2008 Husqvarna 10527SB-LS Snow Thrower with Tecumseh LH358SA-159647A engine. Engine has always run fine until now. Everything on the snow thrower is working fine right now. It gets a lot of miles -- equivalent of 500 ft driveway including dirt & gravel & grass areas. Far northern NY near Lake Champlain/Canada; i.e., frequent usage.

While clearing the last two snow events, after running for about 45-60 minutes, engine started surging mildly and acting like it was going to stall, especially when I was not moving. When I drive ahead into fresh snow, it recovers for the most part under load. Stop moving, and it starts faltering again. Eventually, it seems to just run weak with a load, too, as if bogged down, but still works.

I had already replaced the spark plug for the season, but replaced it again after first incident. Second incident ruled out the plug.

I have always added Sta-bil immediately to newly filled gas cans ... within an hour. And the gas used right now is only a few weeks old. I keep everything clean and lubed. Oil changed around every 12 hours running. Book says 25 hours.

If I let it cool off for a while, it runs okay. After the first incident I let it run for 30 min test after replacing the plug and oil (the oil was already recently changed, too). 30-min. test okay, but wasn't next time it snowed ... trouble in 45 min. Was nearly done for the day because it was only 5" light fluffy stuff so I was able to move fast. Finished shortly after it started acting up. Let it run while cleaning it, and it was erratic. Shut it down, let it cool half an hour, ran fine.

It still starts like a charm just as it always did. One or two pulls, the usual prime & choke routine. Never used the electric starter ... no juice in the shed.

I think go for the breather first, but once I take it apart that far, I feel like maybe I should take the shotgun approach and give it a 10th birthday overhaul ... replace carb, breather, fuel lines, flush out the gas tank, replace coil, muffler and the associated gaskets. MAYBE. Because it's a 75-minute test between each cure I try, and I'd have to wait for parts in the mail between each try.

I don't see a fuel filter or pump, but will replace them if I find them when it's apart.

I've never had the cover off the engine, so we haven't made friends yet, and I never wanted to, but I can do this stuff at gunpoint, and no machine in a snowstorm is gunpoint. Really prefer not to pay somebody else and end up with no fix anyway. Good help is hard to get. One time I let the dealer work on it they broke it two ways. It was the last time.

Here's where you come in. Any experience with this kind of temperamental engine? Any really common, typical known cause and fix?

Thoughts on putting carb cleaner additive into the gas and run it for an hour? (I think that would be a very long shot.)

I might just replace the breather foam and clean the carb (properly).

Thing is, I don't have much time between snow storms to get to it whenever the parts arrive (RepairClinic.com has them all in stock.)

The biggest thing baffling me is how any fuel or air issue could show up only after running for a long time, then go away until next time it's run for a long time, apparently more than 30 min.

Could the coil be acting up only after being hot for a long period?

Any thoughts much appreciated before I get out the shotgun dollars or experiment with gas additive, letting it run for an hour ... twice.

Thanks.

to SBF dk56

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Valve Clearances

My thought as well, especially because it takes time to develop, but goes away once the engine cools.

The Tecumsehs can develop too-small valve clearances over time (with use). The valves apparently kind of hammer into their seats a bit, so they sit a little too far back.

The valve clearances need to be in a certain range. Too-small, and the valves can be held open slightly, due to thermal expansion, as the engine gets hot. This reduces compression & power, since the combustion chamber isn't being fully closed as the engine fires. It can also damage the valve or its seat, over time. If the clearances are too-large, the compression release can't do its job properly, so the engine can be physically harder to pull-start (or electric start).

Checking clearances is not difficult, and doesn't really require special tools. But you do need a set of flat feeler gauges. Adjusting clearances is a bit more involved. But check them first, at least.

An example of feeler gauges, which would also be available at an auto parts store:

This Tecumseh's Technician's Manual is a good reference, especially if you know what procedure you need to do.

https://www.snowblowerforum.com/foru...-4-stroke.html

When a machine works fine for a while then starts acting up it might be a faulty gas cap. Try running it with your cap loosened but still on, or with a piece of plastic with a hole in it covering the hole. If it runs okay then you might have a faulty gas cap which does not vent. That vacuum it creates stops the fuel from entering the system and starves your carb. You can drill a small hole in the defective cap in the meantime until you pick up a new replacement cap. It happened to me last year.

Good point, shame on me for not thinking about that. It's a very easy thing to test for, too.


One way to check for this is to run until you have the problem. Then either shut down briefly (not really required), or just quickly loosen the gas cap (enough that air can get in), and then tighten it down again. If it suddenly runs fine for a while, you have a plugged gas cap, which is not venting correctly.

The advantage to checking this way is you can be sure whether it fixes your problem. If you just loosen the cap, or drill it, and then try running, you have a harder time proving it's fixed. If the problem doesn't appear, it might be because of the fixed gas cap, or maybe you just got lucky. But if you wait and reproduce the problem, and then allow the tank to vent (unscrew the cap), you can see if it's suddenly better. And if it *doesn't* help, you know that too.

To test the cap more quickly, fill the tank as full as you're comfortable with. The less air in the tank, the more quickly you'll draw a vacuum, and starve for fuel. Then try running it, either blowing snow, or just letting it run in the driveway, if needed, until the problem happens.

A fuel venting issue would appear MUCH faster than 45 minutes. My 2 cents.

Good advice Red.

Thanks for the clear and thorough explanation, RedO. Seems to me I used to have a flat feeler gauge cluster. Must've disappeared with my timing light when I stopped replacing points & condensers in cars. I've never had the head off any engine, though. Will look at the manual and explore from there. Not sure I'm prepared to do this but I'm prepared to find out. DIY: learning to learn what needs to be learned and doesn't, and paying for the education.

The head doesn't have to come off to check clearances. You just remove the little crankcase breather cover, and check them there. Also the spark plug, so you can set the piston height correctly.