Question for DVA testing experts - no acceleration, motor bogs

[kjspylite]

motor: 1989 Mariner 75 HP 3 cyl.
clean carbs, compression is good, timing is good, idle mixture screws 1.5 turns out

I am trying to diagnose a bogging, no accelerration problem. Idles fine and revs fine on muffs. Idles fine in water, but has zero acceleration. It will only move forward at barely above idle speed. It never surges or acts like it going to accelerate.

I first wanted to diagnose it as a fuel or ignition problem so I built a DVA adapter from instruction on this site and tested per CDI's manual.

I took DVA measurements while the motor was running, ON THE MUFFS, at idle speed. Everything checked out OK.

Here is my question: Can I trust these readings? Does good voltage out of stator switch box on the muffs translate to good voltage on the water under a load? Do I need to perform the DVA test in the water while trying to accelerate?

I would like to know my DVA test results are accurate so I can concentrate on finding the fuel issue. Thanks in advance.

 

[bktheking]

Re: Question for DVA testing experts - no acceleration, motor bogs

What part of the DVA test requires the motor to be at WOT. As far as I know, the readings are at idle, if all checks out sounds like something else is up. Fuel perhaps, timing?

 

[kjspylite]

Re: Question for DVA testing experts - no acceleration, motor bogs

Thanks for the quick response. I don't think any part of the test is at WOT. However, I wanted to be sure that my readings taken on the muffs were OK, and that I didn't need to perform the test under load.

I think its a fuel issue, but wanted to rule out electrical. When its on the water, it feels like its dropping cylinders, however, my tests are starting to prove otherwise. Further, most posts with people complaining of bogging issues that are fuel related, they experience some sort of acceleration/surging. I have yet to get this motor any faster than a brisk walking pace. It has never shown any signs of surging, trying to accelerate, or clearing itself out, which originally made me think it was electrical.

 

[bktheking]

Re: Question for DVA testing experts - no acceleration, motor bogs

Have you observed the carb butterflies as you move the controls, is everything opening as it should? Have the carbs been off to inspect the high speed jets/orifices. All it takes is a spec of dirt or a plugged filter to mess everything up.

 

[kjspylite]

Re: Question for DVA testing experts - no acceleration, motor bogs

yes, the butterflies open with the throttle. I had the carbs off and disassembled to clean when I purchased the motor. They looked very clean, but I went ahead and soaked the carbs in cleaner for a couple hours, sprayed them with compressed carb cleaner, then blew them out with compressed air. Reassembled with new gaskets. Set the idle mixture screws to 1.5 turns out. Filter is new.

 

[bktheking]

Re: Question for DVA testing experts - no acceleration, motor bogs

I've often heard that there are issues with motors in the lake and not on muffs, warped exhaust plates allowing water into cylinder(s) but only in the lake, not on muffs. Do any of the plugs look water washed?

 

[kjspylite]

Re: Question for DVA testing experts - no acceleration, motor bogs

Its hard me to get the boat in the water (thats what a one month old baby and two year old will do to your time!) so I do almost all of my diagnostics on the trailer. I've had it out 3 times and its always the same bogging. While I have not observed the plugs IMMEDIATELY after shutting down in the water, the plugs always have a nice brown color to it. Also, the cylinder walls look to be water free, as they are not "steam cleaned" and have a minimal amount of build up on them.

 

[bktheking]

Re: Question for DVA testing experts - no acceleration, motor bogs

Got a serial number?

 

[kjspylite]

Re: Question for DVA testing experts - no acceleration, motor bogs

I don't know the whole number off the top of my head, but I do know it starts with either 0BXXXXXX or 0CXXXXXX. I am sure its an 1989.