fuel usage

[chrish]

1986 johnson 85 hp
I think its using way to much gas, at 3/4 speed or crusing speed a 6 gal tank only last about 2 to 2 1/2 hrs, i know the 4 fuel mix jets need to be replaced there worn on the ends, but ive heard of these EFI kits that attach to the carbs but i dont know if it would work or not, kind of like the set up chevy first came out with in the early 80's the carb was there but the fuel was injected into each side at the top of the carb.
any ideas? or live with it,

 

[OBJ]

Re: fuel usage

Sure it's an 86' Chrish? OMC put out an 85horse back in 80' and then again starting in 91'....but not in 86'. In 86', it was a 90hp.

Course, I don't know all there is to know about these things but this is the first time I've heard of jets being worn. Possible I guess.

There are some things you can make sure of that will help with fuel economy....what there is with these blocks....

Make sure the ignition system is in good order, hot spark and correct plugs.

Engine is running at normal temp. A cold engine will waste fuel. Good compression also helps.

Engine timing is correct and link and sync is good.

The engine should be set up and proped out correctly so your not lugging the engine.

A set of Boyesen reeds would help.

My own engine is a 86' 90horse. I can go through a couple 6 gal cans out on the river during a day of tubing and messin' around.

Haven't ever heard of a EFI for these particular engines.

 

[F_R]

Re: fuel usage

I've really don't think that's excessive fuel usage, compared to motors that I've owned. I'm wondering about the "worn" jets. Has somebody been jamming wires or torch cleaners through them or something? They shouldn't wear in normal use.

I'd say make sure the rest of the motor is in good condition and properly tuned, and accept the fact that boats burn a lot of gas.

 

[OBJ]

Re: fuel usage

FR, maybe he's refering to the screw head slot being broke out from wrong size screw driver being used?

 

[F_R]

Re: fuel usage

Yeah, I considered that possibility. Of course that would have no effect on fuel/air ratio, since it is the orfice size that matters.

Actually, it takes a certain air/fuel ratio for an engine to run properly. If it were running so rich so as to be a major concern it would seem that he would be complaining about poor running, not too much gas.

What does anybody else think?

 

[Silvertip]

Re: fuel usage

You don't have a fuel consumption problem. That engine will burn roughly 8.5 g/hr at wide open throttle so you could easily go through a 6 gallon tank in that amount of time. At 3/4 throttle fuel use should drop to about 6 to 6.5 g/hr. So if you can run for 2-1/2 hours on 6 gallons you are doing fine. I have a 75 HP on a 17 foot boat and it burns 7.5 g/hr at WOT and that's being measured with a fuel flow monitor. At cruise it burns 5 g/hr.

 

[OBJ]

Re: fuel usage

Good info.....still, it would be a good thing to know what the plugs look like, engine temp and what the compression is. Might help a little to keep the engine at peak performance and best gph gas usage.

 

[steelespike]

Re: fuel usage

I didn't see what hull type you are running or any indication of the rpm but::
If I'm reading it right Your burning 6 gal. in 2 to 2 1/2 hrs.
My math says that is less than 3 gallons an hour.I would say that is exceptionally good based on the 8.5 gph typical for an 85 at wot.Just for the heck of it I looked up some figures on the etec 90.Typical gph at min planing speed was 3.24.usually best MPG was at faster speed and higher GPH usually by a few tenths.Max GPH at WOT was about 8.2 GPH.Though there was one setup that was about 7.9.
The relation of GPH to speed to MPG is interesting.
ie: 4.02 GPH a@ 23.3 =5.8 MPG ,4.73GPH @ 28.3=6mpg.
Your first assumption when using close a gallon more per hour more would be your using too much fuel when actually your covering much more distance per hour resulting in a faster trip on less gas.Of course if your just out for a cruise the lower GPH might be better the slower speeds on that particular boat resulted in close to the 6 MPG figure when maintaining planing speed.
At any rate it appears your set up is doing pretty well.
If you study the performance charts it may give you an idea where your perfornmance is.