Secondary ignition breakdown. Look for cracked plugs, arcing plug wires
or cracked/carbon tracked dist. cap/rotor. Also, possible open circuit
in dist. pickup wires when advance plate moves with RPM.
JR

Paul wrote:

Hi All,

This is a 4.3 V6 Merc newly rebuilt. EST, magnetic points. Boat is 19
ft B/R with 19P Laser II prop.
Idles OK, goes to 2000 rpm and that's all. When trying to accelerate
above that it backfires and stumbles, rpm drop to below 1500. You back
the throttle off and it speeds up (but not above 2000 rpm). It won't
plane.
Pushing the throttle all the way will cause carb and exhaust backfire
and stumble with rpm drop but it won't die (accelerates and decelerates
on its own erratically).
Wires are OEM Merc old but seem good, distr. cap had a tiny (!) crack
(from constant manipulation) on the outside of no.1 collar but I
covered it with lots of epoxy (no.1 fires OK). Timing 4-8 deg. before
TDC (not much change). Idle at 550 is OK up to 2000 in neutral (never
tried above unless in gear). Problem appears at higher rpm. Don't wont
to kill freshly rebuilt engine...

How to test all ignition components? Could this be fuel starvation
(pump or fuel tank vent)?



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