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3.5 HP briggs

J

JD Mike

Member
I just changed a bad magneto/ignition coil on an older 3.5 HP vertical Briggs and Stratton engine. I put it all back together with new points and condenser and checked for spark before I put the shroud back on. All seemed good. After pulling that thing until my arm about fell off I decided to check spark again and I noticed it fires a little initially, but as I go it gets weaker and then disappears. I got it to sputter a few times but it never did start and four different plugs made no difference. Any ideas?
 
What kind of shape is the flywheel key in? If sheared just slightly and using a points setup the engine will not fire properly. Turning the engine over by hand you may not produce enough spark. Is the flywheel to coil clearance set properly. I always used a business card to set this distance. Briggs once made and still probably does make an electronic kit to install on the old points motors to do away with the points. Good investment. Kind of eleminates the sheared flywheel key thing and actually allows you to advance the engine timing. Could also be a bad spark plug. I had a Honda engiene that would start and run fine for about a minute and then die. Wait a couple minutes and it would restart. I thought it was running out of fuel. The faster you ran the engine the quicker it would quit. After going over and over the carb I changed the plug. Problem solved. Plug was failing when it got hot.
 
Here's what I found out....the flywheel key kept shearing enough to throw it out of time...I believe it was caused by some sort of internal damage to the engine...it started and ran briefly after I put a new key in, but it has a terrible knock. I guess its time for a big teardown! MidTn, you were excatly right about the sheared key...thanks!
 
No, more than likely there is nothing wrong with the engine, you did not tighten the flywheel nut/clutch enough and if you do not do that, it will shear the flywheel key as often as you put a new one in, put a new key in it and tighten it as tight as you can get it, as a flywheel and a crankshaft are tapered at different anglesand the nut has to be tight to draw the flywheel down on the shaft and "lock"
 
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