8 hours out of a set of spark plugs, help?

Jerry Hickey

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Sep 6, 2003
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I'm new to the forum, and could sure use some advice. I've got a 1987 34' bayliner with twin crusader 454's 350 hp. Boat idles and runs fine for about 8 hours then engines start backfiring, sometimes both, some times only one, starts to lose power. Change spark plugs and it runs great for about another 8 hours, then same thing. When I remove spark plugs the colours range anywhere from white to brown to black and sooty. Engines have about 1300 hrs.
 

airman

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Aug 9, 2003
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Re: 8 hours out of a set of spark plugs, help?

Hi Jerry, good to see you here. After you left I realized I should have mentioned this forum to you. (I've got the anchor chain for sale). I still have no idea what your problem is but you'll probably get better results if you mention all the work you've already done (manifolds, ignition system, etc). The more specifics you can give, the better.<br />Ben
 

loadnet

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Aug 27, 2003
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225
Re: 8 hours out of a set of spark plugs, help?

Sounds like you may have water mixed in with your fuel...<br /><br />Have you changed your water seperator - fuel filter recently?<br /><br />At what RPM is the backfire happening?<br />Before it backfires do you here light popping sounds comming from the carbs? resulting in a backfire?<br /><br />What condition are your plug wires in?
 

Jerry Hickey

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Sep 6, 2003
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Re: 8 hours out of a set of spark plugs, help?

I should have mentioned the work I've had done.Changed from std distributors to electronic and back again. New wires, plugs, dist. caps, rotors, water separator,rebuilt one carb and swapped it back and forth. Replaced manifolds and risers on one engine in case water was getting into the engine. Could my problem be camshafts?<br />Good to hear from you airman,I'm still looking for a wildcat.
 

loadnet

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Aug 27, 2003
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Re: 8 hours out of a set of spark plugs, help?

What RPM is the backfire happening at...<br /><br />Are you getting sputters and light popping sounds from the carbs just before backfire occurs?<br /><br />Remove your fuel filter and pour the fuel into a glass containor to see if there's water in there.<br /><br />If there's lots of water content in the glass containor you will most likely have to pull the carbs apart again and clean em out.<br /><br />To test to see if the water is causing the backfire you can run your gasoline feed-pickup line into a 2 gallon containor of fresh gas and take the boat for a run to see if the problem duplicates itself - AFTER - replacing the fuel filters and water seperators.<br /><br />Make sure to change the fuel filters on the carbs as well. - the stone filters.<br /><br />Are your carbs mixture screws setup ok?<br /><br />Turn the mixture screws 'all the way in' then back out 3 full turns, then turn back IN again 1/4 turn.<br /><br />Check to make sure your timing is on the money on both engines..<br /><br />Running lean and retarded timing can cause the backfire and loss of power.<br /><br />Just went thru the same thing with my boat..<br /><br />I had a ton of water in the gas and had to pull the carb down and clean it all out.. reset my timing and the between those 2 the problem went away..<br /><br />You say you updated to new distributer?<br />What kind did you put on there? Pertronix?<br /><br />PB
 

Jerry Hickey

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Sep 6, 2003
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Re: 8 hours out of a set of spark plugs, help?

If it was water in the gas or dirty filters, why would putting in new plugs make it run great for another 8 hours,doesn't it sound like valves or camshafts if the plugs are different colors.(white hot to black and sooty.) Thanks for your input captain.
 

boaterntexas

Petty Officer 1st Class
Joined
Feb 4, 2003
Messages
254
Re: 8 hours out of a set of spark plugs, help?

I bet you mixture screws are out of wack, you said you cleaned the carbs was this before the problem or after.. also are you seeing any smoke?
 

crazy charlie

Vice Admiral
Joined
May 22, 2003
Messages
5,602
Re: 8 hours out of a set of spark plugs, help?

I had a similar problem years ago.When you get the backfiring,look inside the distributor cap if you have one.my problem was condensation inside the cap. charlie
 

KiLer

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Jul 20, 2003
Messages
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Re: 8 hours out of a set of spark plugs, help?

fouling plugs sounds like a mixture problem to me...you said you switch back and forth on the ignition....when you had the conv. one what was the volt rating on either side of the coil ?
 

Jerry Hickey

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Sep 6, 2003
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Re: 8 hours out of a set of spark plugs, help?

If the lobes on my camshafts were wearing down,how would this affect performance and what would this do to my sparkplugs, and valves? Thanks for all the input so far guys.
 

kenimpzoom

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Jul 13, 2002
Messages
4,807
Re: 8 hours out of a set of spark plugs, help?

I think worn camshaft lobes could cause distribution problems. Have you taken the valve covers off and checked that all the rockers and springs look ok. You could easily check for worn camshaft lobes, by turning the engine over and measureing the lift on each one.<br /><br />Have you check the compression? Perhaps you have some bad rings allowing it to burn oil and that is where the black and sooty plugs come from.<br /><br />Do the spark plugs come out looking the same every time for each cylinder or do the dry plugs move around to different cylinders.<br /><br />Ken
 

mabbott

Seaman Apprentice
Joined
May 15, 2002
Messages
37
Re: 8 hours out of a set of spark plugs, help?

A compression test will assist in identifing low compression do to valves or rings. The wrong plugs /improper heat range will cause fouled plugs. What plugs do you use AC Delco MR43T? And as already mentioned, the carbs could be too rich or water in the gas.
 

Bondo

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Apr 17, 2002
Messages
71,285
Re: 8 hours out of a set of spark plugs, help?

Well, It appears you've Thrown enough money at the problem.... <br />We're talking about 2(two) motors here, So, It's rather Important to know Which Color Plugs came from Which Holes, in What Motor.....<br />I Think you may have multipule issues going on..... I'd Start with a Full Engine Survey.... A Compression Test is a good start.. a Leak-Down Test is a help...
 

Jerry Hickey

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Sep 6, 2003
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Re: 8 hours out of a set of spark plugs, help?

Good morning guys, thanks for all the great ideas so far. I had a thought in regards to condensation.I,ve got an air dryer in the engine compartment, but I still get condensation sitting on the distributor. There have been times when I open the distributors after the engines start backfiring through the carbs and wipe them out with a paper towel and they stop popping. The confusing part is there have been times that I've been running the engines for 3 or 4 hours and then they start popping. How could it be a condensation issue when the engines have been warm, wouldn't condensation only happen when you have had the boat sitting for a length of time? Any suggestions on how to seal out moisture from the distributors or is there something I can do to replace the distributors so that condensation won't be an issue?
 

loadnet

Petty Officer 1st Class
Joined
Aug 27, 2003
Messages
225
Re: 8 hours out of a set of spark plugs, help?

Jerhic,<br /><br />Do you have vents on your current distributer caps? If not you may be able to purchase vented caps... It's like a little drain plug sticking out of the side of the cap.<br /><br />I'm still thinking you have bad fuel.. did you check your fuel quality..<br /><br />I had a v8 doing the same thing combined with mixture screws set wrong and bad timing.<br /><br />Made my engine pop at higher RPMs ending in a backfire until I finally got all the water out of the fuel..<br /><br />I've stopped spark from jumping inside a cap by spraying WD40 inside the cap and damp drying with a paper towel.. I leave the WD40 film right in there and it works great for me..<br /><br />Hope you get the problem solved soon..<br />Let us know how you're doing.
 
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