Just a thought here, but have you tried checking for spark while its cranking? You might be surprised at what you find.
My rider was getting ornery and it was taking a long time cranking to get the engine to catch. I do regular maintenance, changing the oil and filter, checking fuel and air filters, and checking/cleaning the plugs much more often than usual, (because the engine is using oil). Did that all again-no difference.
Then i was checking for spark and noticed that when it wouldn't start there was no spark, but the spark was fine once itwas running.
So I checked the magneto's air gap, and it was a tiny bit off, so I adjusted that. Still no difference in starting, and the same pattern of no spark when cranking, but ok whem running. I picked up a "used but good" magneto and swapped that one in. Same thing was happening at cranking speed no spark, but fine once running . I figured the magneto was as bad as mine, returned it for another one. Same thing.
Hmmmmmm. What are the odds 3 magnetos are all bad in exactly this same way?
So I figured that it was most likely something else. But what to check next? I'd replaced the starter solenoid only a year previously, and the ignitionn switch at that same time. The power and ground wires were clean and tight and the battery was up to snuff too.
i didn't want to try the carburetor yet so that the starter as a possibility.
Since starters are available from sources other than Briggs now,(and their price has dropped like a rock) i ordered one. This is the third starter thar's been on the engine, along with a couple more starter gear changes. According to the engine parts list the first 2 were the correct starters for that engine in that application.
My engine is an 18.5 hp horizontal twin and I found out that there are 3 different length starters that COULD be used, one of which is at least a half inch longer than the original, so THIS time i ordered the longest one. Once installed the engine cranked over faster than it EVER had before-even when brand new. I was shocked at how much faster.
After installation of the longer starter it started very easily too- in a second or less, compared to 20-30 seconds or more of cranking before it was in..
This was without changing ANYTHING else besides what had already been done.
So, after doing some research, here's the poop.
On many Briggs engines, the magneto will not produce ANY spark below a certain cranking rpm.
Not just a WEAKER spark-none whatsoever.
Depending on the ambient temp, and other factors, such as battery strength, ENGINE OIL WEIGHT, and what starter is installed, its possible that an engine may be cranking over JUST SLIGHTLY below that needed for the magneto to fire (maybe only 25rpm too slowly)-until you're cranked it over long enough for the engine's internal friction to begin to decrease as it goes through more revolutions, after which it spins over just a LITTLE bit faster, but its enough to be above the rpm needed for the magneto to fire. It's also more liable to start quicker in warm weather-but many engines are-for any of several reasons.
