1973 Johnson OMC 9.5 runs then dies

I bought the motor last fall the seller said it ran great but after cleaning out about a half an inch of gunk on the bottom of the carb I figured there were probably more issues. I am having problems keeping the motor running after about 5 mins on the water. I have tried running it in a large barrel but it only seems to kill under load (I had the prop off in the barrell) it had good spark for about 10 mins (at full throttle) via inline spark checker in the barrel. I think it is probably the coils but I would like the opinion of someone who has delt with the motors before. I have also already pulled the flywheel to check the points, the gap, the coils (visually anyways sometimes they crack) the plugs are fine also. The motor takes a little while to get up to full throttle and once it does it dies.

Re: 1973 Johnson OMC 9.5 runs then dies

Try running w/the cowl off. Those motors sometimes get the shiftshaft seal torn below the powerhead, and exhaust gets under the cowling, effectively displacing oxygen and flooding your motor out.. not enough O2 to combust properly.

Re: 1973 Johnson OMC 9.5 runs then dies

Did you put a new carb. kit in it and clean the carb. with carb. cleaner? Also you should have removed the high speed jet and cleaned it out as well. If it is truly five minutes or any consistent time it makes me think the float is sticking shut or a tank vent problem. Have you tried pumping the bulb when it is about to die? You can pull the plug wires one at a time and see if it dies even if the points look good and are gapped right (.020) it never hurts to clean them. Best of luck. Rick.

Re: 1973 Johnson OMC 9.5 runs then dies

I have tried running it with the cover off because heard they do that but it didn't alter the performance. The carb kit is new along with a new fuel pump. The tank and fuel line are also new. The 5 mins alters too sometimes it's just a few mins. The high speed jet has been cleaned a couple of times because it seems like the obvious fix but it didn't fix anything. The strange thing is that the motor will remain at half throttle until it gets up to full throttle (which is gradual) even though the throttle is open the whole time and then it dies.

Re: 1973 Johnson OMC 9.5 runs then dies

Sure sounds like your not getting enough fuel but I don't understand why it would shut down once you reach top speed rather than sputter or go back to half speed. Try pumping the bulb to see if it maintains full speed. Rick.