25hp Evinrude Loses Power at High Speed

[thull]

Hi all, I have a 1983 25hp Evinrude that ran great all summer, but yesterday was trying to die while running at high speed on our way back in from a day fishing in Mosquito Lagoon (I caught a 30" seatrout!!!). It was running fine at high speed, then suddenly powered down to mid range and then just to low speed. Ran ok at low speed the rest of the way back to the dock, and idled fine at home in a bucket for 1/2 hour. Telltale was peeing strong during the problem and stream was just barely warm. Carb hi speed jet is probably fine since I just rebuilt carb in June this year and it was running great every month until yesterday. Also have fuel filter inline before fuel pump. I'm thinking either it powered down from overheat condition (anyone know it the telltale water would've been hot if it was overheating???) or old electronic components are beginning to fail (I know a failing coil will act up as it gets hot). I plan to try to simulate the condition in a lake closer to home and feel the powerhead for overheat condition. I am more familiar with testing electrical systems on the older points/coils/condensers engines (which this one isn't). Can someone tell me how I can test the powerpack? Honestly, I don't yet know exactly how the powerpack, stator, and external coils work together. Thanks for any assistance!

 

[hardwater fisherman]

Do a cylinder drop test. I think if the power pack went bad you would loose spark on both. And if you find you are loosing spark, switch the coils and see if problem follows. It also could be a bad plug or plug wire. Also check to see that you still have good compression on both cylinders.

 

[racerone]

Quite common for powerpack to fail on one cylinder.---------It is either a coil or the powerpack if it is a spark issue.

 

[thull]

Would it work to check for spark by clamping a timing light to each sp wire while under weigh (ground light on block of course)? I'm thinking of trying that while the problem's occurring (if I can get it to do it again). I'll confirm compression and check spark with a tester. I expect both will appear fine though, since it idles great and the problem only happens when warmed up and running at higher speeds.

 

[thull]

Would it work to check for spark by clamping a timing light to each sp wire while under weigh (ground light on block of course)? I'm thinking of trying that while the problem's occurring (if I can get it to do it again). I'll confirm compression and check spark with a tester. I expect both will appear fine though, since it idles great and the problem only happens when warmed up and running at higher speeds.

 

[racerone]

Yes , just hook up a timing light and observe the flashing.

 

[jimmbo]

Have you checked the fuel filter(s) for water/dirt? Have you tried it with a different fuel tank and/or fuel line? Is the primer bulb retaining its shape or was it collapsing when the engine was running? Did you pull the spark plugs to see if they were fouled and if there were any signs of a misfire?
You said you overhauled the carb, recheck to see if the linkages haven't become disconnected since june

 

[thull]

Did a cylinder drop test by disconnecting wires at plugs with insulated pliers while running engine at idle. The motor idled down a little when I pulled each plug, but still ran ok, just a little weaker...seems like what you'd expect if you removed half the fire from the crankcase. Did a compression test and had 130lbs in each cylinder. Inspected plugs...insulators were dark tan and plug was not fouled. I checked carb linkages...they're fine. Primer bulb was not collapsed during the problem. I really don't think it's a fuel filter issue, or fuel problems at all, since it runs great at idle right now. The power loss wasn't like running out of fuel...it was more like someone just dialed down the revs or governed it down all of a sudden. I still have to check spark with a checker and find time to get the boat to the lake and run it at high speed again to replicate the problem. I found another thread a guy had the same issue and it turned out to be the stator assembly and a coil:
http://forums.iboats.com/forum/engi...-bogs-down-runs-rough-stalls-after-warming-up
How can I test the stator assembly and coils?

 

[jakedaawg]

Instead of one of us typing it all in, get a factory manual or cheaper yet, go to cdielectronics.com and use their free trouble shooting guide.

You will need to do the tests while it is failing most likely. Intermittent issues can be tricky to properly diagnose.

 

[valvebounce]

Was the lake you tried it on at a higher altitude than usual?The air thins out as the altitude increases,so you get less oxygen.
Is the airflow to your carb clear?restricted airflow will cause the symptoms you have.Induction air needs to be as cool as possible,because there is more oxygen
in it.If you are drawing air over a hot engine there is less oxygen content.
Your exhaust needs to leave the engine freely,if not,you get backpressure that acts like and engine brake.Have a look at your exhaust outlet on the leg for restrictions on it.An engine with restricted breathing in or out will act like an overheating engine.

 

[thull]

I solved the problem. I just threw parts at it since I couldn't do the testing on the water and pilot the boat by myself. First, I tried just replacing the power pack (since it was the easiest & of unknown age anyway). That didn't fix the idling down condition. So, I popped off the flywheel and replaced everything under there: stator assembly, sensor coil, and charge coil. Runs great now. Parts weren't that much anyway, around $175, and now i almost have a new ignition system.

 

[Miboat21]

I solved the problem. I just threw parts at it since I couldn't do the testing on the water and pilot the boat by myself. First, I tried just replacing the power pack (since it was the easiest & of unknown age anyway). That didn't fix the idling down condition. So, I popped off the flywheel and replaced everything under there: stator assembly, sensor coil, and charge coil. Runs great now. Parts weren't that much anyway, around $175, and now i almost have a new ignition system.

I'd like to know "charge coil" is it same as ignition coil?

 

[racerone]

Nope.--Ignition coil is on the side of the motor on an 83 model.------There is a charge coil under the flywheel that loads up the capacitor in the powerpack.-----Then there is also a battery charging coil under the flywheel on some models.----MIBOAT ---why the question and start your own topic.----They don't like old , old topics picked on here.