Starting point for idling/performance troubleshooting

[fisher91blue]

1992 4.3L GEN II, 2 BBL, Thunderbolt IV

Recently, have had some issues that I would like to try to resolve while boat is in water for the season. Trying to determine if I should start with fuel, choke (air) or distributor/plugs/wires? Any help from the experienced members would be greatly appreciated.

Symptoms:
1) with fresh gas (albeit only a few gallons) the motor stalled multiple times moving from launch to dock slip when I advanced throttle
2) idles rough and seems low, around 350 RPM
3) at times, when engine is warm or when cold, attempting to start, will crank but doesn't fire, then eventually fires up
4) sometimes with throttle in neutral, when key turned I hear 1 single "click" then nothing. after I wiggle, it will turn over normally
4) noticed some hesitation and surging at low RPM speeds, like travelling through "no wake" zones

I have slightly adjusted idle at carb to increase RPM, fueled 2x since first noticing the issues with no apparent improvement. Batteries are tested regularly and strong. Both batteries on solar trickle charger when boat is not in use.

Open to suggestions for a starting point so I don't try to chase too many rabbits at once.

Thanks

 

[itsathepete]

First off, what is the engine serial number? This will give those with the resources available a chance to look up specifics on the engine. Second, how long have you owned it and what is the maintenance history and how long have the problems been occurring?
I would start with checking the tach for accuracy by using a strobe tachometer. You can download a free app on your phone which works well. Make a white mark on the crank pulley and check a range of rpms against the tach. Adjust tach/idle as needed. Check ignition timing and adjust as needed. Probably needs the water separating fuel filter replaced if not done recently. Pour contents out on a clean paper towel and inspect for water/debris. Cut open if you like. Very possibly needs a carb rebuild. Pull distributor cap and check for burn marks/corrosion. Clean/replace cap and rotor as needed. Inspect plug wires for cracks/dry rot/arcing. Replace if needed. Inspect spark plugs for running condition. White is lean, black is rich, oily or cruddy is burning oil. Make sure the straps are not corroded and they are gapped properly. Replace if needed. Choke should open as engine warms.

 

[fisher91blue]

Thanks itsathepete, I like those as a starting point before I buy a bunch of parts. Will definitely change the fuel filter. I’ve owned boat 5 years and have had seasonally maintained by pros near me. Storage inside for winter.

Serial 0D724261

I attempted pulling distributor cap over weekend but ran into a stubborn screw and didn’t want to strip the head. I’ll have to work that out.

 

[itsathepete]

click your hear when attempting to start is starter relay or slave solenoid or starter solenoid. If your neutral safety switch wasn't working, you would hear nothing. clean off all the electrical terminals on battery, starter, and any other solenoids as well as grounds

 

[Rick Stephens]

I'd agree that starting with wire brushing battery connections is a great place to start. Take them apart and brush until shiny clean, then reassemble. And also agree the usual candidate for trouble is both ends of the ground wire.

After that I foresee a carburetor kit in your near future.

 

[Bondo]

Thanks itsathepete, I like those as a starting point before I buy a bunch of parts. Will definitely change the fuel filter. I’ve owned boat 5 years and have had seasonally maintained by pros near me. Storage inside for winter.

Serial 0D724261

I attempted pulling distributor cap over weekend but ran into a stubborn screw and didn’t want to strip the head. I’ll have to work that out.

Ayuh,..... Don't just change it,.......Examine it's contents for clues, in a clear container,.....

 

[fisher91blue]

I'd agree that starting with wire brushing battery connections is a great place to start. Take them apart and brush until shiny clean, then reassemble. And also agree the usual candidate for trouble is both ends of the ground wire.

After that I foresee a carburetor kit in your near future.

I pulled and replaced plugs, wires, cap rotor and ignition sensor. Set idle and have it running pretty smooth between 600-700 rpm. When I advance the throttle, it "gasps" almost like a suction sound. (my first edit said bogs but the more I thought about it, more like a gasp) I wanted to try adjusting idle mixture screw before moving along but wanted advice on how to adjust? I have a 2bbl mercarb. The front of the carb has a small screw but it's virtually impossible to get at while the boat is running. Any tips for adjustment? Reasonable access is blocked by the intake manifold and front cover. I've read its good to adjust when running? TIA

 

[ROY WILLIAMS]

the engine is a tappet noise ....
did the engine oil is water in it ..

 

[fisher91blue]

Just changed oil and still have old oil in clear jug, no milkiness, no separation. New oil is a bit over full on the dipstick though, which I attribute to the replacement filter being smaller than the original.

I did also have to replace the oil pressure switch, located near the oil filter. After the oil change, I was checking the filter for leaks and found the old switch to be leaking.

 

[Scott Danforth]

I pulled and replaced plugs, wires, cap rotor and ignition sensor. Set idle and have it running pretty smooth between 600-700 rpm. When I advance the throttle, it "gasps" almost like a suction sound. (my first edit said bogs but the more I thought about it, more like a gasp) I wanted to try adjusting idle mixture screw before moving along but wanted advice on how to adjust? I have a 2bbl mercarb. The front of the carb has a small screw but it's virtually impossible to get at while the boat is running. Any tips for adjustment? Reasonable access is blocked by the intake manifold and front cover. I've read its good to adjust when running? TIA

my guess is you need to take the carb apart and go thru it. I would lean toward the accelerator pump not working