Fuel or Ignition Problem ?

[JSM]

Hello All. Helping out a new owner who bought my old boat. They limped into the dock this weekend with the engine sputtering at idle. Increasing throttle only bogs the engine down and kills it.
Last year the engine was given a complete tune up and a new electric fuel pump was installed. Everything was running fine.
So far we have drained the fuel filter (no water), checked fuel flow from the pump, also seems fine. Removed the carb and opened it up, all looked good blew out the interior,jets etc. with carb cleaner and reinstalled to no avail.
My next thought is to rebuild the carb . I owned this boat for 30 years and know that the carb was never rebuilt so we figure a rebuild is in order either way.
Wondering if I should be looking for a possible ignition problem. New points , rotor and condenser and wires were installed last year.
Thanks.

[wristwister]

So the engine starts and runs, just very rough? If so, pull one spark plug wire at a time while it's idling. You should see/hear a noticable difference with each plug. If not, maybe you've got a cylinder or 2 that aren't firing.This will lead you down the path to that cylinder and you can check plug/wire and compression to see why it isn't firing.

If all cylinders are firing, then I suppose I'd suspect fuel issues first. Is the choke stuck closed? Clogged carb ports?

Only other thing I can think of is timing. Maybe the distributor got skewed somehow? Pretty easy to loosen the bolt and twist the distributor around seeing if smoothness improves.

[CajunSpike]

Other thing I read is a plugged exhaust system.

[JOHN COOKSON]

They limped into the dock this weekend with the engine sputtering at idle. Increasing throttle only bogs the engine down and kills it.
Thanks.

Was the engine in gear out of gear during the above test? If the engine was in gear there may be some garbage on the prop.
Does closing the choke change the performance when the engine was dying? If closing the choke changes the performance it points a carburetor\fuel problem.
Also how long has it been since you serviced the advance? (under the distributor breaker plate)

TRUE GRIT

[JSM]

Thanks for the replies. In or out of gear makes no difference. The choke was the first think I checked (had that problem once before).
I sold this boat two years ago and I don't think that the engine has been run more than two hours since then so the advance sounds like a likely culprit.
This is a fresh water (lake Michigan) boat so I don't think the exhaust is a problem but will check that as well.

[Mo]

As mentioned ensure all plugs are firing. If the boat has been running infrequently my first guess, after ensuring it's getting fire to all cylinders / plugs good, is gas...especially if it's an erratic stumble/miss you are hearing. If gas with ethanol in it was sitting in the boat it will absorb water...that starts happening generally after 1 month of sitting. I've sorted out 5 bad gas issues for people this summer...adding gas line antifreeze won't help with this ethanol additive fuel either. Another thing I've seen with boats that sit is stuck valves...a valve starts sticking...good practice to have him start that engine every 2 weeks even if he doesn't go out.