HONDA BF90 Missing Power

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
wp3223
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HONDA BF90 Missing Power

Postby wp3223 » Sat Aug 29, 2020 2:52 pm

[This thread has been moved to REPAIRS and MODIFICATIONS because the goal is to solicit advice to repair the engine--Moderator]

I have a 1999 HONDA BF90. [The BF 90 has] good cylinder pressure, good spark, starts, and runs perfectly.

The DEFECT is the engine does not make its rated 90-HP and [cannot accelerate to] more than 5,000-RPM with the 19-pitch propeller it has always been used with. Boat speed is only 32-MPH.

Point me in a direction [toward a remedy].

Thanks

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Phil T
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Re: BF 90 Missing top end power

Postby Phil T » Sat Aug 29, 2020 3:34 pm

What year and model/length boat is this?

Troubleshooting is process of elimination.

Check one thing at a time ONLY. Make change, test, make change, test. etc. No shortcuts, guesses. Trust but verify.

How long ago did this [reduced engine speed and reduced power] arise? When specifically?

When was the engine last serviced by a professional?

What was done (not requested, done) by above person?

When were the carburetors last cleaned professionally?

Plugs changed when? Who?

Is the prop damaged?

Is the bottom paint worn, lumpy, flakey etc.

Is there marine growth ?

Easy, low cost/free and DIY items:

- Check propeller for spun hub. Engine off, in gear, grab blades with hands and turn. If it turns, hub needs replacement.
- Check for spark on each cylinder (easy, free)
- Run some Seafoam in the next tank. Can help identify and eliminate cause of reduction in power.

Are the under deck areas, if applicable, dry?

Report back answers to ALL questions and information and additional guidance will be supplied.
1992 Outrage 17
2019 E-TEC 90
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wp3223
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Re: BF 90 Missing top end power

Postby wp3223 » Sat Aug 29, 2020 7:03 pm

[The boat being powered by the BF90 is a] 1986 Montauk 17 with a bone-dry hull. I just bought the MONTAUK 17 recently. The hull bottom is clean and smooth with no bottom paint.

From the seller I have [his] receipt for fluids, compression test, and [water pump service to the] impeller.

During the sea trial we could only cruise in no-wake zones. Then we went out in the ocean for a bit. The [sea state was three-foot waves closely spaced] so it was not possible to make a speed run.

[The BF90 engine run time is supposed to be] 300-hours--the engine looks like new.

The [1986 MONTAUK 17] jumps right up on plane, and [the boat] runs perfectly--other than [the BF90 engine] missing the top 1,000-RPM.

[The propeller was ] bent up prop. I figured that may be the [cause of the inability of the engine to develop the full 90-HP and to accelerate to 6,000-RPM or go drive the boat faster than 27-MPH]

I now have a new propeller; now maximum boat speed is 32-MPH.

I have calculated SLIP: the number checks out.

[The HONDA BF90 would accelerate to] 5700-RPM with the junk prop.

With the new propeller [the HONDA BF90 will not accelerate above] 5,000-RPM.

Both [the junk propeller and the new propeller are made of stainless steel, are] cupped, and [are the] same pitch.

I tested and [peak cylinder pressure read] 180-PSI in all four cylinders.

There is good spark.

I ran a [a fuel consisting of gasoline and SeaFoam mixed 1:1]. I let the fuel soak over the weekend. No change [in engine behavior occurred].

Knowledgeable.

[The] fuel line, fuel fittings, fuel filter, and fuel-water separator are new

Common sense points to the carburetors [as the cause of the engine not producing 90-HP and not being able to accelerate to 6,000-RPM]

I have checked the butterflies; they open fully.

I am hoping [the cause of the engine not producing 90-HP and not being able to accelerate to 6,000-RPM] may still be the carburetors.

From my experience there would be some sort or idle or mid range [defect] as well, and not just the missing power at 5,000 to 6,000-RPM.

I am contemplating having the carburetors checked out.

I don't want to sink any money in this unknown engine.

I may have to pick up a new DF90 engine if I can't get this BF90 gremlin figured out.

Any input is greatly appreciated.

[Moderator's note: the pronoun "it" has been replaced with the antecedent noun it appeared to be in reference to in many places in the narrative. Please avoid using "it" instead of the actual noun when explaining problems.]

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Phil T
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Re: BF 90 Missing top end power

Postby Phil T » Sat Aug 29, 2020 8:50 pm

Thanks for the details.

I am going to focus on the prop since the engine "runs perfectly".

Prop selection is a bit of science and a bit of art so selecting the appropriate prop is quite complicated. Prop size is not universal across brands or even models of the same brand. I have been helping Boston Whaler owners with prop selection for over 10 years and there is still many things I have not mastered.

There should be a size/part # stamped on the prop. Often it is on the inside of the hub. What is the make, model and size (diameter x pitch)

Many owners with a Montauk 17 and a Honda BF 90 who tested props (in the archives) recommend the following props:

13.25x15 Solas Stainless Steel
13.25 x 17 Honda Turbo - part number 08M60-ZW7-A10
13.25 x 17 Yamaha Performance Series (Stainless)
*Note size is for the make and model listed and is not applicable to other props. Engine should be mounted 2 holes up, with the top bolt in the 3rd hole counting down from the top.

If you already have one of these props installed and the engine rigged as described above, we will move back to diagnosing an engine cause.
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wp3223
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Re: BF 90 Missing top end power

Postby wp3223 » Sat Aug 29, 2020 9:14 pm

Check and double check on the propeller.

I installed a new YAMAHA 13.25 x 18-pitch.

Also a buddy loaned me a 13.25 x 20-pitch. [That propeller caused a change in engine speed] of only 250-RPM [and a change in boat speed of] 1-MPH. WIth either propeller [the MONTAUK 17] jumps on plane.

Engine mounting height is one hole up from lowest.

I also tried two-holes-up with no difference.

All the way up was a [monstrous propeller ventilation].

[The BF90 engine is] just magically missing that horsepower up top.

The only time [the BF90 engine will accelerate above] 5000-RPM is with the wrecked propeller. [With the wrecked propeller the BF90 accelerates to more than] 5,600-RPM. [The wrecked propeller also known as the junk propeller has] all three blades bent back the wrong way [and the SLIP calculates to greater than] 20-percent.

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Re: HONDA BF90 Missing Power

Postby jimh » Sat Aug 29, 2020 11:03 pm

Your performance data would be much clearer if you presented the information in a table, nicely organized, rather than dribbling out the information in a long narrative and giving us incremental changes in engine and boat speed without giving us the direction of the change. I don't know how we can figure out a change of 1-MPH unless you tell us whether the boat went faster or slower by 1-MPH.

Tell us the propeller details, and give the engine speeds and boat speeds recorded with that propeller in an organized manner using tabular presentation.

I suggest you abandon testing with the junk or wrecked or three-blade-propeller with all blades bend backwards. Running a damaged propeller at more than 5,600-RPM engine speed is likely to cause damage to the propeller shaft bearings and seals.

Tell us the gear ratio of the engine.

Tell us the manufacturer's recommended range of engine speed at full throttle. Tell us the absolute maximum engine speed permitted by the manufacturer.

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Re: HONDA BF90 Missing Power

Postby jimh » Sat Aug 29, 2020 11:05 pm

I am completely confused about the 19-pitch propeller "the boat has always been used with." Is that the junk or wrecked or three-blade-with-all-blades-bent-backwards propeller?

Also, I am not sure what the goal of this inquiry is intended to be. The thread is in PERFORMANCE. But the engine owner seems to be seeking engine repair advice.

Please clarify if the goal here is to optimize the propeller or if the goal is to find a defect in the engine and remedy that defect. If the later, the thread will move to REPAIRS and MODIFICATIONS.

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Re: HONDA BF90 Missing Power

Postby jimh » Sat Aug 29, 2020 11:18 pm

Based on PHIL's excellent searching for comparable boats with BF90 engines, and finding that all used 17-pitch or even 15-pitch propellers, I don't think there is too much MYSTERY when the HONDA BF90 is not able to accelerate to 6,000-RPM when using propellers of 19-pitch or 20-pitch. The notion that the engine should be able to accelerate to its maximum engine speed with any propeller is not a reasonable notion.

Try operating the engine with a 17-pitch propeller and report the engine speed and boat speed at maximum throttle.

wp3223
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Re: HONDA BF90 Missing Power

Postby wp3223 » Sat Aug 29, 2020 11:24 pm

I did purchase and try a POWERTECH SCD3 17 [later corrected to be a NRS], but it [did] not perform as expected. I was able to return it. I then got my YAMAHA 18 locally a few days ago for a great deal.

My error for apparently posting it the incorrect section. My mind was stuck on the fact that I am missing Performance, and did not see or think to post in the repairs section. Please move as needed.

wp3223
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Re: HONDA BF90 Missing Power

Postby wp3223 » Sat Aug 29, 2020 11:26 pm

The goal is to determine the potential cause of my missing high rpm horsepower, as initially stated. Carburetor problems.

Then somehow turned into a prop debate.

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Re: HONDA BF90 Missing Power

Postby jimh » Sat Aug 29, 2020 11:36 pm

The thread is moved to REPAIRS and MODIFICATIONS.

Don SSDD
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Re: HONDA BF90 Missing Power

Postby Don SSDD » Sun Aug 30, 2020 8:14 am

I would suggest your problem is still possibly the propeller and there may be nothing wrong with your engine. You should follow the advice on propeller selection and if that doesn’t help, then go to engine problems, IMHO.

Buying a propeller because it’s a good deal may not be a good deal if it’s the wrong propeller for your boat and outboard.

Perhaps read some of the other posts here on propeller selection in the performance forum and you may see how to analyze propeller choices. A Montauk is well known on this site so you will get good advice to follow. The Honda is a heavy 4 stroke and the extra weight on the stern will effect propeller selection.
1986 Outrage 18 with 2001 Honda 130 HP
Former Owner 1991 Guardian 19 with 1994 Evinrude V4 140HP
Former owner 1987 Montauk with 1998 Mercury 90HP
Nova Scotia

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Re: HONDA BF90 Missing Power

Postby jimh » Sun Aug 30, 2020 8:40 am

I recommend reading

Propeller Power Curve
http://continuouswave.com/whaler/refere ... Curve.html

The article explains the relationship between the ability of an engine to accelerate under load to a particular crankshaft rotation speed and the load produced by a propeller.

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Re: HONDA BF90 Missing Power

Postby jimh » Sun Aug 30, 2020 8:45 am

How many cylinders are used in a HONDA BF90 engine?

wp3223
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Re: HONDA BF90 Missing Power

Postby wp3223 » Sun Aug 30, 2020 9:41 am

Four cylinder. 2.33 gear ratio, and 6000 max rpm.

PATXBill
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Re: HONDA BF90 Missing Power

Postby PATXBill » Sun Aug 30, 2020 10:56 am

Dialing in the propeller is indeed necessary to allow an outboard to reach its maximum rpm range. And the carburetors should be examined to ensure they are clean.

However, because the engine "runs perfectly" and "jumps on plane," I will offer another possible cause for failing to reach maximum rpms:
Have you checked that the throttle advances to its maximum range? It could be the cabling or engine throttle linkage needs to be adjusted

wp3223
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Re: HONDA BF90 Missing Power

Postby wp3223 » Sun Aug 30, 2020 1:31 pm

Yes, cables actuation and carbs opening fully are all 100%

As a last hurrah I may give the carbs a once over, and I just found a used 13.25 x 16 ss prop for the final round of testing.

Otherwise I will probably just pony up for a new Suzuki for 7k. And sell the Honda with water test & full disclosure to offset the expenditure. As having a whaler that cruises in low 20's and is just over 30 @ wot, kind or takes the fun out of things..

Thank you for trying to assist with this head scratcher.

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Phil T
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Re: HONDA BF90 Missing Power

Postby Phil T » Sun Aug 30, 2020 4:23 pm

Please understand .....If you do not list the propeller make, model and size, the information is WORTHLESS.

A Yamaha 18" means nothing. Yamaha has a dozen models of props with dozens of diameters in 18" of pitch in two different materials.

just found a used 13.25 x 16 ss


...see above.

POWERTECH SCD3 17, but it [did] not perform as expected


What were the results of the SCD3 prop, specifically? What was the WOT rpm's and gps speed?
When tested what was the fuel, passenger and gear load?
How does this load compare with the testing conditions of the original prop that only reached 5k rpm.

None of the props you listed are on the recommendations posted above.

Prop performance is NOT universal so not any X by Y prop will work. Each model has unique blade design. Some blade designs are beneficial to Boston Whaler hulls, some are not. We select the diameter based on the lower unit gear ratio and then factor blade design characteristics and pitch based in engine WOT range and desired performance.
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Re: HONDA BF90 Missing Power

Postby jimh » Mon Aug 31, 2020 12:30 pm

wp3223 wrote:Four cylinder[s].


With four cylinders, the HONDA BF90 engine could be running on only three cylinders. At three-quarter power a 90-HP might be making 65-HP. Try testing underway and disconnecting the spark from each cylinder one at a time. If one cylinder is not firing (for any reason) then taking away spark won’t cause any change in engine speed. In this way of testing you can really verify that all four cylinder are working.

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Re: HONDA BF90 Missing Power

Postby biggiefl » Mon Aug 31, 2020 12:41 pm

A 4cyl engine firing on 3cyls usually will not get on plane.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

wp3223
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Re: HONDA BF90 Missing Power

Postby wp3223 » Mon Aug 31, 2020 2:15 pm

I contacted the previous owner last night and was informed the BF90 carburetors were recently rebuilt.

PATXBILL’s [advice correctly diagnosed the cause of the low engine power at full-throttle: linkage was misadjusted].

I had checked all cable actuation and the port side detent previously. Apparently the linkage was indexed incorrectly and the [throttle butterflies] were not fully opening.

I made adjustments then went for a test—the difference [in the power output of the HONDA BF90] is like a night and day.

Using my YAMAHA 13 x 18-pitch Yamaha propeller [the HONDA BF 90] immediately [accelerated at full throttle to an engine speed of] 6,300-RPM and was then held by the rev-limiter. The 1986 MONTAUK 17 boat speed was 40-MPH.

[In another test with a] 13 x 20-pitch propeller, boatspeed at full throttle was 43-MPH. I think the boat speed may improve to 44-MPH [with the 20-pitch propeller] with the engine trimmed higher. [To reach a boat speed of] 45-MPH [may require the engine to accelerate to] 6,200 or 6,300-RPM and hit the rev-limiter

To PATXBILL: thank you very much. You saved me from being impulsive to get a shiny new Suzuki, that probably would have performed exactly at the HONDA does now.

Also appreciate the time of Jim H, and others.

The Powertech SCD will be my next propeller to try—maybe a 21-pitch. I have read many good recommendations for using them on a Montauk17.

Again, a big “thanks to all. As it feels as though I now have the fun, new boat that purchased.

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Re: HONDA BF90 Missing Power

Postby jimh » Tue Sep 01, 2020 12:35 pm

Commenting on my suggestion that the HONDA BF90 engine under discussion might be running on only three cylinders, Nick writes:
biggiefl wrote:A 4cyl engine firing on 3cyls usually will not get on plane.

Let us assume the BF90 makes 88-HP at the propeller shaft. That suggests 22-HP from each of four cylinders.

If one cylinder was not producing any power it would be a load on the other three. The three working cylinders would make 66-HP. We can estimate that perhaps 6-HP would be required to turn the non-firing cylinder due to the pumping loses of the air flow—I think that would be a generous allowance for lost power. The engine would still be making 60-HP at the propeller shaft. A MONTAUK 17 shows minimum power rating as 35-HP.

On the basis that the BF90 could make 60-HP on three cylinders and a MONTAUK 17 should reach plane with 35-HP, I expect a MONTAUK 17 with a three-quarter-power BF 90 would get on plane.

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Re: HONDA BF90 Missing Power

Postby jimh » Tue Sep 01, 2020 12:42 pm

Thanks for the follow up on your repair or readjustment of the BF90 engine remote mechanical throttle cables and linkage to the carburetor throttle plates. Maybe the mis-adjustment occurred during reassembly of the carburetors onto the engine following their cleaning as reported by the previous owner.

When a new problem occurs, to look at the precise time of the onset of the new problem and then compare that epoch to any other action or work or repair done immediately prior can be a useful method for getting “pointed in a direction” toward solving the problem.

Did you remove the noise silencer that covers the throats of the carburetors and directly observe the throttle plate opening?

Or was there a lot of travel left in the linkage that was not being used by the travel length of the remote cable actuator movement, and you inferred the partial opening of the throttle plates by the limited movement?

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Re: HONDA BF90 Missing Power

Postby biggiefl » Tue Sep 01, 2020 1:45 pm

Jim...I wish it were that simple. I will try it one day on my F115.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

wp3223
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Re: HONDA BF90 Missing Power

Postby wp3223 » Tue Sep 01, 2020 6:46 pm

The was a substantial amount of play in the levers that actuate the carburator butterflies. And also noticing the all new gaskets, and missing carburetor bowl vacume lines helped to confirm his claim of recently rebuilt carburetors as well.

I had not been able to gain a clear view of the intake bodies previously. As the air filter box assembly has bolts which are not accessible, with removing the entire intake manifold and all four carburators as assembly.

I'm just super happy that all is resolved. So my only concern is now either pitching my current propellor up slightly, or buying a new one for the correct & safe rpm range.

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Re: HONDA BF90 Missing Power

Postby biggiefl » Wed Sep 02, 2020 11:44 am

They can only cup a prop equivalent to approximately 1" of pitch. To repitch a prop by bending blades and adding length is very expensive and it's probably easier to buy the correct prop.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

wp3223
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Re: HONDA BF90 Missing Power

Postby wp3223 » Wed Sep 02, 2020 3:00 pm

I had the [unidentified propeller—reread the thread and try to figure out which propeller is now being discussed] reworked [to change it in some unidentified way] but there was not enough difference [in engine speed]—less than 150-RPM change [in some unidentified direction].

I bought a like-new Solas Titan HR4 13 x 21p.

My next option is a SCD4.

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Re: HONDA BF90 Missing Power

Postby jimh » Wed Sep 02, 2020 6:23 pm

The thread is in REPAIRS and MODIFICATIONS. The defect in the engine has been found and repaired.

Propeller testing that may be done in the future is not germane to the engine repair.

If in the future propeller testing occurs, report the tested propeller, the test conditions, the data collected, and impressions of the test if desired in the PERFORMANCE forum.

The reporting of actual data and measurements is more useful and interesting than announcements of what might be done in the future.

[Thread closed]