1985 inline6 90

[oldgradywhite]

I have a 1985 90hp mercury inline 6 and I was wondering if it is time to replace it. It runs great but it loves gas. I was told all 2 stroke in this hp range get the same gph. are newer 2 strokes alot better on gas and would they be more powerful. I was a told that old mercury were not measured for hp at the prop. was there any big problems witht his motor that any one knows about?? any info would be great!

 

[kenmyfam]

Re: 90 gph

Re: 90 gph

I have a 1985 90hp mercury inline 6 and I was wondering if it is time to replace it. It runs great but it loves gas. I was told all 2 stroke in this hp range get the same gph. are newer 2 strokes alot better on gas and would they be more powerful. I was a told that old mercury were not measured for hp at the prop. any info would be great!

Welcome to iboats
I thought your title was saying that you were using 90 gallons per hour !!!!
I dont know if they are more fuel efficient or not but a rule of thumb is 10% of your hp at WOT in gallons
I believe that hp used to be measured at the crankshaft.

 

[jimmbo]

Re: 1985 inline6 90

If you have a 1985 90hp(brown band) it is propshaft rated.

Issues with this engine.

On the top of each carb there is a neoprene hose that runs from the carb body to the top of the float bowl cover. Remove this line, place a small ball bearing ball in it and replace it on the fittings. This will disable the 'back drag' feature of the carb. It was added in the mid 1970s to increase fuel economy by leaning out the fuel mix at part throttle, however with todays fuels it becomes too lean and engine damage can occurr.

 

[Chris1956]

Re: 1985 inline6 90

Grady, I had a '77 Merc 1500 (150HP), and now I have a '98 Johnson 150HP V-6. The Johnny has six carbs, versus the three I had on the Merc. It also has oil injection. I think the new motor uses more gas and oil than my old inline. I do not have a way to precisely test this however.

 

[tashasdaddy]

Re: 1985 inline6 90

a 1985 is just broke in. as long as it runs good, check your compression peroidically. run it. have you priced new ones. you can do a lot of preventive maintainance, for the difference.

 

[dajohnson53]

Re: 90 gph

Re: 90 gph

Look in the forum called "Non-Repair Outboard Engine Discussion" There is a very interesting discussion on some data that was posted on outboard fuel economy comparing 4 engines - some 2 strokes, a 4 stroke and a DFI (ETec) engine.

The data show that all of the engines burn are pretty close to the "rule of thumb" for GPH at wide open: about 10% the rated horsepower in gallons per hour. In other words, the 75 hp's being looked at all burn about 7.5 gph regardless of technology. (As an aside, I found the same with my 80s carb'd Johnson V6 compared to a friend's very new carb'd Yamaha V6).

The data in that discussion also show that there are significant differences both in terms of GPH and MPG at various speeds and RPMs. The lesson learned (for me anyway) is that the best technology for my use might be different than the best for someone else's - because we may use our boats completely differently, and therefore need optimal economy at different speeds or RPM's.

One final thought - again, my opinion - the cost of replacing a well -running older carb'd engine could very well far (far!) exceed the benefit in terms of economy. A "25% improvement" could take many, many, many years to be worth while. And, a lot of the savings (depending on usage) are likely to be much less than that.

 

[noelm]

Re: 1985 inline6 90

if you compare the "old" motor to a new "fuel injected" motor (in all their various systems) then the fuel usage will indeed be heaps better, but to compare to another carby motor then HP is HP it takes X amount of gas to make X amount of HP end of story, and if you run it flat out, it will use a lot, but if it has been cared for and not rusted to bits, your old IL6 is just starting to "loosen up" at 20 years of age.

 

[mickjetblue]

Re: 1985 inline6 90

I have an '83 90hp Merc, and I have improved its mileage and performance.
I've had it just over a year, and initially the mileage went from fair to worse.
The reason was because the gas stations I used started adding ethanol to their gas. I switch to convenience store stations like Sheetz and Rutters, who do not add ethanol to their gas. The mileage improved to what it was before, although I still wanted it to be better. I always use octane 89.

I took a gamble, and installed a "whale tail" stabilizer on the lower unit above the prop. It resulted in a significant improvement in gas mileage, overall power, better control, and quicker pull-up of skiers. It made the motor a keeper. I really like running it occasionally at 5500rpm, where it has a quiet hummm, and makes some things right in the world for that time.

I'm just passing on a couple of tips from my experiences, with no guarantees. I know most posters prefer smart tabs to lower unit stabilizers, but I have had good results with both the "whale tail" and the SE Sport. Good luck, and happy boating!

 

[oldgradywhite]

Re: 1985 inline6 90

Thanks for the input I had the motor looked it over. The compression test showed cylender 1# 135 2#100 3#115 4# 135 5#130 6#135 I was told that I needed a rebulid. They has show showed me that the middle carb was dripping out of a screw in the middle carb and that they all needed a rebuilt. Is $600 alot to rebuild carbs and do a link and sync. I have never heard of a link and sync before is this hard to do I know I can rebuild the carbs.

 

[tashasdaddy]

Re: 1985 inline6 90

here are the link and sinc directions for your motor. i would do that, then do a decarb,(cleaning the guts). and recheck the compression. then the carbs rebuild.

http://forums.iboats.com/showthread.php?t=168855

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck

 

[Solittle]

Re: 1985 inline6 90

Don't let a shop talk you into a rebuild untill you have seen the results of TSD's advice. You may be pleasently surprises and leave much coin in your pocket.