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1995 Johnson j90sleoc won’t go over 4000rpm

R

Robssewer

New member
I have a 1995 Johnson 90hp ocean runner on a 17ft McKee craft. 17x13 1/4” prop. Won’t go over 4000rpm at WOT.
What’s been done to this point:
New champion plugs
New CDI power pack
New Johnson coils
New CDI optical sensor
New CDI stator
New CDI plug wires
Carbs rebuilt with new bowls (all Johnson parts)
New fuel filter
Replaced VRO with new Johnson fuel pump
Link and sync done by local Johnson mechanic
New flywheel
All new fuel lines from tank to motor
New vent hose from tank to filler
New pick up in tank (no change on portable tank)
Compression is around 120ish on all 4 cylinders
Replaced tach with new
Motor runs fine at idle, mid range, and no noticeable miss at WOT.
All cylinders arc from boot to plug over 3/4”
I am completely at my wits end with this motor. I have no idea what else it could be.
 
The 17X13-1/4 prop is a huge red flag.-----There is something wrong with the motor.------When the new bowls were installed did you remove high speed jets from old to install in the new bowls , yes or no?----Why all these new parts ??????------Way too many beer tokens have been spent !!
 
racerone said:
The 17X13-1/4 prop is a huge red flag.-----There is something wrong with the motor.------When the new bowls were installed did you remove high speed jets from old to install in the new bowls , yes or no?----Why all these new parts ??????------Way too many beer tokens have been spent !!
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I swapped the 17 pitch aluminum prop for a 15 pitch SS and still nothing. Stops at 4100RPM. Yes, the jets were moved to the new bowls and new float, needle and seats were installed. Also the jets were cleaned when I had them out. Basically doing shotgun trouble shooting with the parts as well as updating the older parts.
 
I had a similar issue not saying related but my issue was the seal around the emotion tube in the carb was not replaced so air was missing and coursing lean on one of the cylinders… again only what iv seen not saying your issue but sounds the same…
 
Checked the reed valves ??----Checked for a cylinder sleeve rotated ?-----Looked into an issue with S.L.O.W. system that kicks in on overheat.----Checked for blockage in exhaust ,----Hopefully a new water pump was installed here.
 
I am pulling the carbs again this week. Just waiting on new reeds to arrive. Rather have them and not need them. I have not check for a rotated sleeve. Didn’t even consider that. Checked the S.L.O.W. Today. Disconnected the temp sensors and the disconnected the system altogether. No change. The really odd thing is I swapped the prop today at the lake. 17 pitch prop ran at 4100 WOT 31mph, 15 pitch SS prop ran at 4100 WOT 29 mph. Absolutely no change in RPMs. I should have had an RPM increase. It’s like something is stopping the motor from reving beyond 4100rpm
 
Tachometer set for the correct # of pulses ?----There is no way that a 17" boat needs a 13" pitch prop.----There is a factory timing tool , was that used to verify timing.-----Are you sure all the wires on the CDI parts are in the correct position in the rubber plug ins ?
 
Tach is set to 6p. I even replaced the tach with a new one just to make sure the tach wasn’t faulty. The local guy here used the timing tool when he did the link and sync and verified the timing. And yes, absolutely certain the plugs are in their correct locations and orientation. What really throws me off is the lack of any RPM change when I changed the prop from 17 to 15. I should have gained roughly 500 rpm’s give or take.
 
Check your throttle cable. The ball that holds it in the control unit could be cracked and allowing the throttle cable to slip not giving it WOT even though the handles all the way down.
 
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