Cracked fuel lines=fouled plugs?

[Davis Senior Member Find all posts View Profile Close Davis]

Has anyone ever heard of cracked fuel lines admitting air, thus causing the oil/gas mix to be upset? The previous owner of my boat said he thinks this is why his plugs were fouling fairly rapidly.

I'll be replacing the fuel lines anyway, but I wonder if there is any chance he could be correct about cracked fuel hose being the cause of this problem. Do the automatic oil mixers ever get messed up and inject too much oil? Or could this fouling business be a result of poor combustion? I have to replace or fix the stator and/or voltage regulator. Previous owner told me the engine did not charge the batteries during the one season he ran the boat and I have no idea whether he knows the stator is bad or if it's a guess. Someone told me that running a good sized outboard straight off of batteries that aren't very peppy is going to give a lot less pop at the spark plug. Though I will find out the answers to these questions as I get each item fixed, I'm just wondering what the most likely culprit for fast fouling plugs might be. Any thoughts will be welcome and appreciated!

Win

[Sailor Senior Member Find all posts View Profile Close Sailor]

No. If the fuel lines were cracked they would be letting out fuel.

I was having problems with charging batteries and it was a corroded ground wire...and then a stator (could have been both). Are you sure your batteries are good? Have they been load tested? Are you running two batteries in your boat? If so, I would make sure you are only using one at a time on your battery switch.

[HungOne Senior Member Find all posts View Profile Close HungOne]

Actually, it's very possible for older Johnsons that don't premix and use an external oil tank. The oil pump and fuel pump mechanically work together. I don't remember the names of each of the parts that handle this without breaking out my Claimor(sp?) manual but the layman's way of explaining it is that each time the fuel pump turns one time it "primes" the oil pump just a little bit. The fuel pump turns a certain number of times and "primes" the oil pump to the point of "release" drawing in a shot of oil to mix in with the fuel. If air is getting into the fuel line, what happens is the fuel pump must turn a whole lot more to draw in enough fuel to feed that engine. The problem here is that because the fuel pump is turning so much more, the oil pump is also being primed a whole lot quicker and a whole lot more times so more oil is being drawn into the mix chamber. This would cause a mix ratio that is to rich and could in-fact foul the plugs. The tall tell sign would be a thick constant trail of smoke as you idle around slowly.

As Sailor said, a cracked line will definately let fuel leak out but since these motors are using a vacume to suck the fuel from the tank, it's also sucking air into the fuel line through that same crack.

[michigan dave Administrator Find all posts View Profile Close michigan dave]

Hungone is correct. If air gets into the inlet side of the fuel/vro

pump the oil mixture will go way rich and smokey. On a motor that old I usually disable the VRO and mix my own fuel. This helps prolong the life of your older outboard. You can then rule out a oil starved failure, as long as you dont introduce human error.[:I]

, battery voltage has nothing to do with quality of spark, once the engine is running. It only affects the cranking speed which in turn affects the quality of spark. dave

[Davis Senior Member Find all posts View Profile Close Davis]

Thanks, Sailor, HungOne and Dave! I'm starting with the fuel line. If nothing else, it's probably hard to over-rate the danger of spilled fuel. I know all the right specs for fuel lines and inside tips for replacement are posted here somewhere... gotta love the search function!

In the meantime, I'll post a question asking where I can buy the antidote for "introducing human error". I wonder if I should post that in classifieds, projects, discussion or shark tank. Hmmm. Referring to myself, the term "human error" is often redundant. I need a smiley that indicates fogbound or confused.

Thanks again!

Win