90 hp johnson no power

[seanross]

hi. i have a 90 hp johnson vro. it runs fine when cold for about the first 10 minutes on the lake. at full throttle im pulling about 4300 rpm. then it starts losing power. at full throttle i can only get 1500-2000 rpm out of it and cant even begin to get the boat to plain if i hit the choke it gets power momentarily. this tells me its starving for fuel. yet at idle its flooding. it dies and requires full throttle to start. gas tank vent checked. carbs drained so no water. any ideas? thank you

 

[bustermin]

Re: 90 hp johnson no power

hi. i have a 90 hp johnson vro. it runs fine when cold for about the first 10 minutes on the lake. at full throttle im pulling about 4300 rpm. then it starts losing power. at full throttle i can only get 1500-2000 rpm out of it and cant even begin to get the boat to plain if i hit the choke it gets power momentarily. this tells me its starving for fuel. yet at idle its flooding. it dies and requires full throttle to start. gas tank vent checked. carbs drained so no water. any ideas? thank you

A little history may help. Is this the first time out since dewinterizing? has anyone done anything to it recently? did you check pick up tube in tank, filters, spark, compression, ect. when was the last time the carbs were rebuilt? what do the spark plugs look like? is it running hotter than normal, when was the last time the impeller and thermostat were changed, is there water coming out of the tell tale, is it too hot to touch?

 

[seanross]

Re: 90 hp johnson no power

i just bought the boat. new fuel. compression good. not overheating (pumping water fine). im leaning towards carb trouble. does anyone know anything about these two barrels? what type of carb are they? thanks for the help

o and yes the pickup tube is clear. fuel filter is good. no air filter.

 

[Evinrude Boater]

Re: 90 hp johnson no power

Does the gas line bulb stay firm when running the engine. Do the rpms speed up if you manually pump the bulb when you have the problem?

 

[seanross]

Re: 90 hp johnson no power

bulb stays firm. havent try'd pumping it while at wot. but like i said choking it does give a momentary boost.

 

[tashasdaddy]

Re: 90 hp johnson no power

1st question, no one asked. what 90 hp, they have been built since the 60's. year model #.

 

[cdoliver]

Re: 90 hp johnson no power

need model number as Tdaddy has already said

1. Clean/rebuild carbs
2. make sure it has correct plugs
3. Check spark on all 4
4. I'd decarb a new-to-me engine
5. 4300RPM's isnt enough, we need at least 57-5800rpms @ full throttle-Recheck that after you clean carbs.

Don't run this motor again until you service these carbs

 

[Home Cookin']

Re: 90 hp johnson no power

Let me ask you this: If you have this problem, and don't try to restart but let it cool down for 30 minutes-an hour, does it run well for the first 10 minutes again and then start slowing down? If so, it suggests to me that it is overheating, or (worse) that it was run hot previously, and that did enough damage that the warped parts show themselves when you get good and warmed up, but not so much damage to stop it completely.
I had a VRO that ran dry of oil. The next day it started fine and ran for a short while, then "slowed down" like it did before. Mechanic verified the damage, but my experience suggests there could be a lesser degree of damage. But I'l say this: I've had experiences but don't have the knowledge, so the pro's here can say if my assumptions are way off base.

 

[seanross]

Re: 90 hp johnson no power

found the problem. top left hand cylinder (dont know what number that would be) is taking on water. head gasket?

 

[emdsapmgr]

Re: 90 hp johnson no power

The head gasket would be the first thing to replace. You could also have an exhaust cover water leak, though most of these show up with water in the lower cyls.

 

[bang4dabuck]

Re: 90 hp johnson no power

I'm curious, did you do a compression test before you bought it ? I'm no expert so I'm not sure it would have found that problem a 100% of the time. Then again it might of happened right then and there on the lake. My novice guess is it overheated and head gaskets or water jackets are gone from saltwater use. Not sure why the adjacent cylinder wasn't affected.