Low Power at WOT

[amk54055]

Alright guys, I need some help. I have a 1996 Mercury Outboard 75hp 2 stroke 3 cylinder. My issue is loss of power at WOT. The engine cranks and idles fine. When I push the throttle down to wide open there is just very little acceleration. Once I get going down the river there will be a sudden surge of power for 1/2 a second like I think the engine should be running. When my tach was working a few days ago, I was running in the 3000 range, I believe I was at 5000 when It was running properly a year or so ago. So my issues today are, loss of power and tach was intermittent at first now it has completely quit working. Things I have done, replaced plugs, verified spark on all 3 cylinders, Seafoam in carbs, then rebuilt the carbs,(they looked great), Compression test (130 on all 3), and I looked at the pistons through the spark plug holes and #1 and #3 look the same with a build up of carbon on each. #2 piston looked clean. Before discovering this, I was on the road of fuel. This makes me think my issue is electrically related. What is my next step? Your help is appreciated.

 

[amk54055]

Re: Low Power at WOT

**bump** Someone please help!! Also, I replaced the coil on that cylinder last year.

 

[crash666]

Re: Low Power at WOT

That's too funny (not funny ha ha either)
My 90 hp is doing same basic thing, I'd appreciate it if you let me know if you figure something out. I'll do the same.
No power but doesn't sound abnormal right ? like the throttle doesn't go past 1/4 ? Then out of nowhere it kicks in ?

 

[amk54055]

Re: Low Power at WOT

Exactly the same thing. Runs great, idle, low rpms... then hammer down and very little power.. Trigger?, Stator?, Rectifier? Something electrical I betcha... Someone?? Please

 

[jackd1023]

Re: Low Power at WOT

I have the same motor and was having the same problem.

I did a few things to repair and I am honestly not sure witch one was the cure,

I rebuilt and cleaned the carbs, replaced the fuel line and bulb, rebuilt the fuel pump. and Spark plugs. I also replaced the fuel filters and the separator.

All prretty simple things and not real costly.

Good luck I wish I could specify witch one fixed it but I figured they were all low cost parts and a couple hours of labor and viola.... runs like a top.

 

[crash666]

Re: Low Power at WOT

Yeah was thinking the same, but was hoping for a cheaper thing to look into. I have checked those with a tester but due to the erratic way it behaves I think i'll try it again. maybe different results. Probably not the rectifyer though, Didn't help mine when it stopped charging i had replace it. It did fix my tach though.

 

[amk54055]

Re: Low Power at WOT

**bump**

 

[quantumman29]

Re: Low Power at WOT

does that motor have switch boxes on it?
if it does,test it with a volt meter,chances are you may need a new switch box,or a new stator

mike

 

[furr]

Re: Low Power at WOT

I have the same motor ,and have had probs in the mid range ,with a loss of power , l re-cond the fuel pump, Now runns sweet , maybe a new fuel pump kit could be for you.

 

[asm_]

Re: Low Power at WOT

WOT power issue are usually caused by either Fuel delivery problem or ignition problem.

If I were you, I will start out checking fuel delivery. Rebuild Carb, check fuel pump to make sure there is no blockage.

 

[amk54055]

Re: Low Power at WOT

I think it is likely a ignition issue. I have rebuilt the carbs, new fuel filter, etc. I havent touched the fuel pump but I have squeezed the bulb at WOT and it does not change anything. By doing that I should be forcing more gas into the engine and that should change things if I was starving the engine of fuel. So I am leaning towards the ignition system now. My tach is intermittent and I think the power pack or switch box controls it. So intermittent motor, intermittent tach, Im thinking electrical. One thing that makes me think electrical is the difference in appearance in the #1 and #3 cylinders versus the #2 cylinder. I dont think #2 is getting turned on (by the electrical system). Just my thougths, yall are the experts...

 

[crash666]

Re: Low Power at WOT

Hey bud, I thought i'd share something i found real interesting. I was looking at new stators and was confirming with their install pdf to make sure things were the same and the troubleshooting section refers to our problem. They say in there if after you install and have that problem before returning as faulty you should rotate stator plate by one bolt hole. I don't have time to try till next week but for three hundred bucks it's worth a shot.
Maybe over time it gets a dead spot ?

 

[crappie14]

Re: Low Power at WOT

I have a 1990 Mariner 75HP that would take spells of basically not taking fuel. It would normally act up right after I would launch and disappear after had run (or warmed up a bit). I would give it fuel, it would only run 4-6 mph regardless of how much fuel above idle I would give it. Bulb stayed firm, changed filters, plugs, rebuilt carbs, nothing seemed to help.

Changed out the power pack and problem, at least for the immediate, disappeared. This is a 3 cyclinder motor and it was a guess by a local mechanic and it appears to have been correct.

While it was not running correctly, occasionally when I was giving it more throttle than it was using, it would almost try to start running correctly for about a 1/2 second.

It turned out to be a $125 fix that I did myself but it was after I had done the routine maintenance such as filters and plugs.

 

[amk54055]

Re: Low Power at WOT

So, i took my boat to the shop and they said I needed a new switch box/power pack. After $300 for the part and another $200 in labor I still have the same issue. I took the boat out yesterday and I ran 1 battery down ttrying to get it started. Once I finally got it started, I idled out of the no wake zone and pused teh throttle to WOT and it had more power than it ever has. I immediately thought Awesome! I was going about 5 mph more than I ever had and it got there quick. But.... then it started to miss. I stopped and started again and it had good power again. Did it a third time and back to the same thing, loss of power... Drove down river for a bit, reduced power and intermittant surging ever so often.
What in God's name would you try next? They said my voltage regulator was bad and my tach. I have both of those on order so I am going to fix that next week. Will that help my problem? I am almost certain this is a electrical issue and involving cylinder #2 not firing all the time. Any thoughts?

 

[westexasrepublic]

Re: Low Power at WOT

rectifier, and crank at night with the cover off to see if any of the plug wires are bad and arching off the block. while you're there check all the coils, maybe #2 is just bad coil or plug wire not pushed in making good contact inside coil.

 

[sschefer]

Re: Low Power at WOT

Find yourself another Mechanic. Guessing at problems is expensive and rarely fixes it. He should have put a Multimeter with a DVA on it the minute you told him that tach wasn't working right.

Disconnect the two yellow wires from the rectifer/regulator and see if the problem clears. If not, have the stator tested by someone with more than guesstimating tools.

 

[amk54055]

Re: Low Power at WOT

What should happen when I disconnect the two yellow wires? I suppose I should do this on the water. I wouldnt suspect that doing this idling in my yard would tell me anything?? Not sure, sry for the basic questions.

 

[crash666]

Re: Low Power at WOT

Get your boat goin yet ?
Looks like it was the switchbox on mine. Found one on ebay 45 $ in alaska and now she's cured.
smooth idle and full power.
There was an other auction on there too, just something to keep in mind.
:

 

[amk54055]

Re: Low Power at WOT

My boat is fixed. It was the Trigger. Funny how I took it to the experts and they replaced the switchbox for $500 and didnt help. I simply used a DVA to check the resistance on each wire per the spec and one wire was out of range. So I ordered a trigger and now it runs like a scalded dog. However, one other issue. It seems that I not have a starting issue. IT has always fired off real good until now. It is hard to get this engine to fire now. Any thoughts on why I would be have starting issues now? It seems to not be firing/ not hitting, like no spark... Any ideas on what to check?