1978 85hp not getting full power

[Evergold]

My 1978 evinrude 85 hp has always run well
all of a sudden I'm not getting full power
and it won't get out of the hole like it used to
Compression is 120 119 115 117
I did a spark test and it has good spark
I rebuilt the carbs and took them apart for the second time to recheck them they are definatly clean
I tried doing a cyl drop test they 3 of the cyl you see a big diffrence in the way the motor runs but on one of the cyl the motor changes the way it runs when I pull the plug wire but not as much of a diffrence as the other 3cyl
also I didn't do a link&synk whem I rebuilt the carbs
I have the factory Repair Manual but I'm confused and don't understand how to do it
I'm stumped on this

 

[racerone]

The one cylinder that does not change much is the problem.----Find out what is wrong with it.---I do not believe the much " hyped up " link and sink " has any thing to do with it.

 

[oldboat1]

Might also check for water in the fuel or in the hull.

 

[Evergold]

The hull was just redone this winter so I know its bone dry
the gas is only a week old
It there any way I can check if the bad cyl is getting gas

 

[racerone]

Remove the high speed jets from the carburetor bowls.----No need to remove the carburetors to do that !!------Possibly one is BLOCKED.-----Do NOT RUN this motor until you confirm carburetors are clean.----A blocked jet may mean you are starving one cylinder of fuel.----And of course OIL as well.----Your motor could suffer big $$$ damage if you continue to run it as is.----Or bring it over as it sounds like an easy fix right now.

 

[Evergold]

I've cleaned the high speed jets ....no change
I rebuilt the carbs again ....no change
I did notice on my test run this last time it took off really fast like it used to for about 8 seconds then it lost power again and when I'm going slower you hear the motor occassionaly surge with power for a split second then it goes back to not running properly
I switched all the coils around and switched the power packs around and still that one cyl dosent make a big diffrence in the way the motor runs if I pull the plug wire
What should I look into next ?

 

[racerone]

Which cylinder is the trouble cylinder ?-----Also inspect fuel pump diaphragm.

 

[Evergold]

If your looking at the motor from the back it's the lower right cyl
I replaced the fuel pump with an extra one I had on hand that I know works with no change
Could it be an electric issue possibly something under the flywheel

 

[racerone]

Hook up a timing light to # 1 cylinder.----Take boat for spin on the river.-----Observe the flashing light.------Repeat test with other 3 cylinders.----Post what you see.------If spark is good on all 4 then likely not a spark problem.-----Could be a bad plug wire / boot shorting to the cowling as well.----Run boat / motor on the river while shining a strong flashlight into each carburetor bore.-----Observe / compare fuel coming up the main nozzle.

 

[Crosbyman]

can you run it in the dark and look for arcing ?

 

[Evergold]

I will try running it in the dark tonight
Will any timing light work?
Could I be overlooking something like an airleak between the carbs and manifold?

 

[racerone]

If the motor takes off and runs properly for 8 seconds there is NOT a problem with an air leak on the intake side !!-----Do some simple trouble shooting here.

 

[Evergold]

What will i be looking for with the timing light

 

[racerone]

???----If the light flashes continually without black spots spark is good !------Why has simple trouble shooting gone ---" the way of the Dodo bird " ?

 

[Crosbyman]

Manufacturing industry made it happen.... nobody can fix a toaster or a TV these days everyting is welded, glued, molded, fragile, complicated and
cheaper to replace so why bother . the next generation of home handymen better have lot of cash .

 

[Evergold]

Sorry guys...... im a big do it yourselfer and I work I've worked in a body/collision shop my entire life but a timing light is one thing I've never used
Im going to test it this week

 

[Evergold]

Ok I tried the timing light I didnt see anything that caught my eye
Rechecked spark and it was good
Rechecked compression
I think I'm going to tear down the carbs again
I'm really starting to think it's a fuel issue

 

[oldboat1]

Ok I tried the timing light I didnt see anything that caught my eye
Rechecked spark and it was good
Rechecked compression
I think I'm going to tear down the carbs again
I'm really starting to think it's a fuel issue

How are you checking spark? Should be measuring it with an open air tester -- close to 1/2 inch is "good", indicating ignition is doing its job.

 

[Evergold]

yes I've tested it multiple times with an open air tester

 

[Spartans]

Ok. Seen this before. Again my motto is low hanging fruit. You have swapped the suspect coil out with a known good coil and no change. Start there and work backwards in through the harness. If a good coil is not working it’s not getting a proper feed

My issue was mice and I could not readily see the damage to the wire