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Spark plug amp carb diagnosis 115 merc L6

jon

Regular Contributor
" I winterized the engine w/ f

" I winterized the engine w/ fogger, spray oil, fuel stabilizer (which I run year-round anyway) last November. On Saturday, I took it down to the lake. It started right up & ran perfectly for a 30 minute test cruise, I took it through all RPM ranges & to WOT, no problems.

Today I pulled the plugs out, expecting to find carbon to clean. The top two plugs were almost dry, with just a touch of black on the electrode. The next two down were a little wetter, the bottom two were oily. The insulation on every plug was fairly white.. the top two drier plugs had some specs of rust on them - that concerns me, but it's been a long winter.

Is 30 minutes just not enough to carbon the plugs up? Does this sound like it's running lean? I'm a little hesitant to rebuild the carbs when it's running so nice, but is that warranted just by differences in the plugs? Should I go ahead & richen the top carb's low speed jet, or should I run it for another 20 hours & then take a look? What do you think? Thanks for any/all replies,

Jon "
 
"Jon,

When you are dealing


"Jon,

When you are dealing with multiple carbs, serious problems can result when one carb begins to malfunction. Since you are concerned about the carbs, I would advise you to remove them and check them out thoroughly. Why take a chance? Removing the carbs is not a big deal. If I owned that engine I would remove the carbs before starting at the beginning of every season.

The rust on the spark plug might be a problem. If the engine was properly winterized, you should not notice any rust on the plugs. Maybe there was some water in the carb. Maybe you have a leaky gasket in the exhaust manifold. Keep an eye on this. If it continues to happen you must get to the source, or it will only get worse.

"
 
" Tony,

Thanks and


" Tony,

Thanks and yes, I'll keep an eye on that. If it gets worse and I have reason to believe water is making it into the cylinders, can I get into that area to inspect/replace the gasket without cracking the crankcase? I rebuilt this engine last year & left those covers on, for fear of needlessly snapping bolts. If I don't need to crack the crankcase, it doesn't look too hard to get back in there though, when compared to a rebuild anyway.

Jon "
 
" Jon,

I'm not sure if


" Jon,

I'm not sure if there is enough room to remove the exhaust cover with the block in place. You might be able to loosen the bottom cowl and provide enough access on that engine, but you have to look at it and decide if it will work.

I wouldn't recommend doing this job unless you think it is absolutely necessary, because as you say, there is a good chance that you will break a few bolts. In fact, I don't remember doing this job on this particular engine, and breaking only one screw. Once I broke eight, and actually managed to drill all of them out and install heli-coils, and it went back together without a problem. I remember feeling extremely lucky about that.

Tony "
 
Jon...I dont know if things a

Jon...I dont know if things are different in the states but here in australia it is a standard service procedure to replace the gaskets on those exhaust plates every 3 years along with the lower crank seals due to water intrusion. Id check first by putting a dirty spark plug in the suspect cylinder and running the motor. If its taking water it will clean the plug. The rust spots you speak of may only be moisture while the motor was sitting. To do the exhaust plates I have found that its so much easier to pull the powerhead off (its pretty easy on those). You will need a rattle gun on a low impact setting to have a chance at not breaking bolts. As Tony says there is a good chance you may break some. I have done many without broken bolts but it probably depends on when the last time they were done.
 
" Thanks guys; yes, if I go in

" Thanks guys; yes, if I go in there I will go ahead & pull the powerhead off - it's good to know though that I can pull this off without cracking the crankcase, that's where things get more difficult.

Tony - Yes, that is pretty damn lucky. Drilling out bolts may actually be my least favorite engine repair procedure.. and stainless has gotta be by far the worst. I think if I end up in there & break a bunch off, it will require a trip to the machine shop - those guys are miracle workers with that type of headache. Lets hope she holds together for another season though,

Jon "
 
Jon...Ill give you a little t

Jon...Ill give you a little tip that I use with broken bolts and I have about a 99% success rate. Only downside is that you need a mig welder. Hope you got one. When you break a bolt even if it breaks flush put a nut over it and then weld the nut to the broken bolt. When you weld with mild steel wire this wire wont weld itself to the alloy of the block. The heat from the weld helps free the broken bolt and the nut gives you a head to grip with a spanner or socket. The threads also remain intact. No drilling no tapping and no heli coils. On very stubborn bolts you may need to repeat this process a few times. Hope this helps.
 
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