Lower RPMs in hot weather

[Mark Hofman]

Last weekend, I had the first chance to take the boat out with just me in it, about a 1/4 tank of gas and NO water in the livewell.



Talk about a holeshot!! Hooollllllyyyyyy Crraapppppp!



Anyway, air temp was in the mid-90s and water temp in the low to mid 80s. I noticed that my RPMs were only around 5,000 at WOT. The speedo was plugged by a piece of wood (someone told me that this would happen sooner or later) so my speed read about 10 mph. My eyes were still watering, but not enough that I didn't notice the reduced RPMs.



Does hot weather affect carbed outboards that much, to the tune of about 400-600 RPMs? Or do I have a problem that needs checking (compression, mixture, etc.)?



Thanks, guys!

 

[Tom(fishfafun) Lutz]

Mofish,



Cooler outside temps always improve engine performance (just as in NASCAR racing) so hotter temps will bring the performance down. Just how much is the question here. My old 40 hp Tracker/Johnson would see about 100-200 rpm drop in RPM going WOT from the AM run to fish to the PM run back to the ramp. (only real difference was air temp and a lighter load of gas)

Not sure if it's your problem though...I don't notice very much difference in my 2001 Optimax 135.



Tom

 

[TrepMan]

Darn Bob - I wish I knew that 2 years ago, could have used that logic on my wife.



"But honey! We need to go up to the 60hp, 'cause that 40 will only be 34hp in the heat of the summer and that ain't enough juice baby!!!"

 

[Barry Loos]

I always have about a 200 - 300 rpm drop between a 6 am run and a 2 pm run. I'm used to it but I do hate being passed by canoes.



Bear