producing soot while trolling.

[rolmops]

1985 3.0 liter mercruiser on a 19 foot islander.
When I troll at 800 to 1000 rpm, things go fine until I increase rpm. The engine will cough up a pile of sooth and run very irregular for a while until all the black stuff has burned off. Usually the plugs will turn black,but after running at WOT the plugs will clean up again. Any suggestions on how to solve this problem?
Thank you ,Cornelis

 

[Grub54891]

Make sure the choke is opening properly, and yes they do carbon up when idling along for long periods of time. A kicker motor will use less fuel for fishing times, and is a good backup if the main breaks down.

 

[Scott Danforth]

agree on checking the choke. also drop a few inches in pitch will keep the RPM's up a bit more to get the carb out of the idle circuit. I used to troll with the 15p that I used for motor sports to keep the motor up in revs.

 

[dingbat]

water temps where you're fishing?

Had the same problem with my 3.0 when we fished the Steelhead run at Sodus years back. A higher temp thermostat seemed to help.

If that's not the issue, you have a vacuum leak, carb float out of adjustment or perhaps a stuck PVC valve perhaps.