J.K.

No acceleration on Yami F250

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Hello guys.  Wondering if anyone else had this issue?  I was out fishing all day and the boat ran great for 6 hours out on the ocean.  I came inside and anchored up to tog and was relocating due to tide change.  This is when I noticed a vibration on my outboard Yamaha F250.  It's my 8th season and has about 350 hours on it.  Everything is fine at 1200 rpm running about 4mph.  Once I give it throttle, it starts vibrating.  There is nothing tangled up in the props.  The engine revs up 3000 to 4000 rpms with no problem but the boat wont accelerate beyond 12mph with vibration.  At some point I decided to keep rev'ing and keep it there to see if the boat will accelerate.  It took about 10 seconds to finally get the boat on plane and was slowly able to get the boat up to normal 30 - 35 mph.  Has anyone had this problem?  Can it be the bushing in the prop?  I heard it's not even worth repairing that these days and just buy a new prop.  I really don't think it's anything with the engine itself.  If not the prop, perhaps something with the lower unit?  Would appreciate some feedback.  Thanks.

Edited by J.K.
wrong word in a sentence.

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When was the last time you checked your fuel water separator or changed the fuel filter............maybe try some Stabil.

Edited by Mr. Bigdeal

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6 hours ago, Mr. Bigdeal said:

When was the last time you checked your fuel water separator or changed the fuel filter............maybe try some Stabil.

I replace every year.  It's good.  I used Seafoam last fill up.

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5 hours ago, MakoMike said:

Did you check to make sure you weren't dragging something around with you?

Yup, that's the first thing I checked to make sure nothing was tangled up in my prop.  Not dragging anything.

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Do your basics first.

 

Was primer bulb hard? Does it  arrow face towards the sky if not the check valve fouls out  alot if not..Check  tank vent for clogs.

 

Could be spun prop. But unlikely if you got back on plan though.  

 

Did you drain vst tank and fuel rail with the motors gas filter....water builds up in those places to. 

 

Check plugs and maybe time to change them.  At 350 hrs.  

 

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Did you throttle up in neutral with no vibration, no hesitation?   Fuel issues like plugged vst screen or filters often cause surging, any noticeable?   

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2 hours ago, 757saltwater said:

Do your basics first.

 

Was primer bulb hard? Does it  arrow face towards the sky if not the check valve fouls out  alot if not..Check  tank vent for clogs.

 

Could be spun prop. But unlikely if you got back on plan though.  

 

Did you drain vst tank and fuel rail with the motors gas filter....water builds up in those places to. 

 

Check plugs and maybe time to change them.  At 350 hrs.  

 

I didn't check the primer bulb but it's been fine and oriented correctly since day 1.  No changes. 

I'm leaning towards the spun prop due to vibrations and very very slow acceleration to get on plane.  I assume it'll deteriorate enough soon where it won't be able to move the boat.

Haven't had a chance to check anything on the vst since my boat is on the water.  I'll check the fuel filters but the plugs are new.  Thanks.

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1 hour ago, Billybob said:

Could be the vst, or injectors, or fuel pump.

You're not getting hi temp at low rpm are you?

All temps are fine.

Thing is I had the engine pretty much rebuilt 2 years ago (removed power head and replaced 2 valves) because the mechanic couldn't find my oil leak.  After all that work, still leaks. 

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55 mins ago, JimW said:

Did you throttle up in neutral with no vibration, no hesitation?   Fuel issues like plugged vst screen or filters often cause surging, any noticeable?   

No vibrations in neutral.  Only when I start reving up the rpm it starts to vibrate.  There weren't any noticeable surges.  I thought I did smell fuel though.  I started her up this morning tied up and didn't feel the vibrations even though I was giving her gas.  The engine did sound a little different today at idle. 

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49 mins ago, J.K. said:

I didn't check the primer bulb but it's been fine and oriented correctly since day 1.  No changes. 

I'm leaning towards the spun prop due to vibrations and very very slow acceleration to get on plane.  I assume it'll deteriorate enough soon where it won't be able to move the boat.

Haven't had a chance to check anything on the vst since my boat is on the water.  I'll check the fuel filters but the plugs are new.  Thanks.

I've never spun one, but I don't think you'd get vibrations from a spun prop.

 

sounds more like some kind of misfire under load to me

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