Yamaha OX66 225s- Tell me everything

[SkunkBoat]

Question for all the mechanics out there...
Tell me what I need to know about 2000 Yamaha OX66 225s.

[Destroyer]

Ummm... Their made by Yamaha. They are 225 horsepower and they are Model OX66's...


Sorry Skunk... I just couldn't help myself....

[phatdaddy]

Only thing i know is they like yamalube and this magic stuff called ring free.

[THEFERMANATOR]

I don't have much experience with them myself. I know it's an old school 2 stroke design engine with basic fuel injection, but I believe the ox66's used an oxygen sensor mounted in the powerhead in the top of the exhaust port to provide air/fuel data to the ecm to help eek some milage out of them. I know I've read the O2 sensors were problematic in them and required frequent cleaning. Otherwise they're supposed to be some of the best engines Yamaha turned out.

[spareparts]

good solid engines, basic EFI. They like gas though. If you want to get ahead of the curve and get it all ready for next season. Plan on doing some off season maintenance to them. O2 sensors are easy to clean, remove from housing, heat till cherry red with a MAp torch, let cool off and reinstall. Make sure to clean the passage into the cylinder and the little barbell thing with Merc power tune or parts cleaner of your choice. Yamaha sells the gaskets needed as a kit. Replace thermostats, be care full, those little bolts break off easy. Replace water pump impeller, use Yamaha factory kits only. If it doesn't have a water separating filter for each engine, install one(new fuel hose doesn't hurt). If you're up for it, take the VST(fuel tank assembly on the engine) apart, clean it out, replace the screen on the fuel pump. While its off, check or replace the mechanical fuel pumps. Tighten the bolts holding the pumps together, there are three of them. If you think you need diaphragms, check the price on the whole assembly, they're not much more than the rebuild kits. Run good fuel, good oil and ring free and you should have good service out of them. Items of note, they only run on four cylinders at idle, so don't get freaked out of it seems like they aren't hitting on all 6, they aren't. Trim motors and fuel pumps are very expensive from Yamaha, the aftermarket is supplying good alternatives for them now.

[SkunkBoat]

Originally Posted by spareparts

good solid engines, basic efi. They like gas though. If you want to get ahead of the curve and get it all ready for next season. Plan on doing some off season maintenance to them. O2 sensors are easy to clean, remove from housing, heat till cherry red with a map torch, let cool off and reinstall. Make sure to clean the passage into the cylinder and the little barbell thing with merc power tune or parts cleaner of your choice. Yamaha sells the gaskets needed as a kit. Replace thermostats, be care full, those little bolts break off easy. Replace water pump impeller, use yamaha factory kits only. If it doesn't have a water separating filter for each engine, install one(new fuel hose doesn't hurt). If you're up for it, take the vst(fuel tank assembly on the engine) apart, clean it out, replace the screen on the fuel pump. While its off, check or replace the mechanical fuel pumps. Tighten the bolts holding the pumps together, there are three of them. If you think you need diaphragms, check the price on the whole assembly, they're not much more than the rebuild kits. Run good fuel, good oil and ring free and you should have good service out of them. Items of note, they only run on four cylinders at idle, so don't get freaked out of it seems like they aren't hitting on all 6, they aren't. Trim motors and fuel pumps are very expensive from yamaha, the aftermarket is supplying good alternatives for them now.

thanks!

[bgreene]

Friends with em ' tell they burn a LOT of fuel and a LOT of oil.

Outdated technology and performance.

[THEFERMANATOR]

Originally Posted by bgreene

Friends with em ' tell they burn a LOT of fuel and a LOT of oil.

Outdated technology and performance.

Outdated technology I'll give you, outdated performance is a big negative IMO. I know DFI's run good, but it's tough to beat the performance AND lighter weight of the old school 2 strokes. And the 225 ox-66's were true beasts utilizing the larger displacement block of the 250's. So yes, they use 5-10% more fuel and probably 25% more oil than a DFI in an average outing, but they do have there benefits to many boaters still.

[SkunkBoat]

OK so we've run them a bit now.

had to replace a thermostat housing (cracked at bolt and dribbled very slightly)

Stbd engine tops out at 4600. Port over 5000. Prop on stbd had work done, maybe problem???

Rpms/throttles match up until 4000, then stbd has to be pushed farther than port.

Both at 4200 she hums along at 33 mph/33gph and sounds great. Had it up to 38mph.

best fuel burn at 25 mph/22gph.....ouch!!!! (has yammie fuel flow meter)

tilt position sensor on stbd not working...haven't investigated yet.

Stbd fuel pumps look brand new.

HATE the blue smoke. Haven't had a 2 stroke since 2003. You really get used to breathing....

LOVE that the boat was easily worth $22k without any motors so I can't complain about running motors.

Hope to run these next year and scrape and save and beg and borrow to get new 200 yammie or zuki I4 four strokes in the future. That'll last me right to retirement....

[spareparts]

based on a twin F150 repower I just completed, you should be able to buy over 10000 gallons of marina fuel and oil for the price to repower that boat

and by the way, those engines are highly sought after in offshore countries as they are not as fuel finiky as four strokes