brand new 20 hp merc not reaching full rpm

[yknoh]

Just bought new 20 hp merc. After putting around during break in period finally hit full throttle a few times. It seemed to not rap out like it should tried setting trim at every different angle didnt change rpm at all. Im in a 16 ft flat bottom had a 76 evinrude 25hp prior to this new motor and it ran out a lot better than this one. If this is all this merc has to offer im wont be a happy camper. Any thoughs on what the problem could be? Oh yeah and when i first started it im talkin brand new it was so quite i couldnt tell if it was running at idle. Now it is quite a bit louder. Thanx for any input.

 

[racerone]

Re: brand new 20 hp merc not reaching full rpm

4 stroke motor ?

 

[Georgesalmon]

Re: brand new 20 hp merc not reaching full rpm

sounds like the prop is the wrong size. what's your WOT rpm?

 

[Texasmark]

Re: brand new 20 hp merc not reaching full rpm

sounds like the prop is the wrong size. what's your WOT rpm?

That would be my guess too on a new rig. Too much pitch.

Mark

 

[yknoh]

Re: brand new 20 hp merc not reaching full rpm

It is a four stroke. im not up to speed on the pitch of the prop? For the last few years I just got in the boat and fished using that old 76 evinrude. I just figured this new motor would really run out better than the old one. How do I tell about the prop. Its the one that came on the motor from mercury. I'm also cunfused on where to set the trim old motor was rigged so just one trim setting.

 

[Texasmark]

Re: brand new 20 hp merc not reaching full rpm

Get your owner's manual and look up the recommended Wide Open Throttle rpm range. On 2 strokes I prefer the top end. Probably wouldn't be bad for the 4's either as it makes for a better "hole shot".....getting up on plane. Get your boat out on relatively calm water with your usual load of passengers and gear. Find a quiet place where you are pretty much alone and get up on plane and advance the throttle to max. Watch your rpms and speed and move your trim in and out until you get the most speed and highest rpm. If that rpm is not near the top of the range, somewhere around 5500 I'd guess, get another prop. Figure on 150-200 rpm per inch of change. So if you are only running 5100 at WOT and the engine is rated 5000 to 5500, I'd find the same prop with 2" less pitch. Diameter will change slightly but don't sweat that.

Mark

 

[yknoh]

Re: brand new 20 hp merc not reaching full rpm

Ok ill try that. im on all manual trim tiller handle. so i have to manually change trim. I dont have tach either. Thinking about getting a tiny tach.

 

[Mi duckdown]

Re: brand new 20 hp merc not reaching full rpm

BRAND NEW MOTOR? dealer should take care of your problems???

 

[GA_Boater]

Re: brand new 20 hp merc not reaching full rpm

You drop 20% in power and you expect it to perform better than the 25, even an old, good running one? Bet the new 4 stroke weighs more than the old Rude 25, too. Yeah, blame Mercury.

Did a dealer rig the motor?