Yamaha 6HP Four Stroke Oily Spark Plugs

[shanester]

My new to me Yamaha 6HP four stroke has some minor issues. 2005 model F6MLHD. This is the one that I posted about being stuck in reverse. That is fixed now. I fired it up today for the first time since I brought it home. Fresh gas. It started on the second pull. Shifts perfect. Great.

Here is what I observed:
It runs a tad rough for a two cylinder even after running for five minutes but it never died.
It has a minor hesitation when revving from idle.
I noticed a light coating of oil over most everything under the upper cover.
The spark plug gaps are good and appear new.
There seems to be a lot of oil on the spark plugs and inside the combustion area for a four stroke.
There is a light coating of oil inside the air intake.
I pulled the breather hose on the carb intake and there was a light coating of oil in it.
The valve cover end of the breather hose appears dry.
The timing belt seems loose. I can deflect it 1/2" easily when the slack is taken out.
I did not see a timing belt adjuster like on a car engine.
The oil looks brand new on the dipstick and is a tad over filled.
Everything looks super clean and new through the oil fill plug. (cam and followers)

Questions:
Do I need a new timing belt or is there an adjustment?
Could the oil inside the combustion have somehow leaked in from transporting it on its side?
What could cause the minor hesitation and rough idle?

I need to buy a repair manual but would like to fix it soon as we are taking it to FT Myers in about two weeks. It does runs good enough to go if push come to shove.

 

[centerline]

it could be that some one fogged the inside and out side of the engine with oil for lay up... it could also be that transporting it in the wrong position could have caused the internal oily residue...
its also possible that the previous owner of it did not know any better and mixed his gas with oil, and you are still burning out to old gas mix in the carb....(ive seen it happen a few times)

5 mins run time at near idle is not enough to clean up the residue in a fogged engine.....

it would be best to put it on the boat, in the water, and run it that way for about 20 mins, UNDER POWER..... which means putting it in gear. you can do this either tied to the dock or take it out for a short cruise.

but.... before you go, pour some sea foam additive in the tank and let it work on the fuel system, as the hesitation and stumble could be caused from the gum residue from dried out ethanol gas. the sea foam will begin to dissolve it fairly quickly, and within 30 mins run time you should see a difference.
even as the sea foam sits in the system when its not running, it is working to dissolve the gum... then you can burn it out when you run the motor.

 

[kloudie1]

No belt tensioner, probably needs a new belt. Before you do that, check the timing marks on the cam and crank .. if they are right on, and the belt does not have any cracking around the base of the tooth roots, you're probably OK.. A half inch sounds like a little too much, though.. it will not be "tight" like a serpentine or a regular belt since it has to have a little slack to be able to replace it and it doesn't have a tensioner to aid in that..
a little too much oil and storing on wrong side or on rear legs will oil the plugs. Take it out and put some load on it. for a bit.

 

[Bill Roosa]

Not familiar with this engine but I've NEVER seen a 4 stroke overhead cam engine that did not have a tensioner of some kind. You would have to install the belt with the camshaft if there where no tensioner. I suspect that the idler roller is the tensioner and it is spring loaded so there is no manual adjustment. This could also account for 1/2" play as when you push on the belt it just springs the idler pulley.

 

[Benny17441]

The oil is likely from transporting it on its side but nevertheless check the oil weight to make sure is not too thin. Remove any excess oil. Replace or clean the spark plugs and insure they are of the correct heat range and properly gapped. Disassemble and clean the carburetor and go to a marina that dispenses ethanol free gasoline and fill up your gas can. Run the engine under load at 85 to 90% throttle for at least an hour.

 

[shanester]

Good suggestions so far. It sounds like it just needs run under load for awhile to burn up excess oil (wherever it came from).
I will purchase a new belt as it seems too loose for me. If there is a belt tensioner I can't find it.
The spark plugs looked and gapped good but I forgot to check to make sure they were the correct type.
It can't hurt to try the Seafoam.
My owner's manual states using gas with up to 10 percent ethanol is fine.

 

[shanester]

The oil is likely from transporting it on its side

This is how the manual states to transport it. How can I prevent this from happening? Drain the oil and add it back when I get there?

 

[Ron20324]

This is how the manual states to transport it. How can I prevent this from happening? Drain the oil and add it back when I get there?

There is a certain side to rest it on. Look in the book, or look for a couple of "feet" on the power head that it will rest on. Wrong side down, and oil can run into the open valves.

 

[kloudie1]

Bill, the distance between the cam and crank pulleys on many small OHC outboards is so small that an idler or tensioner is not used. My old (1980) Honda 7.5 was like that and this series of small Yamahas is built that way as well. I believe all the small Tohatsu engines are that way. I think that they start putting a tensioner/idler on at around 25 HP.
Shane, if you transport it on the proper side as in the manual AND the oil level is correct, you won't have a problem.. You mentioned that the level was too high.

 

[shanester]

Shane, if you transport it on the proper side as in the manual AND the oil level is correct, you won't have a problem.. You mentioned that the level was too high

In reading the manual this morning more carefully it states this: "If storing or transporting the outboard motor on its side (not upright), put it on a cushion after draining the engine oil." Add that to the list of things to do at the launch ramp parking lot.

 

[Bill Roosa]

koulid1
I'll take your word for it. With that said then 1/2" play would seem to indicate a "well worn" belt and I bet it is a bear to change out!

 

[shanester]

I bet it is a bear to change out!

Not compared to replacing head gaskets on my '05 Powerstroke V-8 turbo diesel.

 

[kloudie1]

Bill, Yes.. but there is a trick that folks use. Ya mark a point on the cam pulley and on the crank pulley..count the number of cogs between the those marks on the old belt, and make marks that many cogs apart on the new belt .. after pulling the recoil starter housing, and without moving the cam or crank, carefully and evenly lever up the belt off the cam cog. it should be loose because it is worn. Then loop the new belt onto the small end and carefully barely engage the marked cog of the newbelt with the marked place on the cam pulley.. then without letting it slip, slowly rotate the new belt onto the cam pulley.. not easy, but not that bad .. has to be exact .. and it helps to have another pair of hands to rotate while you guide..

 

[shanester]

I ordered a timing belt today so we will see how tight a new one will be. It still sounds strange to me that the manual says to drain the oil every time it is transported laying down. Do the manuals of other brands say this and does anybody do this on their four strokes? As if I don't have enough to do when launching and retrieving. The thought has crossed my mind about making a bracket that hooks over the transom and attaches to the outboard allowing it to stay on its own bracket when travelling down the road. It would also be nice to lock it to the boat somehow for anti-theft.