My wife found this lawnmower just up the street while out walking with our granddaughter and hauled it home for me.
It's a Sears Canada Model 944.364372, Serial No. 050905M 005419. Engine is a Briggs & Stratton 6.75 MRS (Most Reliable Starting). No. 125K-0506-E1 05041258. (I don't know what to make of "6.75" -- evidently the engine has 6.75 of something, but there's no indication of what.)
The mower looks to be in not bad condition. The deck shows no rust bubbling up, and the safety bail is operative. Let's take a tour and see what's up with it.
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Muffler
An obvious fault is that the muffler is missing one of its two attachment screws.
That will likely call for a trip to the small engines place in Pickering, if I can't kludge a replacement.
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Muffler Update -- WEDNESDAY, SEPTEMBER 25, 2019
The small engines place fixed me up with a salvaged screw. Here's a view of the complete fastener complement for the muffler.
The screws have 2 1/4" long, 3/8" diameter shoulders, with 1/2" long, 1/4"-20 threaded ends. The hex heads are 7/16" A/F (across flats).
And here's the completed muffler installation, with the keeper ends cinched. (I applied anti-seize compound to the screws' threads.)
Much better.
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Oil
The oil looks reasonably clean, but it measures way overfull on the dipstick -- overfull enough that I'll want to siphon some out if I can get the machine running.
Sump capacity is 591 ml or 20 US fluid ounces.
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Oil Update -- WEDNESDAY, SEPTEMBER 25, 2019
My siphoning rig's pickup tube wouldn't fit down the dipstick hole. The idea of tipping the entire machine to drain out oil didn't appeal to me, so I've left the engine overfull with oil. It doesn't blow smoke when it's running, so it should be ok with that.
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Fuel
The tank looks empty. On the fuel tank's cap there's written "FRESH START CONTINUOUS FUEL PRESERVER". On the underside of the cap there's a little vial affair attached that says "REPLACE WHEN EMPTY", like so.
It looks empty to me. I guess it had fuel stabilizer in it that's dispensed at some slow rate. That feature is a new one on me; I've never seen it before.
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Blade
The blade is on the right way around, and it doesn't appear to be distorted, or badly nicked and dull. A sharpening will be in order, though. The blade screw's hex head takes a 9/16" wrench.
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Spark Plug
The spark plug is a Champion RJ19HX. Hex size is 13/16" A/F. (An acceptable substitute for the RJ19HX is RJ19LM.)
It's in reasonably good condition. Gap is a snug 0.030", as it should be.
A spark test revealed that there is spark, so there's hope for the engine.
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Compression
Compression measures 60 psi, which in my experience is fairly typical for well used mower engines. The engine should still have plenty of useable life in it.
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Air Filter
Loosening off a single, captive 5/16" A/F hex head screw gives access to the air filter.
This one is pretty dirty. A replacement is in order. (Replacement filter P/N is 491588.)
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Fueled Up And It's No Go
I took the air filter off so I could observe carburetor priming, and nothing happens. There's no evidence of fuel being pushed up out of the main jet when the primer bulb is pressed. The engine won't start. So, the carburetor has to come off for inspection.
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Carburetor Removal
- Air cleaner cover and filter element.
- Small black cover above the air filter -- one pan head No. 2 Phillips recess screw, 10-32 x 13/16".
- Air cleaner base -- three hex washerhead screws, 10-32 x 5/8", 5/16" A/F. Note the gasket, which will likely remain stuck to the carburetor. Note also the crankcase ventilation tube to be reconnected at reassembly.
- Fuel supply tube at carburetor -- one spring clamp. Be ready with a suitable plug to plug the end of the tube. A bit of 5/16" diameter rod, or the shank end of a 5/16" drill will do nicely.
- Carburetor -- two hex washerhead screws, 1/4"-20 x 5/8", 3/8" A/F. Unhook the governor link. Note the O-ring at the intake tube. That O-ring must be in place and intact.
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The Carburetor
The carburetor is an ultra simple float bowl type, having no adjustments. There's no idle circuit to get clogged up; there's only the main jet that's easily checked for clogs.
To remove the float bowl, use a 1/2" socket wrench on the bowl's fastener. The float bowl on my carburetor was clean and free of debris.
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The Primer Circuit
Some study of the air cleaner base and its gasket will reveal the operation of the primer circuit. Pressing the primer bulb closes off the bulb's vent hole, and forces air through a channel in the air cleaner base. Priming air is ultimately delivered to the carburetor via a small orifice at one side of the carburetor's mouth. From there, air is channeled within the carburetor to the float bowl, where it forces a dollop of fuel up the main jet and into the carburetor's throat.
Given that the primer bulb is sound, priming failure is most likely due to poor seating of the air cleaner base to its gasket and the carburetor's mouth. The integrity of that seating is absolutely crucial to primer operation. Replace the gasket if in doubt.
On my engine, the primer resumed working after I reinstalled the air cleaner base on the carburetor. The engine became startable. Something must have been amiss with the seating of the air cleaner base.
The engine ran poorly with the air filter element installed; the air filter element is evidently badly clogged. The engine runs fine with the air filter element removed.
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Update -- THURSDAY, SEPTEMBER 26, 2019
With a new filter element installed, the engine runs fine. I've never seen a filter element so badly clogged as the one that was on this engine.
Further to the matter of the air cleaner base gasket, I obtained and installed a new gasket (P/N 795629), and that didn't work -- with the new gasket, I had no priming. Reinstalling the old gasket restored priming. Here's a view of the inboard side of the air cleaner base, and the two gaskets.
The old gasket that works is at the left; the new gasket that doesn't work is at the right.
On the old gasket, note the full impression made in the gasket's surface by the priming air channel's ridges. That gasket fully seals the priming air channel; hence, priming is enabled.
On the new gasket, there's little impression from the priming air channel's ridges. The air channel leaks, and priming doesn't happen.
The fault lies in the design of the air cleaner base's fastening scheme, and the non-rigidity of the air cleaner base. The gasket doesn't get squeezed with uniform pressure all the way along the length of the air channel.
Maybe if I left the new gasket in place for long enough, the gasket would get squeezed sufficiently that it would seal the air channel. Another solution might be to install the gasket with a smear of silicone gasket maker.
Anyway, for now I've left the old gasket in place, ragged though it is.
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In Conclusion
The lawnmower was discarded on account of two minor faults that had a big impact on the machine's behaviour. The leaky primer circuit was causing failure to start, and the clogged air filter made for very poor engine performance when I did get it running.
I attribute the leaky primer circuit to questionable design. The clogged air filter was just neglect of routine maintenance.
With attention paid to those two faults, I've got a perfectly serviceable lawnmower, with plenty of life left in it.
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