Yamaha F40 runs badly

[Gary13]

My 2008 Yamaha F40 4-stroke is plagued with a re-ocurring problem with poor running. It is carbureted, has in-line 10-micron fuel filter, and always-fresh fuel contains RingFree and Startron. It idles poorly, surges and cuts out at all rpm ranges, has acceleration flat spots that will cause engine to die and currently will not run above 4500 rpm(not prop problem). History is:
Hour 6.5: Taken to dealer for above problem. Carbs cleaned and rebuilt
Hour 7.0: Taken back to dealer with same problems. Carbs cleaned and rebuilt again.
Hour 7.33: Back to dealer with same problem. Yamaha tech did ultrasonic cleaning and rebuild.
Hour 8.0 Returned to dealer with same problem. Eventually Yamaha tech replaced carbs.
Hour 61: Engine to different dealer with same problem. Carbs cleaned and rebuilt. Inside of carbs was clean on disassembly.
Hour 61.5 Exact same problem made no better.
Boat parked until problem solved.

Thanks for any input/suggestions

Gary

 

[99yam40]

Re: Yamaha F40 runs badly

What happened between hour 8 and 61? Did it run fine? if so I would think you have carb problem again.

 

[robert graham]

Re: Yamaha F40 runs badly

Sounds like your carbs should be very clean. Maybe a problem somewhere else in your fuel delivery system? Fuel pump? Good Luck!

 

[rodbolt]

Re: Yamaha F40 runs badly

what was top RPM when new.
should have been propped to run 5800 to 6100.
that motor is incredibly sensitive to overpropping.
other than that find a dealership with a techmate and a test wheel so the problem can be quickly and easily isolated.
no techmate vacum mate and no test wheel will lead to hours of frustrating on water time .
I would also use my Kv tester to check secondary spark voltage.
most techs dont know how to use or why the dynamic function is on the techmate.
those of us who do use it regularly to check the mechanial air flow into the intake and can watch misfires on it and then know what cylinder is or is not misfiring.not something thats taught at school by the way.
only comes from understanding what the 4 stroke engine is and what the tool does.

 

[Gary13]

Re: Yamaha F40 runs badly

99Yam40-Between hours 8 and 61 it ran fine. Thanks for the response.

Robert Graham-Without a doubt, I have the cleanest carbs on the planet. All the fuel delivery hoses were checked for deterioration and there is no residue in the clear bowl of the filter or the on-board filter. I can't answer as to whether they checked the fuel pump but they did pull the lines from the pump to the carbs and found nothing. Thanks for the response.

Rodbolt- Top rpm's when new was 5500...repropped to 5950 WOT. I don't know what kind of test equipment they use (if any) at the dealerships so I can't answer to that. I did pull the spark plugs when the last incident occured and they showed normal combustion was taking place (my estimation). Thanks for the response.

 

[rodbolt]

Re: Yamaha F40 runs badly

thats the great thing about a test wheel.
it allows me to check the engine at the RPM the issue is occuring against a known load.
that way I can check fuel pump pressures,fuel pump inlet vacum,spark advance and a host of other tests with a known load and at the ramp or in a test tank.
the techmate can show any misfireing cylinders and the Kv tester can show secondary spark voltage on all cylinders.
if Kv tests ok,fuel pump pressures ok and intake manifold pressures ok and timing is advancing properly keep hunting carb issues.

 

[Gary13]

Re: Yamaha F40 runs badly

Rodbolt... that techmate sounds like a great piece of equipment. The description reminds me of the old Sun Microsystems engine analyzer. I am going to check with the local shops to see what they use. I doubt it is anything that advanced.....most of them just got indoor plumbing
Thanks for the response

Gary

 

[robert graham]

Re: Yamaha F40 runs badly

Gary, sorry I couldn't be more help on this. Rodbolt is the guru on the real technical/electronic issues. My electronic experience mostly just includes getting shocked on a spark plug lead! I'll be very interested to hear what your problem turns out to be...keep us posted and Good Luck!

 

[Gary13]

Re: Yamaha F40 runs badly

Robert...Thanks for the response. This has brought some of the best (according to them) to their knees .
I gave up on getting shocked by spark plug wires and moved up to the big time....house current .
I will let you know if/when the problem gets solved and what they did. In the meantime, the boat is parked and the canoe has been taken out of moth balls and recommissioned as "Have Stripers....Will Travel". More to follow (eventually)

Gary

 

[rodbolt]

Re: Yamaha F40 runs badly

I am far from the best just never been beaten.
had a few jobs I lost money on over the years but all do.
however with the correct diagnostic equipment, a thoughrough understanding of the systems being tested and how each subsystem affects the other it gets rather boring.
electrical issues are so rare on yamaha stuff it can kick a techs butt when the rare failure occurs.
but its all testable.
all the techmate vacumate is, its an electronic manometer that measures intake manifold pressure(vacum). you can read an average on all 3 cylinders for carb syncing or you can look at intake pressure dynamically to find misfires or leaking valves.
test wheel allows me to put a known load against the engine while being stationary at the ramp or in the tank.

 

[Gary13]

Re: Yamaha F40 runs badly

UPDATE Having run out of local mechanics and Yamaha's Finest, there is finally a solution...the engine will be replaced under warranty. I have never seen one single engine throw so many people. Although I will probably never know what the final straw was, that 15-month ordeal is OVER!!
Thanks to everyone that gave me input. I will let you know how the new one works when I get it in FEBRUARY!!!
This should also answer the question "Is Yamaha's warranty any good?" As with all good things, if you are willing to wait, it will come to you.