old Murray/Briggs push mower

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I was cleaning out the shed by my grandmaws recently an decided to get the old Briggs push mower running that has been sitting for about 10 years, its around 15 years old. Its a flathead 3.5 or 4 hp, I drained the old gas, put a new diaphragm on the carb (carb mounts to tank) new air filter as the old one was dry rotted and a new spark plug and she runs like a champ. I do have a few questions. I drained the old oil and filled it with some Rotella 15W40, it holds half a quart, would it be safer to go with some SAE 30 due to concerns of viscosity breakdown or will the 15W40 suffice? Also, its a throttle free design, pull the lever and start it but If I tie a rope on the handle for it to stay running I can go by the throttle lever and rev it up by hand. Am I missing a spring that allows it to stay at a constant speed? Would Champion RJ19LM be the right spark plug? Thanks for any info. My grandmaw is glad that its running again. I offered to cut her grass but she refuses as she wants to do it, at 76 years old if that makes her happy I'm not arguing with her.
 
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It was spec'd for SAE30 so you can use that oil - no problem. The handle you are tying down is likely for the blade brake, a safety device. Many mowers do not have a throttle control and run at constant speed. Does it try to hold rpm on it's own? You are overriding the governor when you move the throttle lever. It should go back to "normal" when you let the throttle lever go. The RJ19LM should be correct. If you can post the engine model info we can be certain.
 
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It's a preset governor. There should be a spring pulling the throttle plate wide open when it is stopped. When the engine revs up to about 3000 rpm, the governor lever or air vane will pull the throttle plate closed. There's no interaction between the user control and the governor. Releasing the deadman lever stops the engine by cutting the ignition and engaging a flywheel brake. If the governor spring is missing, it will run but it will bog down and stall when trying to cut even a small amount of grass.
 
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SAE 30 may be best for it but I wouldn't worry about draining the 15w40 before running it a few hours - at least use it as an engine flush. I've messed with countless of those engines and never seen one that showed detectable internal wear. I think you could run it at 100% load with 0w20 and it would still last hundreds of hours.
 
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Originally Posted By: mobilaltima
Am I missing a spring that allows it to stay at a constant speed?
We won't know unless you post up the engine numbers. Use 30 weight oil.
 
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I have been running whatever inexpensive 15W-40 oil is available in all of my OPE for nearly 30 years with no ill effects. SAE 30 is fantastic oil,..... but the engine will last the same amount of life on 15W-40, also
 
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Hard to hurt those old Briggs, practically any oil will do in that. I have used J19LM, J8, CJ8 or H10 plugs in those, whatever I had.. They all work well.
 
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mobilaltima

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I drained the Rotella yesterday and used some Havoline straight 30. As far as engine numbers, the model is 10H902, the type is 0522 E1, and the code is 05031454. Its a 4.5 SQ
 
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