Johnson 88 fuel use

[surrender]

Ok, yesterdsay we cruised up the waterway to fish but wind came up and ended up...cruising. Ended up traveling 24 miles round trip with 95 percent of the time at around 4500 rpm. Was fully topped off to start so I topped it off when we brought boat home. Put 9.4 gallons in her. 24 miles per 9.4 works out to 2.55 miles per gallon. Any thoughts, and what if anything can I do to raise that. 4500rpm pushes boat to around 27 mph. That works out to over ten gallons per hour at 4500 rpm. Seems high. motor is a 1996 Johnson 88 special with a 13 3/8 X 17 three blade prop. max rpm are 5400 at 34 mph.

 

[5150abf]

Re: Johnson 88 fuel use

Sounds like you ar dead on with your prop so there really isn't anyhting you can do.

A bigger prop will cause the engine to lug which is bad.

Boat motors run a high RPM which uses alot of gas, imagine driving your car around at 4500 rpm for a couple hours, you certainly wouldn't get very good mileage.

Try a decarb and make ure she is tuned up right and that is really all you can do.

 

[MAW31]

Re: Johnson 88 fuel use

Me thinks your going about the equation all wrong...

Think in tems of ballast reduction...

Think: "What passengers can we do without this trip"...

*smiles*

---------------

PS: I have a 94 88SPL pushing an 18 CtrConsole, no trim tabs, i get the same results for the most part in choppy waters.

 

[surrender]

Re: Johnson 88 fuel use

I hear you on the passangers. Had on myself and two others on board. A little crowded to fish. Boat is perfect for two to fish on(17 McKee craft offshorefisherman) Plus both passangers were not exactly slim

 

[MAW31]

Re: Johnson 88 fuel use

ya. When I was a lad, three of us could fish all day on a boat that 'big' .haha.

Just remember, when ya hit the boaters "watering hole' afterwards...that most other boaters will not be very sympathetic to your 88HP gas usage plight...

...talk to the guys running dual 250's and such...now THOSE are REAL horror stories LOL.

gotta say, I'm quite happy with the performance and operational cost of my lil 18 CC with the 88...

cheers.

 

[surrender]

Re: Johnson 88 fuel use

I was thinking about the guys with the bigger engines when I saw a 34 fountain advertised that cruised at 49 burning only 33 gallons an hour total. Thats with triple 250 mercs! My mileage sucks compared to him when you think about it.
http://www.thehulltruth.com/boats-sale/267274-34-fountain-refurbished-very-nice-boat.html

 

[ezeke]

Re: Johnson 88 fuel use

34 mph at 5400 RPM is over 20% slip, which indicates that you are still overpropped (or overloaded). You should try to prop the motor for 5800 RPM max with your average load.

 

[surrender]

Re: Johnson 88 fuel use

I plan on going to a 15 inch four blade when I can find one for a decent price. Hopefully in the next two weeks I'll report back when I do a run again.

 

[MAW31]

Re: Johnson 88 fuel use

i could be wrong, but aren't the 4 blade props better for low end pulling (like pulling a skiier up) at the cost of high rpm cruising?

also, how was speed determined.

 

[ezeke]

Re: Johnson 88 fuel use

Unless you were pushing a barge, four blades or three would not make much difference; it's the pitch that matters most.

 

[surrender]

Re: Johnson 88 fuel use

Unless you were pushing a barge, four blades or three would not make much difference; it's the pitch that matters most.

If you know the Mckee 17 its not far from a barge. The rounded bilges(chines?) make for very little lift in the stern. Really need to put some tabs on her to help with the lift and to get the bow down in the chop. I thought about making some rails to fasten to the hull at the stern to add lift, kind of in the shape of spray rails up front. Then I thought again and figured tabs would be easier. I think the Smart Tabs would be good but I want something adjustable

 

[kenmyfam]

Re: Johnson 88 fuel use

Agree with your WOT RPM being on the low side. You do need to be at the 5,800 mark. Has it always been like this ??? I would suggest fine tuning the outfit to your average load. Motor height, trim, weight distribution of people and gear etc. Is the motor healthy ??? I have known some folk that re-propped for maximum rpm and the root cause was a weak spark and the motor was in a huge need of a major decarb. (at least they now have an emergency prop as a spare) Does the boat have any waterlogged flotation foam ??
There can be no such thing as miles per gallon when boating. Distance travelled divided by fuel used simply does not work. You have to take into account the currents, wind direction and water condition (waves)
Banging through a couple of feet of waves going against the current with a headwind will certainly reduce your distance travelled per gallon of fuel used. Add the amount of weight you are pushing through this when loaded up with different amounts of people, pet's, coolers etc and the variables are endless.
Gallons per hour is the easiest and best guideline without getting really technical with fuel flow meters and such.
My 2 cents,
Ken.

 

[surrender]

Re: Johnson 88 fuel use

I hear you Kenny on the mph. the motor was neglected when I got it. We literally found it. the boat was up in the marsh and the Coast Guard called the "last registered owner" who happened to be a buddy. He no longer lived in the area and called me to see if i wanted to go get it. He had sold it years ago but the buyer never registered it and apparantly abandoned it. We checked with all sources to locate him but per the laws in this state we went through the process of registering it and now we are tweeking it. Carbs have been rebuilt, one coil was bad so we replaced all 4. New rectifier and tach, new fuel lines and filter and drained tank and have been through a bunch of new fuel. The weak spark is interesting. When we were figuring out the coil issue we noticed a weak spark on all four. As I said one coil would cut out when hot so we changed all 4. Spark was better but I dont think its great. I think stator is good, I have checked with the CDI troubleshooting guide, and battery charges great so good on that end. I do notice that if I move or hit anything around the power pack a cylinder seems to cut in and out for a second. Could my pp be going. All connections have been cleaned and re torqued. New plug wires with new coils. maybe pp? Might buy a known good used one ($40.00) and test with that before we go prop route.