Mercury 90/65 Jet issue. Lost power at full speed.

[suznjames]

Ok, I need some help with my Mercury 90/65 (2002) 2-stroke, 3 cylinder jet motor. I was using it earlier in the year until it lost power - suddenly, at top speed it became about 2/3 of the normal speed for a few seconds, then recovered. Next time it happened longer and now all the time. It used to get top speed 30+ with just me, now just 20mph. Other than that it seems to work great; starts fine and runs great. I haven't been using it much until I can figure exactly what's wrong.

I have tried the following:

Changed spark plugs
Changed fuel filter
Removed and cleaned carbs (they were really clean; and floats moved free)
I also noticed the charging circuit on my battery voltage was crazy (flipping -100 to +100volts); so changed voltage regulator and now that is Ok but boat top speed didn't change.
I did have electrical fire in the motor 2 years ago; ground shorted out and melted a lot of plastic wires. I used some electrical tape and it worked fine - so repaired the wires that were melted and the motor was fine for the next year.

When using an inductive tachometer (very cheap one); I see lower chamber runs 1000rmp while top two would sit at 2000rpm testing last week. This week the same setup the lower one shows 4000rpm; which I know isnt' right. But it's different to the top two. Based on this I'm suspecting the Trigger may be bad (possibly Stator too, not sure). I've ordered a new trigger to try out which comes in a few days; since that's cheaper.
I've moved the CDM module between two spark plugs but the RPM's reported didn't follow; so I don't think that is an issue (unless my really cheap tachometer is lying to me - I've ordered another as a backup getting here soon).

Could a bad Trigger cause a loss of top speed? My guess is currently something with the CDM; trigger or Stator?

Any other ideas, or if I'm doing something wrong in diagnosis please let me know and send tips!!!!

Thanks

James.

 

[flyingscott]

What is your compression? Have you done an open air spark test? Have you tested the stator and components. www.cdielectronics.com has the testing procedures for your ignition. Your tach is probably reading wrong because it is a 4 strk tach. You need to have a 2 strk tach because a 2 strk fires twice as much as a 4 strk. I would guess the switch box but testing needs to be done.

 

[suznjames]

Thanks for the link to CDI, that's useful.

I have not done open air spark test; just used some spark plug tester with a light which shows some spark getting to each one.

I also don't have the right part to test the Voltage yet on the Stator; but I'm getting that tomorrow so will test then - plus the flywheel removal tool I get tomorrow so I'll make a visual inspection. The resistance was ok I believe, but I'll double check.

I did check the CDM's and they seem ok; however they all show resistance of 840 ohms on A to C (where it should be 1000to 1250); but all the other numbers and diodes seemed ok. Since it's the same on each CDM I'm wondering if it's just the OEM part?

Thanks for the pointers!

 

[Texasmark]

Squeeze your primer bulb next time it does it. If you recover, cracked fuel line, diaphragm in the fuel pump or a valve therein, or feed line to engine and squeeze bulb need replacing and tank screen needs a check...cleaning.

My 2002 OEM fuel line from the gas tank was grey and looked like it was made of silicon. It decided to develop a tan scale inside that flowed with the fuel and clogged up the squeeze bulb and then the fuel filter......happened about 4 years ago....putting the engine at 12 years old. Going to bet if you are still running OEM fuel line then time to redo the tank to engine line and bulb, and while you are at it go ahead and replace the rubber under the cowl.

Disconnect the fuel line at the engine connection and in an appropriate container squeeze some fuel out and check it for scale. Will answer that question real fast.