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Elevation adjustment?

D

Daveelko1

New member
I just purchased a 2024 BF9.9D outboard motor. The manual states the carburetor fuel mixture should be adjusted if operated above 3000’. I’ll be operating it at 6000’. Does anyone how much the performance will be affected? If an adjustment is required how can I do it? I’m in the boonies, 200 miles from a boat shop.
 
Hi,

There's a "rule of thumb" about elevation and engine performance that states an engine will lose approximately 3% of power per each 1000 feet. IE: 6000 ft elevation = 18% loss.

It's primarily due to there being less oxygen available for combustion the higher your go.

Honda provides an optional main jet for the carb that should be installed for better starting and running at altitude. See item 25 in the link below.


Of course, if you return to operating at sea level, you would need to install the original jet. Not doing so could result in lean burn combustion, elevated cylinder temperatures and possible engine damage.

Good luck.
 
jgmo said:
Hi,

There's a "rule of thumb" about elevation and engine performance that states an engine will lose approximately 3% of power per each 1000 feet. IE: 6000 ft elevation = 18% loss.

It's primarily due to there being less oxygen available for combustion the higher your go.

Honda provides an optional main jet for the carb that should be installed for better starting and running at altitude. See item 25 in the link below.


Of course, if you return to operating at sea level, you would need to install the original jet. Not doing so could result in lean burn combustion, elevated cylinder temperatures and possible engine damage.

Good luck.
Click to expand...

jgmo said:
Hi,

There's a "rule of thumb" about elevation and engine performance that states an engine will lose approximately 3% of power per each 1000 feet. IE: 6000 ft elevation = 18% loss.

It's primarily due to there being less oxygen available for combustion the higher your go.

Honda provides an optional main jet for the carb that should be installed for better starting and running at altitude. See item 25 in the link below.


Of course, if you return to operating at sea level, you would need to install the original jet. Not doing so could result in lean burn combustion, elevated cylinder temperatures and possible engine damage.

Good luck.
Click to expand...
I ordered the main jet, item 25, you mentioned but, in the specs I didn’t see anything that said it was the main jet for 6000’ altitude. How do you know this jet is for 6000’. I’m only going to run this motor on this lake at 6000’.
 
Well, I don't know that it's actually appropriate for that elevation.

Back in the day, There were typically several jets offered to cover different elevations but....well....today is today and the 98 is your only alternative....today.

I probably should have told you to try the outboard as is and see if it works for you. It might because I believe that 6000 ft. Is right on the cusp of possibley needing that jet.

If it runs rich, frequently fouls the plugs, doesn't idle worth a dang, has crap power or floods on you then the undersized jet will likely clear most, if not all, of that up.

I've never had the pleasure of dealing with that so my knowledge, in that regard, is limited at best.

Good luck.
 
I agree with JGMO. I'd run it with what jet is currently in there. It's not going to really hurt the engine like leaning out the jet. At least run it enough to do a plug reading.
 
I realize outboards are ridiculously expensive, but why the eff are they still using carburetors? I would think the EPA/CARB, etc would have put an end to those and if these were injected, there would be no need to mess with anything WRT fuel mixture because a MAP sensor would check baro and compensate, automatically.
 
jimn said:
I realize outboards are ridiculously expensive, but why the eff are they still using carburetors? I would think the EPA/CARB, etc would have put an end to those and if these were injected, there would be no need to mess with anything WRT fuel mixture because a MAP sensor would check baro and compensate, automatically.
Click to expand...
I understand what your saying, but if I was isolated, low tech all day!

I assume it's just the smaller motors.
 
Agreed....an FI engine requires a 12 volt battery to run the fuel pump to pre charge the fuel rail for starting and to power the ECM so basic sensor checks....baro...tps...engine temp...can be made. So....more complicated.

I have seen prototypes discussed that use a generator to produce enough juice when pulling over to eliminate the need for a battery but I know of no major manufacturers that offers that system yet.

It's probably coming though.
 
jgmo said:
Agreed....an FI engine requires a 12 volt battery to run the fuel pump to pre charge the fuel rail for starting and to power the ECM so basic sensor checks....baro...tps...engine temp...can be made. So....more complicated.

I have seen prototypes discussed that use a generator to produce enough juice when pulling over to eliminate the need for a battery but I know of no major manufacturers that offers that system yet.

It's probably coming though.
Click to expand...
It's actually already here. Starting in snowmobile. I had a 99 Arctic Cat 600 that had battery less efi. If engine was cold, it only took two pulls. First one energized fuel pump and gave a shot of fuel.
 
jgmo said:
Well, I don't know that it's actually appropriate for that elevation.

Back in the day, There were typically several jets offered to cover different elevations but....well....today is today and the 98 is your only alternative....today.

I probably should have told you to try the outboard as is and see if it works for you. It might because I believe that 6000 ft. Is right on the cusp of possibley needing that jet.

If it runs rich, frequently fouls the plugs, doesn't idle worth a dang, has crap power or floods on you then the undersized jet will likely clear most, if not all, of that up.

I've never had the pleasure of dealing with that so my knowledge, in that regard, is limited at best.

Good luck.
Click to expand...
Thanks for the feedback, I couldn’t get squat for an answer from Honda Marine service; seems they don’t have a single technical person employed. Only the 15 hp and below have carburetors. I’ll run it as is and if it’s too rich try the other jet I ordered.
Cheers to all!
 
jgmo said:
Agreed....an FI engine requires a 12 volt battery to run the fuel pump to pre charge the fuel rail for starting and to power the ECM so basic sensor checks....baro...tps...engine temp...can be made. So....more complicated.

I have seen prototypes discussed that use a generator to produce enough juice when pulling over to eliminate the need for a battery but I know of no major manufacturers that offers that system yet.

It's probably coming though.
Click to expand...

With a robust stator/regulator, the ability to charge a battery for this wouldn't be a problem- motorcycles have had fuel injection for a long time and they don't use a large battery. Does this motor not use a battery?
 
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