Johnson 9.5 hp wont hit high rpms, why!??!!?

Question

I have a 1967 Johnson 9.5 hp outboard. It has been sitting awhile and I have ran almost 3 tanks of fuel through it. A few days ago the motor, which pushes a 14ft Alumacraft, ran better that it has since I got the dang thing. This last weekend I took it to the lake to go fishing. I had half a tank of oil fuel mix left and decided to top it off. I put more gas in and kinda guesstimated on the oil input. I also added half a can of Sea Foam. After getting into the lake and trying to go wide open, the motor hesitated and just did not hit the rpms it was the day before. I have been asked if the rubber exhaust boot is cracked causing exhaust to recurculate to the carb. Not an issue. The plugs are good, points were checked. Could it be that I mixed the oil too thick when I put more gas in? Or would the half a can of Sea Foam affect anything? I took the carb and intake off today and cleaned everything I could and still runs low rpm. Any suggestions?? Thanks Travvis

Answer 1

make sure the tank vent is open, and that the fuel line isn't sucking air.

soak the carb overnight in berryman's b-12 chemtool.

evaporating gasoline leaves behind a varnish that clogs the tiny passages in your carburetor.  You can't detect it visually, and you can't really get in there to clean it out manually.

The seafoam will clean the carbon deposits out of the cylinders (that's a good thing), so the motor should be smoking like crazy from that, and it'll probably foul the plugs -- if they're good, you can clean 'em & put 'em back in.

Too much oil will have a similar effect.  I've never believed that precision is required when mixing the oil, but I usually measure to the nearest ounce or so.  ;)

Might want to check the compression, but I bet a good soak for the carb will do the trick.

Answer 2

First, I agree with everything jtexas says.  Clearly he knows his stuff.  Now, empty your fuel tank and start with fresh 6 gal, even use high test if you like.  Mix 50:1 oil, use TWC2 or 3.  Drain the carb or run the gas out before hooking up the new fuel.   Don't forget the stuff left in the hose. Clean the plugs.  And check the fuel filter.  A screen under the black plastic connector.   Now start it up.   If it still want run, hook up a timing light to first the top cly, then the bottom one.  Try running up to speed and watch the light.  Good Luck!!!!1