1999 250 Yamaha SWSII

[Pmead]

I just purchased a 1999 250 Yamaha and got everything all mounted and when we took it out it won't go past 3200 RPMs and then falls back to around 800 RPMS. The motor sat for 5 years, the guy did put it away right (he is a small marine shop) and when he got it out he ran double oil so not to screw up the cyls. I changed the plugs but still nothing more than 3200 and it dies out when it gets that far. Any ideas?

 

[KCLOST]

Re: 1999 250 Yamaha SWSII

Make sure that your oil tank on the engine is keeping full. If is doesn't the auto-rev limiter will kick in...You should also get an alarm at that point (if you have it hooked up).

 

[rodbolt]

Re: 1999 250 Yamaha SWSII

clean the injectors,VST tank and filter,replace the low pressure pumps and clean the filter behind the fuel pressure regulator and remove the check valve between the engine filter and low pressure pumps. then test fuel system vacum at the low pressure pump intake.
clean and test per the 3 tech bullitens, the O2 sensor especially after double oil.
also install a water pump kit and t-stats and pressure valve grommet. it only takes one lean out or overheat to destroy your toy.
I dont care how ya put it away 5 years is a lot of deterioration for fuel,oil and cooling systems.
I would also clean both oil tanks and oil filters.

 

[Pmead]

Re: 1999 250 Yamaha SWSII

If I don't have the alarm hooked up will it automatically put me into limp mode? It is not even on there right now! It is still in the box.

 

[rodbolt]

Re: 1999 250 Yamaha SWSII

RPM reduction wiull occur regardless of audible or visual alarms. it will cause the engine to shake badly and limit RPM to about 2500 or so.
why dont ya fix it right BEFORE a piston lets go instead of after ?
either way all of the above maint needs to be done. the only difference between before or after piston replacement is the cost of the additional parts.

 

[Pmead]

Re: 1999 250 Yamaha SWSII

Yeah roger that! I will get after that right now. Thanks for the help. The motor only has 280 hrs on it and it would be a shame for it to blow.

 

[Pmead]

Re: 1999 250 Yamaha SWSII

Can you clean the O2 sensor or do I have to replace it? They are like $280!

 

[bernieb]

Re: 1999 250 Yamaha SWSII

Can you clean the O2 sensor or do I have to replace it? They are like $280!

try this report from bass&walleye boats........http://www.ask.com/web?q=servicing+yamaha's+super+sniffer+by+bill+grannis&qsrc=0&o=0&l=d

 

[rodbolt]

Re: 1999 250 Yamaha SWSII

just make sure the threaded portion of the sensor,especially the crimped area, does not get soaked, the test harness to insure its working is about 20 dollars.
digital meter at radioshack is about 30 dollars, a sweet running 250 is priceless.
the 250 EFI yamaha was a solid notor but the maint MUST be done or they tend to self destruct.
the ECU is rather stupid and will lean out the mix if the o2 sensor tells it to. above 4000 it can go lean enough to burn a piston. the injectors have 10 micron filters in them that can and will clog, the vapor seperator has a filter on the pump and a filter behind the fuel pressure regulator.
all are easy to clean/replace.
fuel issues kill more yamahas than about all other failures combined.