high speed miss fore 125

[fisheymikey]

hi everyone

i took the boat on the water after a long winter and found the force 125 1988 get a small miss at top speeds

is there most likely the module or the trigger.

resistance on the trigger are fine but is there an other way to trouble shoot.

or should i try the modules

thanks mike

 

[Jiggz]

Top speed miss is really very hard to troubleshoot for it can be caused by anything, i.e. electrical, mechanical, fuel etc. The thing to do before even starting to remove the first screw is to write down all the symptoms. First, at what rpm does it starts to miss. Is the miss constant with certain rhythm? Does the miss sounds like a misfire from the motor or is it like a mechanical slip like a clutch slip? Is the miss the same with the cowl off? Does the clear fuel filter stays at least 1/2 filled at top speed? Write them all down and then post them here. From there we can do a very good diagnosis.

 

[fisheymikey]

excellent here we go...

fuel filter stays full
it does it at various rpm speeds most noticible at top speed 44-1700
it certainly feels like a misfire but hey im no pro
all conectors changed
it does seam after 3500 it starts to do the misfire and then has a surge of power
yes the cowl was off and on no change
it sonds like every 2 secs it does the miss
also view pic definatly jumping all the way

i think im going to take a video of the symptom
ill do that tomorrow

 

[scout-j-m]

I can't offer any help but where did you get that spark tester/grounder?

 

[Jiggz]

The surge of power following the misfiring is a critical symptom. As this could indicate a faulty carb, either with improperly set float or a semi clog jet. Otherwise, if you are for sure that it is a misfire (could be slipping clutch) and the carbs are clean and set properly, it is most likely electrically caused. And the only thing that I can suspect initially will be the trigger. When throttle is advanced as we are all aware, the trigger also gets mechanically advance. It has been a common cause that some wire gets either pinch with the flywheel or they have failed insulation that when moved they get closer to the flywheel or other metal parts to get shorted out to ground. But then it can also be a failing CDM that cannot handle hi-speed.

If you have a known working spare CDM, now is the time to put it into use by replacing the CDM's one at a time and hopefully discover the cause of the misfire. If not, I would isolate each of the wires coming off the trigger and read each wire to ground with a multimeter (ohmmeter) while at the same time manually advancing the timing tower back and forth to see if you can read resistance between any of the trigger wires to ground. If you do then you know one of the wires is touching ground when the trigger advances.

 

[fisheymikey]

ok just checked the resistance to all trigger all at 47oms
cleanning carbs and getting ready to check modules testing will be ongoing
thanks post later video and findings

thanks

 

[jerryjerry05]

When you have the carbs off look into the reeds.

Scout, the tester can be bought from Mercury, Johnson, Yamaha.
Google outboard spark tester.
There's a few on there.
One company is selling a kit with everything you need for basic testing $350

 

[Jiggz]

FisheyM, remember it's not the internal resistance we are looking for in the trigger wires, but failed insulation that could be touching ground when moved or advanced at hi-speed. There are 4 sets or pairs of wires. Each pair is internally connected to each other. So that means you will need to check resistance between a wire from each pair and to ground (use small alligator clips) while manually moving the timing tower from low to high speed or from zero degrees to max or WOT position. You should not read any connection or low resistance. If you do that is an indication you have a wire shorting to ground caused by failed insulation in the wire. Another option is to do a visual check but that means removing the flywheel. The advantage of the visual check is you can also check the integrity of the magnets, which can also cause such misfire.

 

[fisheymikey]

ok either i have a problem with my trigger i did not understand you Jiggz

i set multimeter to oms one of the leads goes to the ground the other goes to one of the wires to the trigger. one of the pair goes to 49oms the other goes to 1 om.

either wwire i advanced and retarded the throttle without any changes.

btw took the carbs apart they were good but not they look fantastic!!

i hope i make sense

 

[Jiggz]

No Title

Were each pair of wires disconnected from the terminal board before you took the ohms reading to ground? If so, the pairs with 1 ohm and 49 ohm readings have low resistance to ground and most likely grounded. What was the readings on the other remaining two pairs of wires? Here's a wiring diagram with the four pairs of wires highlighted. You need to disconnect each pair before reading to ground and while reading move or advance the timing tower to see if you can read low resistance to ground.

 

[fisheymikey]

no they were not disconected from the terminal.

sorry did not know needed to diconect them.

do i check only to the trigger or also to the module?

thanks