Wednesday, March 12, 2014

Briggs & Stratton 3 5 Hp Won'T Start/Run

I have a 15 year old pushmower with a 3.5 hp Briggs Stratton engine that suddenly died on me. I bought this at Murphy's Mart/Ames before they went out of business and the engine model is one of the first I bought that had a blade-brake on the handle (deadman switch) and priming-bulb on the engine. I think this was one of the early models that didn't use an aluminum shear-pin on the blade-to-shaft mounting -- so, when you hit something you have to buy a new mower.
Anyway, I've replaced the carburetor/priming-bulb maybe 4 years ago and I was mowing Saturday. It was acting like it was running out of gas, which wasn't unusual but when I re-filled with gas and restarted - it kept dying out like it was still running out of gas. Finally dying and no amount of gas priming, pulling or even using starting fluid would get it going.
Priming bulb was throwing plenty of gas, I could see it when I took off the air cleaner. I pulled the spark plug and it was very clean AND dry with a slight 'whitish' cast on the tip rather than covered with any carbon soot.
I'm suspecting this is an electrical problem but seem to remember this mower was built so you can't pull off the flywheel to get to where the condenser/points normally are...
Anyone familiar with this make and what if anything I can do to get it going?

Did you check for spark when you had the plug out?? Also was there any backfiring, smoke or other noises etc when it quit?? If you post the engine numbers I'm sure the pros will help you out soon with the flywheel (I've never seen a flywheel that won't come off, But may look like it with the starter clutch on it).. Roger

I doubt the engine has points if it's only 15 years old. I'm sure the flywheel comes off (they all do), and has a shear key. The dry white plug makes me wonder if you have compression. Does it? Was it out of oil?

I haven't had a chance to even look at the mower but will post the engine #'s when I get them.
It's been awhile since I've had to work on this mower; just remember that it was not as 'field serviceable-friendly' as older mowers.
Regarding the oil... I had just changed it, sharpened the blade and cleaned the plug. This was the first mowing I was doing with it this Spring -- basically ran through one tank of gas and it died. I'll look for spark tonight too. When I had the problem it was bright and sunny so I couldn't really see the spark -- and fortunately, I have a spare mower that fired up and finished mowing with.
Does the fact that the priming-bulb was squirting a good stream of gas indicate that the relatively new carburetor is probably Ok!?

It indicates you at least have fuel @ the carb that's why Cheese is asking about compression.. It should make the plug wet if you get a good stream from the primer.. If you don't have a compression gage, put you'r finger over the plug hole as someone pulls the starter.. ((Keep the rest of fingers away from the plugwire, or you may test for spark the hard way LOL)). You should feel a good pull push on you'r finger it may even push you'r finger out of the hole.. Lets Hope.. Roger

I didn't get to work on mower last night but did get the model #'s ...
Its a Murray lawnmower 2022 X 2B
Briggs and Stratton 3.5 hp 95902-3107-01-96020852
Just looking for any things known to fail on these engines...
From some other recent forum posts here, I'm guessing that there are no points on this mower under the flywheel and that if it is an electrical issue that there's possibly a replacement electronic unit that can be installed (?)
Any estimate on the cost? How do you install the replacement electronic module?

It has an armature that can be replaced, but that is it for electronic components. There is a kill switch that is operated by the deadman bar cable that could be killing the engine, or the armature/coil could be bad. Testing for spark would be the first order of diagnosis.
The mower is 13 years old and has no points. The flywheel is removable on this just like all others, and has a shear key, but these shouldn't be of concern unless you hit something and sheared the key.

Tags: briggs, stratton, start, Briggs Stratton, this mower, flywheel that, good stream, have compression, post engine, push finger, replacement electronic