01 Johnson sparadically loosing RMP's at WOT

HELP-01 Johnson sparadically loosing RMP's at WOT

I have a 70 HP 2001 Johnson that speradicaly looses power at WOT and rpm's drop to 2800-3000 but it still runs smooth.

Sometimes it will run fine all day but most often after a mile or so is when the power loss occurs.

The marina replaced the power pack, same issue, they then replaced the stator, same issue. It's not carbs as they were rebuilt last year and the marina took them apart to check again this year.

Thought it was gas issue but ran 15 gal of fuel out of the tank put new gas in and that didnt help either, even replaced the fule filter/seperator several times but no water and little to no sediment.

Any ideas? Thank you!

 

Sounds like you are losing a cylinder intermittently. When it loses power, and after a period of running that way, check the appearance of the spark plugs. They should all be looking dry and a grey/tan colour. If one is looking oily, it is likely the cylinder you are losing. I assume they replaced plugs and tested ignition coils and leads. If there is an oily plug, it likely isn't a fuel problem, but an ignition one.

 

Thanks for the info. they did put in new plugs in and I too assume they checked the coils and leads but maybe i should ask them to be certain. I'll pull the plugs next time I have it out when it acts up and check them.

if it is a cylinder failing intermittently how is that corrected? new gaskets?

 

If you are dropping a cylinder it is either no spark or fuel starvation, preferably the former since prolonged lack of lubrication from no fuel is no good for those parts not receiving it through the 2-stroke oil. An engine with multiple carburettors can experience a fuel supply problem that affects just one cylinder, but lack of spark is more likely.

 

Make sure its not fuel. A two stroke actually requires more fuel than is needed for combustion. It has to have additional fuel to actually cool the cylinder. Lack of this extra fuel leads to expansion of the aluminum piston which creates extra drag in the cylinder. Lean mixture. Although it may not be running lean enough t stop running, it may be enough to cause internal damage. But it sounds to me like the problem might be in the exhaust port cover. Leaking water port jackets may not be a problem until engine reaches a certain tempature and the metals start to grow with the heat. One thing to check for sure would be to make sure you have the proper spark plugs. More than libkely you should have a l77j4 or l77jc4 which is a copper elimate plug of the same heat range....the wrong plugs can also be self destruction.... two strokes are real tempermental to all of these issues. Its something that's really hard to diagnose without being able to to see or being there first hand.

 

sensor coil or plug coil

 

I hate to bring this up but it may be water getting onto your plugs from a rusted out cylinder liner or a leaking water jacket gasket.I experienced this myself and it was horrible.

 

Only gasket in that year/model that can let water in is the head gasket
A head gasket on a 2 stroke outboard should be viewed as a consumer-able and be changed every other year, you also get a look inside to be sure.

Enough water to kill a cylinder will leave water on the plug so will be easy to find.
Small leak usually goes unnoticed and then rusts the internals away.
That era 56ci OMC is pretty tough, its the culmination of over 20 years of development in the 3 cyl engine.
There were some mods to the cooling system on some particular years then, ( due to block casting changes) ask your dealer to check his Service Bulletins

 

Is the fuel line in good shape? Sometimes they can look OK but have internal restrictions.
Verify the fuel tank vent is not clogged.

 

Well?