Issue Shorthand Name: "Fast Starter Syndrome"
Symptoms: (some or all)
- Bike won't start
- Bike has sat for a period of time (perhaps days or weeks)
- Hit the starter and in the first 1/2 a second it just doesn't sound quite right.....and after a couple seconds not a hint the bike firing.
- Starter seems a slightly higher pitch.
- Starter seems to spin a little faster than usual.
Okay. this is interesting as it happened to me just last week. Here's my scenario.
- The bike had sat for 2-3 weeks in a heated garage (temps ranged from +5c to +15c)
- Pressing the starter and the bike turned over as usual for maybe a half second
- Suddenly the pitched change and the starter was spinning much faster.
- The behaviour of the bike was very much like the starter was not even engaging the engine. The usual pronounced "chuffing" that occurs when a bike is starting was almost gone. But there was still a faint hint of it.
- I had my Dad try starting the bike and I went around to the back and put my hand over both exhausts. There was virtually no air pressure coming out the exhaust. And in fact I could feel a slight suction, then a slight pressure (and I do mean slight) in both directions as the starter was spinning.
- I Gave up on the bike. Worked on some other stuff in the shop came back and tried again one last time about 15 minutes later. It fired up without a problem.
To my mind this has nothing to do with sticking valves or flooding. If it was related to a sticky valve the bike should have still started on 3 out of 4 cylinders. If it was flooded you would either get hyrdaulic lock on one cylinder and nothing would move. Or the bike would just be stubborn to start (but still turn over at the same rate and with the usual chuffing).
First a bit of background.
The starter clutch on motorcycles is of a "slipper" clutch designed. (Dunno if that is the techinical term). While designs may differ usually involves two surfaces/gears joined with ball/roller bearings and a sloped surface. The whole thing works such that if one shaft spins faster than the other (the engine spins faster than the starter) then the ball rolls to the deep end of the slope and nothing happens. If the other shaft spins faster it forces the ball into the narrow end of the sloped surface (wedging it in) causing the slower shaft to engine the normally faster moving shaft. This is why on a motorcycle you can thumb the starter when the engine is running and do no damage. (On a car there is an actual gear that has to engage, and if you hit the starter when engine is running you get grinding noises, not good).
So here is my guess that I made at the time, and it still seerms to fit.
I think in these cases (or at least mine) the balls or roller bearings for whatever reasons were not "wedging" in. Effectively meaning the starter motor was not engaging the engine.
I think in my case there was just enough friction to cause the engine to slightly engage but as the compression of the cylinder built up it overpowered the slipper clutch before it could turn it over, the crank then rolled backwards with the residual compression (same effect when turning the crank by hand). This is where the slight suction\pressure cycle was being generated at the rear exhaust.
And the reason why the slipper starter clutch did not engage? I dunno! I am guessing anything from lack of oil cause it sat a bit. Or maybe too slippery an oil (Although the oil I am running is
approvied for wet clutch motorcycles). Or possibly the metal parts (ball, wedge and I think there is a spring in there) are getting worn and polished with age (the bike does have 178,000 km -- 110,000 miles).
All the above is my $0.02, IMHO, pure conjecture, etc etc etc. Especially since the problem happened only once and I haven't had a chance to pull anything apart and inspect anything.