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Author Topic:   Frustrating engine behavior

69boo307 posted 03-12-2009 09:27 AM ET (US)
I have sought advice for this on a couple of engine-specific forums, with limited response. Figured I'd see if the collective wisdom here had any ideas.
I've had problems with the 1990 60hp Johnson 2-cycle on my Striper ever since I bought the bought last fall. Long story short, I worked out many of the problems, and it has the following new components:
-powerpack
-coils
-plugs
-fuel lines
-carbs cleaned/rebuilt
If I take the boat out and run around at cruising speeds without alot of stopping, it typically runs great. The problems develop if I am fishing and doing alot of stopping/starting, or it is sitting turned off for a long period in between running. For example, tuesday I spent about 2 hours fishing, with the engine only being run for a few short periods of time. On the way back to the boat ramps I kick it up to 5200-5300 rpm, and after about 2 minutes the boat simply loses power and will not go over about 3800-4200 rpms. I can throttle it back and it will run like that the rest of the way, but doesn't respond to the throttle beyond that. I can stop and it'll get back on plane just fine, but again won't get up to cruising speed.
It almost seems like the fuel supply becomes restricted, or I am dropping a cylinder. I have heard of a malfunctioning SLOW system on OMC engines that is basically an RPM limiter, but usually that is remedied with the new power pack.
The spark plugs look good, the fuel line bulb doesn't go slack when this occurs, there are really no 'tell-tale' signs of a problem. I've done all kinds of diagnosis from spark checks to tracing circuits for possible grounding, going through the fuel system, I just can't find a problem.
Any ideas? I'm up for anything at this point.

adlert posted 03-12-2009 11:40 AM ET (US)
Sounds like you still aren't quite sure whether or not you have an ignition or fuel problem causing your symptom. You're going to need to perform a test to determine which it is and sometimes these sorts of tests are best performed while the engine is actually acting up.
Testing for proper spark on a boat on plane is easy and can be safely done. I suggest that you pack an inductive timing light aboard next time you head out. If you clip it over each spark plug lead in turn when the engine is acting up (you're going to need a buddy to drive) and then point it at yourself you'll be able to see whether or not a particular cylider is indeed firing real time as your symptoms are occurring.
Causes of ignition problems that you have not yet addressed through your parts-swapping include charge coils and trigger coils. Both of these components are located under the flywheel and often first exhibit breakdown symptoms when warmest. It is not uncommon for powerhead temperatures to peak a short time following a running period and subsequent shutdown.
The charge coils are incorporated into the "stator" and the triggers are mounted on their own swiveling base.
tedious posted 03-12-2009 11:53 AM ET (US)
Is this motor up to date with service bulletins? As I recall there were 4 or 5 TSBs intended to address overheating problems.
Tim
69boo307 posted 03-12-2009 04:50 PM ET (US)
I wasn't aware of any service bulletins, I'll have to try to find that information.
The stator and/or timer base are indeed the only ignition components I havn't checked or touched. I don't own the tools to remove the flywheel, and i haven't tried to borrow or 'rent' them yet. I've been suspicious of those components, but wanted to rule out all the more affordable options first. Considering that the epoxy on the back of the ignition coils and powerpack were all cracked from age, it's possible the more expensive parts under the flywheel are in the same condition.
tedious posted 03-12-2009 05:57 PM ET (US)
I'd recommend checking it for overheating before you spend any more on expensive parts. Have you tested the temp sensor and warning buzzer? I believe these motors tend to overheat if run consistently at about 3/4 throttle; at that point you're at maximum spark advance but you're not running as much fuel through as you would be at full throttle.
I'm probably all wet, but your symptoms are consistent with overheating.
Tim
Phil T posted 03-12-2009 07:25 PM ET (US)
I think the simplest thing is to rule out a fuel problem. How old is the tank, bulb, hose and fittings?
Run the boat on a seperate fuel tank and fuel line.
powerstroke posted 03-12-2009 07:58 PM ET (US)
fuel
69boo307 posted 03-13-2009 10:51 AM ET (US)
Thanks all.. I have pretty much ruled out a fuel issue, I have thoroughly been through the fuel system. If it was fuel, it seems like it would be more consistent. Doesn't make sense that I could run for 2 hours without missing a beat one day, then have a problem the next. The difference seems to be the operating conditions, ie. amount of stopping and starting or idling.
thanks adlert for the tip on the timing light, I am going to try that out (when this crappy weather moves out and I can take the boat out again).
Tohsgib posted 03-13-2009 11:08 AM ET (US)
Trigger or stator is probably going south.
Landlocked posted 03-13-2009 06:41 PM ET (US)
If it were a semi clogged inline fuel filter, it would run strong until the fuel in the line downstream of the blockage ran out and then it would stall. Allowing it to sit for a moment would then allow fuel to work through the blockage once again filling the downstream portion of the line.
It would be a cheap test to replace the filter and see what happens.
Ll.
Landlocked posted 03-13-2009 10:03 PM ET (US)
Blockage in the filter could also be intermittent. I once had one on a lawn mower that had a water bubble in it. When the bubble got in the way, fuel flow stopped. When the bubble was on the side, fuel flow was unaffected.
Ll.
wezie posted 03-14-2009 12:50 PM ET (US)
Once upon a time, I was told that after great problems with the engine, the problem was a fuel filter/screen in the bottom of the fuel pick up inside the tank.
After replacing this very small item, all was well.
Just a thought.
wezie posted 03-14-2009 12:50 PM ET (US)
Once upon a time, I was told that after great problems with the engine, the problem was a fuel filter/screen in the bottom of the fuel pick up inside the tank.
After replacing this very small item, all was well.
Just a thought.

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Author	Topic: Frustrating engine behavior
69boo307	posted 03-12-2009 09:27 AM ET (US) I have sought advice for this on a couple of engine-specific forums, with limited response. Figured I'd see if the collective wisdom here had any ideas. I've had problems with the 1990 60hp Johnson 2-cycle on my Striper ever since I bought the bought last fall. Long story short, I worked out many of the problems, and it has the following new components: -powerpack -coils -plugs -fuel lines -carbs cleaned/rebuilt If I take the boat out and run around at cruising speeds without alot of stopping, it typically runs great. The problems develop if I am fishing and doing alot of stopping/starting, or it is sitting turned off for a long period in between running. For example, tuesday I spent about 2 hours fishing, with the engine only being run for a few short periods of time. On the way back to the boat ramps I kick it up to 5200-5300 rpm, and after about 2 minutes the boat simply loses power and will not go over about 3800-4200 rpms. I can throttle it back and it will run like that the rest of the way, but doesn't respond to the throttle beyond that. I can stop and it'll get back on plane just fine, but again won't get up to cruising speed. It almost seems like the fuel supply becomes restricted, or I am dropping a cylinder. I have heard of a malfunctioning SLOW system on OMC engines that is basically an RPM limiter, but usually that is remedied with the new power pack. The spark plugs look good, the fuel line bulb doesn't go slack when this occurs, there are really no 'tell-tale' signs of a problem. I've done all kinds of diagnosis from spark checks to tracing circuits for possible grounding, going through the fuel system, I just can't find a problem. Any ideas? I'm up for anything at this point.
adlert	posted 03-12-2009 11:40 AM ET (US) Sounds like you still aren't quite sure whether or not you have an ignition or fuel problem causing your symptom. You're going to need to perform a test to determine which it is and sometimes these sorts of tests are best performed while the engine is actually acting up. Testing for proper spark on a boat on plane is easy and can be safely done. I suggest that you pack an inductive timing light aboard next time you head out. If you clip it over each spark plug lead in turn when the engine is acting up (you're going to need a buddy to drive) and then point it at yourself you'll be able to see whether or not a particular cylider is indeed firing real time as your symptoms are occurring. Causes of ignition problems that you have not yet addressed through your parts-swapping include charge coils and trigger coils. Both of these components are located under the flywheel and often first exhibit breakdown symptoms when warmest. It is not uncommon for powerhead temperatures to peak a short time following a running period and subsequent shutdown. The charge coils are incorporated into the "stator" and the triggers are mounted on their own swiveling base.
tedious	posted 03-12-2009 11:53 AM ET (US) Is this motor up to date with service bulletins? As I recall there were 4 or 5 TSBs intended to address overheating problems. Tim
69boo307	posted 03-12-2009 04:50 PM ET (US) I wasn't aware of any service bulletins, I'll have to try to find that information. The stator and/or timer base are indeed the only ignition components I havn't checked or touched. I don't own the tools to remove the flywheel, and i haven't tried to borrow or 'rent' them yet. I've been suspicious of those components, but wanted to rule out all the more affordable options first. Considering that the epoxy on the back of the ignition coils and powerpack were all cracked from age, it's possible the more expensive parts under the flywheel are in the same condition.
tedious	posted 03-12-2009 05:57 PM ET (US) I'd recommend checking it for overheating before you spend any more on expensive parts. Have you tested the temp sensor and warning buzzer? I believe these motors tend to overheat if run consistently at about 3/4 throttle; at that point you're at maximum spark advance but you're not running as much fuel through as you would be at full throttle. I'm probably all wet, but your symptoms are consistent with overheating. Tim
Phil T	posted 03-12-2009 07:25 PM ET (US) I think the simplest thing is to rule out a fuel problem. How old is the tank, bulb, hose and fittings? Run the boat on a seperate fuel tank and fuel line.
powerstroke	posted 03-12-2009 07:58 PM ET (US) fuel
69boo307	posted 03-13-2009 10:51 AM ET (US) Thanks all.. I have pretty much ruled out a fuel issue, I have thoroughly been through the fuel system. If it was fuel, it seems like it would be more consistent. Doesn't make sense that I could run for 2 hours without missing a beat one day, then have a problem the next. The difference seems to be the operating conditions, ie. amount of stopping and starting or idling. thanks adlert for the tip on the timing light, I am going to try that out (when this crappy weather moves out and I can take the boat out again).
Tohsgib	posted 03-13-2009 11:08 AM ET (US) Trigger or stator is probably going south.
Landlocked	posted 03-13-2009 06:41 PM ET (US) If it were a semi clogged inline fuel filter, it would run strong until the fuel in the line downstream of the blockage ran out and then it would stall. Allowing it to sit for a moment would then allow fuel to work through the blockage once again filling the downstream portion of the line. It would be a cheap test to replace the filter and see what happens. Ll.
Landlocked	posted 03-13-2009 10:03 PM ET (US) Blockage in the filter could also be intermittent. I once had one on a lawn mower that had a water bubble in it. When the bubble got in the way, fuel flow stopped. When the bubble was on the side, fuel flow was unaffected. Ll.
wezie	posted 03-14-2009 12:50 PM ET (US) Once upon a time, I was told that after great problems with the engine, the problem was a fuel filter/screen in the bottom of the fuel pick up inside the tank. After replacing this very small item, all was well. Just a thought.
wezie	posted 03-14-2009 12:50 PM ET (US) Once upon a time, I was told that after great problems with the engine, the problem was a fuel filter/screen in the bottom of the fuel pick up inside the tank. After replacing this very small item, all was well. Just a thought.