Yamaha Four-Stroke 250-HP: Octane Requirement

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Belize Whaler posted 05-29-2005 07:23 PM ET (US)
I just bought a 250-HP Yamaha four-stroke outboard. A web review states this motor needs to run on mid-range 89-Octane gas. Where I live, I cannot get more than 87-Octane gasoline. Should be a concern?
Locally we have lots of 225-HP Yamaha four-stroke engines running on this gas with no problems. I just looked at the Yamaha-Canada site and they give the recommended minimum Octange rating 87 for the F250. The Yamaha-USA site does not give this info. The compression is the same (for both engines). We have them running down here just fine on our weak gas.
kglinz posted 05-29-2005 08:39 PM ET (US)
The owner's manual for the F250 does say 89 Octane. There may be a differance in timing. I'd call Yamaha.... http://www.yamaha-motor.com/outboard/service/viewmanuals/viewmanuals.aspx?ls=outboard
Belize Whaler posted 05-30-2005 07:34 AM ET (US)
Oops. Yes, it is 89 for the 250 and 86 for the 225! Weird. The compression is the same in both motors: 9.9 to 1. You do not do higher octane without higher compression. I will have to call around.
bigjohn1 posted 05-30-2005 08:44 AM ET (US)
What about simply running some octane booster in your gas? One more thing to buy and mix but since you're in that position with the locally available gas, your choices are limited. An engine designed to run at a certain octane level will tend to build up more deposits over time when run on lower octane fuel. Some will simply retard spark advance (timing) for the lower octane level but why go this route on a new prestine engine. Give her the octane she was designed to run on.
Belize Whaler posted 05-30-2005 08:52 AM ET (US)
I cannot use octane boosters. They cost too much and they are hard to get where I live. I only get 86-octane at the pumps. I have not opened the box yet and I won't until I can get an OK answer. If I do not (get confirmation that the Yamaha 250-HP four-stroke outboard can be properly run on gasoline with only a 87-octane rating], I will return the motor--which I don't want to do!
jimh posted 05-30-2005 01:34 PM ET (US)
If the owner's manual and the published specifications call for using a fuel with a minimum octane of 89, I don't understand how you expect to receive confirmation that you can use the motor with fuel of only 87-octane and still be in compliance with the specifications. It may well be that on lower-grade fuel the engine will not produce the rated horsepower. This begs the question, why pay a premium for the 250-HP model if you will not be able to produce the rated horsepower due to the low-octane fuel?
The Yamaha website does offer this advice:
Use the proper grade of gasoline.
Use the octane specified by the engine manufacturer. A high-performance outboard is similar to a high-performance sports car — to run properly, it needs the right fuel. A lower-grade gas may foul the plugs and decrease performance, burning more fuel.

Belize Whaler posted 05-30-2005 01:42 PM ET (US)
I didnt know and the dealer didnt tell me. all other yam's run on 87 octane. the 250 and the 225 hp have the same powerhead and compression. so not sure why the 250 needs more octane...usually this is for higher compression and slower burn. so need to find out why the 250 wants more potent fuel - it might not be for any critical reason.
where i live we have always bought yamaha export version that are stripped down so the specs are different on paper for the same machines...esp with emissions. who knows..maybe the 250 has a cleaner exhaust with higher octane but runs the same on either fuel mix.
we have contacted our rep at the factory in japan so should have the ans in 24 hrs.
LHG posted 05-31-2005 01:21 PM ET (US)
The higher octane is how they stretch the extra power of it. As it is, even the 225HP rating is a stretch from what I have been able to tell. Squeezing 250 HP out of that block is really pushing it.
Mercury ups the octane for the higher HP ratings also, as in the 250 Optimax and 275 Verado.
jimh posted 05-31-2005 01:25 PM ET (US)
I did some more research on the F225-F250 motors. It appears the principal difference is the F250 uses cam phasing (variable valve timing) to add more horsepower, otherwise the motors are very similar.
Higher octane fuel tends to suppress ignition knock. It may be that the ignition timing on the F250 is different than on the F225, and as a result the fuel needs more octane to suppress knock (or pre-ignition).
Your point about the emission regulations is a good one. It had not occurred to me that there could be multiple variants of this motor, set up for sale into different parts of the world. Perhaps they do have a model which is tweaked for regions where engine emissions are not regulated and fuel is often of variable quality.
Keep us posted on your results.
Belize Whaler posted 05-31-2005 02:06 PM ET (US)
The japanese central american rep emailed back fm japan and said recommended min gas is 89 oct. The motor has a knock sensor and will retard timing if is senses some pings. If so then will lose a little performance..but he didnt say WHY the motor needs the extra bit of additive - I am curious as the compression is the same as 225hp. one thought is that the exhaust valve has a slight delay in opening so that could cause for an increse in compression over the 225hp. I spoke to the dealer who sold me the motor and he wasnt concerned - a good point he brought up is that regular gas varies in octane fm lo to high 80's depending on age and the 225hp has not had any probs running on mediocre gas. They have exported the 225hp all over the caribbean and mexico and only had some motors sent back that were fed extra dirty fuel. So this might be a precautionary feature that yam has built in to ensure constant performance. I know what mexican gas is like! horrible.
So who knows and i am taking the risk - not that i perceive much of one. will report back when have some results.
kglinz posted 05-31-2005 02:31 PM ET (US)
I would expect that Yamaha has added a few degrees of timing advance in the 250. I don't have a 250 manual, but the 225 spec is 24° B.T.D.C. at 5500 RPM. Maybe your dealer can tell you the 250 spec. The knock senser on the 250 probably just backs off the timing if there's detonation.
Belize Whaler posted 05-31-2005 04:20 PM ET (US)
Very probable on timing. I have a manual on order. I guess when i get all lined out i can run the boat for a while on reg gas - take off to full throttle and note the fuel used, mpg/gph and top speed. and then plug in a 6 gal tank of premium and repeat the same process under same conditions and note the diff. it prob wont be much because will not be loading up the engine - 22 ft outrage - not exactly a 3500# deep vee whatever with 125 gal fuel tank.
handn posted 06-02-2005 06:19 PM ET (US)
Just a note to let everyone know that Yamaha 225 4-strokes do run fine on third world gas.
Mexican Magna Sin is posted at 87 octane, but who knows. My Ford Expedition with a V8 knocked and rattled on it. The Yamaha 225's run great with no plug fouling or other problems. I added Racors to take care of the dirt and water which occurs occasionally in the fuel.
I would go with the 225's, 25 horsepower isn't worth the potential problems.
Belize Whaler posted 06-02-2005 08:15 PM ET (US)
good to hear that!
the 250's have an anti knock sensor so they retard the timing if the gas pre-ignites. maybe the ford dosent have that??
the extra hp is not the plus..it is that these motors have a variable cam that supposedly improves performance in the dead zones of the 4 stroke power band...so they are supposed to give you a hole shot.
will report when i have the test drive down next week.
rbruce posted 06-05-2005 08:51 PM ET (US)
Perhaps you can buy some AV-Gas and mix 1/3 to the available 87 RON, this will definitively increase your octane rating. I did this when 95 RON was not available in my country Costa Rica for my 1984 BMW 318i that required 98 RON and it quieted the pinging.
Today we have 95 RON and the pinging still persists but sold my BMW and my car now has a catalizer and the lead present in AV-Gas would plug it. I still see my BMW running and I would only guess that the mixture didn't reduce its life!
Good luck and enjoy your new motor!
Belize Whaler posted 06-06-2005 07:33 AM ET (US)
i have a feeling that this motor will prob run fine for me on 87.here is the only test report i have found on the motor:
http://www.robalo.com/filedisplay/pdfs/R225%20Smooth%20Operator.pdf
as you can see the 250 is adequately pushing 1/2 again the boat as a 22 ft outrage. so even if it de-tunes a bit then there should still be plenty of power. i have always stayed away from 4 strokes before because i run/takeoff in shallow water - however i have been told that the 250 has the low end power to pop you up on plane like a 2 stroke. my gamble and reports to follow.
yes - if have been looking into mixing but cant buy av gas legally in belize by the drum ( coke plane refueling!)
however - during my recent education on what octane and pinging is all about - i did learn that octane boosters are a rip off!
rbruce posted 06-06-2005 04:35 PM ET (US)
I had the same feeling as you on Octane Boosters, unless they work this way: somehow the kerosene burns hotter than the gasoline and burns off the carbon deposits in the cylinder heads, then after running these additives the motor will lower its compression close to the intended by the manufacturer.
I have not noticed improvement (lack or pinging under load) in my Jimmy with or without the octane boosters of a much publicized brand, however, my trusted Chrysler mechanic in MO has recommended to run occasionaly Power Tune from Mercury and any other additives that are approved by the outobard motor manufacturers.
Your motor is new, so excess carbon would be far away in time, and the occasional spirited or liberal use of WOT would maintain this motor carbon free for years, but I would ocassionally use one of the additives or sprays (which might not be your case as this motor is EFI) to remove carbon off the head and cylinder rings. In such case (where you can't spray down the admission of the motor) a liquid additive used to remove carbon and condition the gasoline recommended and probably sold by Yamaha, might be all that is needed.
It's like when you were a kid that your teachers told you to go to mass every Sunday, I think this might be an overkill so I try to go there occasionally, in the end it might be of help!
Belize Whaler posted 06-12-2005 08:44 AM ET (US)
launched the boat yesterday! I have been driving mid size boats nearly every day for the last 18 yrs and I can truly say that this 250hp yam 4 stroke is the most amazing motor i have driven. it feels like it has the same response as a fuel injected 2 stroke and sounds like a mini turbine engine. you can barely hear it at idle and at 35 mph all you hear is the water shootin off the chines.
it pops the boat up on plane like a 2 stroke. if you are running 3500 rpm and slam down the throttle you had better be hanging onto the t-top! the variable cam makes this day and night in comparison to the f225. i havenent pushed it to the limit yet but did make a 'quick peek' and it looks like about 50 mph at wot. 3 blade stainless factory prop. 19 in x 14 1/4 i think.
it is heavy on the transom - 600 lbs - but at the threshold and not over weight.
once the motor is broken in will post some performance results ..including running on reg vs premium. i am not sure what gas i am running right now..the tank is half full of 5 month old regular ( w/stabilizer) and tooped off with fresh premium. so building in the age factor i am probably running closer to a regular octane.
i have owned a 25 and 18 OR and montauk-guardian. I can say that the 22 footer wins the all around class award in my books.
TightlinesPE posted 06-15-2005 01:51 PM ET (US)
"Where I live, I cannot get more than 87-Octane gasoline."

How did you top off with premium fuel if you cannot get it in your area?
Belize Whaler posted 06-15-2005 06:04 PM ET (US)
I had the seller top it off with premium before he shipped it to me overseas.
Iam only half way thru that tank of gas so will have the test report when i run it on regular. i can already tell you what the report will say now that i have run the engine = no diff!

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Author	Topic: Yamaha Four-Stroke 250-HP: Octane Requirement
Belize Whaler	posted 05-29-2005 07:23 PM ET (US) I just bought a 250-HP Yamaha four-stroke outboard. A web review states this motor needs to run on mid-range 89-Octane gas. Where I live, I cannot get more than 87-Octane gasoline. Should be a concern? Locally we have lots of 225-HP Yamaha four-stroke engines running on this gas with no problems. I just looked at the Yamaha-Canada site and they give the recommended minimum Octange rating 87 for the F250. The Yamaha-USA site does not give this info. The compression is the same (for both engines). We have them running down here just fine on our weak gas.
kglinz	posted 05-29-2005 08:39 PM ET (US) The owner's manual for the F250 does say 89 Octane. There may be a differance in timing. I'd call Yamaha.... http://www.yamaha-motor.com/outboard/service/viewmanuals/viewmanuals.aspx?ls=outboard
Belize Whaler	posted 05-30-2005 07:34 AM ET (US) Oops. Yes, it is 89 for the 250 and 86 for the 225! Weird. The compression is the same in both motors: 9.9 to 1. You do not do higher octane without higher compression. I will have to call around.
bigjohn1	posted 05-30-2005 08:44 AM ET (US) What about simply running some octane booster in your gas? One more thing to buy and mix but since you're in that position with the locally available gas, your choices are limited. An engine designed to run at a certain octane level will tend to build up more deposits over time when run on lower octane fuel. Some will simply retard spark advance (timing) for the lower octane level but why go this route on a new prestine engine. Give her the octane she was designed to run on.
Belize Whaler	posted 05-30-2005 08:52 AM ET (US) I cannot use octane boosters. They cost too much and they are hard to get where I live. I only get 86-octane at the pumps. I have not opened the box yet and I won't until I can get an OK answer. If I do not (get confirmation that the Yamaha 250-HP four-stroke outboard can be properly run on gasoline with only a 87-octane rating], I will return the motor--which I don't want to do!
jimh	posted 05-30-2005 01:34 PM ET (US) If the owner's manual and the published specifications call for using a fuel with a minimum octane of 89, I don't understand how you expect to receive confirmation that you can use the motor with fuel of only 87-octane and still be in compliance with the specifications. It may well be that on lower-grade fuel the engine will not produce the rated horsepower. This begs the question, why pay a premium for the 250-HP model if you will not be able to produce the rated horsepower due to the low-octane fuel? The Yamaha website does offer this advice: Use the proper grade of gasoline. Use the octane specified by the engine manufacturer. A high-performance outboard is similar to a high-performance sports car — to run properly, it needs the right fuel. A lower-grade gas may foul the plugs and decrease performance, burning more fuel.
Belize Whaler	posted 05-30-2005 01:42 PM ET (US) I didnt know and the dealer didnt tell me. all other yam's run on 87 octane. the 250 and the 225 hp have the same powerhead and compression. so not sure why the 250 needs more octane...usually this is for higher compression and slower burn. so need to find out why the 250 wants more potent fuel - it might not be for any critical reason. where i live we have always bought yamaha export version that are stripped down so the specs are different on paper for the same machines...esp with emissions. who knows..maybe the 250 has a cleaner exhaust with higher octane but runs the same on either fuel mix. we have contacted our rep at the factory in japan so should have the ans in 24 hrs.
LHG	posted 05-31-2005 01:21 PM ET (US) The higher octane is how they stretch the extra power of it. As it is, even the 225HP rating is a stretch from what I have been able to tell. Squeezing 250 HP out of that block is really pushing it. Mercury ups the octane for the higher HP ratings also, as in the 250 Optimax and 275 Verado.
jimh	posted 05-31-2005 01:25 PM ET (US) I did some more research on the F225-F250 motors. It appears the principal difference is the F250 uses cam phasing (variable valve timing) to add more horsepower, otherwise the motors are very similar. Higher octane fuel tends to suppress ignition knock. It may be that the ignition timing on the F250 is different than on the F225, and as a result the fuel needs more octane to suppress knock (or pre-ignition). Your point about the emission regulations is a good one. It had not occurred to me that there could be multiple variants of this motor, set up for sale into different parts of the world. Perhaps they do have a model which is tweaked for regions where engine emissions are not regulated and fuel is often of variable quality. Keep us posted on your results.
Belize Whaler	posted 05-31-2005 02:06 PM ET (US) The japanese central american rep emailed back fm japan and said recommended min gas is 89 oct. The motor has a knock sensor and will retard timing if is senses some pings. If so then will lose a little performance..but he didnt say WHY the motor needs the extra bit of additive - I am curious as the compression is the same as 225hp. one thought is that the exhaust valve has a slight delay in opening so that could cause for an increse in compression over the 225hp. I spoke to the dealer who sold me the motor and he wasnt concerned - a good point he brought up is that regular gas varies in octane fm lo to high 80's depending on age and the 225hp has not had any probs running on mediocre gas. They have exported the 225hp all over the caribbean and mexico and only had some motors sent back that were fed extra dirty fuel. So this might be a precautionary feature that yam has built in to ensure constant performance. I know what mexican gas is like! horrible. So who knows and i am taking the risk - not that i perceive much of one. will report back when have some results.
kglinz	posted 05-31-2005 02:31 PM ET (US) I would expect that Yamaha has added a few degrees of timing advance in the 250. I don't have a 250 manual, but the 225 spec is 24° B.T.D.C. at 5500 RPM. Maybe your dealer can tell you the 250 spec. The knock senser on the 250 probably just backs off the timing if there's detonation.
Belize Whaler	posted 05-31-2005 04:20 PM ET (US) Very probable on timing. I have a manual on order. I guess when i get all lined out i can run the boat for a while on reg gas - take off to full throttle and note the fuel used, mpg/gph and top speed. and then plug in a 6 gal tank of premium and repeat the same process under same conditions and note the diff. it prob wont be much because will not be loading up the engine - 22 ft outrage - not exactly a 3500# deep vee whatever with 125 gal fuel tank.
handn	posted 06-02-2005 06:19 PM ET (US) Just a note to let everyone know that Yamaha 225 4-strokes do run fine on third world gas. Mexican Magna Sin is posted at 87 octane, but who knows. My Ford Expedition with a V8 knocked and rattled on it. The Yamaha 225's run great with no plug fouling or other problems. I added Racors to take care of the dirt and water which occurs occasionally in the fuel. I would go with the 225's, 25 horsepower isn't worth the potential problems.
Belize Whaler	posted 06-02-2005 08:15 PM ET (US) good to hear that! the 250's have an anti knock sensor so they retard the timing if the gas pre-ignites. maybe the ford dosent have that?? the extra hp is not the plus..it is that these motors have a variable cam that supposedly improves performance in the dead zones of the 4 stroke power band...so they are supposed to give you a hole shot. will report when i have the test drive down next week.
rbruce	posted 06-05-2005 08:51 PM ET (US) Perhaps you can buy some AV-Gas and mix 1/3 to the available 87 RON, this will definitively increase your octane rating. I did this when 95 RON was not available in my country Costa Rica for my 1984 BMW 318i that required 98 RON and it quieted the pinging. Today we have 95 RON and the pinging still persists but sold my BMW and my car now has a catalizer and the lead present in AV-Gas would plug it. I still see my BMW running and I would only guess that the mixture didn't reduce its life! Good luck and enjoy your new motor!
Belize Whaler	posted 06-06-2005 07:33 AM ET (US) i have a feeling that this motor will prob run fine for me on 87.here is the only test report i have found on the motor: http://www.robalo.com/filedisplay/pdfs/R225%20Smooth%20Operator.pdf as you can see the 250 is adequately pushing 1/2 again the boat as a 22 ft outrage. so even if it de-tunes a bit then there should still be plenty of power. i have always stayed away from 4 strokes before because i run/takeoff in shallow water - however i have been told that the 250 has the low end power to pop you up on plane like a 2 stroke. my gamble and reports to follow. yes - if have been looking into mixing but cant buy av gas legally in belize by the drum ( coke plane refueling!) however - during my recent education on what octane and pinging is all about - i did learn that octane boosters are a rip off!
rbruce	posted 06-06-2005 04:35 PM ET (US) I had the same feeling as you on Octane Boosters, unless they work this way: somehow the kerosene burns hotter than the gasoline and burns off the carbon deposits in the cylinder heads, then after running these additives the motor will lower its compression close to the intended by the manufacturer. I have not noticed improvement (lack or pinging under load) in my Jimmy with or without the octane boosters of a much publicized brand, however, my trusted Chrysler mechanic in MO has recommended to run occasionaly Power Tune from Mercury and any other additives that are approved by the outobard motor manufacturers. Your motor is new, so excess carbon would be far away in time, and the occasional spirited or liberal use of WOT would maintain this motor carbon free for years, but I would ocassionally use one of the additives or sprays (which might not be your case as this motor is EFI) to remove carbon off the head and cylinder rings. In such case (where you can't spray down the admission of the motor) a liquid additive used to remove carbon and condition the gasoline recommended and probably sold by Yamaha, might be all that is needed. It's like when you were a kid that your teachers told you to go to mass every Sunday, I think this might be an overkill so I try to go there occasionally, in the end it might be of help!
Belize Whaler	posted 06-12-2005 08:44 AM ET (US) launched the boat yesterday! I have been driving mid size boats nearly every day for the last 18 yrs and I can truly say that this 250hp yam 4 stroke is the most amazing motor i have driven. it feels like it has the same response as a fuel injected 2 stroke and sounds like a mini turbine engine. you can barely hear it at idle and at 35 mph all you hear is the water shootin off the chines. it pops the boat up on plane like a 2 stroke. if you are running 3500 rpm and slam down the throttle you had better be hanging onto the t-top! the variable cam makes this day and night in comparison to the f225. i havenent pushed it to the limit yet but did make a 'quick peek' and it looks like about 50 mph at wot. 3 blade stainless factory prop. 19 in x 14 1/4 i think. it is heavy on the transom - 600 lbs - but at the threshold and not over weight. once the motor is broken in will post some performance results ..including running on reg vs premium. i am not sure what gas i am running right now..the tank is half full of 5 month old regular ( w/stabilizer) and tooped off with fresh premium. so building in the age factor i am probably running closer to a regular octane. i have owned a 25 and 18 OR and montauk-guardian. I can say that the 22 footer wins the all around class award in my books.
TightlinesPE	posted 06-15-2005 01:51 PM ET (US) "Where I live, I cannot get more than 87-Octane gasoline." How did you top off with premium fuel if you cannot get it in your area?
Belize Whaler	posted 06-15-2005 06:04 PM ET (US) I had the seller top it off with premium before he shipped it to me overseas. Iam only half way thru that tank of gas so will have the test report when i run it on regular. i can already tell you what the report will say now that i have run the engine = no diff!