2001 Yamaha SX250 smoking more than usualat idle

[Robert Louis]

Before I start looking for a remedy, I thought I'd ask the forum for advice:
For the past 5 years, my 2001 SX250 2 cycle has always started after 5 or 6 seconds of cranking, but lately has been putting out more than the normal amount blue smoke at start-up and frequently at idle (no noticeable smoke at higher rpms).

I've received a lot of advice including changing the thermostats, replacing the 3 fuel pumps, replace the oxygen sensor, to much oil is being metered in...

Where would you start with repairs? Thanks in advance for any advice. Robert Louis.

[99yam40]

If you have not replaced stats and fuel pumps in last few years then do that.


I do not see how O2 problem would cause smoke, but it should be cleaned and tested from time to time.

Do you monitor the oil used to see if it is using more than it should?

[tonynorie]

I had a similar situation with my 200hpdi and after a year of trying to diagnose the problem it turned out to be my engine oil resevoir over flowing and sending the excess oil to the air bafflle which of course means the air intakes get a lot of oil. The smoke was most noticeable at start-up, especially after running at high RPM's for a while. Once I fixed the overflow situation the problem went away.

[Robert Louis]

Thanks for the feedback. I took the cowling off, oil all over below the air box, took the air box of the intake and oil inside the air box. does this sound like the overflow situation ( excess oil from the engine oil reservoir)? Thanks

[Robert Louis]

Thanks 99yam40. Independent of what the real problem is, I will change out the (3) fuel pumps and stats. They have not been changed in 5 years. Thanks for the advice.

[Robert Louis]

If you have not replaced stats and fuel pumps in last few years then do that.


I do not see how O2 problem would cause smoke, but it should be cleaned and tested from time to time.

Do you monitor the oil used to see if it is using more than it should?

As mentioned, I have not replaced stats or pumps for ~5 years. If not the problem, I will at least do that as PM. I generally burn 250 gallons per year/summer season, and I usually add 1 gallon of TCW-3 oil to the remote oil reservoir (located in the bilge area) at each fill. I don't believe I'm using an excess of the oil, I usually keep it topped off after each fill (I will pay more attention to that). Again, excess smoking is at idle, and I usually don't idle that much, idle at start-up and then return to the dock. I do a lot of *****ing to and from the Race, at usually 1100-1200 rpm, and don't experience any noticeable smoking during that run time. Typical day is travelling 10-15 miles.
I do add Ring-Free at almost every fill.
Thanks for the feedback. Robert Louis.

[tonynorie]

Thanks for the feedback. I took the cowling off, oil all over below the air box, took the air box of the intake and oil inside the air box. does this sound like the overflow situation ( excess oil from the engine oil reservoir)? Thanks

That's the scenario I faced....oil in and below the air box. I'm not an expert and only know my motor configuration and on mine there are two hoses going in to the air box. I can follow one of the hoses up to the top of my oil resevoir and of course that's where the overflow eminates from. What does your oil level read? Are you between the lower and upper lines?

[Robert Louis]

That's the scenario I faced....oil in and below the air box. I'm not an expert and only know my motor configuration and on mine there are two hoses going in to the air box. I can follow one of the hoses up to the top of my oil resevoir and of course that's where the overflow eminates from. What does your oil level read? Are you between the lower and upper lines?

My oil level (from the Yamaha meter) says full. I need to visually recheck the oil tank on the motor. I think it was full.
I also have the small black hose on the bottom of my air box that runs to the top of the oil reservoir.
Hopefully that's the problem.

Was your fix to clean-up the oil level gauge assembly, or did you have to replace parts?

I'll let you know what happens. But for now, just got back from the boat (I live 65 miles away from the shore) and won't be going back until mid next week. Thanks for the feedback, much appreciated. Robert Louis.