Yamaha 40N/50N 40 and 50 HP Outboard Motor Service/Shop/Repair Logo

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Anonymous Posted on Mar 24, 2017

I have a set of 2005 Yamaha 250 Four Stroke engines with 1300 hours on them. They were just serviced and on our first trip offshore fishing after running good all day one engine started surging slightly between 3 to 6 hundred rpm's and continued to get worse until I had to slow down and idle for a while. Tried to run again and after a few minutes of running at 4300 rpm's it started again same scenario over & over. I checked fuel system and all filters everything was prestine no water or trash. Eventually both motors started the same symptoms. They each have designated tanks, hoses, filters and everything is individualized. I pulled the fuel pump box and checked everything again all is clean. Any ideas?

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Bill Boyd

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  • Yamaha Master 53,816 Answers
  • Posted on Aug 20, 2017
Bill Boyd
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For 2 separate engine operating on their own fuel systems after a service and have the same fault is more than a coincidence
check for the vents on the fuel tanks for starters
Take them back to the shop that did the service and have the fault codes read
point of interest do they run off the same battery/s and are the batteries connected
indicates that the voltage of the battery/s is dropping below required voltage to run the systems
check battery connections and electrical wiring for corrosion

merc racing

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  • Contributor 36 Answers
  • Posted on Aug 20, 2017
merc racing
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Need to hook up YDS diagnostics and check for codes first. Second you need to hook up a fuel pressure gauge on the motor and make sure your keeping steady fuel pressure. Did you check the grommet on top of the high pressure pump for a split in the rubber?

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5 Related Answers

Anonymous

  • 36 Answers
  • Posted on Nov 29, 2008

SOURCE: 2 1/2 Briggs......doesn't run smoothly....surges at all speeds.

Hi, Check that you have the correct spark plug fitted or fit a new one as it sounds like your plug is getting hot then shorting out.
Sometimes the magnito can do this as well. but I would start with the plug.

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Anonymous

  • 59 Answers
  • Posted on Dec 22, 2008

SOURCE: engine stalls

my friend had one that did the same and he replaced throttle positioning sensor and it fixed it. but when you put a new battery in them they wont idle until you hold at steady low rpm for almost a minute because it has to relearn its position. so check your voltage meter and make sure it is around 13-14 volts when running and not on 12 while running because it could be too low of voltage for it and would be the same principle as disconnecting the battery because it takes 12 volts to keep computer on. hope I wasnt too confusing but I just want you to check your voltage for free before you buy electrical parts.

Anonymous

  • 12 Answers
  • Posted on Feb 07, 2009

SOURCE: rough idle / engine surges until power is applied

Sounds like a possible vaccume hose leak?

Anonymous

  • 131 Answers
  • Posted on Feb 10, 2009

SOURCE: '99 chevy Silverado Z71,5.3 engine.....will not rev when hot.....

try replacing your EGR Valve, or your Oxygen Sensor

Knight 007

Murtaza Akberali Versi

  • 767 Answers
  • Posted on May 12, 2009

SOURCE: 2003 yamaha wrf 250 carb problem

(1) You will need to adjust the float pin to get the correct amount of fuel in the float chamber of the carburator.
(2) You will also need to set the air-mixture screw , but before you do tht remove the spark plug and see whats the condition of it, is it black , is it brownish, or is it whitish.
If its blackish = means rich too much of fuel, if its browinsh= ok, if its whitish = its too lean.
(3) As for hesitation, check the needle at carbs piston on the accelerator cable, and blow the main jet with high pressure.
(4) Check too the spark plug gap and if its as per the manufacturers specs.

Hope this helps!

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