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Mystery BF150 (new engine) using too much fuel and not reaching expected speed

I

islander17

New member
First, I want to apologise if there will be double or triple posts about this topic, as I tried posting 1-2 weeks ago but couldn't due to being a new member.

I have a new (2016) boat with a Honda BF150. Boat does 33.5 knots at WOT at 6000 RPM, with a newly cleaned bottom. Also, there's no noticeable difference in speed going from 5700 to 6000 RPM.

A perfectly IDENTICAL boat, same engine, same prop, same manufacturer, same driver, does 37 knots at WOT at 5500 RPM. And I've read about two additional boats with these exact stats, so mine is the odd one out...

I'm obviously under warranty. Honda hooked up their computers to the engine during a run, but couldn't find anything wrong with my engine. From what I can tell, the boat also consumes 20-30% too much fuel (per distance) compared to the stats I've seen.

Any help is appreciated.
 
Generally a new car engine does not perform as well as one that has covered a few 1000 miles. Maybe your engine is still breaking in?
Same might apply to the fuel consumption.

Same engine height as the other boat?
Same fuel load?
 
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Thanks for getting back to me so quickly!

It's definitely still breaking in, the engine has had only 30 hours or so, which probably adds up to about 1000 miles in total. Can the difference in performance be that big? I've seen a magazine article testing this exact boat with the BF115, BF135 and BF150 respectively for comparison, and even the BF115 was able to do 33.2 knots at WOT, which is basically what I'm seeing with my BF150...

I haven't confirmed the engine height, but I would guess it's correct unless they made a serious error in production with my boat only. This may be worth looking into.

I don't know about the fuel load specifically, but one of the stats I have had three people on board doing 37 knots, mine did 33.5 with just the driver, so the weight should at least even out. I've also had this level of performance consistently since I got the boat, regardless of load. One of those other boats belong to someone I know personally, who says his boat does 35-36 knots consistently even when the bottom isn't clean. Btw. he was the one driving my boat at 33.5 knots, just to rule out user error, and he's had his boat for maybe 5-6 years.
 
Are you running the same weight in gear,fuel,How many hours on yours and the others? Are they trimmed the same? Possible compartment filled with water
 
I've been told that the big Honda's take 150 - 200 hours to break in properly, which then gives you better compression and efficiency. My 225 certainly did.

Having said that, check your engine mounting. The anti-cavitation plate that sits above the prop should be even with the lowest part of the transom. If you have an engine bracket that offsets it from the transom, the anti-cavitation plate should by raised one inch for every 12 inches of offset from the bottom of the transom.

If your engine IS mounted correctly, then the 20% to 30% more fuel consumption is very troublesome. The first thing I would do is pull the plugs and inspect them. They should have a light brown coating on the electrodes. If the coating is black on all plugs, that's a telltale that you are dumping in too much fuel. If all plugs are blackened, ask the dealer to swap out your ECU for a a known good one. If only one plug is blackened, then you may have a stuck or malfunctioning fuel injector.

One other possibility is that you intake air bypass (IAB) baffles are stuck open or closed. I'm not sure how to diagnose that on a 150. On the 225 there is a vacuum diaphragm mounted above the HP fuel filter. Disconnect the vacuum hose and take a pair of needle-nose pliers and pull the diaphragm arm into the diaphragm as if the vacuum had activated it. It should move in rather easily. Then let go, and it should spring back in place. If it doesn't do that, the spring may be broken, or the baffle pivot rod could be corroded, or one of the baffles has come loose and has jammed the mechanism.
 
Thanks everyone for getting back to me so quickly!


I've tried replying to this thread already, but it seems I'm too new of a user to be able to reply to threads yet, due to forum restrictions. This is my second attempt!

Prop and weight is the same as the other boats. Engine is definitely still breaking in (about 30 hours).


Having had the hull and prop cleaned, I visited the boat the other day to see that my prop wasn't damaged (it was perfectly fine) and to check that it didn't have a hub slip issue, which I hadn't, but then I also noticed that, indeed, my engine is mounted two holes higher than all other boats of the same model in the same docks.


I'm going to try and have the engine lowered as a first step. I've tried to read up on the subject, and although there's lots of info on having engines too low, I couldn't find as much on having the engine too high, so I'm not sure what to except. There's a lot more info out there on the effects of having the engine too low, than the other way around, it seems.

I got the boat to 34 knots yesterday, heavily trimmed out, but it's still way low. From my stats, even the BF115 should do 33.5 knots with this boat. But what's more important for me is that I still have a fuel use 25% too high, more or less consistently from 3500 RPM and up.
 
Islander17 sent me a private message:

"I've actually replied, but my replies aren't posted, because due to being a new member. Due to forum policies the reply must be approved by a moderator before being published. I'm still waiting for posts made two weeks back to be approved, and I've tried contacting admin without success unfortunately.

I've looked around and have found that my engine is mounted two holes higher than other identical boats. So to begin with, I'm going to have it lowered and see if that helps!"
 
Cavitation plate should be about even with lowest portion of hull "keel",to low will create drag,too high not enough "bite" with prop.
 
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