need help, merc 260 thunderbolt IV engine dying

Make a long story short, started season and when running sounded like water in the fuel. Lot of coughing in the carb. rpm would not get over 3K. Checked fuel and filters. (all good) Knew I had cleaned my distributor housing before and there was some residue in there. Decided to change distributor and coil. Replaced and engine started no problems, sounded good, timed correctly. Went for a ride and engine quite after 30 minutes of idle speed. Would not start back up. Got towed, at mooring played with the carb and started back up, would run for a minute or 2 then just die and then the backfiring began. Carb had not been done in years so I purchased a rebulit carb (rochester quadrajet). Started up, adjusted idle and appeared just fine. a little back fire, but not much. Then if it sat it would start, run for 5 to 15 min. back fire and die. Run period got smaller and smaller.

Now it will fire up, run for 5-10 seconds and backfire and die.

I have replaced distributor, starting coil, carburator, plugs and wires are 6 months old, clean. Checked fuel pump, checked tank vents, plenty of fuel getting to carb. Could the ignition sensor have anything to do with this?

mercruiser 86 engine 260hp thunderbolt IV, 700 hours

Please advise or HELP!

Re: need help, merc 260 thunderbolt IV engine dying

You said it sounds like it was running on water but make no mention of cleaning the fuel tank out. I would run it off a separate auxiliary tank and see how she does.

Re: need help, merc 260 thunderbolt IV engine dying

thanks, but tried the auxilary tank already and same results.

Re: need help, merc 260 thunderbolt IV engine dying

Are you sure the float is set correctly?

Re: need help, merc 260 thunderbolt IV engine dying

The distributor sensor and ignition module could be a cause of this. do a search for thunderbolt iv ignition test. hopefully it is the sensor, because the module is almost 500 buckaroos.