Yamaha Outboards

[blitzcraig]

just because it's a yamaha...

my dad has a 350 hp v8 4 stroke yamaha outboard that was new last year. we just put it back in the water this weekend. all fluids were changed, was properly winterized, all that kinda stuff. yesterday we took it out and she was running smoothly. started right up, sounded perfectly normal. once we got going, she sat at 3500 rpm for about a minute and then it was like the engine was starved of gas and it dropped down to like 500 rpm. then she wanted to pick up again, but i eased off the throttle. did this a few times. she runs great at all rpms below that 3500(ish) mark, but above that she chokes. i thought it could be old or bad gas (she was drinking the gas that had been in there over the winter). i thought maybe the guy who winterized it didnt put stabil in or something. today i took her to the gas station and put about 150 gallons in. got underway again, same thing. she stayed steady up to 3500 and then dropped down. all the while nothing sounded bad, no funny noises, engine didn't shut off or anything, etc. it was just like the fuel line got strangled for a few seconds. so at least i have ruled out bad gas. i'm thinking either a bad fuel filter, some kind of problem with the gas line, or dirty fuel injector. we're going to take it to the marina to get it worked on, but for peace of mind it would be nice to diagnose it if possible for the moment.

i assume this kind of thing works perhaps like any other 4 stroke. anyone have any ideas please? perhaps someone has had similar symptoms on their bike, and was there a diagnosis? thanks as usual for any info :cheer:

here's the link to her:

http://www.yamaha-motor.com/outboard/products/subcathome/81/home.aspx

 

[champion221elite]

I have a Mercury 2 Stroke EFI outboard, but I'll take a shot at your problem. It sounds like your motor is starving for fuel. Check the inline primer bulb between the fuel tank and the motor. The rubber can deteriorate, and the check valves can fail. A quick way to test the primer bulb is to pump it until hard. Wait 10 minutes and try pumping the bulb again. If the bulb is still hard, your problem lies elsewhere. If the bulb is soft, you've got a leak and it will need replacement. Skip Tempo products or other off brand stuff. Stick with Genuine Yamaha replacement parts.

Also, check the fuel filter for water and replace it with a new canister. DO NOT under any circumstances, add a second water/ fuel separator such as the Racor unit. The combined restriction from running two filters can starve the motor of fuel during high RPM/ fuel demand. Replacing the factory fuel filter should be part of your yearly Spring maintenance anyway.

Our new Ethanol fuel is hydroscopic and will absorb atmospheric moisture like a sponge.

 

[hardheaded]

not sure if it will help, but a friend of mine had engine lagging problems with a 4 stroke yamaha 40hp. took it to the dealer and there were 6 or 7 fuel filters all clogged due to the ethanol in the fuel.