Increased RPMs

[Barry Loos]

I need some information. The air temperature is starting to drop in my area and the humidity has also lessened. The air temperature went from the high 90's to the mid 70's with no humidity. Back in the hot and humid days of summer I ran about 400 rpms less than what I have turned the past two weekends. Since it is a 2001 engine, a fellow told me that it was just loosening up and as it continues to break in the rpms increase slightly. I guess that could happen but the engine consistently ran the same rpms at wot during the heat of summer. Now as the temperature and humidity have dropped the rpms increased. I think Russ addressed this topic once before but I couldn't find his post. Got any ideas for the increase?



Thanks,

Bear

 

[Tom(fishfafun) Lutz]

Barry,



With my 1990 40hp Tracker Johnson I'd get 4100+ rpm WOT running out in the cool mornings and only 3900 rpm coming back in the heat of the afternoon, but I haven't noticed that kind of drop off or increase with my 2001 135hp Optimax (after break in 5600 rpm WOT anytime of day) so if your running a carb motor it's probably weather related. (Not sure if an EFI will be affected by outside temperature?) Shouldn't be a problem unless for some reason your exceeding recommended RPMs (enjoy the extra speed!)

 

[Barry Loos]

I did check the prop and it is perfect. I forgot to mention that there was a speed increase of a couple of miles an hour along with the rpm increase. I will just go with fact that the cooler weather results in a few more rpms and leave it a that. Thanks for the replies.

 

[TrepMan]

Barry - What RPM's and speed (GPS if you've got it) were you running before and what now?? And which 175 do you have the Pro Team or the Pro Crappie ('cause the Pro Team should be a little heavier this year due to the all Welded and 10 inches of increased width from 2000 and the 2001 Pro Crappie)





My 2000 Pro Crappie 175 with 40 Merc (everything factory set up) runs at almost exactly 5500 RPMs from day one and today (1 1/2 years later) when trimmed out and running. I can't get her to go up any more RPMs (not that I want to since that motor has a 5500 red line) but she is running right at max at trim out.



TrepMan

 

[Jon Puhalski]

Tom:

It sounds like you need to get another 1000 RPM's out of your 40 HP. What size prop are you running?

 

[Tom(fishfafun) Lutz]

Jon...



Sorry, memory slip!!!!!!!!!!!



Might have been 5100 down to 4900, sold the boat in March, but I do remember talking to prop shop and mechanic about RPM difference due to weather conditions and they both confirmed good speed (25mph) and RPMs for that boat/motor.



Thanks for the memory jog!



Tom

 

[Scott S.]

Ditto Here.. I have a '93 Johnson 60 HP. RPM Range is 5500-6000 RPM WOT. I typically turn 5700 with 2 aboard and lots of gear. With the coolfront we just had I now get 5900. Low 50 degrees VS High 70's to 80's