115/80 johnson jet losing rpm

[JoshKeller84]

backstory - new fuel lines, carbs cleaned. first run of the day it ran good. 5500 rpm constantly. fished an hour, hammered down again, shot up to 5500, then slowly fell back to 5300 with quiet, fast exhaust pops. occasionally you could hear it cut out to 5100 then pick back up. went home, checked carbs again, new fuel lines, new spark plugs. went back out this evening, first run, ran geat. 2 miles of 5500 rpm. shut down, fished an hour, started back up, started at 5500 rpm and fell to 5300. pushing key in to primer doesnt change anything, nor does pumping the bulb. i did however, notice the nattery is intermittantly charging, but dont believe thats my issue. any suggestions?

 

[oldboat1]

Is the motor overheating?

 

[JoshKeller84]

head temps at idle are 145, 146, and 115 at wot

 

[boobie]

Sounds like you have an ignition miss. Put a timing light on each cylinder, turn the timing light around and look into it. If you see any black spots, that's the cylinder that's missing.

 

[JoshKeller84]

timing light is at home and im on a fishing trip. i do have a multimeter and i ohmed out my coils. 3 produced readings of 0.775 - 0.785 ohms, and the 4th tested at 1.460 ohms. am i to assume that is my issue?

 

[boobie]

Then do a cylinder drop test on it.

 

[oldboat1]

Can test spark from all cylinders with a simple adjustable tester. See if the spark generated by the suspect coil is any weaker (or nonexistent).

 

[JoshKeller84]

replaced coils and wires. motor ran good for a 4 mile run. shut down. fished half hour, started back up and back to dropping rpm. questioning maybe the stator now.

 

[racerone]

Test run with cowling off if a crossflow motor?----Could be as simple as a plug wire shorting to cowling latches.

 

[JoshKeller84]

just ran with cowling off - motor still acts up. motor only does it with the throttle maxed. back off to 5000 rpm and its as smooth as can be - but also only does it after the inital run on cold motor.

 

[JoshKeller84]

went and bought a spark tester, all 4 have good clean blue spark that jump 7/16" easy

 

[oldboat1]

Should indicate all coils are good. But could still be dropping a cylinder when components heat up (see post 4). The other way is to pull off plug wires one at a time when the motor is acting up. No change indicates that cylinder isn't firing.

It's possible you have a lean condition for some reason at high rpms -- pump diaphragm, possibly.

 

[JoshKeller84]

i actually have a spare powerhead with me that i know runs good, and swapped the 4 coils. would the bad pump only show up after the initial run? we ran 4 miles this morning and it worked perfect. i honestly thought we fixed it, until we fired up the motor after fishing for an hour. i also had my buddy pumping the primer bulb while running, and pushing the key in to activate primer solenoid changes nothing either. looks like my next time is to buy or rent a timing light since mine is back at home.

 

[oldboat1]

sounds like you've tested for fuel pump issues. Maybe a rental compression tester and timing light....

 

[JoshKeller84]

compression is 118, 119, 116, 116

 

[JoshKeller84]

update - swapped powerpacks and she is running good now. thanks to everyone who helped save our fishing trip!

 

[oldboat1]

Sounds like a well-planned trip! Glad it worked out.

 

[JoshKeller84]

update - still running good!. one more question, and it goes back to the non charging. the tach will work up to 2500 rpm, then cut out. battery isnt charging using the regulator. if i hook the grey tach wire to either yellow wire, it works as it should. I rigged up a rectifier using a bridge rectifier, some wire, and a fuse holder, and it is charging the battery now. is it safe to assume the stator is good, and the regulator just needs replaced? here is a pic of my contraption, this was just running wires and test fitting - ive added a fuse to the output wire, and tidied up the wires out of the way.