Weather vrs performance

[cloumar]

I red on it and I heard about it, but I did know that the change between hot summer weather and cooler like october could make that much difference unless I have a problem. I got my boat last year at the end of the summer in September and didn't have much chance to use it, but this year from May up to last weekend I did use it a lot and last summer with 2 adults a regular load in gas and gear I was reaching the top RPM of 5100 to 5200 -last weekend I went on the river to get it prepared for the winter with fuel add., decarb and fogging and the engine went up to 5500 to 5600 RPMs with the same pattern in term of load - Is this normal to have that much difference between hot and cool weather ? ( engine Force 1998 - 75 HP - prop: 10.5 by 13''<br /><br />Thanks <br /><br />Smoky

 

[cloumar]

Re: Weather vrs performance

Any ideas ?????<br /><br />Thanks

 

[Forktail]

Re: Weather vrs performance

Not sure if you mean you had an increase in rpm after decarb, etc., or the increase happened prior to winterizing?<br /><br />Temperature greatly effects the outboard's air/fuel mixture. Colder temperatures mean the air is more dense, and therefore it contains more oxygen. So colder temperatures cause the fuel/air mixture to be "lean". Lean means that, while the same amount of fuel is being metered to the engine, more oxygen than normal is being supplied. This increases the air to fuel ratio.<br /><br />In a 2-stroke, a lean air/fuel mixture will cause rpm increase at WOT. It also creates more power and heat. Most outboards are jetted for a liberal temperature fluxuation. But be careful. In extreme cases, this can lead to engine failure.

 

[cloumar]

Re: Weather vrs performance

Thanks Forktail,<br /><br />Yes I had a RPM increase before doing any decarb or winterizing, the outside temp in my place last Saturday was around 45 to 48 Farhenheit<br /><br />Smoky

 

[Dhadley]

Re: Weather vrs performance

Trailer Boats magazine Sept 03 page 34 -- The Power of Weather -- How weather affects engine performance.<br /><br />Good luck and happy reading!

 

[catfish1]

Re: Weather vrs performance

enlighten us Dhadley, i'd like to hear about it without buying the mag.

 

[ob]

Re: Weather vrs performance

From summer to winter months in South Texas ,ambient temps ranging in the 90's thru the summer and from the 50's - 60's in the winter ,my 70 hp Evinrude typically picks up between 100 - 150 WOT rpm in the winter months.