Yamaha OX66 225s- Tell me everything
- Thread starter SkunkBoat
- Start date
THEFERMANATOR
God
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
God
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
God
thanks!
THEFERMANATOR
God
Outdated technology I'll give you, outdated performance is a big negative IMO.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
God
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....
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 $22k without any motors so I can't complain about running motors.
Hope to run these next year and scrape and save and beg and borrow to get new 200 yammie or zuki I4 four strokes in the future. That'll last me right to retirement....
spareparts
God
based on a twin F150 repower I just completed, you should be able to buy over 10000 gallons of marina fuel and oil for the price to repower that boat
and by the way, those engines are highly sought after in offshore countries as they are not as fuel finiky as four strokes
and by the way, those engines are highly sought after in offshore countries as they are not as fuel finiky as four strokes
Last edited:
wellcraftv20step
Senior Member
I have the ox66 250, this is only my first year with it. And since Spare help me get this thing running rite its been a great motor with gobs of power . And everyone I speak with that has one is very pleased with it.. that's all I can tell ya.
SkunkBoat
God
Yep I know its a big nut...and I'm a cheap b@st@rd...The thought is to run a full year and really decide if going BIG was a good move. If I decide this is the boat for the next 15 years then...
Factors for repowering-
Really can't stand the smoke
200 four strokes would probably double the mpg...canyon trip 100 gallons vs 200 gallons...over 15 years that is a big number to help offset repower$.
These are 17 years old so they will require constant repairs, some nickel and dime(just ordered an oil tank pump) and some not so cheap..
That means more down time and this is a big boat/no trailer...$$ and hassle to pull to work on.
Likely that at some point I will be forced to repower anyways so I might as well do it early.
These running motors are worth something to sell right now to lessen the hurt of repower.
Factors against-
from a total $ perspective its only worth it if I keep the boat for 15 years or so.
Have to tell wife I'm spending $35K on motors
THEFERMANATOR
God
You will not double your milage unless you troll ALOT, and I do mean ALOT! The fuel economy diffetence for long runs is no where near as much as most think it is. At idle to low load situations, yes, you will see a big jump, but at cruise to wot the realistic improvement should be in the 10-25% range of improvement. I currently havea 4 stroke because that is what was on the boat I found I liked, but I would have just as easily have gotten one with 2 strokes. If you're after mpg, then a direct injected 2 stroke will most likely beat out even the 4 strokes in most areas.
As to hating the smoke, have you tried a better quality oil like pennsoil synthetic blend? Yamalube is a good oil, but I had the least amount of smoke with the pennsoil. Also make sure the oil injection pumps are adjusted correctly. Even 1 turn out of adjustment can make the difference between smoke or no smoke. I had a 25HP Suzuki YEARS back that fought me fouling plugs, ended up being the pump was 2 turns out of adjustment. It actually fell within theallowable limit, but adjusting it dead on cleared up all the smoke and no more plug fouling.
As to hating the smoke, have you tried a better quality oil like pennsoil synthetic blend? Yamalube is a good oil, but I had the least amount of smoke with the pennsoil. Also make sure the oil injection pumps are adjusted correctly. Even 1 turn out of adjustment can make the difference between smoke or no smoke. I had a 25HP Suzuki YEARS back that fought me fouling plugs, ended up being the pump was 2 turns out of adjustment. It actually fell within theallowable limit, but adjusting it dead on cleared up all the smoke and no more plug fouling.
spareparts
God
its not supposed to run without a battery,
two big fuses and a spare under the back cover on the port side of the engine, Yamaha engines have two charging systems, nice to use if you have a separated house battery.
https://www.google.com/search?q=ox6...hVGxFQKHfjeBVEQ9QEILjAC#imgrc=Ed1-Sduze4rOrM:
.
two big fuses and a spare under the back cover on the port side of the engine, Yamaha engines have two charging systems, nice to use if you have a separated house battery.
https://www.google.com/search?q=ox6...hVGxFQKHfjeBVEQ9QEILjAC#imgrc=Ed1-Sduze4rOrM:
.
SkunkBoat
God
so I replaced the rectifier (without really troubleshooting cause I am a dummass). rectifier didn't fix it. So measured the stator (green wires) 0v AC....open resistance between all 3 green wires...looks like stator....
anyone know if you can pull that flywheel with a steering wheel puller?...don't have the yamaha tools for that.
hoping I find a fixable broken wire cuz its $600 new and $150 used and used is a crap shoot.
anyone know if you can pull that flywheel with a steering wheel puller?...don't have the yamaha tools for that.
hoping I find a fixable broken wire cuz its $600 new and $150 used and used is a crap shoot.
SkunkBoat
God
I don't want to seem like I am doubting you, just asking for a little more info...
We figured since it has an emergency pull start rope, that it should run without a battery...so we tried it and it shut off...
Then we turned off the battery to the running Stbd engine and it kept running...
after that we read the warning on the switches "Don't shut off while engines running"
did I mention I don't have battery switches on the V20 and was just winging it. Had been running them on BOTH which caused the uncharged battery to drain the charged ones when I left the switch on Both overnight....new boats!!!
I think the PO had some inkling as to a charging problem because all 3 batteries were brand new and he had both Stbd and Port Aux charging wires to the port battery.