86 Johnson GT150 Overfueling?

[Saperry]

Well I finaly got the boat in the water after replacing transom and floor. What a job. (Never Again!!!)<br /><br />While I had the motor off I removed carbs and completly dissassembled and cleaned them also replaced impeller and changed lower unit lube.<br /><br />The moter seems to run fine. Starts easy, Idles fine, runs smooth. WOT RPM about 4300 with 3 adults and two kids (3 and 4 yrd old).<br /><br />The problem I have is fuel consumption. We went through 18 gallons of fuel in about three hours of running time on motor. Most at about 1/2 - 3/4 throttle or less.<br /><br />While tubing you could smell exhaust fumes on the tube 50' behind the boat. Smells like there is unburned fuel in the exhaust. <br /><br />As smooth as it idles and runs I don't think it is missing on one cylinder.<br /><br />Is that fuel consuption high?<br />How can I check that all cyls are firing? Remove plug wires one at a time while ideling? <br /><br />18Ft Skeeter SF180 Starfire<br />86 Johnson GT 150 (VRO Disconnected)

 

[Saperry]

Re: 86 Johnson GT150 Overfueling?

Also, can I Install a temp guage on this motor?

 

[JerseyJim]

Re: 86 Johnson GT150 Overfueling?

something isnt right with your WOT rpm...you should be pushing 5500 or so... one cyl could be missing at high RPMs??

 

[Saperry]

Re: 86 Johnson GT150 Overfueling?

?

 

[Hooty]

Re: 86 Johnson GT150 Overfueling?

Just as a rule of thumb, the engine will burn 10% of it's horsepower gals/hr. at wfo. A 150hp engine will burn 15gph & wfo so your fuel consumption is probably about right.<br /><br />c/6<br /><br />Hooty

 

[Hooty]

Re: 86 Johnson GT150 Overfueling?

Oh, three adults, two little 'uns, tubing and an 18' boat is a pretty good load for a 150hp. engine. See how many revs it turns with one person and no tuber. That should be about 55-6000rpm.<br /><br />c/6<br /><br />Hooty

 

[Saperry]

Re: 86 Johnson GT150 Overfueling?

Hooty,<br /><br />I never had it to WOT with tube. Without tube and one person WOT about 5000 RPM. With load but no tube WOT 4200-4300 RPM.<br /><br />Is that low? This is the first trip to the lake with this rig. With other boats I have had no one has ever complained about exhaust while tubing.<br /><br />Also this is the first johnson I have ever had and the largest outboard. The others were a 65HP Suzi and a 120 Force.

 

[Saperry]

Re: 86 Johnson GT150 Overfueling?

up

 

[Saperry]

Re: 86 Johnson GT150 Overfueling?

BTW the prop is 14 1/2 x 22..<br /><br />Thanks in advance for any thoughts or advise.

 

[Hooty]

Re: 86 Johnson GT150 Overfueling?

Yep.<br />42-4300rpm @ wfo is low. Have you played around with the trim? Where is the cavitation plate in relation to the bottom of the boat? I'd do some of that first, but you may end up having to change props. B&B Propeller over in Ft.Worth are real knowledgeable guys. If you start thinking about reproping, they'll help ya out. <br /><br />c/6<br /><br />Hooty

 

[Saperry]

Re: 86 Johnson GT150 Overfueling?

Reproping would not be out of the question but I am not convinced that is the problem. I am wondering if there is a cylinder or two not firing. Somehow unburt fuel is in the exhaust. I am going to replace the plugs before the next trip out. The one's in it now are non gap type(for lack of a better word). Is that the correct plug.<br /><br />Would a prop make a difference in the exhaust?

 

[Saperry]

Re: 86 Johnson GT150 Overfueling?

What position should the red pointer on the priming selonoid be in? <br /><br />Also should I change the plugs before or after runnung the OMC Engine Tune through the motor?<br /><br />Thanks <br />Sean

 

[Hooty]

Re: 86 Johnson GT150 Overfueling?

I Don't think you've got a dead cylinder. You may have, but I doubt it. If you do, you can look at the plugs and tell. The one(s) not firing will look different then the rest. Probably wetter and maybe newer looking. Change plugs after the Engine Tune. If you're gonna use gapped plugs, use Champion L77JC4's gapped @ .030.<br /><br />c/6<br /><br />Hooty

 

[Saperry]

Re: 86 Johnson GT150 Overfueling?

Thanks Hooty, I just want to be sure that the moter is running as well as it can before I start trying different props. In your opinion what would be better on the plugs non gao or gap?<br /><br />Also what about the red pointer (lever) on the priming selonoid. What position should it be in?<br />up, down, middle?<br /><br />Thanks<br />Sean

 

[Hooty]

Re: 86 Johnson GT150 Overfueling?

Personally, I run the L77JC4's in my 'rude even though the manual specs the surface-gap plug. The surface gap plug doesn't load up at low speed as bad as the L77 but I don't do much trollin'. Plus, I think the gapped plugs are easier to "read". <br /><br />The red priming lever (arrow) should be pointed down.<br /><br />c/6<br /><br />Hooty

 

[Duck Loads]

Re: 86 Johnson GT150 Overfueling?

Would someone please explain what function the red primer lever has?<br /><br />Thanks,<br />Duck L.

 

[Hooty]

Re: 86 Johnson GT150 Overfueling?

When the lever is pointed down (the normal operating position) pushing the start key "in" primes the carburetors. In case of a dead battery and you have to rope start the engine, moving the lever to the up position allows the carburetors to be primed with the pressurizing bulb.<br /><br />c/6<br /><br />Hooty

 

[Hooty]

Re: 86 Johnson GT150 Overfueling?

I guess I should have finished. After the carbs are manually primed(with the bulb) and before attempting to start, the lever should be moved to the down position to prevent flooding when the engine starts. <br /><br />c/6<br /><br />Hooty

 

[Saperry]

Re: 86 Johnson GT150 Overfueling?

Hooty,<br /><br />The red lever on mine rotates 180 deg from about <br />8:OO to about 2o oclock. The 8:OO oclock position is paralell with the primer selonoid body and perpendicular to the diaphram. At 8:OO it also feels like there is a bump or catch in the travel. Would this be the off or normal position of by down do you mean 6o oclock.<br /><br />Thanks <br />Sean

 

[bonitoman]

Re: 86 Johnson GT150 Overfueling?

I would be running a 17-19 inch prop on that setup. 22 inches is no good. Buy an aluminum. They are 100 -120 bucks. Make sure the engine is running fine. Check all plugs and make sure they have that nice tannish color. Check your compression. If engine checks out then just change your prop. Do not forget to trim your motor up as your running and look at your tack to see if rpms increase. Last thing stop at an omc dealer and pick up a can of engine tuner. It has a hose that you connect to your primer bulb. Once you have decarbed the engine take her out for a run and run the boat wide open for several minutes. If you still cant get rpms up to 5800 you must go down in pitch size on the prop. Good Luck