1987 200hp Johnson Mileage

[Ultra Rider]

I have a 200 HP 1987 Johnson on a 30' pontoon with hard deck on top.
I am getting awfull mileage. WOT running at 22 MPH per my gps. I use about 9 gal. in about 30 minutes and this is after I back off of and am cruising at 20 MPH.
It has good compression on cyls. I have to choke it when ideling (even after warm) to keep it running. Once I get up tp about 8-10 mph I do not have to choke it anymore but the fuel use is crazy.
I ran a can of seafoam through both of my tanks but no improvement.
Any ideas what I could do to get better mileage?
Thanks for any info or suggestions that you might give me.

 

[countvlad]

Re: 1987 200hp Johnson Mileage

I have a 200 HP 1987 Johnson on a 30' pontoon with hard deck on top.
I am getting awfull mileage. WOT running at 22 MPH per my gps. I use about 9 gal. in about 30 minutes and this is after I back off of and am cruising at 20 MPH.
It has good compression on cyls. I have to choke it when ideling (even after warm) to keep it running. Once I get up tp about 8-10 mph I do not have to choke it anymore but the fuel use is crazy.
I ran a can of seafoam through both of my tanks but no improvement.
Any ideas what I could do to get better mileage?
Thanks for any info or suggestions that you might give me.

u have some issues there... when were the carbs last time rebuild???

have you checked the timing? spark on all cylinders? do you have a tachometer on the boat? are you running at the recommended WOT?

 

[wilde1j]

Re: 1987 200hp Johnson Mileage

WOT for that motor ~ 20 gph. Backing off to ~ 4000 RPM will cut that to ~ 14 to 15 gph. Carbs need to be cleaned, if you need choke to keep running at low rpm. See here:
http://forums.iboats.com/showthread.php?t=244013

Probably won't improve fuel consumption, but you have one or more cylinder running lean, so it may save your motor from very expensive repairs later.

 

[d.boat]

Re: 1987 200hp Johnson Mileage

Like wilde1j said, that actually is pretty normal for wide open for that engine. The rule of thumb is gallons per hour at wide open = HP/10 (200/10 = 20 gph at wide open for you). You're getting 18 GPH which is in that ball park.

By the way what RPMs are you getting at wide open?

The wide open fuel consumption in terms of gallons per hour is the same no matter what speed you're going. It simply takes that much gas to produce the 200 hp. Nothing you do will improve that.

You could maybe improve the actual speed you're going at any given RPMs with trimming of the boat itself or changing the prop (depending on what WOT your engine should be getting per spec. and what it's actually getting with the current prop). This would change your MILES per GALLON, but not your GALLONS per HOUR.

The only thing you can do to improve overall gas usage is to back off the throttle and figure out what speed gives you the best MILES per GALLON, if that's what you're looking for. That's what I look for because I do a lot of long range cruising.

That is usually about 3/4 throttle or somewhere around 4,000 give or take 2-300. If you can't really measure speed and fuel consumption that easily, the rule of thumb is 3/4 throttle maximizes economy in terms of miles/gallon and it's generally pretty close in my experience. Much slower will probably give you better gallons per hour than 3/4, but you won't be going as fast or as far per gallon.

The choking issue has been answered, but to repeat, probably won't improve your GPH at WOT.

 

[Ultra Rider]

Re: 1987 200hp Johnson Mileage

Hi all and thanks for the expertise that you give so freely here. I do not have a tach so I am not sure what the RPMs are running.
This past weekend was the first time I had her out on the lake with this motor. We spent three days on the lake and I feel like I need to take a loan out to pay for the fuel that I had to buy.
I appreciate your suggestions and will do the things that ya'll (yep, I'm from Arkansas) have suggestions.
Thanks also for sending the links to other posts that will help me.

Clay

 

[paw2000]

Re: 1987 200hp Johnson Mileage

Hi, Looking at the size of the boat and about of wind resistance you get, you are probably like others said right in line. It hurts if you have a small fuel tank and have to buy more often. My boat has a 65 gal tank, I put $90 in it Monday morning, brought me up to 3/4 tank, ran 20+ miles to Ship John Shoal in Delaware bay (striper fishing, only got 1) figure I travel about 50 miles total for the day, back to 1/4 tank. Maybe 2 miles per gal, I have a 140hp. I put close to 100 miles on the boat for the 3 day weekend.

My cruising speed is 19-22 knts and top speed is 30knts. I feel your pain on the pump, in my area (delaware bay) everything is 5-10 mile ride, doesn't take long at speed, but adds up. I won't leave the dock with less then 1/2 tank.

 

[kenmyfam]

Re: 1987 200hp Johnson Mileage

200HP = 20 gallons Per Hour at WOT. Simple as that.
Backing off on the throttle will reduce fuel consumption per hour but you will not go as far.
Smaller motor will reduce consumption but at the expense of performance.

 

[walleyehed]

Re: 1987 200hp Johnson Mileage

This rating only holds true on the carbed engines. My crossflow 200 will burn 25gph at wot. Our Ficht 200HO burned about 16gph....both at 6000rpm. The lower the wot rpm, the higher your fuel consumption will be. I'd buy a tach and prop for 5800 with a normal load...this will allow about the best MPG you will get on that 2.6L