Johnson 90 hp a weird one

[That old Mercury]

Hi
New boat to me , i have done some work on it myself carbs , plugs and new gas tank and black rubber gas hoses and a water fuel seperator and new priming bulb.
In all my years I aint never saw this problem working on my boat motor and friends motors.
Model # J9OTLETS
Compression 120 psi on all four cyclinders.
Primer bulb was firm all the time.
Opened tank cap in case it was not getting air.
Tilted and trimmed in case this motor has a trim limiter
Took off carb silencer and with it running i revved it up and and put my hand over both carbs one at a time in case one had trash in a jet.
Gas is good and i am running high octane.
Freshwater fishing.
It acts like it went into limp mode
2,500 rpm max
I was going up a river running 34 mph , a bass boat passed me doing at least 60 and they were so close i think they got a drink out my cooler.
Well when i hit thier wake my boat dropped to 12 mph with the throtle still almost wide open . I pulled it back to idle and it idled fine, shut if off and it cranked when i touched the key.
But it would not go any faster than 12 mph. I used my little kicker to get me where i wanted to fish.
After an hour or so i started it back up and still ran 12 mph .
After a mile it was up to 15 mph.
2 or so miles latter it was up to 22 mph , by this time i was at the ramp and loaded it up and went home.
Any ideas?
Sorry for the long post!
Thanks

 

[racerone]

Do not run this motor until you correct the issue.---Plug wires shorted to the cowling ??------Make sure high speed jets are clean.----Check flywheel key.----Does spark jump a gap of 7/16" on each lead?-----Running with tested VRO ?----Conventional pump mounted directly over pulse port on intake manifold?----Lever on the electric primer valve in the correct position ?-----Tested the overheat horn ?

 

[Chris1956]

Check your compression. Hopefully it is still good after the ride. If so, check for spark on all cylinders. Next would be carb cleaning, again.

 

[That old Mercury]

Do not run this motor until you correct the issue.---Plug wires shorted to the cowling ??------Make sure high speed jets are clean.----Check flywheel key.----Does spark jump a gap of 7/16" on each lead?-----Running with tested VRO ?----Conventional pump mounted directly over pulse port on intake manifold?----Lever on the electric primer valve in the correct position ?-----Tested the overheat horn ?

This started right when i hit the first wake.
Last seven trips boat has ran flawless
Vro been deleted at some time .
Never seen plug wires short to a plastic cover.
I did run it without the cowling off to make sure it did not have an exhaust leak and verify all linkage was working.
Fuel pump looks original.
Electric primer is correct i checked that be removing one hose from carb, No fuel flow with primer bulb tight untill i press in the key.
When i ran the throttle at Max boat slowly increased in speed getting faster and faster but not to max speed.
I will check the other ideas .
Some of the gauges and controls have been rewired right before i bought the boat.
Trim gauge reads backwards but all trim switches are correct , up and down switch positions are correct.

 

[That old Mercury]

Check your compression. Hopefully it is still good after the ride. If so, check for spark on all cylinders. Next would be carb cleaning, again.

I will check the compression.
Carbs do need new fuel bowls one leaks internally .
I have all the information now and i need to find replacement OEM ones.
I will be posting where to find
Metal or plastic OEM bowls.
All the compatible bowls i see dont have the correct fuel ports .
Thanks for the Help

 

[racerone]

???----If you look closely at the cover you will see the METAL pieces.----Wires have been know to short to them----I can not touch your motor.-----But good luck with your motor.

 

[That old Mercury]

???----If you look closely at the cover you will see the METAL pieces.----Wires have been know to short to them----I can not touch your motor.-----But good luck with your motor.

The wires do not come close to touching the metal latches . But i will look at that.
I normally only go 20 to 25 mph but this time i did run it on up to 37 mph , not wide open and it could have ran hot just at that speed and it didnt have anything to do we the other boats wake.
But if it ran hot there was no alarm . If it even works .
But after it cooled it should have ran fine unless a relay or contact stuck.
Gotta a lot of testing to do.
Thanks for the ideas

 

[tphoyt]

Did you inspect your flywheel key yet?

 

[racerone]

Some simple trouble shooting will what the issue in minutes.----Good luck with it.

 

[saltchuckmatt]

Hit the wake and slowed down. Hmmm.

Junk in tank? Fuel pickup screen might be clogged. Install a spin on Racor filter and remove screen from pick up tube. Typically when you have that situation the primer ball is collapsed.

What I analyzed, went south after hitting wake, then slowly got better.

 

[That old Mercury]

Hit the wake and slowed down. Hmmm.

Junk in tank? Fuel pickup screen might be clogged. Install a spin on Racor filter and remove screen from pick up tube. Typically when you have that situation the primer ball is collapsed.

What I analyzed, went south after hitting wake, then slowly got better.

It's a new tank that i bought for my bass boat , maybe a month ago.
No strainer on fuel pickup.
Was clean inside , ran new black rubber fuel lines , installed new water fuel seperator has a spin on filter combined. Also already had clear fuel filter after it in case something got past it from the install.
Last 7 trips been running fine No problems going 20 to 25 mph all day long. Its wehn i opened it up to 37 ish for a mile or so and hit another boat wake that it dropped to 2,500 rom instantly and stayed that way . So i fished some, caught all i wanted to clean.
Started it up stayed on 2,500 rpm and the further i went it started getting faster and faster , when it got to 25 mph i was at boat ramp.

 

[That old Mercury]

Did you inspect your flywheel key yet?

I am going to work on it tomorrow hopefully!
Going to start by ohming out temp sensors to see if one is bad.
Check compression .
Check spark at cranking speed and at full throttle.
Check trim sensor in case it thinks motor is out of the water since i was trimming it up and down on the way back and it was slowly increaing in speed.
Look at fuel lines around engine since they are old.
If i dont see anything then i will check fly wheel.
Thank for the help

 

[saltchuckmatt]

Wire harness bounced up and down and scorched it....? Sensors go bad and their a problem to get.

 

[cyclops222]

Classic case of throttle cable assembly becoming loose . Use 2 people to check throttle plate position at WOT position and idle.

 

[cyclops222]

Classic case of throttle cable assembly becoming loose . Use 2 people to check throttle plate position at WOT position and idle.

You have a jet pump drive. It is clogged inside with something. Remove cover & clean the impellor.

 

[That old Mercury]

Wire harness bounced up and down and scorched it....? Sensors go bad and their a problem to get.

I kind of thinking that too
Thanks

 

[That old Mercury]

You have a jet pump drive. It is clogged inside with something. Remove cover & clean the impellor.

No jet drive, classic prop
Thanks

 

[That old Mercury]

Classic case of throttle cable assembly becoming loose . Use 2 people to check throttle plate position at WOT position and idle.

Checked that on the lake with carb cover off , trigger moved to full advanced and but carb butter flys were open dead center, and ran it back to ramp with cowling off and watched it while i accelarted and decellerated.
Just to make sure something was not acting up.
Thanks

 

[racerone]

If there is foam inside the cowling -----What does foam inside cowling look like.---Any pictures?

 

[racerone]

Check the reed valves.