metriccrescentwrench
Commander
- Joined
- Oct 22, 2007
- Messages
- 2,598
1990 Johnson 200. A little history (apparently this engine has multiple issues): Compression is 80 to 82 on all cylinders. Previously this engine, as soon as quick-start turned off, would intermittantly drop rpm and often die. The OMC service manual test procedures indicated I had a bad timer base, so I installed a new timer base and that particular problem is gone. (Note - it also has a new power pack - that is the one and only time I listened to an "expert" and replaced a part without following the factory test procedure - the new power pack didn't change anything).
HOWEVER, both times I've had the boat out since replacing the timer base, after running for 15 or 20 minutes it would idle very poorly and die, requiring me to keep my foot in the throttle just to keep it running, whereas for the previous 20 minutes or so it idled fine. Once I get on plane it seems to run ok, but feels like it's down on power just a little. I'm pretty sure it's had this problem all along, it's just that the bad timer base overshadowed what it's doing now. I retested the timer base last night after getting back from the lake and all results were essentially unchanged from when I had originally installed the new one, so it's not the timer base all over again.
I'm pretty sure the stator is OK, resistance to ground is infinite, port charge coil is 734 Ohms, starboard charge coil is 767 Ohms (spec is 985 +- 25 but I'm using a Fluke instead of an analog meter, and I've been told as long as both sides are close it should be ok), and charge coil cranking outputs are 183 and 188 volts (spec is minimum 130).
I don't feel like this is a fuel or carb related problem because of the fact that it only seems to show up after running a while. The aluminum fuel tank was thoroughly cleaned when I rebuilt the boat last year, it has all new fuel lines, new primer bulb, and a new Racor filter/separator.
All I can think of right now is a coil going bad, but how can I test for that other than blindly swapping out coils one at a time? Would I be able to tell anything by checking the insulation resistance between primary and secondary windings with a megger? Maybe heat the coils to 160 F (?) in an oven and then do a resistance check?
Thanks in advance (and my son will appreciate the help also, he's ready to ski and wakeboard).
HOWEVER, both times I've had the boat out since replacing the timer base, after running for 15 or 20 minutes it would idle very poorly and die, requiring me to keep my foot in the throttle just to keep it running, whereas for the previous 20 minutes or so it idled fine. Once I get on plane it seems to run ok, but feels like it's down on power just a little. I'm pretty sure it's had this problem all along, it's just that the bad timer base overshadowed what it's doing now. I retested the timer base last night after getting back from the lake and all results were essentially unchanged from when I had originally installed the new one, so it's not the timer base all over again.
I'm pretty sure the stator is OK, resistance to ground is infinite, port charge coil is 734 Ohms, starboard charge coil is 767 Ohms (spec is 985 +- 25 but I'm using a Fluke instead of an analog meter, and I've been told as long as both sides are close it should be ok), and charge coil cranking outputs are 183 and 188 volts (spec is minimum 130).
I don't feel like this is a fuel or carb related problem because of the fact that it only seems to show up after running a while. The aluminum fuel tank was thoroughly cleaned when I rebuilt the boat last year, it has all new fuel lines, new primer bulb, and a new Racor filter/separator.
All I can think of right now is a coil going bad, but how can I test for that other than blindly swapping out coils one at a time? Would I be able to tell anything by checking the insulation resistance between primary and secondary windings with a megger? Maybe heat the coils to 160 F (?) in an oven and then do a resistance check?
Thanks in advance (and my son will appreciate the help also, he's ready to ski and wakeboard).