2005 MPT1200 350 Spark, fuel, fires intermitten, compression 118 both no run

RedfishM1

As in the title. Ran fine, jump started my mower and this condition appeared. Could the jump start have damaged the ignitor which would make it fire intermittently and not run but fire in a weak manner as if out of time. Also, new timing belt months before and no issues.

BGW

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Cartmaster

check all the plastic connectors in the ignition circuit for corrosion or a loose connection. If it is firing, i doubt the igniter is bad, its usually all or nothing with those. Also check your ground connections and battery terminal for the same.

RedfishM1

Could it be that the voltage regulator is messing with it since it happened after I jumped my mower?

Cartmaster

I cannot really se the VR making any difference to the ignition circuit, unless something is pulling too many amps. More likely to be a poor connection somewhere that was made worse, by pulling a lot of amps to jump start another vehicle.

RedfishM1

Contact cleaner and wire brush time. As I think about it, it seems to fire super retarded..atdc as the exhaust gets warm but no pop with the manifold loosened. Has anybody tried a honda style igniter from GY6 type engine? I'm not a scooter guy for sure but the engine family is the most popular and cheapest in the land.

Cartmaster

Dont quote me on this, but in all my years working on Those engines, i never had an ignitor part fail. either you got a spark, or you didn't. 99.9% of ignition issues have been either bad connection somewhere or a faulty coil. Check also the the little plug that connects the pickup / pulsar in the engine. These carts commonly suffer with corrosion in the plugs/sockets that connect the ignition parts to the wiring.

RedfishM1

Have you ever seen a flywheel shear a key? That is my next try.

RedfishM1

What puzzles me is that the spark is consistent but not the firing. All connections are good with no impedance variation before and after. Original condition: Cart was set on 1/4 throttle to charge mower...mower started drove off, came back and cart was not running but starter was driving /turning the engine. Seems 1 cyl fires on downstroke (very weakly). Driving me crazy.

CP241

Are you sure on the 118psi compression number? That seems awfully low to me.

Perhaps the jump start was just a coincidence and has no real connection with the motor not running now.

If you just changed the timing belt, perhaps it skipped a tooth and timing is off? Or have you checked valve lash adjustments?

Cartmaster

Good call CP. Or maybe the tensioner has come loose, or maybe the top cam pulley. Easy to check that one. Regarding shearing a key, no, never seen it as the crank is also on a taper, so rarely comes loose.