86' Evinrude 90 hp Consuming too much fuel.

[LawRude]

I have 86 Evinrude 90hp on a 17' cc that is give a range of only 40 miles on a 16 gal. tank cruising at approx. 4300 rpm (2.5 mpg) . I recently changed the plugs with the right gap spacing (.30), also use the right fuel/ oil mixture (50:1) and the carbs are clean. The boat runs like a champ, and has no problem starting right up but according to some calculation its supposed to consume 9 gph( 4.4 mpg) at W.O.T. I have a feeling it's running a bit rich. Do you guys have any suggestions or how to lean it out a bit?

 

[Outsider]

Re: 86' Evinrude 90 hp Consuming too much fuel.

2.5 to 3 mpg average sounds about right for a 33 yo engine. Aside from the fact Johnrudes oil burners have never been known for their economy, two cycles tend to burn pistons when run too lean, so I'd be real careful there ...

 

["G"]

Re: 86' Evinrude 90 hp Consuming too much fuel.

Besides the fact those old V engines are fuel burners... try checking your float levels. That's a dead giveaway for bad economy.

 

[tashasdaddy]

Re: 86' Evinrude 90 hp Consuming too much fuel.

first outboards are not measure at MPG, the are measured at GPH, (gallons per hour) at wide open throttle. your motor will burn in the range of 8-10 gallons per hour. to improve effieceny, get rid of excess weight in boat. proper load balance, make sure the hull and motor are properly set up, (engine height). that the motor is propped correctly for the hull. ( 1986 90hp should turn 5200-5800 rpm at wide open throttle.) this will allow motor to run more efficently, at lower rpms, with out lugging the motor.

also make sure you are fully tuned, timing, link n sinc. clean carbs, fuel hoses change to alcohol resistant hoses, carbs to tank. also check compression, low compression will increase fuel waste.

 

[ezeke]

Re: 86' Evinrude 90 hp Consuming too much fuel.

You should prop to reach near 5800 RPM at WOT with your average load. Anything much less than that will lug the engine, waste fuel and contribute to carbon build up.

The V engine is not the reason for the difference in economy for carbureted vs DI engines; the crossflow design is inefficient and wasteful.