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1998 Johnson 150 Blowing O-rings

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nfelan10

New member
I've got a good one here guys. I have a 1998 Johnson 150 it has blown O-ring head gaskets twice on starboard top cylinder and starboard middle cylinder and now fowling out the plugs amd bogging after about 5 minutes of running 75% throttle. I have replaced thermostats and water pump after the over heat problem. The VRO is bypassed and am currently mixing 50:1. The only thing i have not replaced is the temp. sensors. I know they are bad because the last time it overheated it melted them. I don't think the temp. sensors are the problem. Any help would be appreciated i have a couple of problems here not sure if i should re connect the VRO or change my oil to fuel mixture for the bogging problem if that would fix it. The blown o rings have me stumped though.
 
IS this a FICHT or FastStrike motor?

Bogging and plug fouling has nothing to do with pre-mix. You either have a weak spark/failing ignition component or your carbs are bad and over-fueling the engine.......Or both.

Blowing 2 sets of O-rings the exact same was is odd. I'd bet your heads are now warped and that is causing your repeated problems. Also, if you got hot enough to melt the temp sensors you likely have bigger problems. At bare minimum you need to have the heads checked for flatness and machined if possible. If they can't be machined you need to find good replacements.

Be sure to inspect the condition of the pistons and cylinder walls when you pull the heads. If it got that hot you could have damaged the pistons.

KJ
 
kevinj said:
IS this a FICHT or FastStrike motor?

Bogging and plug fouling has nothing to do with pre-mix. You either have a weak spark/failing ignition component or your carbs are bad and over-fueling the engine.......Or both.

Blowing 2 sets of O-rings the exact same was is odd. I'd bet your heads are now warped and that is causing your repeated problems. Also, if you got hot enough to melt the temp sensors you likely have bigger problems. At bare minimum you need to have the heads checked for flatness and machined if possible. If they can't be machined you need to find good replacements.

Be sure to inspect the condition of the pistons and cylinder walls when you pull the heads. If it got that hot you could have damaged the pistons.

KJ
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The tops of the pistons are charred and black not sure what that would indicate the cylinder walls were pretty clean but the pistons were pretty bad a bunch of this black stuff that I couldn’t get off by whiping with a rag.
 
Whats your compression numbers and heads have to be warped to blow o-rings. The 60° motors just dont have this type of problems
 
faztbullet said:
Whats your compression numbers and heads have to be warped to blow o-rings. The 60° motors just dont have this type of problems
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Port side compression
Top: 90
Middle: 90
Bottom: 90

Starboard Side compression
Top: 95
Middle: 92
Bottom: 85

This is with putting new o-rings on starboard side yesterday and running it at 75-90% throttle for about an hour before the new o-rings the top starboard was at 60 that was second time it blew
 
A FICHT does not have VRO.----A FICHT can not run on a 50:1 mix of fuel.----Any pictures of this motor including a few of the powerhead !!
 
Why yes the model # says it is a carbed motor.---Have a pair of these V-6 motors myself.-------Then the OP says it is a FICHT.-----So I do not know what he has !!
 
Either Ficht or carb doesn't matter...heads are warped and need to go to a machine shop and have trued...glass and sandpaper aint going to true these..If over .030 have shop cut radius back into head.
 
nfelan10 said:
The tops of the pistons are charred and black not sure what that would indicate the cylinder walls were pretty clean but the pistons were pretty bad a bunch of this black stuff that I couldn’t get off by whiping with a rag.
Click to expand...
That's just combustion residue which is good. Completely clean means you're ingesting water and 'steam cleaning' the tops of the pistons.

On the cylinder walls can you still see cross hatch? Are there are cuts or grooves?

Overall it sounds like your pistons and cylinders are okay.
 
faztbullet said:
Either Ficht or carb doesn't matter...heads are warped and need to go to a machine shop and have trued...glass and sandpaper aint going to true these..If over .030 have shop cut radius back into head.
Click to expand...
This or find some good used heads to replace them. You're going to keep blowing o-rings because these heads are waaayyy out of true. You're beyond the point of replacing gaskets now.

Also, be certain to replace those temp sensors and it's also a good idea to run a water pressure gauge up at the helm so you can get a look at water flow into the engine.

KJ
 
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