Yamaha 115 Cutting out

[E. Harry]

I have a 115 Yamaha that is about a dozen years old. It has been an excellent motor but now it has a problem that I wonder if anyone else has experienced or is familiar with the cause.
It runs great at any RPM lower than about 4200 but when I push the RPM up beyond that it cuts out.

[lucky2]

My guess would be either a blocked fuel system or defective ignition module. Not much else ever goes wrong with those

[MacEFL]

Sounds like your water seperator needs changing!

[KingFisher85]

I have somethin kinda the same problem with my Merc 90
It sounds like it is missfiring? I changed the plugs, it didn't do it as bad.

[Boat Doc']

Rev Limiter? Changed props or excessive clearance in the jet?

[E. Harry]

Thanks a bunch. I have changed the plugs and as near as an amateur can tell I have spark and fuel. However, I have not checked the clearance on the impeller in the pump. Actually I did not know that there was a rev limiter
Thanks again.

[snit]

Bear with me, and maybe Boat Doc can expalin better, but we worked on my buddies 115 2-stroke for quite awhile until it got fixed. It had the same symptons are yours, and we exhausted all possibilities that 2 dummies could do. Then an outboard mechanic friend of mine ended up drilling into the "throttle body" (I think) to access part of the fuel supply area that can get residue in it. Once he drilled (and tapped) into that are, he was able to "clean out/blow out" the area and he then installed a plug into the threads. It's been running great for a couple of years now. Sorry for not being too specific, but if all else fails ask around about this "fix".

[Tall-tailer]

Take a strong look at your fuel delivery system, I had a similar problem that about drove me nuts. Turned out to be a very small crack in the fuel pickup tube at the fuel tank, under heavier demand the motor would suck air thru the crack and starve the engine for fuel. A good way to test this is to take a small portable fuel tank and hook it up direct to the motor and see if it runs fine at the higher RPM's. It could also be a blockage at the fuel pickup or a fuel line that is collasped partial. Changing your fuel lines every 3-4 years is a good practice.

[tyeeterror]

I have mariner 115 hp, and had the same problem as you, when it was brand new. It would run great, until you got in the higher RPMs. I took it to the shop several times, and they couldnt figure it out. Went to a new shop, and they had to put it in the water and run it, to get it to miss. To make a long story short, my motor has several cylinders, and each cylinder has its own coil. One of the coils was bad, and would only crap out under heavy load. Just something to look at.

[KingFisher85]

How much are coils going for?

[E. Harry]

Thanks for all of the suggestions. Several sound promising. I do not think that it is the separator as that has been changed and I looked at the impeller and I think that it is shimmed properly. I have taken it to a mechanic twice and the ignition was checked. But a couple of the suggestions about a fuel problem make sense to me and I will look into them. Other than this it has been a great motor and very trouble free.

[Patman]

You may have a bad fuel pump. Your motor will starve for fuel, especially at wide open, if there is a pin hole in either of the two diaphrams. To test the fuel pump: Remove the fuel line from the outlet side of the fuel pump at the T. Place the end of the line in a clear jar. Disconnect the spark plug wires and ground them. Have someone else crank the motor over 6 to 9 times. You want the fuel pulse to be exactly the same each time. If erratic pulses are seen you have a weak fuel pump. The diaphrams can be bought from the Yamaha dealer. You can either rebuild the pump or buy a new one, your choice. Just depends upon your mechanical abilities. Once you take the fuel pump apart it will be easy to see if pin holes are present. Good Luck! Patman

[Jason S]

Five Dollor fix for you. Check your fuel pump up bulb. They have a tiny little check valve in them that goes bad. Same thing happened to my Suzuki 70 in my last boat. Besides its only about $5 which is way cheaper than a mechanic. Your out a Big Mac meal if I am wrong. Seen it more than once.

[E. Harry]

Patman, Jason S,
Your recommedations make sense to me. I will check the fuel pump. Thank you. If you turn out to be right it will save me a heck of a lot more than a Big Mac meal.

[GearUp]

I have the same motor vintage 1991 and have had the symptom that WOT would only get about 4600 RPM instead of 5300. The engine seemed fine until you pushed past 4600 and then it would hesitate. Not jerky but just would not deliver and the RPM's stayed low. This has happened 3 times on this motor and every time the fix was a carb kit. It was really my fault as I never winterize and just let the boat sit for long periods of time between uses. Anyway the fuel in the carb bowls turns to varnish and either plugs or minimizes fuel flow through the main jets that pick up fuel from the bottom of the bowls.

The last time I rebuilded the carbs my self but previously would pay a mechanic to do it. The 2nd time this happened the mechanic did not do a thorough job cleaning out the varnish and did not fix the problem. This was very frustrating. It took a second mechanic at another shop to find the problem. Even after I rebuilt the carbs this last time I didn't get all the varnish either and had to take the carbs off a second time to get them totally clean. A mechanic friend of mine told me to take the boat out with the carburators exposed and with WOT spray a small amount of starter fluid into each carburator to see if the engine rev'd up. Well one of the carbs had the problem and when that carb had starter fluid sprayed in it the engine rev'd up to 5300 for a short period. None of the other carbs had an impact on RPMs. So I knew which carb to focus on.

Hopefully this is helpful.

Chuck

[KingFisher85]

I just wanted to let you all know...I tightend up my gas lines and gas plug and that fixed the problem! When I grab a hand full I get lots of power now!
The gas plug is just old and lose and needs replaced. Simple cheap fix.

[GearUp]

I just wanted to let you all know...I tightend up my gas lines and gas plug and that fixed the problem! When I grab a hand full I get lots of power now!
The gas plug is just old and lose and needs replaced. Simple cheap fix.

Sorry but what do you mean by the gas plug?

[KingFisher85]

What do you call it then? The little fixture that you plug into your gas line that plugs into your motor.