1997 Yamaha 250's

[tomwwalker]

One of my 250's is fouling the number 4 and 6 spark plugs. They carb up in about one hour of running. I have changed thermostat, o2 sensor, injectors and swapped the computer to eliminate it as a possibility. Any ideas?

 

[arboatdr]

Re: 1997 Yamaha 250's

Assuming you have checked compression and your fuel delivery system and they are up to par I'd look at the the resistor spark plug cap. They can sometimes break down under a load. They should ohm out somewhere around 5kohms.

 

[tomwwalker]

Re: 1997 Yamaha 250's

i<br />I have checked the compression and fuel delivery system. In fact changed the injectors and as you suggested the resistors. THANKS for taking the time to suggest fixes. I am stumped at the moment.

 

[rodbolt]

Re: 1997 Yamaha 250's

hello<br /> if after eliminating all other sources check the stator output voltage after an hour or so of run time.if it falls below about 100 volts with a peak reading meter the plugs will foul after trolling. you will need to monitor the plug firing KV as well as the ign coil primary voltage.<br /> good luck and keep posting.

 

[Lloydramdeen]

Re: 1997 Yamaha 250's

Password<br /><br />I recently went down this road and found out I had to replace the stator. The whole process took six weekends of trouble shooting as I work during the week. I hope this is not the case though as it could be heavy on your wallet. Rodbolt will tell you dont go buying parts unless you are sure.You should have the tech to do a diagnostic light test as a breakdown in the stator could cut the voltage and cause you to run too rich. This was exactly what was happening to me. You are on the right track but dont buy a stator unless you are sure.

 

[Lloydramdeen]

Re: 1997 Yamaha 250's

rodbolt,<br /><br />I dont believe it, we were actually on at the same time. I see Password is having the same problem. Thanks for your help. Mine has been running fine- like a new motor.

 

[BRIAN03]

Re: 1997 Yamaha 250's

Check the low pressure fuel pump diaphrams. Its common to load up two holes together. 2/4

 

[tomwwalker]

Re: 1997 Yamaha 250's

do those fuel pumps take fuel to the injectors? There is three of them. Does any one of them serve cyl 4 and 6? i think those have been checked but i may do that again.

 

[vinney]

Re: 1997 Yamaha 250's

The low pressure fuel pump uses crankcase vacuum to make the fuel pump work. When the diaphram fails the fuel is pushed into the crankcase and the cylinders. If the primer bulb will not get hard check the low pressure fuel pumps. Service(low pressure) the diaphrams every 200 to 250 hours of service.

 

[rodbolt]

Re: 1997 Yamaha 250's

hello<br /> the other classic signs of a low pressure pump failure is a lot of fuel spots on the water at idle. the other is it dies about 5200 rpm. an easy test is just to pump up the primer bulb and see if it stays hard when you keep squeezing it or does the primer constantly leakdown while squeezing,<br /> good luck and my other posts will tell you replace the low pressure pumps every 3 years and odds are you wont have much problems.<br /> good luck and keep posting