Yam F 350 lost 200 rpms after winter layup

[user64]

Had my F 350 serviced late last season (only plugs, t stats anodes etc) ... computer printout showed no problems. Boat ran great for the rest of the year. Upon splashing this year, boat won't go above 5600 wot ...last year was 5800 no problem.

Is it possible the stored gas had lost some octane over the 6 month layup and thats why I cant get to 5800? I cant think of anything else thats changed since layup until today. Any thoughts appreciated.

 

[99yam40]

pull and inspect plugs to see if one cylinder is not burning properly

 

[user64]

Will do...thanks.

 

[99yam40]

what kind of fuel you running?
E fuel goes bad quickly

 

[Sea Rider]

Run it with fresh fuel and check if the lost wot rpm was restored. If engine runs at same MPH now as did as before is a tach related issue...

Happy Boating

 

[user64]

Yes..its running on E-10. Previous years the boat ran at 5600-maybe 5700. Never hit 5800 until the plugs were changed. I assumed that it was some kind of plug problem from the factory and that the plug change had solved it. Computer showed everything was fine.

The fact that the problem has reoccured makes me think its what 99yam40 said in his first post...a problem with a particular cylinder. I will pull the plugs and check it out...but think I will wait until after I fill up with fresh gas from this year and maybe save myself a step.

Searider..doubt its a tach problem as wot mph has dropped by 2 ....along with the loss of 200 rpm.

Thanks for all of the input.

 

[99yam40]

if the fuel you have is going bad and you add more to it, you will have more bad fuel\

adding fresh fuel or additives will not make bad fuel good again

 

[user64]

if the fuel you have is going bad and you add more to it, you will have more bad fuel\

adding fresh fuel or additives will not make bad fuel good again

Understood....my point was I will run it down to almost empty and then fill it,,i take 140 gals. Again, I think your first call was a good one...problematic cylinder.

 

[99yam40]

if it is not from a bad plug and from lean running cylinder, it could harm motor by just keep running it

how many hours on you motor and when was last flywheel changed?

 

[user64]

if it is not from a bad plug and from lean running cylinder, it could harm motor by just keep running it

how many hours on you motor and when was last flywheel changed?

About 200 hrs....flywheel /ECU done at 67 hours. Looking at the plugs again should give me a hint and I'll check back in.. As I said everything checked out in the fall...computer run, compression test.

 

[99yam40]

I have read flywheel needs to be done every 80 hours over a certain RPM

running a motor with a problem is never good., find out what it is

 

[user64]

I have read flywheel needs to be done every 80 hours over a certain RPM

running a motor with a problem is never good., find out what it is

Yeah..80 hours between 3400-4250 IIRC. The ECU sends you a warning when you meet that number. Looking at my last engine I didn't rack up those numbers for 5 years according to my printouts.