1997 Yamaha 225 with momentary shut down at 4300 RPM,s

[<moosecaller>]

Engine runs like a champ up to about 4200 RPM's then experiences momentary "hitch" where it completely shuts off for about a second then recovers and runs OK for 15 to 20 seconds when the problem occurs again.

Dealer has replaced oxygen sensor, fuel filter, plug wires, injectors with no effect. Anyone with any ideas?

Thanks.

[<boats.net>]

The most common problems are battery voltage, monitor battery voltage while running if it drops below 10 volts the engine will shut down and fuel pressure, install fuel pressure gauge and watch for drop in pressure.

[<getyouten>]

you have 1 of your 3 fuel pumps that is bad, Hole in the diaphram. and I would get 3 diaphram kits.

[<moosecaller>]

All good advice/ideas. Thank you for your help.

[<bkshea>]

We had similar problems with our yamaha engine and found out that they changed the gas here in New England. They took out the MTBE's and put in Ethanol instead. 10% of our gas is Ethanol. We were told by several dealers that this is causing many problems with engines. The ethanol apparently stirs up the gunk on the bottom of your gas tank and runs it through the engine causing problems. Our boat was running fine and then started having these cut outs of power. Our local yamaha dealer cleaned out the fuel pump and fuel line pump. It still hesitates a little when we first accelerate but is so much better after the cleaning.

[<John Madison CT>]

Sounds like a partially clogged VST filter from the Ethanol fuel.

Did you check this yet?