Make sure the points are set properly. Check em with a dwell meter. The coil
could be breaking down or the tach could be acting up. If you have
electronic ignition instead of points, you can add the sensor in the
distributor and control module to the list of things to check.
JIMinFL
wrote in message
oups.com...
I'm at my wits end....My 1998 Mercuiser 3.0L has been very reliable
until the end of last year and the beginning of this year. My engine
will start fine, idle fine and run great until I get up beyond 3000rpm
or 30+ mph. At this point the engine acts like it backfires (best
description), lunges, and loses power, but never stalls. The tachometer
goes to 7000+ but the engine is not running 7000rpm. After the engine
warms up running at 3500 rpm the tach returns to normal and the noise
(backfiring) goes away. If I stop the boat and sit fro 30 minutes the
process repeats. I've done the following:
1. Changed plugs
2. Changed rotor/ditributor
3. Changed plug wires
4. Replaced fuel filter
5. Cleaned carburetor

Any help would be appreciated. Thanks, Dave