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Old 15 July 2016, 09:51   #1
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Honda BF20 low RPM

Hi guys,

Last year I have bought a Honda BF20 2005 with standard 4 blade prop, but this engine was never able to get higher than 3000rpm, always at some 2950rpm with the lightest load.

I have a 12ft Excel 365 HD inflatable, total weight about 100kg, plus some gear, fuel tank, 2-3 bottles of vodka and myself. Total load would be some 250kd max. Still the engine was never revving very high. The tacho comes from eBay, btw. Top speed at 22knts.

I have replaced the prop for a Solas 3 blades 11 pitch, to get more speed. The revs dropped by some 200rpm only. But I got 1knt more, no big deal.

I dropped my engine by a local Honda dealer, which insured he is unable to adjust the correct rpm unless have the engine mounted on a boat and goung WOT. I have hard time to believe it, it could just run it in a tank and get at least some basic rpm readings, what he refused to do. Anyway, even in a tank with no load it does never go above 2800-2900.

The engine is in a very good condition, and since I bought it I use SeaFoam in every tank. Very happy with the SeaFoam results btw, never had a clogged carb.

Could anyone give me a tip on what should I look to adjust my rpm? The Honda dealer was useless and not very helpful, replaced 2 spark plugs without my consent, adjusted the tiny screw (fuel mix) and charged me 75.00 for it. The previous plugs had only 4 hours. Very disappointed.

Any help will be very appreciated.

PS bought another tacho, just in case, to check the actual one.
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Old 15 July 2016, 10:14   #2
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I think it is very unlikely you would reach 22kts at 3000rpm.

I would suspect your tacho is set wrong for your engine.... this is quite common. Is the new one on order or do you have it yet? If you have it what does it show compared to the old one?
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Old 15 July 2016, 10:22   #3
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Hi Fenlander,

Thanks for quick reply

My new tacho is
https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

Should come this WE, will fit it.

My actual comes from eBay for just few quids, I decided to spend more for may be more reliable results.

The actual tacho shows 900rpm in neutral, as per manual, which sounds ok. If I try to lower the rpm (following this tacho readings), the engine starts struggling.

Could it be just a wrong set up? I have simply wrapped the tacho wire around the plug cable. That's it. Could it be some interferences at high speed?
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Old 15 July 2016, 10:31   #4
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Well yes the idle revs sound OK around 900.

I have this tacho which I bought as it has a screened signal lead with earthed outer to stop interference which can be an issue.

https://www.amazon.co.uk/Runleader-R...866SQ5S362V5H1
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Old 15 July 2016, 10:50   #5
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Could it be that the higher rpm reading are false cause of some interferences but the low rpm are ok? I don't know if this is possible
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Old 15 July 2016, 11:25   #6
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check with a proper non contact rev counter i.e. one that reads crank rpm not ign pulses would be my first step then go from there
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Old 15 July 2016, 11:53   #7
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if at 22 kts your at WOT and the tacko reading wrong the new one at 900 rpm tick over is good but if you rev the engine out of gear it will hit the rev limiter and not get near WOT as fenlander says check the settings also try winding more round the spark plug wire, on mine it stated 5 turns but i had to do 7
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Old 15 July 2016, 12:04   #8
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>>> rev the engine out of gear it will hit the rev limiter

Jeff I guess your Suzuki will be about the same as mine... if I remember a 2950rpm limiter out of gear.
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Old 15 July 2016, 12:23   #9
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Quote:
Originally Posted by Fenlander View Post
>>> rev the engine out of gear it will hit the rev limiter

Jeff I guess your Suzuki will be about the same as mine... if I remember a 2950rpm limiter out of gear.
yes david from memory i think my 90 was the same rpm too.
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Old 15 July 2016, 19:45   #10
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Quote
The Honda dealer was useless and not very helpful, replaced 2 spark plugs without my consent, adjusted the tiny screw (fuel mix) and charged me 75.00 for it. The previous plugs had only 4 hours. Very disappointed.

both of my Honda 25 have 3 spark plugs-strange they didn't do them all
Hank
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