I want to upgrade my engine. Right now I have a 93' yacht twin 6 hp 2 cylinder. Pushes the boat fine but uses lots of gas. About a gallon an hour. I found a like new johnson 8 horse that is the same dimensions and weight for $900. Both are 2 cycle. will the 8 use more gas? Or less because it is not working as hard? So I would like to know the reasons to go with a 4 cycle. Other than the obvious fuel consumption difference. Used 4 cycles are much more expensive, and seem to have problems with the ethonal gas.
reasons for not getting an 8 hp outboard?
- Thread starter txtowman
- Start date
yah it'll use more fuel.
Love my 4stroke and I'd have to say anything modern will get along fine with ethanol blends. unless your trying to put the 80% blend in it.
Personally I'm in love without actually getting one the new tohatsu (sp) engine the runs on propane either a small bottle or it can run on the big bottle. Clean no gas spillage and easy to get propane.
Anyway been eyeballin that motor for awhile.
Love my 4stroke and I'd have to say anything modern will get along fine with ethanol blends. unless your trying to put the 80% blend in it.
Personally I'm in love without actually getting one the new tohatsu (sp) engine the runs on propane either a small bottle or it can run on the big bottle. Clean no gas spillage and easy to get propane.
Anyway been eyeballin that motor for awhile.
A 2 stroke is a 2 stroke as far as gas consumption is concerned, although newer fuel injection models may be just a tad less. If your 6 hp worked fine, then one could make the point that an 8 hp at partial throttle would use trhe same amount of fuel.
As far as your boat is concerned, you're right that weight is the most important factor. If your transom and bracket are fine with your existing engine, go for it. We had a Merc 7.5 2 stroke on our 1981 and it was just fine even with the heavy currents we get here.
As far as your boat is concerned, you're right that weight is the most important factor. If your transom and bracket are fine with your existing engine, go for it. We had a Merc 7.5 2 stroke on our 1981 and it was just fine even with the heavy currents we get here.
it will use more gas....
with the 6hp that you have now, I am assuming you have it tuned and running properly, with the correct pitch of prop.
so if you are burning a gallon an hour, you must be running almost wide open throttle, in an attempt to get the boat to go as fast as it can...
this is wrong for fuel economy.... in a boat, you can either have speed or economy, but not both.
if you cut the throttle and cruise along at 3.5 knots like most of us do, the economy will double what it is now, because it takes very little power to slip the hull thru the water at that speed.
the closer you get to hull speed, the more power you will need to maintain and the more fuel you will burn to get that power, no matter the size of the engine.
a bigger engine will only give you more excess power, but burn a bit more fuel due to the bigger displacement.... (more displacement means, more air passing thru the cylinder on every stroke and with more air you need more gas to keep the air/fuel ratio perfect for efficient combustion).
if you run the numbers (knots/miles made good vs. gallons per hour used) you will see a big difference in range, although it will take you longer to get there...
the only way to win the battle you are fighting is to slow down...
with the 6hp that you have now, I am assuming you have it tuned and running properly, with the correct pitch of prop.
so if you are burning a gallon an hour, you must be running almost wide open throttle, in an attempt to get the boat to go as fast as it can...
this is wrong for fuel economy.... in a boat, you can either have speed or economy, but not both.
if you cut the throttle and cruise along at 3.5 knots like most of us do, the economy will double what it is now, because it takes very little power to slip the hull thru the water at that speed.
the closer you get to hull speed, the more power you will need to maintain and the more fuel you will burn to get that power, no matter the size of the engine.
a bigger engine will only give you more excess power, but burn a bit more fuel due to the bigger displacement.... (more displacement means, more air passing thru the cylinder on every stroke and with more air you need more gas to keep the air/fuel ratio perfect for efficient combustion).
if you run the numbers (knots/miles made good vs. gallons per hour used) you will see a big difference in range, although it will take you longer to get there...
the only way to win the battle you are fighting is to slow down...
I spent a lot of time with a 2 stroke before.I have a 6 horse Tohatsu sailing special.It's very quite smooth plus charges the battery while you go.The other thing not mentioned though is there is no smell or smoke from the burning oil which is real nice.The former owner gave me a receipt for 1595.00 though.
any small engine will get better economy on ethanol-FREE fuel than it will on the regular ethanol fuel.... and other benefits as well
the engine will run smoother, start easier, stow for months at a time without carburetor issues and generally run longer without needing serviced. (although the yearly PM is just good sense)
I think this argument can probably be made for larger engines also, our little outboards need the best available fuel to give us the most dependable service in the harsh environment we use them in..
Oh yeah, it's proven that corn alcohol additive reduces efficiency along with the other problems the crap causes.
Ethanol fuel poses bigger threats to 2-cycle motors than 4-cycle. Both can suffer from deteriorated seals, O-rings, fuel lines, etc. But, when the ethanol separates from the gasoline in a 2-cycle mix (as it will over a fairly short time), it sinks to the bottom of the tank, and there will be no 2-cycle oil in that ethanol since they don't mix. What you'll do is suck raw ethanol until your motor uses it up or the motor fails (whichever comes first). At least the 4-stroke will run on the raw ethanol without too much issue.
My choice: 4-stroke outboard and buy only ethanol free fuel. Less finicky, less stinky, more convenient, fewer ethanol issues, but (unfortunately) more expensive to buy.
My choice: 4-stroke outboard and buy only ethanol free fuel. Less finicky, less stinky, more convenient, fewer ethanol issues, but (unfortunately) more expensive to buy.
I completely agree on ethanol fuels - regardless of 2 or 4 strokers - it sucks and causes problems universally both in injected and carbed motors.
The fuel economy debate is somewhat at odds with my experiences.
My 1976 C-22 came with an older Merc 9.9HP 2-stroke I burn nothing but ethanol free gas in. I put four gallons of 50:1 fuel in, in May and ran all season on that lone fill - and still have 1/4 of a tank left! Call it 3 gallons consumed.
I would guestimate my total motor run time for the entire season at between 4-5 hours. This would give me a consumption rate of roughly 3 quarts an hour.
Running at half-throttle seems to be ideal as the boat approaches hull speed and more throttle seems to become wasted rather than "productive" past 1/2.
The fuel economy debate is somewhat at odds with my experiences.
My 1976 C-22 came with an older Merc 9.9HP 2-stroke I burn nothing but ethanol free gas in. I put four gallons of 50:1 fuel in, in May and ran all season on that lone fill - and still have 1/4 of a tank left! Call it 3 gallons consumed.
I would guestimate my total motor run time for the entire season at between 4-5 hours. This would give me a consumption rate of roughly 3 quarts an hour.
Running at half-throttle seems to be ideal as the boat approaches hull speed and more throttle seems to become wasted rather than "productive" past 1/2.
Years ago when we lived in the Midwest and he had our original C-22,(swing keel), I did some fuel consumption testing because I was looking at a trip up the Illinois River to Chicago from the Mississippi. The boat had a 6 HP 2-stroke Johnson. Pushing the boat at hull speed, which required about 3/4 throttle, and we kept a lot of stuff on board, so she was fairly heavy, the engine would burn 3/4 of a gallon per hour. Fast forward 25 years and our C-22 MK-II wing keel version with a 5 HP 4-stroke Honda pushing our boat,(cruising mode she comes in around 3,500 Lbs), at 5.5-6 MPH, which required slightly over half throttle, we get slightly over 20 MPG, (we motored 60 miles up the California coast and filled up in Dana Point, GPS said we covered 60 miles from San Diego, and to top off the fuel tank it took 2.8 gallons). We've since purchased a new Tohatsu 6 HP 4-stroke and really like the front shifting on the new Tohatsu's,(easier pull starting also for my 1st Mate). For what it's worth, these little engines burn so little, I just always use good quality premium fuel from Shell, Chevron, etc. I never try to save a little money with a cheap brand of gas.
Don
Don
txtowman: You got good advice from Centerline and dubious info from Dougo. With your Yacht twin you should be at hull speed BEFORE the motor is at top RPM. You could put a 4 blade prop on it also and cut your RPM's even more. Your motor is an excellent motor! If you are well versed or have a friend who is accomplished in tuning 2 strokes: check spark plug color,(grey or tan is good)and change to smaller jet if dark. If it uses a needle also, drop down a notch at a time to achieve grey color (NOT white!). ALWAYS stir or shake your gas mix before going out to ensure suspension of your oil.
Chief, ex Yamaha Dealer
Chief, ex Yamaha Dealer
txtowman: You got good advice from Centerline and dubious info from Dougo.
I may not be an "expert", but I make my living operating & maintaining 2-cycle blowers, trimmers, chainsaws, and the like. We had a chainsaw with one day's use seize-up due to phase separation, so I'd say the dangers are real.
My comments are based on literature I've read and seminars I've attended on the subject. Echo published this article some may find interesting:
http://www.echo-usa.com/Warranty/Learn-About-Ethanol/Ethanol-Fuel-062512
Doug
Letting fuel set for long time frames is obviously asking for trouble! Not properly mixing your gas each use is also just asking for trouble! Not burning all the gas through your carb when finished is also going to be a problem. The manner of presentation was my main problem!
Chief
Chief
in my opinion, what you said qualifies as good enough to steer a person in the right direction, and that is really all that matters....txtowman: You got good advice from Centerline and dubious info from Dougo.
I may not be an "expert", but I make my living operating & maintaining 2-cycle blowers, trimmers, chainsaws, and the like. We had a chainsaw with one day's use seize-up due to phase separation, so I'd say the dangers are real.
My comments are based on literature I've read and seminars I've attended on the subject. Echo published this article some may find interesting:
http://www.echo-usa.com/Warranty/Learn-About-Ethanol/Ethanol-Fuel-062512
Doug
everyone should know, or needs to know that ethanol fuel does leave a black sticky residue in the bottom of the fuel tank, as well as in the bottom of the carburetor. this sticky residue getting into the carburetor is one of the reason the motors start hard, run poorly, or not at all..... and needs to be cleaned out by a service technician, which is expensive, time consuming, and troublesome to get it to the shop for them to work on it.... another reason it causes trouble is because when they add the ethanol to the fuel, it reduces the combustibility of it...
if anyone wants to prevent the $200 dollar service charge, the time and the trouble of having their carb cleaned at the most inconvenient time, switch to ethanol FREE fuel and let the motor live happily ever after... the extra cost of the clean fuel will be cheaper than repair costs, no matter if you use a 2yr or 10yr cost analysis to figure it out...
given the fact that we do need to use whatever fuel is available to feed the engine, the only thing worse than using ethanol fuel in it, it to add "HEAT" or some other brand of "moisture removing" additive to the tank.... unless you plan to remove all the fuel from the tank within the next 12 hours, as it will compound the problem rather quickly.
This seems to be a discussion about ethanol so I will ask the obvious question. Does the use of Stabil reduce the negative affects of ethanol as they claim. I use it on my outboards and my engines run fine year after year. I have 2 cycle and 4 cycle engines and use Stabil in both.
marine stabil helps.... the regular stuff not so much.
but unless you have a good clean system and run the non ethanol fuel for a few tanks, you can never know how much better the perfomance will be...
running non ethanol in a dirty system for a tank or two will do nothing for you...
try this. buy a new lawn mower and run clear fuel in it for a while so you can get used to how nice it runs... then halfway thru mowing the yard one day, dump the gas out of it and run it dry.
then fill it with ethanol fuel.... and see the difference.(it will run kinda like the air filter is restricted a bit) leave it in there, and see how much harder it starts next week when you go to mow the grass again.... it doesnt take long to see the associated problems with the ethanol when you have a clean system and are used to clean fuel, then switch...
and the more you use it the more deposits form in the system...
about the best way to describe ethanol fuel in the fuel system, might be understood better by some by comparing it to our own system.. because,
its actually kinda like plaque build up in your blood vessels... it builds up over time in the nooks and crannies of the system... and sometimes a chunk may break off and terminally clog the system up...
but even if nothing terminal happens, you can sluggishly get by with it for awhile, yet not really notice its bad effects until its almost too late.
and if you keep on without getting it serviced, its only a matter of time before you will have premature failure...
you can have it cleaned out and go again for awhile, feeling fresh and better, and if you keep living with the same habits its gonna catch up with you again soon.
but if you have it cleaned out and change your habits and only put in stuff that is good and clean for the system, the chances of it running strong and healthy for a long time will be increased many times over..
the only difference between the 6HP and 8HP is the carb from what I understand. I don't see how a 5 HP with a small 2 blade prop is going to push My boat at the same speed and use less fuel than My 6HP with a 10" three blade prop? The Johnson also has a small 2 blade, which may be why it has little evidence of being used.
