Engine problems

What was in the old fuel filters? Was there a lot of white murky looking stuff? Sediment? Water?

That could be a lot of things and most not good. I'm guessing you lost a cylinder or crank but hoping not. Take an oil sample immediately on the off chance that someone used super heavy weight or sawdust to disguise a problem. Otherwise you may have bought a problem. It could however be something as simple as a bad wire. Here's hoping.

Hi,

It is a long time since I did much on a gas engine but here are a few basics to check.

Does the non running engine crank over at a reasonable rate similar to the one that starts?

Do the engines have Carbs or Fuel Injection?

If it's getting Fuel but no Spark, the plugs in the engine should be wet with fuel.

Can you remove a spark plug wire and put a spark plug into the lead and crank her over and check for spark?

Are all the wires on the engine looking to be in good condition and tight?

If it all looks good and you are not very mechanically inclined it may save a lot of time and headache to call a mechanic- a car mechanic with some older vehicle experience might be as good for this one as a marine mechanic who is not familiar with these engines.

A couple more: Pop off the ignition wires one by one (replacing it before moving on to avoid later confussion). Listen for one that doesn't change the engine sound. Check that all vacuum hoses are attached and in good condition. Have you checked the fuel line for partial clog or a pinhole leak? Even without getting to the carb or injectors it really is a long list of possibilities and is best diagnosed by someone who can hear and experience it. If you do use an automotive mechanic make sure he understands the importance of the flame arrestor and the need to use marinized parts.
Just caught post 6. Does it sound like you're losing one cylinder or like it's being starved for fuel? Spray in a little Carb Master to see if that smooths it out. When running with that flame arrestor off be sure to have a fire extinguisher at hand.

Did it run well for the sea trial?
How long did it run on the trial?
How old is the fuel in the tanks?
Does it smell like old paint?
Were you using the same fuel tank during the sea trial as you did when the problems showed up?
Was the engine backfiring and coughing or spitting or just running rough?
Was there any smoke in the exhaust? If so what did it look like?
Do the engines start easily?
Do the engines idle smoothly?
Is the problem only under load?
Can you run them up to full rpm in neutral?
Did you drain the carb bowls to check for water?
Were engine temperatures normal?

Gas doesn't have to look old to be old. Modern gas seems to break down after only a few months. They were breaking up over 2400 on the sea trial???

In your last post you said only one engine cranks. I assume by that -the one that does not crank does nothing when you turn the key. If so charge the battery or check voltage see if you have 12 volts (cheap volt meter $30 good for all sorts of trouble shooting). If you have 12 volts than we have a solynoid or starter issue which can be checked with the volt meter. If it is turning over then we can move on. Always remember when trouble shooting all internal combustion engines: 3 things are needed; fuel, air and fire(ignition). I would remove the air cleaner, make sure you have plenty of ventelation in the engine room(possible fire hazard here) put a few squirts of fresh fuel in the carb, try starting immediatly, if it trys to start but dies, try squirting fuel again a couple of times. hopefully we just needed to prime it to get it started. If this does not work we can move on. while the air filter is off actuate the throttle and see if fuel is pouring in through the carb.
The running engine sounds like an ignition problem, maybe we arent getting a spark advance at high rpm. What kind of distributer; points, h.e.i? It might need something as simple as an adjustment in timing or some simple distributer maintenence. let me know Tom Pond

Breaking up? Do you mean they would begin to run rough or "stumble" at that power but ran acceptably smooth below that level?

Gas ages rapidly these days with the new formulations. Smell is a better measure, does it smell like paint? How many months did it sit in the Florida heat and humidity? I would start the repair process by draining the fuel system if it is more than a couple of months old.

I don't know what carb you have but there should be a drain plug located at a low point on the square body of the carb. You are looking for water. Look where the fuel line goes in then look at the bottom of the near that. Don't spill fuel in the bilge and make sure you have lots of ventilation! Or have your mechanic do it ... this creates a fire and explosion hazard.

One will not start? Does it "try" to start? Does it fire on any cylinders?

This is beginning to sound like a combination of bad fuel and and ignition problems. It may be as simple as old damp spark plug wires or you may have failing or failed components. Like K1W1 suggested, pull the spark plugs and check them for condition, then attach the wire and look at the now properly gapped plug to see if you have a nice fat blue spark. If not then you have at least half the problem identified.

Find a local marine gas engine guy and make sure your checking account is well stocked. Good luck.

You may have noticed that the guesses are all over the place. This really needs sight, sound and smell aka: a mechanic on scene. Be extremely careful about pouring gas into the carb or when doing anything else with the flame arrestor off (especially turning the key). Good ventilation, a fire extinguisher close at hand and someone watching from outside the blast zone.

..........Put the flame arrestor on before you turn the key...........make sure it is a type "C" fire extinguisher or the fire could get worse. I stand corrected

After you sea trial give us the benefit of your recent education. Let us know what it turned out to be and how you fixed it. Thanks, and good luck with the boat.