Got a real stumper here... Please help!

Please help... I have a 1998 Reinell 200c with a 5.7 liter mercrusier and a alpha one outdrive. Stock everything.
I bought the boat from a guy who told me it was rebuilt and had less than 5 hrs on it. The boat started and ran fine on a hose and so I made the purchase. We took the boat out and under load at 4400 rpms it began to backfire through the carb. Checked plugs wires timing etc..... Here's where it gets good. I pulled the plugs out and the number 5 cylinder looked like it wasn't firing. So I cranked the motor a few times without the plug in it and then put the plug in the wire and up to the block to check for spark and it was sparking. Took the boat out on the water and it ran like a champ.. No miss no backfire. idled perfect all day and ran like a brand new boat!!!
Loaded up the family today for another night on the boat. Got 2 minutes into our trip and the motor starts backfiring and missing so bad it wont stay running at all. It wouldnt even start. So I figured it was valve related? maybe a stuck valve? So I pulled the number 5 plug and the cylinder behind it and cranked it over a couple times. Checked that the plugs were firing and put them back into the cylinders and the boat started right up. Still running rough but it limped back to the dock......
Is this a valve issue? Why would it run perfect for 5 hrs and then the next time out (3 days later) miss backfire and stop running?

Please help! Thanks Guys!

Re: Got a real stumper here... Please help!

Sounds like that motors running lean to me. Carb backfires and white plugs...you have a fuel starvation issue or coil ignition issue.

Re: Got a real stumper here... Please help!

hivoltg said:

Sounds like that motors running lean to me. Carb backfires and white plugs...

Click to expand...

Maybe--- but Why would pulling the plugs and turning the motor over a couple times allow it to start running again? It also ran perfect a few days ago with no issues. Then after sitting a few days it starts running so erratically it wont even start until I pull the plugs and crank it over...
After the day that it ran perfect I pulled a few plugs when I got home and they were not white but like coffee and cream colored....

Re: Got a real stumper here... Please help!

If that coil is over heating it will act like that. Then it cools off and acts normal. Was the spark orange when it was happening instead of blue?

If you ever left the key on with the motor not running, that the number one reason why they fry.

Re: Got a real stumper here... Please help!

Are you sure wires are good.sounds to me like may have been sparking off motor at first then you moved the plug wire.did you try running at night to see any sparks,or did you put new wires on it?

Re: Got a real stumper here... Please help!

hivoltg said:

If that coil is over heating it will act like that. Then it cools off and acts normal. Was the spark orange when it was happening instead of blue?

Click to expand...

Spark was blue...... If its the coil overheating... Can they overheat one day and not the other day? Somebody told me they though it was a intake valve on the starboard side? They suggested I lap in the valves?

Re: Got a real stumper here... Please help!

theblob said:

Are you sure wires are good.sounds to me like may have been sparking off motor at first then you moved the plug wire.did you try running at night to see any sparks,or did you put new wires on it?

Click to expand...

No new wires..... New plugs, cap and rotor.... I think I'll try new wires and see what happens....

Re: Got a real stumper here... Please help!

Valves dont fix themselves. So I dont think thats it.

Easy to test the coil primary and secondary with an ohm meter.

Re: Got a real stumper here... Please help!

Sounds like you need a new distributor. I had this sort of issue in one of my mustangs.

Re: Got a real stumper here... Please help!

Pulling the wires on and off can mess them up.you said that plug was oily maybe just switch that one wire see if it makes a difference.at night you can definitly see sparks if you have someone to look why you use throttle.

Re: Got a real stumper here... Please help!

I'm leaning towards plug wires.... I just ordered some online and ill post back when I put them on..... I hope that's the issue! The plug wire on the number 5 cylinder was loose but I didn't take it seriously enough I guess... Would a bad plug wire cause other plugs to foul out once it stated running rough? Because today once it stated to backfire it felt like it dropped a few cylinders because it wouldn't even idle...

Re: Got a real stumper here... Please help!

You can go to autozone get the wires with warrenty and just pull off every year and get a new set.did it for years and years.

Re: Got a real stumper here... Please help!

Change your fuel filters and check for air leaks in the fuel lines. Also check the anti-syphon valve. And don't forget to check the filter/s in carb. As you didn't supply a serial number I can't look up and see exactly what you have (carb, engine, ignition system etc)....

Please supply serial number so we are all looking at the same thing... But do your fuel filters.

Chris......

Re: Got a real stumper here... Please help!

Get a new distributor...one wire won't cause all that. If one wire is bad it will cause a miss, not back fire. You may need new wires but that won't fix your problem.

Re: Got a real stumper here... Please help!

Ill tell you what i did on a car to get home but wouldnt advise it on a boat,but i cut wire about half way used a exstinsion cord wire twisted around the end of plug and taped good.may be a way to just test it.if it dont pop out of carb youll know thats the problem.make sure none of the wires touching engine if you got to tie em out the way.they have clips but alot of people ignore the clips and thats why wires go bad.

Re: Got a real stumper here... Please help!

Fuel filters and gas are good.... Check those right away... Drained all gas and put new... Ill get my serial in the am.....

Re: Got a real stumper here... Please help!

Do you know what temp the engine is running? Does it have thermostat? Should run around 180 for top performance.

Re: Got a real stumper here... Please help!

joshmce said:

Fuel filters and gas are good.... Check those right away... Drained all gas and put new... Ill get my serial in the am.....

Click to expand...

Check the anti-syphon valve, or air leaks in the lines? This problem smacks of a lean condition, nothing to do with electrics....

Chris.......

Re: Got a real stumper here... Please help!

Another thing you sure fireing order is right.i know it doesnt happen often,but wires could be in wrong place.

Re: Got a real stumper here... Please help!

I'm telling you its the distributor...I had this issue on my mustang. I may not know much about boats but I KNOW engines!