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Yamaha 115 problem

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YosemitePhil

New member
I took the boat out today and my 115 had no power when I put it under load. This motor has always had a problem cold starting. This morning it kicked up okay but sputtered unusually in neutral until it warmed up.

I took it out of the marina (a no wake zone). As I left the marina and gave it full throttle, the engine barely gave up a few more knots. I don't have a tach, but the rpm's would not have made it much better. In neutral, it seems to rev normally.

I ran it last Thursday, and it ran like a stopwatch. Any thoughts from highest probability to lowest? Thanks for any help.
 
I fill up with non-ethanol high test only. I changed the spark plugs to no avail. My guess is the temp sensor or ignition control system. I'm taking it into the dealer. Prepared to be raped.
 
The simplest tests cost no money--------------------Test compression and test the spark , it should jump a gap of 7/16" on each plug wire.
 
What is the water temp where you are running this? If you touch the engine block when its running are both sides up to temp? I had a customer with a 115 on a proline a few years back. The water jacket gasket on the cylinder head was rotted through and one side of the engine would not get hot. Water would condensate in the combustion chamber and short the spark plug. Only happened when the water temp was very cold.
 
I live in E. Central Florida and I run the boat in the Indian River Lagoon. Water temp is in the low '70's this time of year.

The engine ran perfectly the week before in the same location (and has for years).
 
Compression tester are worth about half of an hrs labour at a shop.----------------Automotive store has them with instructions.-------------A dealer will not charge much to do it for you.
 
I just returned from Florida where we have twin F115s on our boat. We have been experiencing fuel related filter plugging problems for a few years and I finally had both aluminum tanks replaced and replaced the VST filters and cleaned all injectors including replacing filters in them. In our case the tanks were installed improperly and degraded, which combined with bad fuel plugged up the filters in the engines. The engines now run like new.

I bought a fuel rail pressure gauge for about $50 and it is the first thing I'd check. If your VST is plugged, your fuel pressure will drop under load at higher RPMs. I'd also drain the fuel water separator filter to see if there is any junk showing up in there.

In talking to the Yamaha mechanics in the area, the vast majority of power loss problems are fuel related. And given the regularity that ours were acting up at, I got tired of paying a mechanic 8hrs of labor to change the filters on both engines, so I did it my self. Now that I know how I'd say it takes about 3hrs per engine to service the vsts and injectors.
 
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