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V4 motor has no power with cowling on, runs fine with it off

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PhilSch

Regular Contributor
I brought this issue up a while back but I'm still having the problem and can't find the old post so I will start over. 1988 110HP Johnson has 2.5 hours run time since total rebuild. My initial outing the boat ran great with the cowling on, approx 60 minutes. After that every time out the motor makes no power (won't get on plane) with the cowling on. Boobie suggested an exhaust leak so I tried looking for smoke around the powerhead but I can not see any, even when squirting oil in the carb throat.

The lower engine pan has a generous size thermostat access port cut out with a removeable panel. The first time I took the boat out the access hole was open as I had not yet fabricated the panel and I thought maybe that opening evacuated any exhaust fumes which would explain why it ran good with the cowling on initially. I took the boat out again today and motor would not make power with cowling so I removed the panel covering that access port but still no power. Take the cowling off and motor runs great.

I will attach a picture of the access port cutout.

Is it likely an exhaust leak would develop after running 60 minutes on the first outing? If there is an exhaust leak large enough to choke off the motor why can I not see any smoke around the back of the powerhead? Wouldn't it seem that large access port would evacuate any exhaust gasses if they were present?

I have considered spark plug wires grounding out on the cowling latch but that seems unlikely too. I hate running the boat without the cowling...it's noisy and ugly. I appreciate any inputs!!
 

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Is there something covering up the air intake for the hood ?? Be on the bottom of the motor. Another thought is maybe use more oil in the carbs to get it smoking better.
 
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You can remove the latches from the cowling and put the cowling on without them to test. Sparking to the latches is a known issue with these v4s.
 
Mine on occasion would grab the lower port side plug wire just enough to make it run like crap. Even properly secured.
 
Boobie said:
Is there something covering up the air intake for the hood ?? Be on the bottom of the motor. Another thought is maybe use more oil in the carbs to get it smoking better.
Click to expand...

Nothing foreign in that area except some build up of oil residue but not enough to choke off the motor.
 
Jay1234 said:
Mine on occasion would grab the lower port side plug wire just enough to make it run like crap. Even properly secured.
Click to expand...

I've had that happen but I have rerouted the wires to prevent it and am super careful whenever I install the hood.
 
???-----Install a timing light on #3 plug wire.----Install cowling.-----Take boat for spin.-----Observe flashing light.------Repeat with #4 plug wire.
 
Is it possible that there is something on the cowl that is rubbing up against the throttle advance? Holding it one way or the other. Might only happen after warm up because the foam heats up and expands slightly, or becomes softer??

Like someone else said, the air intakes are covered by a foam that can get gunked up. Not enough air, or enough air, but not enough cool air can cause issues like that.
 
TheBearAK said:
Is it possible that there is something on the cowl that is rubbing up against the throttle advance? Holding it one way or the other. Might only happen after warm up because the foam heats up and expands slightly, or becomes softer??

Like someone else said, the air intakes are covered by a foam that can get gunked up. Not enough air, or enough air, but not enough cool air can cause issues like that.
Click to expand...

Foam is clean and in good condition. Even if it was touching the throttle linkage it is not dense enough to impede travel.
 
racerone said:
???-----Install a timing light on #3 plug wire.----Install cowling.-----Take boat for spin.-----Observe flashing light.------Repeat with #4 plug wire.
Click to expand...

I hooked up the inductive timing light to each of the lower plug wires, reinstalled the cowling and when engine is running the timing light is flashing. I also removed the vent on the back top of the cowling (see attached) to to further investigate if there is an exhaust leak. When idling there is zero smoke under the cowling around the powerhead. I am running 25:1 mix as motor is freshly rebuilt so there's plenty of smoke coming out of the exhaust.
I can see no smoke with a very bright flashlight shining into the hole and can smell no smoke with my nose directly over the hole.

The motor ran great with the cowling on the first time out after rebuild. As mentioned previously at some point I switched from suppression plug wires to generic 7mm solid core wires. I am not 100% sure when I made that switch but I think the first time out I had not yet switched the wires. Does it make any sense that putting on solid core wires could cause the problem?
 

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The motor finally runs properly with the cowling on. I made two changes so I am not sure which was responsible....

1. changed the plug wires on the lower two cylinders to genuine Evinrude wires and boots

2. flipped the coil on cylinder #4 so the secondary post was up instead of down. Close inspection showed the plug wire boot was up against the cowling latch, now the boot it well away from the latch.

Next time out I will put the old wires back on the bottom two cylinders to know for sure what was causing the problem. I'm inclined to think it was the coil mount orientation rather than the wires.
 
You are probably correct but I will let you know when I have the chance to test again. Boating in CA really sucks now....all the lakes within an hour of me are 5 mph because of low water levels due to severe drought. I finished rebuilding the 110 hp motor months ago and I have a whopping 3 hours on it.
 
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