96 Honda bf8a stalls after 15-20 min. running

I changed all the oils, impeller looked fine. It seems like it gets hot and then it stalls. Sometimes it will restart. Let it sit and it runs 15-20 min. Could it be spark plugs or did the head get warped due to overheating.....Any ideas?

Is it overheating? You mention overheating and head warpage....DID it overheat at one time?

Is it pumping a good stream of water from the tell tale?

If it is overheating and shutting off "by itself" that is NOT good. Each time that happens a little more engine damage is likely occurring. You should run it as little as possible to determine if it is overheat causing this.

If it is not overheating....then it COULD be an electrical problem in the ignition system. If you can be certain it's not overheating then you will need to find out if it has spark or not when it shuts off. The easiest way to do that is to pull a plug and ground the electrode "strap" on the end and watch for the spark to jump the gap. Doing this in the dark or with a blanket over your head and the engine makes it MUCH easier to see.

If it still has spark and is not overheating....then it COULD be a fuel delivery issue. Sometimes it can be as simple as the gas tank vent is not opening all the way and, as the outboard "sucks" fuel out of the tank, a vacuum builds up in the tank and stops the flow of gas. This usually happens within a couple of minutes for a completely closed vent screw....but a partially plugged one might take a while longer. Simply running the outboard with the fuel cap loose on the tank would eliminate this as a possibility.

Another thing that can happen with these older engines is that they will develop an exhaust leak and, after a while, the fumes build up under the hood and simply starve the engine for oxygen. You can test for this by simply running the outboard with the cover off and secured. If the engine runs without stalling with the cover removed...then it is likely an exhaust leak that was causing the stall.

PLEASE determine if it is overheating or not and then...and only then....continue to run it to try the other stuff.

Good luck.

Another thing that can happen with these older engines is that they will develop an exhaust leak and, after a while, the fumes build up under the hood and simply starve the engine for oxygen. You can test for this by simply running the outboard with the cover off and secured. If the engine runs without stalling with the cover removed...then it is likely an exhaust leak that was causing the stall.

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This happened to mine, the exhaust tube was indeed cracked and had to be replaced.
fairly labour intensive