Hot day = high speed lean out?

[oldslowandugly]

This is the '85 Evinrude 30hp again. I put a new prop on today and when I tested it I got a high speed lean out, no detonation, but rpm's wandering about 500 up and down, anything above 4000 rpm. Takeoff was good and jumped right up on plane, no hesitation. I squeezed the fuel line primer bulb, the bowl was full and pump working fine. This has never happened before but today was 97? and humid. I have a fixed high speed jet and adjustable idle. I also needed to turn the idle screw 1/4 turn lean to idle right. I thought that might have affected the high speed mixture so I went back 1/4 turn and tested, no difference, so I leaned it out again for a smooth idle. All I can think of is the hot weather since a fixed jet is at best a compromise.The prop is the same diameter and pitch as the old one and shouldn't affect the motor at all.

 

[Joe Reeves]

Re: Hot day = high speed lean out?

Assuming that this is a slow up/down type surge such as slowly running out of fuel might produce.................

At the higher rpm, does the fuel primer bulb have a tendency to collapse somewhat? If so, this would indicate a fuel restriction between the fuel pump and the fuel supply.


If no fuel restriction, does pumping the fuel primer bulb constantly correct the problem? If so, this would indicate either a air/fuel leak at some point between the fuel pump and the fuel supply (pump drawing air) OR a failing fuel pump.

 

[oldslowandugly]

Re: Hot day = high speed lean out?

Yes, it was wandering up and down, like running out of fuel. The primer bulb was hard, and I could feel the fuel pump pulsing. Pumping it did not correct the problem. I had played around with jet sizes and settled on the one that's in there because it ran the best under all conditions. This heat is unusual though.

 

[oldslowandugly]

Re: Hot day = high speed lean out?

CONCLUSION- weather had nothing to do with it. The new prop is the culprit. I tested using my spare prop, which has 2" less pitch, and the motor revved like a champ. So the aluminum prop is not acting like the SS prop even though the diameter and pitch are the same. I started a new topic about this in the prop section. http://forums.iboats.com/showthread.php?t=563019&p=3866006#post3866006