EFI vs. Carburated

[Yellowstone]

Have had both the Honda 90 carb and Mercury (Yamaha) 115 EFI on different 22's. The only problem with the Honda was when I was careless in maintenance during storage and the carbs varnished up. The Merc 115 has been flawless for five years.

My opinion. The Merc 115 is overkill at sea level, but if you get into higher elevations, it is nice to have. I believe in the concept that when you have the ponies, you have to feed them, and I doubt if the 115 EFI will ever be as efficient at lower rpms as the 90 carb. But on plane the bigger engine doesn't have to work as hard, if, for example, you are holding at 4,000 rpm. All tradeoffs. The Honda 115 EFI is just too darn heavy. Merc, Yamaha, and Suzuki make excellent 115 EFIs.

Go for the bigger engine with EFI.

John

[Rob & Karen]

[Sea Wolf]

Maybe someone who is a dealer or has special knowledge of the Yamahas could comment on this:

I was waiting for Yamaha to convert the carbureted F90 to EFI for several years before 2005, when it was first done, and at which time I immediately bought one, which has been a great engine.

They had been making the EFI F115 for a number of years, but dealers wouldn't mount one on my CD-22 because of the H.P. restrictions because of the limit of 90 on the sticker on the boat, but that's not the point here. Later, after the recommended H.P. was increased, F115's were mounted fairly regularly.

However, I studied the F115 during those waiting years. It has essentially the same 1697 cc powerhead of the F90, except that they claim quite a few of the parts have been especially hardened for the higher horsepower engine, and, in addition, the EFI computer carried a different designation than that eventually given to the new F90 EFI's system.

My question is: Is the F115 really any different internally and in terms of EFI from the F90 EFI, except for the obvious difference in program curves for the fuel/air mixtures and related differences between the two engines?

Would the F115 EFI have essentially the same torque curve at lower rpms as the F90 (and F75 EFI, for that matter), since they have the same displacement?

And finally, in light of all of this, is the top end performance all that really distinguishes these three engines?

Joe.

[Yellowstone]

Joe - Interesting questions. Sorry we missed you at the Boat Show.

Your last question. is to me both yes and no. Definate high end performance with the extra 25 ponies. But as I have discovered over the years, going over 30 mph with the 115 and things get somewhat dicey. You will recall when the 22' was being built, the designers thought 70 HP was the ideal. And the Honda 70 was then the engine of choice from the factory. But boaters started to examine the specs and lo found out the Honda 90 didn't weigh anymore than the 70. So why not spring for the 90 HP? Which most people did. Then when the 115 EFI came out, people began to look at the weight factors, and again, discovered no weight increase between the 115s and the 90s (with the exception of the Honda 115)

Since I have used both engines in question, I can say without reservation that the 90 hp is slightly more economical, but that again varys from skipper to skipper. Engineers who design these modern day motors talk about total weight (boat, gear, people, etc.) versus hull design, and other variables, when fuel economy is under consideration, and we know that an extra hundred pounds, here or there with the 22' can make the difference of easily getting on plane.

A motor with higher hp doesn't have to work as hard to maintain certain speeds compared to the lower hp motor, but as the old cliche goes, there is no free lunch. Using more hp and expecting fuel consumption to remains the same has not been my experience. But the EFI just has more benefits than the carbs.

My Merc 115 (2006 model) is a strange beast with Yamaha block and Merc. cosmetics. Merc claims they wrote the book on EFI. Who knows with all these made- in-whatever country parts, if every motor out there is just a hybrid with a tweak here or there to avoid patent lawsuits?

John

[C-Nile]

If the stern can handle it, such as a CD 25 or larger, or a Marinaut 215, in my opinion, the Honda BF115 EFI is the only way to go. This high torque, low RPM motor is amazingly efficient. When I had a CD-16 Cruiser with a Suzuki 40 HP main engine and Yamaha 4 HP kicker, I achieved approximately 5.5 MPG at 5400 RPM. This was calculated through reading the total statute miles traveled on the Garmin 540 and having a known quantity of fuel. Please see the observed figures for the Marinaut 215 in my photo album "C-Nile"

[Matt Gurnsey]

I'm not sure what years the Yamaha 90 and 115 shared a block. Going back to 2006 (my start of work at Kitsap) they F90 and F115 had different displacement. The F90 was a 97 cid block, and the F115 a 106 cid block. Bore is the same, the F115 has a longer stroke.

This may mean the basic block is the same, but the F115 weighs more by about 30 pounds, so I can only assume that there is a significant difference between the engines. Usually when engines share a platform the cowls are interchangable, and the F90 and F115 are different. Biggest difference may be in the mid section and lower unit.

All things being equal, the F115 should have more torque at all speeds due to the longer stroke.

[Sea Wolf]

Joh, C-Nile, and Matt-

Thanks for the various answers: Good Thinking!

I had forgotten the displacement differential between the F75 & F90 (1597 cc) and the F115 (1750 cc). My memory is getting a bit imprecise with age!

Joe.

[Jimbo]

I bought a used 115 Merc EFI in 2009 that was a fishing camp exlease that had 900 hours when I bought it. It had a brand new bottom end installed and was great.
I did have an electrical problem last year but figured out it was my own fault as I had a bad battery issue that sent the alternator into overload.
I have put another 250 hours on this motor and it starts and runs like a charm. I would definitely say go with EFI over carbs.
jimbo