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'94 15hp no start

J

JonnyFish

New member
Friend of mine had a great running 15hp that sat for a couple of years and now it won't run so he gave it to me. I fiddled with it last fall and and got it to fire up a little if I pulled the ignition advance and throttle levers out a little so I though maybe the primary circuit was plugged in the carb.

This spring I tore the carb down and gave it a soak even though it looked great inside, made sure all the passages where clean and put all new parts in it. Put it back together and still wouldn't start. Fiddled with the timing advance lever again and it fired right up and ran great at idle for a minute until it slowed to a stall and now will not start again.

Just to be sure I checked for spark on both cylinders and it seems good and I'm getting 95psi on both. If I pull it to much I get fouled plugs so I know I'm getting gas. Beginning to think I've got some erratic ignition timing. At this point any suggestions would be appreciated. I downloaded the service manual and will start checking components but I'm hoping someone knows of common problems that might cause this.
 
I have had portables that had a toasted crank seal "run kinda" if you really messed with the spark advance.

I also blew a transfer cover gasket on my own 15 horse (1991 model) while I was back in the woods for a week and got that to run by messing with the advance and running the carb super rich.

In both cases the motors are "sucking extra air AND blowing fuel out of the ruptures".

Get a spark tester and make sure you have good spark.

If your spark is good start looking for a toasted seal.
 
Pulled the flywheel and they key is fine. No leakage from the upper seal either. Could be lower but that's a pita to check. No fuel leaking out from under the motor though. Can't find my spark tester so I'm getting another and will test spark strength tomorow.

I'll start ohm testing per the service manual after that I think.
 
Stator and trigger coil test fine with an ohm test. Going to test the ignition coils next. I'm beginning to think it's got to be the switch box. I looked up my part number (339-7452a13) and the only replacement I can find is CDI electronics for $150. Does anyone know if 339-7452a19 or another will work? I can find most others for around $80.

EDIT: Think I'm getting ahead of myself. I'm going to put the flywheel back on and use an appropriate spark tester. Correct me if I'm wrong but since the timing is mechanically controlled on this motor if I have strong spark then the switch box and stator are working correct?
 
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Got a new spark tester and low and behold weak spark. Upper cylinder will only jump a 1/4" gap and lower will only jump an 1/8" gap with the kill wires unhooked. This motor ran before being stored for about 5 or 6 years so I'm thinking the capacitors in the switch box have gotten weak? I know the stator could still be bad even though it passed an ohm test but I've never seen a coil go bad from sitting.
 
Before you go the cost of a switch box (and CDI makes a fine replacement for these models), you might want to drag the motor down to a local shop - doesn't have to be a "marine" place, anyone that works on 2 strokes (dirt bike place is fine) and get them to check it with a DVA meter or at least with a DVA adapter.

If you can confirm that the stator is throwing enough voltage (150-300 volts at (cranking) speed) then you know the stator is ok. The voltage being passed by the switch box to the sparkplug coils should be similar (they, the spark coils up it into the 35,000-40,000 range).

So for maybe half hour of shop time you can isolate "where" you are losing power in the system.

Alternately, if you can get ahold of a DVA adapter (used to be able to get them on-line for 20 bucks or so - can check Amazon) it simply plugs into your multi-meter (becoming the leads) and turn it into a DVA meter - works fine for home use...
 
I'll try to get my hands on an adapter. Seems like something I should have anyway. All the 2 stroke guys are booked for the next month around here!
 
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