Yamaha 250 Saltwater series 95 model

[colliercrew]

Hi! Im writing for my poor frustrated husband. He owns a 250 Yamaha saltwater series 95 model 2 stroke engine. The problem is losing rpm . He has replaced just about everything- pumps,coils,plugs,hoses,carb cleaned. Everything that has been posted to try on other posts ,, he has tried. His engine starts "missing" after 4800 rpm. It runs very smooth before that. He says he loses a cylinder after around 4800 RPM. He has done all of the fuel systems (please bare with me, I am female)and tried new tanks and you name it!! Anyway, if anyone can give me some answers that I can tell him (he will think I've gotten smart on motors ha), I would greatly appreciate it!!!

 

[rodbolt]

Re: Yamaha 250 Saltwater series 95 model

has he tested the T-stats?<br /> I also need a model number<br /> the saltwater series shows up as a 96 year first production run.<br /> also test the plug caps. the diagnostic lamp is about 70 dollars and is very handy for accesing ECU information. be aware that with the diagnostic lamp attached no automatic oil transfer will occur but all alarms will function normally.a quick test is to remove the airbox and have a trusted helmsman ,not any one connected with any life insurance policies, operate the boat until it misses. then use a sqirt can ,like the lever type oil cans, to squirt pre-mixed(at 50/1) fuel into each carb throat and observe engine RPM. the carbs on a 250 are very touchy. also the stator can be failing and give the same symtoms. a CDI output test will require a meter capeable of peak reading. some DVM's have an avalible DVA adaptor. I reccomend the stevens CD-77 but its a bit pricey, buts its time to eliminate fuel or ign as the culprit. the ign and fuel control circuits on that engine are complex but easy to test if you follow the manual and understand what each part does to the other.

 

[colliercrew]

Re: Yamaha 250 Saltwater series 95 model

thanks so much, he is testing the t-stat ( the thing near the stater?) sunday in hope of solving the problem, i will pass on all info i get thanks again

 

[rodbolt]

Re: Yamaha 250 Saltwater series 95 model

there are two thermostats. located on the top of the block just fwd of the cyl head to block parting line. if they the stick open and the engine runs to cool it will run #6 fuel bowl dry.<br /> if he is going to attempt to continue testing the motor himself the diagnostic lamp from yamaha will be invaluable. will save a lot of time not chasing ghosts

 

[colliercrew]

Re: Yamaha 250 Saltwater series 95 model

thermostats have also been replaced, headed to a yamaha mechanic Sunday to try again with this motor, other than missing at 4800 it really runs good, but he says if prob is not fixed it will eventually blow the engine, financially i hope we get answers sunday.. this forum is great, even for the amatuers like me (a wife ha) !