about a 4 hp.
I removed the gas filter bowl and it was clean. No change after cleaning and reinstalling. Started right up and ran for 10 minutes..
After it dies hot, it will not start or even try to start. The pull compression feels about the same hot or cold. But I can't measure the vacuum (or can I?)
Has to cool down and at some point it cools enough to start on first pull and runs good for 10 minutes.
I will check for spark next time it is dead.
Sherman
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I fail to see the problem. With a strategically placed cooler of beer, you are being forced by nature to take appropriate breaks. This is for yourgood health.
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wrote:

Actually, I lied. My spouse does the mowing and she is getting angry at me because the mower is dying. Don't get me wrong, I will mow when it needs it, but in 30 years, she has never let it get long enough to need it.
I need to get this thing diagnosed and fixed pronto.
I'm thinking I could use one of those piercing shroeder valves on the intake manifold to measure for vacuum while I yank the rope. Wonder if it would work. Or I could test compression thinking maybe the compression would be different if the suction was off due to valve not seating..
Sherman
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Sherman wrote:

Your wife mows? Get her this: http://www.cleanairgardening.com/brillux38ree.html
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wrote:

Ok, I'm also thinking I could pull the valve cover and observe the valves when hot or cold. What am I looking for? As the crank lets the valve close, it should become loose and I should be able to grab the stem and lift and let go and hear the valve seating - right? It would probably be a different sound if it was not seating.....
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Sherman wrote:

If they're not seating, you won't have compression when you crank...
Did you find out if you have spark when it's hot or not yet? I'm still thinking electrical is more likely the culprit...
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Forget the damn valves, that's not the problem. You've been given sound advice by several people: check to see if you have spark when it's hot and not working. I'm betting you don't, because the magneto has failed.
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Doug Miller (alphageek at milmac dot com)
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replying to Sherman, D Mecate wrote:

Until the electrical issue is addressed, you're simply fiddling with parts that are more than likely functional; change out that ignition coil.
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wrote:

This is an outside possibility, but I had a lawnmower with a leaking head gasket. Problem was it would leak only when the engine was hot. The problem was getting worse and worse and I could not figure out what was wrong. The gasket finall degraded to the point that that when I happened to brush my hand ove the head, I could feel the hot gases leaking from the head gasket. Gary Dyrkacz snipped-for-privacy@comcast.net Radio Control Aircraft/Paintball Physics/Paintball for 40+ http://home.comcast.net/~dyrgcmn /
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Sherman wrote:

Many, many air-cooled engines develop this problem. The odds are overwhelming it's your ignition module, and they're a bastard to troubleshoot [except, of course, by replacing the module].
As soon as the engine starts to cool -- long enough to check for spark -- the module cools down enough to check as OK. It's very possible you'll check the spark and it'll be OK.
They're easy to change, but shop carefully. The price for replacement can vary radically.
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