2001 twin 250Yamaha ox66 rough idle stalls no acceleration

[dwwesley]

Rodbolt or ? engines have approx 480 hours. starboard engine idles rough and will die and will not accelerate. port engine runs perfect. have checked, cleaned or swapped port to starboard the following parts: o2 sensors, vst with new filters, cdi unit, stater assemblies, plugs. fuel pressure looks good - constant 35psi with gauge attached. checked all 3 lift pumps and diapragms look good. loosened and cleaned all ground connections found. also checked main harness connection. racor water separator filters replaced. disconnected fuel rail and observed all 6 injectors while cranking. all 6 operating. should injector create a stream or cone type pattern? if i shoot starting fluid into the intake ports, it fires up strong. could it be quenching the spark with injector pulse too wide? don

 

[cousinabe]

Re: 2001 twin 250Yamaha ox66 rough idle stalls no acceleration

have you checked your spark plug caps for resistance? each boot unscrews off the wire. Should read between 4k-6k to be in spec. anything higher or no reading at all is defective.

Also want to make sure your TPS voltage is ok

have you tried using a different fuel source in the bad engine?

 

[kandil]

Re: 2001 twin 250Yamaha ox66 rough idle stalls no acceleration

did you clean the carb?

 

[rodbolt]

Re: 2001 twin 250Yamaha ox66 rough idle stalls no acceleration

quit splatter gunning.
lets do some actual testing.
first test compression,needs to be within 10 psi on all 6.
next test spark,needs to be able to jump a 7/16th" gap on all six when cranking.
to test the plug caps unscrew them from the plug wire and test with an ohm meter per the service manual.
once we know the ign system is ok and the engine is mechanically sound its on to the fuel system,test fuel rail pressure,needs to be 35 psi at any engine speed.
so far there is no good test for the injector screens,if injectors are suspect then a service like flagship marine will be in order.
lay off the starting fluid,its very very hard on 2 strokes.
your describing a lack of fuel in the cylinder we just gotta find out why.
if you must inject a fuel in the throttle body use a squit can with a 50/1 premix of gasoline/2 stroke oil
use the diagnostic test lamp and check for codes or use the service manual and you can test each sensor with a multi-meter.
TPS voltage is very important as is the correct crank position sensor output voltage.
all can be easily tested by the average DIY.
but I gotta warn ya,spatter testing ALWAYS leads to more headaches.

 

[dwwesley]

Re: 2001 twin 250Yamaha ox66 rough idle stalls no acceleration

thanks for the responses. i will check tps and crank position sensor output voltage. will let you know the outcome.

 

[dwwesley]

Re: 2001 twin 250Yamaha ox66 rough idle stalls no acceleration

Had a yamaha mechanic check the engine. He replaced plugs, checked tps voltage, and crank sensor voltage. Engine seems to sneeze which he said indicates a lean condition. Fuel pressure gauge indicated constant 34 to 35psi. Heading back to the dock, attempted to plane with both engines, faulty engine drops rpms until it stalls. What now?