Low RPM @ WOT

[markdido]

I have a 2006 8 hp 4 stroke that has less than 10 hours on it. It was purchased new at BPS about 2 months ago.

I put a Tiny Tach on it last week, and took it out yesterday to check the RPM's.

At WOT, the tiny tach was showing 2710 RPM. The boat is a Gheenoe Classic with myself and the wife aboard.

I'm assuming that the prop that came installed on the engine came from the factory, so I don't know that prop pitch would be a problem. BPS preps the motors before delivery.

Is it possible that the factory settings are off?

 

[Silvertip]

Re: Low RPM @ WOT

Do you have the correct tiny tach. You probably have one for a two stroke. A four stroke engine fires a cylinder every other rev. A two stroke fires every rev. Therefore a two stroke tach on a four stroke engine will read 1/2. In your case 2710 would equate to 5420 which would be a more correct reading.

 

[markdido]

Re: Low RPM @ WOT

I sent an e-mail to Tiny Tach giving them my engine specs and this is what they sent me. Not saying that they may have shipped the wrong unit.

I was thinking the same thing. 2700 rpm equates to 5400 which would put me in the correct range. WOT with just me on the Gheenoe gets me about 16 mph, which I guess would be average for an 8HP motor.

If I was only running at 1/2 the max RPM I shouldn't be getting anywhere near 16 mph.

 

[Silvertip]

Re: Low RPM @ WOT

What model number did they send you?

 

[markdido]

Re: Low RPM @ WOT

I don't have the original packaging, but the sticker on the back says:

2072 RXL

Mark

 

[markdido]

Re: Low RPM @ WOT

BTT

My manual says I should be turning 900 rpm in fwd gear at idle and 5000 - 6000 rpm at WOT.

Tiny Tach reads 890 rpm at idle in fwd gear, but only 2800 rpm at WOT.

I thought that maybe they sent me the wrong tach, and that I would have to double the reading to get the right WOT rpm, but since the idle rpm is right on the money, shouldn't the WOT rpm be also?

Motor is an 8 HP 4 stroke, new (less than 10 hours)

Not sure of the prop pitch, but it is the one that came with the motor