B&S Quantum starts on first pull, but then refuses to restart unless sat overnight

Kerryn

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Hi, I'm new here. I have a 12 year old Toro SR4 with the B&S Quantum (model 120000) engine. This engine has had minimal maintenance, honestly I don't recall last time spark/oil/air were changed, but it has always started on the first or second pull, though admittedly it has been sounding rough the last year,,,.

Well the brake cable broken recently so I gave it a full service, new oil, air filter, plug, blade and tuned up the traction cable and installed the new brake cable. Upon pulling the starter, it fired up first time and sounded great. I stopped it and then put everything away and came back to it an hour later to mow. This time it would not start at all. I check oil level, gas, removed and reinstalled the spark. I tried numerous things, through I don't really know what I am doing. In the end it just would not start so I gave up and put it away.

Today, I pulled it out again so see if it would work and it started before I even finished the first pull. I ran it for about a minute and it sounded okay but there was some "flutter" in the motor. Still it sounded better than before the service. I stopped it and got ready for the mowing. Came back 5 minutes later and it refuses to start again, exactly like the prior day.

I'm at a loss as to what to try next with this engine. It seems like the carb is getting flooded but there is no carb control on this engine that I am aware off. Also there is no primer or oil filter.

What do it need to look at next?
 
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Scrubcadet10

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Does it have a choke?
supply us with the full model number, should be stamped into the metal blower housing above the sparkplug or on flap above the muffler.
 

Kerryn

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The only identifying number in the engine I can see is this: 126T02-0224-B1 08021856. Is that what you are after?

Here are some pictures. Is this an oil filter? My operators manual makes no mention of changing an oil filter.

IMG_1259.jpeg

Number stamped on the engine.

IMG_1262.jpeg

No choke, primer etc, but what is this mechanism?

IMG_1263.jpeg
 

Scrubcadet10

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That is the carburetor... mixes air and fuel and delivers it to the engine...
Aha! you have an auto choke system... im willing to bet it isnt work like its supposed to. When the engine is COLD (hasn't run within a few hours) open the air box with a flat head or 5/16" screwdriver, remove air filter, in the hole is the venturi of the carb.
with the engine cold, you should see the choke valve (a brass color to it) you should see it closed. I would also clean all that grass off of it too... it's possible if its packed enough it may impede on the function of the choke.
here's a good video on the subject.
 

Kerryn

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That's video is really informative! Thank you. Looks exactly like my mower as well. Going to take it apart now....
 

Scrubcadet10

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Cool, if you have any questions, just holler.
there are no stupid questions
 

Kerryn

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I investigated the auto choke and the carburetor. Everything looked really clean. Auto choke appears to move like it should and the carb I took apart and cleaned with choke cleaner and air blasted it clean. There was no debris in it as far as I can tell and it had plenty of fuel so fuel delivery to the carb at least appears fine. It still doesn't start though.

At this point I'm now wondering if I am getting spark. Taking the plug out I see it is wet from my attempt to start so again, it looks like I get fuel into the cylinder. Going to test for spark now.
 
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Kerryn

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Testing outside I thought my coil might be dead as I was getting no continuity with it at all. But now inside, I am getting a reading of about 7.6 k ohms. Videos of this say it should be about 2.5 - 5 k ohms. Is my coil good or bad?
 

Scrubcadet10

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Testing the coil is meaningless, as hall effect trigger coils have internal components which affect the readings
usually coils only work, or the dont... now when they get older and heat up after the engine has been running they can start to fail when hot...
you should see a black small kill wire going to the coil, unplug it, and start the mower, if it runs good something is intermittenly grounding the coil and killing spark.
 
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tom3

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That engine with that automatic choke should have a thermostat on the exhaust outlet right at the muffler inlet. Will hold the choke open with the engine warmed some. Might check this to see if it's working.
 
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