1996 4.3 Mercruiser issue

[Ztharris06]

New to the forum. I have a 1996 Rinker with the 4.3 Mercrusier Gen +. It starts and runs like a top. After about an hour in the water it starts backfiring and doesn't want to take throttle. Will idle fine at this point as well. Have changed coil, cap and rotor. Any suggestions. Does the ICM on these motors give issues?

 

[alldodge]

Use an IR temp gun and verify its not overheating. Measure the thermostat housing
Check your timing, TB4 is 8* and TB5 is 10* BTDC
If all is good, get it warmed up and check compression

 

[achris]

Sounds like it's running lean. So why is it taking an hour to run lean? I would suspect the tank vent is blocked. That would also explain the idling ok. Next time it does it, open the fuel tank filler cap and listen as you do, you may hear air rushing in. If that fixes the problem, or you hear that air rush, find the vent blockage and fix it. Do you get 'blow back' when filling your tank? If so, that's another indicator that the vent is blocked.

Chris..........