1990 Johnson GT150 Eating The Fuel

[daselbee]

Eighty? Five mpg? What??????

I get 2.5 mpg, and I feel lucky. Geezzz what and how did you ever expect 80 mph, and getting 5 mpg gas?

If you were hitting 80mpg, you probably would be getting 1 gal per mile....JMHO.

 

[sutor623]

Get into the rough, I'm pushing gallons per mile....lol

Hahaha, nice.

 

[Smurph]

Only way that rig will see 80 is on the interstate behind a good truck :lol: Good stable fishing rig...

Daggers, daggers to the heart. That was cold . . :faint:

 

[emdsapmgr]

There is a fuel economy point in the throttle range. It's about 7/8 throttle. Pull the cowling off and look at the throttle linkage at WOT. If you pull back at WOT, you will see the spark stays fully advanced to the rubber stop. It's the throttle cam which will start to close the carbs first. If you pull back just enough the slightly close the throttle butterflys, but keep the spark at full advance, that's the sweet spot for max economy. Again, it's about 7/8 throttle.

 

[Smurph]

Thanks emd for that tidbit. So I guess the wider the throttle opening doesn't necessarily mean bad mileage. Whole bunch of other factors are at play there, like the power to weight ratio. I am gonna mark my throttle where that spot is on the control and use that info (guess that's about 75 on the little boat). :behindsofa:

 

[Smurph]

UPDATE / PICTURES My original complaint of eating the fuel has gotten a bit better than it was thanks to this forum. It has helped me to find this issue that I didn't even know I had. My fuel economy is a bit better and the out of the whole is also better. I am a happy camper.
I haven't checked the compression yet, sure plan on that and the decarb thing too.
I was looking to check my throttle placement at 7/8 throttle like you told me EMD, so I moved it to WOT at the lever, pulled the cowl, and looked up at the spark advance thingy, and it was not touching the rubber stopper. So I pulled back to neutral at the lever, moved it back to WOT, and found the same thing, not touching the stop. It appears to me that the previous owner has had a new spark advance, or whatever it is called cause I'm not sure, but its fresh looking, as so is the stator I think it is, but they are new looking and clean as a whistle. I looked down at the harness to the advance part and found a zippy tie wrapped up a little high I thought and pulled super tight on that harness. With the throttle set back to neutral, I snipped the zippy tie, and once again advanced the throttle to WOT, low and behold the spark advanced slammed against the stop. I moved it back and fourth between neutral and WOT and it hit the stop every time. Good show EMD, I then marked the throttle lever at the 7/8 setting so I could see it while running down the river, put it all back together, took it out the next day for a spin and was pleasantly surprised.
I had mentioned earlier in my post that the little boat seemed to like around 35 ~ 38 mph, that it seemed to be relaxed, well guess what, I looked down and that throttle was set dead on the marked that I had painted on the lever earlier . . :biggrin-new:​ Now can you believe that. Man its good when a plan works out like that.

Thanks to this forum and everyone who helped out.

TOP PHOTO; When advance to WOT at beginning. Not touching the stop

SECOND PIC; The zip tie position as found on spark advance

THIRD PHOTO; After cutting zip tie loose it now hits stop

​

 

[sutor623]

Man I am sure glad that you checked that!!! Having your spark retarded like that at WOT is terrible for the motor, not to mention will eat up fuel without the full benefit. Amazing how something as simple as a zip tie can ruin the whole show.

Do a decarb before your next outing!!!!

 

[Smurph]

No kidding. Wonder if the guy that done that ever realized it. Live and learn. Thanks sutor.

 

[jeff_ontraio]

I have an '86 GT150 on a FW 190 Horizon. That motor is a work horse. It goes and goes asking little in return but high test fuel and good quality oil. It is a pig, but it's a big, strong V6 so what really could you expect? You have a quality piece of machinery there!