Yamaha 175

[src222]

I have a Yamaha 175 2 stroke year 2000. The engine runs ok but it is only firing on 5 cylinders most of the time. When you throttle up to full power it all of a sudden accelerates and decelerates via the 6th cylinder kicking in and out. A mechanic replaced all the plugs, tried a new coil on the problem clyinder (not sure what number but it is the center clyinder on the left side) Tried a new stator I believe (the switch next to the flywheel) He now says it is the main cdi box. Any help?
Thanks Scott

 

[robert graham]

Re: Yamaha 175

drain carb onto a clean white rag on the cylinder that's cutting out to see what may be in it...maybe dirty carb on that cylinder. do you have a fuel/water seperator? run motor hard and then check spark plugs for indication of problems. Good Luck!

 

[src222]

Re: Yamaha 175

The carbs were freshly rebuilt but didnt solve the problem, one cylinder is only firing intermitently

 

[rodbolt]

Re: Yamaha 175

I would reccomend finding a trained tech with a Kv tester,a peak reading multimeter and test wheel yb1624.
or be prepared to simply toss parts at it till its fixed.
with a peak reading multi meter you can test stator out put voltage, pulser coil output voltage,crank position sensor output voltage and CDI output voltage.
all the above tests can be done by a trained competent tech in about 30 minutes and eliminate or confirm an ign problm.
your tech seems to prefer the old school pokenhope method that can get very expensive and blow pistons while chasing issues.
the Kv tester can quickly and efficiently check secondary spark voltage and usually eliminate the above tests for all cylinders.
at least you now own a known good spare stator.

 

[bigbrownbuku]

Re: Yamaha 175

a good test to do before all that useful stuff rodbolt posted is the spark plug boot resistance, it can be done with a simple ohm meter and can affect ignition significantly. they just screw off.

on a side note an intermittent problem can sometimes be a real drag even for the best trained tech. its far easier to fix if its just broke all the time.

 

[rodbolt]

Re: Yamaha 175

and thats why a Kv tester is so handy.
if the cap resistor is open you will see that cylinder fireing 5 Kv or so higher than the others.
normal Kv range on that engine is about 7 Kv loose compression or foul a plug and you will see about 2 KV, open a plug resistor or open the cap resistor or increase compression due to carbon and you will see 10 to 15 KV.
test equipment in the hands of a properly trained tech can make it a simple job.
the correct test wheel allows the tech to use the boat ramp or a test tank of sufficient size while testing inputs to the CDI and outputs from the CDI.
the crank position sensor on that motor controls 2 cylinders.