2002 bf 225 spark knock ??

I spent the winter rebuilding my BF 225 outboard had 3 cracked pistons all on the port side of motor. Replaced 3 pistons all 6 cylinders were honed and all new rings had the heads rebuilt which had 3 bent valves . from the damage I believe the motor went out of time which cause severe detentation. Replaced all belts (fun getting the cams in time but I got it) Last weekend was the first time getting the boat out took it easy first 45 minutes (below 2000rpms)Ran fine until on the way back after about 2 hours then the motor began to surge between 3200 and 3400 rpms. Then a loud popping or maybe even a banging sound every 40 to 60 seconds slowed down to 2000 rpms with no alarms sounding made it back home but now I'm at a loss ! Just thinking of doing another compression check to make sure no valves hit the pistons and thinking maybe the fuel lost its octane from sitting al winter but it was treated with startron as is all my fuel. ANY THOUGHTS WOULD BE GREATLY APPRECIATED THANKS , Rob.

Simple things first - Sounds like a classic misfire, so eliminate the fuel as a problem by hooking up a portable tank with good fuel. Remember, at idle, it takes at least 15 minutes to burn out all the old fuel. Pull the plugs and check them for carboning up, or for no burn at all. I assume you used new plugs on the reassembly. If not, install new NGK's. While doing that, test each coil. Your shop manual will have the specs. I assume while you had the ngine torn down you cleaned the VST and changed the high pressure filter. Still, you might want to re-do that since it is very easy for debris to get into the fuel system during a rebuild.

I like (as usual) chawk_man's suggestions and would add to check to see if it has logged any codes. If it has, that could get you started on a troubleshooting path.

Also, if it were me, I would go back over all the timing components that I had reinstalled. It is not unheard of for a tensioner or pulley bearing to be bad right out of the box. That could put you out of time and more bent valves in the near future.

Chawk_man makes a good point about the coils. The only problem is, if you do have one or more "breaking down" as they heat up, they might still pass a continuity check. The only sure way to know is to put them on an oscilloscope and look at your wave patterns compared to known good patterns. Not a procedure most of us can do at home.

Hopefully it's something stupid simple.