Unburned oil in spark plug Yamaha VMAX 150 hp

saltysway

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I have a 2007 Yamaha VMAX 150 hp. I have never had any issues with the engine. Yesterday as I was cruising along at about 27 mph or 3300 rpm the motor noise went from normal to a somewhat throaty sound. I backed off plain for a bit and checked for water in the fuel and made sure the spark plug wires were all on properly. Those items checked were all good. I restarted the engine and gave it throttle. It got on plain, but slowly and weak. The engine will not make it to full rpms or speed. When I got on land I removed the spark plugs. The top two left side spark plugs had quite a bit of unburned oil on them and the other 4 looked normal. The plug looked as if they were not firing. What could be the cause for this issue?
 

Scott Danforth

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you lost spark on those two cylinders
 

99yam40

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testing needs to be done to find out what is going on, guessing make for expensive repairs
 

saltysway

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I've done some more research into my issue and several different sources say that long periods of idle speed can cause similar issues as the one that I am experiencing. This particular trip I traveled approximately 7 miles at idle speed before moving up in my speed. The manatee season is now in affect in my area. Some of the information that I have read stated that the 2 stokes and long distances of idle can cause the plugs to flood with oil leading to the miss fire. Can anyone agree? Why just the two plugs? I will change them out, test for fire and try her again. Does this seem like the most logical place to start?
 

dingbat

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I've done some more research into my issue and several different sources say that long periods of idle speed can cause similar issues as the one that I am experiencing. This particular trip I traveled approximately 7 miles at idle speed before moving up in my speed. The manatee season is now in affect in my area. Some of the information that I have read stated that the 2 stokes and long distances of idle can cause the plugs to flood with oil leading to the miss fire. Can anyone agree? Why just the two plugs? I will change them out, test for fire and try her again. Does this seem like the most logical place to start?
i troll (900 rpm) a 200hp for 8-10 hours a day fishing. If the water is cold It can be a little ?rich? when first coming out of the hole but burns off by the time I?m up on plane.

Two out of six cylinders isn?t idle loading. Never played with a yammie 2stroke. What is common to both cylinders?
 

QBhoy

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Is check the coil packs to the 2 affected. Or even just try changing the plugs.
I’m not sure it would oil up that bad, just by going slow. Maybe on an older engine, but I’m almost certain your engine has progressive and variable oil injection and is pretty sophisticated.
Check the fuel filter too. This may be the last two cylinders to be fed with fuel. If there is a restriction , it may oil up if the oil feed is still flowing to each individual cylinder (if it?s not communal to the fuel system previously in the delivery)
Simple things first.
 

saltysway

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Thanks for the input guys. I purchased new plugs last night after work and hope to try them tonight and check for a spark. I haven't really got a chance to troubleshoot it too much because I'm stuck here at work for the next ten days.
 

racerone

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Plugs foul when there is no " heat " produced in the cylinder to keep plugs clean..------Check compression and see if spark jumps a gap of 3/8" or more.-----Or test run with a timing light to see if you are loosing spark.
 

saltysway

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I checked the spark on the two plugs last night and it was bad. I changed the plugs and the spark was good. I went ahead and changed the remaining plugs and went to the lake. The motor fired and ran perfect. Thanks fellas for the replies and information.
 

robert graham

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2 stroke outboards(especially premix models) can lay up some oily carbon over time....For my 1999 C90 I've used for many years a $15 Harbor Freight Spark Plug sand blaster to keep the plugs clean of carbon....Usually blast 'em a couple of times a year.....Works great for mowers, blowers, chain saws, etc. spark plugs also...Mostly plugs don't wear out but just get fouled....
 

mycobia21

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Mar 13, 2018
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Good idea, aircraft recip engine spark plugs are cleaned the same way at 100hr intervals if I remember correctly
 

Grub54891

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I've used the spark plug sandblasters in the past, yeah the plugs come out looking new, but after hearing a couple stories of grit getting stuck in the plug, and coming loose when running, I quit using them. I don't need cylinders/pistons scored up from them. Jmho.
 
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robert graham

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I've used the spark plug sandblasters in the past, yeah the plugs come out looking new, but after hearing a couple stories of grit getting stuck in the plug, and coming loose when running, I quit using them. I don't need cylinders/pistons scored up from them. Jmho.

After sandblasting I clean each plug with carb cleaner and an old toothbrush, then blow it off with my air gun....no grit on plugs....a drop of oil on threads, then back in motor....no problemo!!!
 

Sea Rider

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2 strokes outboards doesn't like to run at idle, fast idle trolling speed for long time periods. Will tend to foul plugs. Plugs becomes self cleaning when reaching temp over 450 degrees. That's why is a must go for a long wot run as if stealing the combo after trolling for extended time periods.

Happy Boating
 

Faztbullet

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Unless your running premix plugs wont foul at troll speeds as the oil is metered and injected in front of the reeds. 2 cylinders adjacent of each other needs compression test as possible blown head gasket. This will cause them to be oily also....
 

scoflaw

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What would reeds have to do with it? The combustion chamber is last in line to get the 2 stroke mix. Throttle body, reeds, lower end, combustion chamber in that order.
 
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