99, 5.0L Mercruiser, Carbed- misfiring and backfiring

[johno270583]

Hi Again

Boat had been running well apart from some hesitation issues from idle on acceleration, until a couple weeks ago.

This was even worse on last outing, I put a 1' spacer under carb to lift away from motor and try get some more low end torque. Motor coughed and backfired to start off, then eventually started running better. However hesitation at idle was much worse, and had to double pump throttle to help get it going.

Pulled plugs the next day and they were BLACK. Cleaned, regapped and reinstalled.

Fired up in the driveway, however was pushing alot of black smoke, and leaving a film of black muck on the drive, floating on the water. Not sure what this is, but thinking/hoping unburnt fuel? Also was backfiring occasionally when revved in neutral.

At idle, motor is noticeably missing. I have hooked up timing light to check, and the light would only flash occasionally, or for a short while, which at first I put down to my gun not working properly, but the more I think of it, maybe because the lead isnt actually getting a spark.


Have 12V at the coil, only 11 at the Red/White lead on the ignition sensor/distributor. Also hooked an ohmmeter up between red/white and green/white leads on Ignition sensor, and there is no reading, manual says should be 100 ohms.

If the Ignition Sensor is bad, will the boat run at all? With the above test of no reading between the 2 leads, its about all I have left in my inventory to check.


Im just about out of ideas on what this could be, Distributor Cap, rotor, sensor wheel, ignition sensor, leads are less than a year old. Holley carb which I have had off, cleaned and checked. Timing set to mark on crankshaft, which I assume is correct because there is only the one mark. I have this week pulled off the intake manifold and resealed with new gaskets and sealant, and also the carb, so am now assuming any air leaks would have been taken care of.



Any ideas would be greatly appreciated.


Also, anyone want to but a 1999, 1900SR in Australia??!!!!


Thanks

Andrew