1990 Johnson GT150 Eating The Fuel

[Smurph]

Hello to all, new guy from Alabama. In 2012 I bought a 1990 Ranger Comanche 363V. The man before me loved this boat and took very good care of it. I am concerned that the 1990 Johnson GT150 is using way to much fuel and oil. I have owned a few Bass Boats ( one with a GT150 ), a Pontoon Boat, and a few Runabouts, so I know enough to know they won't get 20 mpg's or anything, but I feel like I'm at something like 5 mpg's. I can't go anywhere that I don't have to fill up. My engine smokes some but not excessive. I am having this problem where it starts up, goes dead, then restarts, maybe dead again, but finally she will idle. I have been thinking the Carbs need rebuilding due to possible trash, but it just seems to be flooding, instead of starving for fuel.

My question is, could previous owner have had his carbs set up to run rich so as to provide engine with extra amounts of 2 stroke lube. Is that possible? This boat flies down the lake, just a really good running boat when up on the pad. It runs so good I hate to go into carbs, but the mileage just sucks so bad, I am looking to maybe take it to the Dealer or a Pro. Would love to hear some thoughts from you guys that know something about these things. Thanks for any and all feedback.

 

[sutor623]

Mileage......... 5MPG is actually pretty good for a boat. We go by something called GPH or gallons per hour. General rule, take the HP of the motor (150) and divide by ten (15) and that is how many gallons per hour that you will burn at wide open throttle. If you are buzzing around balls to the wall, expect to pay more at the pump. You could probably cut that fuel consumption almost in half if you throttle down some. Although I know you bass boys like to get there fast!

I think you are crazy to tear the carbs down on a great running motor. These motors have fixed fuel jets, so unless this boat was set up for a different altitude and the open throttle jets were changed, there is not much you can do.

Another thing you may be experiencing is cylinder "blow by". As an engine ages, the cylinders/rings wear out and some of the fuel can blow right by the rings and out the exhaust. You can check compression and put an end to this theory.

Your motor may not be idling well because A.) You are not advancing the throttle so that it warms up properly, or B.) Your idle is set too low. That is where I would start as they are the easiest fixes.

 

[Bosunsmate]

thats a good answer^, the only thing id add would be whether you have the right prop pitch

 

[emdsapmgr]

These engines do tend to accumulate carbon around the ringsets after many hours of use. You may find the engine can benefit from an application of Bombardier's Carbon Guard product. (maybe two.) An aerosol cleaner which cleans up the carbon in the combustion chamber and around the rinsets. You may find a little less smoking and better idling as a result. Also helps to run Bombaridier's XD50 oil. A clean-burning oil with a small amount of carbon guard mixed in-works as you run the engine.

 

[Faztbullet]

Ranger is a heavy hull and the crossflow motors tend to use more fuel...

 

[racerone]

Whar is the actual horse power of a GT 150 ??

 

[Smurph]

Mileage......... 5MPG is actually pretty good for a boat. We go by something called GPH or gallons per hour. General rule, take the HP of the motor (150) and divide by ten (15) and that is how many gallons per hour that you will burn at wide open throttle. If you are buzzing around balls to the wall, expect to pay more at the pump. You could probably cut that fuel consumption almost in half if you throttle down some. Although I know you bass boys like to get there fast!

I think you are crazy to tear the carbs down on a great running motor. These motors have fixed fuel jets, so unless this boat was set up for a different altitude and the open throttle jets were changed, there is not much you can do.

Another thing you may be experiencing is cylinder "blow by". As an engine ages, the cylinders/rings wear out and some of the fuel can blow right by the rings and out the exhaust. You can check compression and put an end to this theory.

Your motor may not be idling well because A.) You are not advancing the throttle so that it warms up properly, or B.) Your idle is set too low. That is where I would start as they are the easiest fixes.

Thanks Pete, Okay, I will do just that. I looked at trying to idle up in 2012 when I bought it but shy'd away because of lack of outboard knowledge. I will research on finding that procedure.

The other thing you mentioned about advancing the throttle, you are spot on there, I haven't been doing that until this past week, I just got tired of it and thought I'd blow out some fuel, so I pulled out lever and gave it a quick rev a couple of times, and then came back to the spot right before lever kicks off fast idle and man, much better. So today, I will fire it up, go straight to fast idle, even though its warm here, and see where that leads me. Thanks for reminding me of something that I have forgotten about a GT150, gotta properly warm'em up.

You mentioned ball's to wall, and to throttle down, and I know its a coming, but I haven't even been above 4K rpm's yet. This weekend the wife and I idled around the local Camping parks with our dogs and it still seemed to just use to much fuel. I am check compression today or tomorrow and will post results. I don't see alot of fuel coming out exhaust into water at idle, so hoping that's a good sign.

My thought process has been to make sure carbs aren't lean, so I have purposely stayed away from WOT. As you might have figured out by now, I haven't been using boat much because I didn't like it that much. I have changed my mind and like the little boat, so time to fix the short comings.


Mik

 

[Smurph]

thats a good answer^, the only thing id add would be whether you have the right prop pitch

Thanks Mate, that is the other thing that has me concerned, It has a brand spanking new Renegade Bass 4 blade on it now. Not a scratch on it either, so I know the guy that owned boat before me hasn't logged much time in the water most likely. So I am currently looking for prop info and wanting to try something else. I just don't know where to start, but I will continue till I do know which brand and pitch to try.

The boat seems to have all the power that I want in a little boat like this on upper end, even though I haven't had it above 4k rpm's, it just flies to me. Its the lower end that I don't like. At 30 ~ 32 mph the engine sounds to me like its in a constant strain. I can just tell its wants to get up and go, so when I bump up the speed to around 35 ~ 38 mph, it is much happier, and me too. That's why I think running around at a lower speed gets about the same as at higher speeds. It certainly is a more relaxed sounding engine at the higher 35 to 38 speeds.

Mike

 

[Smurph]

These engines do tend to accumulate carbon around the ringsets after many hours of use. You may find the engine can benefit from an application of Bombardier's Carbon Guard product. (maybe two.) An aerosol cleaner which cleans up the carbon in the combustion chamber and around the rinsets. You may find a little less smoking and better idling as a result. Also helps to run Bombaridier's XD50 oil. A clean-burning oil with a small amount of carbon guard mixed in-works as you run the engine.

Thanks MGR. I have read about the carbon issues. I bought a Sea Foam kit early last year, something with Deep Creep and a how to procedure for using it, and never applied it. I am checking the compression this week so I will apply that for now. Maybe try the Bombardier stuff next time. Bet it won't hurt to do that procedure twice aye.

What do you think about this, I am running Marvel Mystery oil through the engine's fuel system. I have used it in everything I own with a combustion engine for many years with no problems or issues. Its an excellent top end lubricant and fuel system cleaner. Just .4 tenths an ounce per gallon ( 4 ozs. to 10 gallons ). Do you think that its really needed in an outboard engine with the 2 stroke lube already being mixing in with the fuel. Just a thought on that, I may be wasting my time and money on that.

Mike

 

[sutor623]

So I am currently looking for prop info and wanting to try something else. I just don't know where to start, but I will continue till I do know which brand and pitch to try.

At 30 ~ 32 mph the engine sounds to me like its in a constant strain. I can just tell its wants to get up and go, so when I bump up the speed to around 35 ~ 38 mph, it is much happier, and me too. That's why I think running around at a lower speed gets about the same as at higher speeds. It certainly is a more relaxed sounding engine at the higher 35 to 38 speeds.

Mike

What you have found is your ideal "cruising speed." That is the sweet spot for your boat/motor combo. It is pretty easy to find on most rigs because you dont feel like you are dogging the motor, yet you also feel like the boat is up and out of the water. ANY speed above or below this spot will reduce your MPG's, not necessarily GPH, since you can idle all day long and only burn a few gallons, but how far will you have traveled?

Check back once you get some compression numbers. Like others have said, you may have carbon built up around the rings and just need to run a decarbonizing component through your gas. Personally, I have only ever used sea foam and it has worked well for me. (But EMD's idea sounds better.) I put a heavy mix in, and let her run at idle, then let it set for a few, and do that for a few cycles. Then I run straight gas/oil through her at WOT to clean out all the residual sea foam.

After you do this you can check compression again. Typically it will get better. This means you have freed your rings up and have a better chance of not frying a ring and scorching a cylinder.

 

[Smurph]

Ranger is a heavy hull and the crossflow motors tend to use more fuel...

Thanks for your comment Bullet. Looks like I purchased the wrong boat for GPH. Its a looking a whole lot like I am going to have to keep this GT150 fuel system and piston ring sets clean as a whistle and just deal with it. That's what I plan on doing for now. I will play with the prop pitch's and brands maybe for a little ways, but if it worsens I can always go back to what I have in a prop.

Mike

 

[emdsapmgr]

Your 150GT model has more in common with a 175 than with the basic 150 engine of that year. Your engine will make about 165 hp. Has different heads and usually has the larger 1 5/16" carbs. Some of the late 80's 150 GT's even used the huge 235 1 3/8" carbs. Nice engine.

 

[Smurph]

Your 150GT model has more in common with a 175 than with the basic 150 engine of that year. Your engine will make about 165 hp. Has different heads and usually has the larger 1 5/16" carbs. Some of the late 80's 150 GT's even used the huge 235 1 3/8" carbs. Nice engine.

Well that is good for me to know. That makes me feel great. I got something kinda special then to me. I bought a Procraft 1780V new back in 88 and it had the GT150 on it. That engine never gave me a minutes trouble. Come to think of it, it was cold natured. Had to start it a few times. Don't believed I used the fast idle feature like I should have back then either.

 

[V153]

You definitely bought the wrong boat for GPH. Not that I have a problem with that ...

If you can find a prop that'll let you cruise around 30 mph at about 3K rpm. Then you've found the sweet spot for that motor.

 

[boobie]

One thing to remember is the old rule of thumb. A motor will use 10% of its horsepower in gal per hr at WOT.

 

[Smurph]

You definitely bought the wrong boat for GPH. Not that I have a problem with that ...

If you can find a prop that'll let you cruise around 30 mph at about 3K rpm. Then you've found the sweet spot for that motor.

Thank you 53. This past weekend was the first time I have rode in the 30 mph range. After reading the feedback on my issue, which I thank everyone so much for their time and expertise, it is with confidence that I now am looking at this thing from a whole new prospective. I have a gas hog no doubt, but I can work within the limits of this motor and just try and find a happy place and do it for a whole tank (or tanks - little boat holds 36 gallons) and see how she does on fuel consumption.
Maybe I won't be able to watch the gas hand move as I do . .

 

[emdsapmgr]

To maximize your boat's performance and fuel economy, make sure the engine is propped to run right at 5500 maybe to 5700 rpm's at WOT. If it only runs, say 5200 at WOT, the engine is lugging. That means slow out of the hole and worse fuel economy.

 

[Smurph]

To maximize your boat's performance and fuel economy, make sure the engine is propped to run right at 5500 maybe to 5700 rpm's at WOT. If it only runs, say 5200 at WOT, the engine is lugging. That means slow out of the hole and worse fuel economy.

Thanks MGR. I guess that I should have done that right out of the gate instead of the path I took. But no harm done and that's my next move is to go WOT. I guess now I get to see what the top end speed is. That is something that I have been wondering, yet didn't really want to know that the little boat I now love owning, has a lower top speed than I thought. Guess I need to lower my expectations down from eighty. . .

 

[Faztbullet]

Guess I need to lower my expectations down from eighty. . .

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

 

[dingbat]

I'm running an Evinrude 200 with 4 blade offshore Renagade. My boat is a good bit heavier that yours but, cruising at 27 kts in a light chop, I'm getting 1.9 -2.0 mpg with Floscan. Get into the rough, I'm pushing gallons per mile....lol