Mercruiser 5.7L misfiring

[Cruisers1]

1992 5.7L with TB-IV ignition.

Did a tune-up- plugs, wires, cap and rotor. Timing is right on at 8degrees. Sensor in distributor and coil were changed 2 seasons ago.

When cold start engine is misfiring and will continue to misfire even when it's warmed up.

If it's shut off after warm-up and restarted 10 to 20mintues later it fires up and there is no misfire huge difference in engines performance.

Next day tried to start , same thing when cold rough operation clearly misfiring. Pulled plugs and found 7 of 8 have fuel traces. Installed new MR43Ts gapped to 35 thousandths.

Allowed engine to warm up as it continues to misfire. Shut it off waited 20 mintues and restarted it. Misfire was gone and engine had significant change in time and reaction to throttle.

Stumped....anyone have an idea?? Or what step to take next?
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Thank You!!!

 

[Scott Danforth]

look at your fuel system

start with the contents of your fuel filter, make sure its pure fuel and no water or crud

 

[Cruisers1]

The filter water/sep was changed at end of last season before layup. I can certainly pull it and check again. Thank you!

 

[Scott Danforth]

remember, when you pull the filter, you need to install a new one.

when was your carb last taken apart and serviced?

 

[Cruisers1]

Carb was overhauled beginning of last season. Engine ran well all last season.

 

[alldodge]

If your distributor has the 2 wire sensor and not the 3 wire, suggest replacing it. This may not be the issue but there is an issue with the 2 wire loosing its ground

 

[Cruisers1]

It has the ground wire. I verified it was clean and tight. Last night.

Very puzzling.

 

[alldodge]

Connect a voltmeter on the + side of the coil and leave it there. Find out if there is any voltage issues