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Old 31-10-2018, 16:03   #61
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Re: Two stroke or four stroke

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Everyone keeps going back to weight, which is a real issue.
However that depends on size, the 20 HP Zuki is “Only” 99 lbs.
Find me a 20 HP two smoke that weighs in at 99 lbs?
BTW, that is 5 lbs per HP.
Someone check my numbers, but I believe the venerable 15 HP Yamaha Enduro is 5.87 lbs per HP?

Four strokes are getting as light or lighter than two stokes, Honda manufactures a line of tiny motors for lawn and garden that are just as light as two strokes, I powered a Dahon bicycle with one, and its way quieter, smoother, better idling than a two stroke.
I see the Suzuki 15 (and 20) HP EFI engines at 97 pounds. The Yamaha Enduro 15 clocks in at 91 lbs. Both short shaft. Since they're both in the needs-a-hoist category I agree - the difference is meaningless. I'll see if I can find an article I saw a couple years ago on the Suzuki EFI engines, but from memory, side by side the Suzukis in the 15-20 HP range consumed less than half (around 45%) of the fuel of an Enduro. The EFI engines have also developed a great durability reputation.
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Old 31-10-2018, 16:32   #62
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Two stroke or four stroke

As far as can you send one swimming, well unfortunately I did, I was passed very close by a Center Console in Key West when running my dink wide open, about 30 kts, when I got passed it got into chine walking and spit me out.
Because I didn’t have the screws as tight as I should have, the engine came off and fell into the water when it was still running.
Only thing that saved the motor was the fuel hose, but it was still about 6 Ft under for probably 4 or 5 min until I could collect myself, recover my wallet that was floating by, climb aboard and very gently raise it by the fuel line.
I got it aboard and it took at least 30 min for me to row back. Did I mention that I don’t think anything is worse to row than a RIB?

Go to the big boat, hoisted the motor to its mount on the rail and pulled the plugs and drained the crankcase. Flushed everything I could with fresh water, including the cylinders, and started pulling the starter cord, over and over spraying I think WD-40 into the cylinders every now and again.
When it looked like there was no more water coming out of the cylinders, I washed the plugs off with alcohol as they wouldn’t fire wet, put them in and it cranked, but ran very poorly, missing badly, with the check engine light on.
Drained oil, refilled oil, ran it for a couple of minutes, drained oil, repeat until oil stayed clear.
Motor started running a little better, put in my spare plugs and it ran fine.

I thought sure I would still lose the wiring harness though as I have seen salt water creep into the end of a wire, and over time rot out the wire.
However it’s been over two years now and it continues to run fine, and I assume if I were going to lose the harness, I would have by now.

Thing that surprised me the most was the guy who passed me, who had to have seen what happened, didn’t return to help, nor did anyone else who was around, no one offered to tow me when I was rowing either.
This was in the KW mooring field.

In the Fl Panhandle, if you remove an engine cover, within 2 min, five people will come over and ask if you need help, S Fl is a different world.
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Old 31-10-2018, 16:41   #63
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Two stroke or four stroke

Look at this chart, it will explain where you get phenomenal fuel consumption. The fuel injected Suzuki’s go into lean burn at mid RPM’s. They don’t at low RPM as too lean will cause rough running at low speeds, and at full throttle or close to it, they like almost all engines go full Rich for max power and charge air cooling.

17 to 1 is very, very lean.
The fuel burn is nuts, I honestly get almost 20 hours of running off of a 2.5 Gl tank, at mixed speeds. I have an hour meter/ tach so I know the actual run time.Click image for larger version

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Old 31-10-2018, 16:50   #64
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Re: Two stroke or four stroke

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Sorry, this is simply not correct. Almost universally, 4 strokes have replaced 2 strokes in racing because the rules have forced the change. 4 strokes are not lighter and more powerful.



In GP motorcycle racing, the 500cc 2 strokes were replaced by 1000 cc four strokes.



250cc motocross bikes became 450cc four strokes. 125 two strokes became 250 four strokes. And the 4 strokes were still down on power at first. And MUCH heavier. 250's had a 98kg FIM minimum weight, which they easily met even with steel frames. At first the 4 strokes were oveweight even with alloy frames.



4 stroke outboards are cleaner, more fuel efficient yes. But for equivalent HP they're heavier.



The BIG four stroke fallacy has always been about torque, and low revs. The truth is, 2 strokes make more torque, and rev lower. They have much longer strokes for one thing, due to the need to pressurise the crank and transfer fuel/ air. They also fire every cylinder every revolution.


I know, I was around. Actually the 500cc 2T was replaced by 750 cc fours or 1000 CC twins, there were also breaks for single overhead cam, and pushrod motors depending on what racing sanction of course.

However now the four strokes are lighter and more powerful than the two strokes ever were.

Likely about as powerful as the two strokes ever got was Yamaha’s extreme TZ-750 wouldn’t you say? Few people except Kenny Roberts could even ride the thing.
At its best it made 120 HP, a number that has been way surpassed by even production liter motorcycles today.
https://en.m.wikipedia.org/wiki/Yamaha_TZ750
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Old 31-10-2018, 16:53   #65
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Two stroke or four stroke

The Kawasaki Ninja H2R, named after the famous two stroke H2’s of our youth, is an over 300 HP motorcycle, and YOU can buy one.
https://en.m.wikipedia.org/wiki/Kawasaki_Ninja_H2

There has never been even close to a 300 HP two stroke motorcycle I don’t think.
The fastest two strokes I have ever seen were H2’s running on Nitrous and built by a guy named Paul Gast, who owned a bike shop cells “Fast by Gast”
We ran against him in the world finals in Gulfport Missippi about 1980 with our turbo Kawasaki 900. We beat him, but it wasn’t a whooping, he was fast.
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Old 31-10-2018, 19:44   #66
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Re: Two stroke or four stroke

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I know, I was around. Actually the 500cc 2T was replaced by 750 cc fours or 1000 CC twins, there were also breaks for single overhead cam, and pushrod motors depending on what racing sanction of course.

However now the four strokes are lighter and more powerful than the two strokes ever were.

Likely about as powerful as the two strokes ever got was Yamaha’s extreme TZ-750 wouldn’t you say? Few people except Kenny Roberts could even ride the thing.
At its best it made 120 HP, a number that has been way surpassed by even production liter motorcycles today.
https://en.m.wikipedia.org/wiki/Yamaha_TZ750
Yes, there are 1000 cc four stroke engines around today that are more powerful than near 50 year old 750cc two strokes. Still doubtful if the engine (not the bike) is would be lighter though...

There's been just a bit of engine development in the intervening decades wouldn't you say?

Two stroke development basically stopped years ago, apart from Evinrude E-Tec, nobody has spent a dollar on improving 2 strokes. Why would they, when it's always been a matter of time till they were banned.

But even so, even with modern fuel injected four strokes, I think you'd still struggle to find any four stroke outboard in the 2 -15 hp range that isnt heavier than most 2 strokes. And the fact is, most current 2 stroke outboards are pretty ancient designs.
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Old 01-11-2018, 00:03   #67
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Re: Two stroke or four stroke

4 strokes can have their problems but they do avoid the issue if you are just puttering about an anchorage.

I recall being taught with 2 stroke engines, you need to run them wide open for a few minutes every hour or two or the plugs foul out. The high HP (40+) where they have oil injection and such are better but it was always a pain.
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Old 01-11-2018, 05:36   #68
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Re: Two stroke or four stroke

https://www.evinrude.com/en-US/evinrude-difference.html

Just wish they would make the G2 in a 8-10hp (:
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Old 01-11-2018, 07:07   #69
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Re: Two stroke or four stroke

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Yes, there are 1000 cc four stroke engines around today that are more powerful than near 50 year old 750cc two strokes. Still doubtful if the engine (not the bike) is would be lighter though...

There's been just a bit of engine development in the intervening decades wouldn't you say?

Two stroke development basically stopped years ago, apart from Evinrude E-Tec, nobody has spent a dollar on improving 2 strokes. Why would they, when it's always been a matter of time till they were banned.

But even so, even with modern fuel injected four strokes, I think you'd still struggle to find any four stroke outboard in the 2 -15 hp range that isnt heavier than most 2 strokes. And the fact is, most current 2 stroke outboards are pretty ancient designs.


Agreed, two strokes are a lot like aircraft piston engines, any development there ceased decades ago.

But that is irrelevant, what is relevant is that there is a lot of development work in four strokes, and that today’s four strokes are vastly different than ones of just a few years ago. Four strokes are the future, two smokes aren’t.

The TZ-750 made 120 HP at the peak of its development, the H2R at 998 cc makes over 300. 25% displacement increase, about %300 power increase. Mass produced street bike that meets all emissions standards and of course meets reliability requirements, makes “Only” 200 HP.

Today, due I’m sure to the small number of them, two strokes are ignored by legal bodies, a lot like leaded fuel for aircraft was, however just like the leaded aircraft fuel, you have groups that are suing, mostly in California to end production and use of leaded fuel.
It may be tomorrow or not that the “Friends of the Earth” wake up and decided that all those nasty little motors are next. It’s not beyond the realm of possibility that any two stroke made after they were banned may not be used, or maybe an out right ban, at least in US waters.

It is actually against Federal law to bring your Yamaha 15 Enduro you bought in the island back to the US.
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Old 01-11-2018, 08:49   #70
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Re: Two stroke or four stroke

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. . . Two stroke development basically stopped years ago, apart from Evinrude E-Tec, nobody has spent a dollar on improving 2 strokes. Why would they, when it's always been a matter of time till they were banned.. . .

Well, Bombardier is a very serious engineering company with huge resources. They own Evinrude, and they own Rotax. Their Rotax engines are the dominate power source for snowmobiles, which are rather like airplanes in that every gram of weight counts.


I believe that development continues at least there. These engines are crazy:


https://www.rotax.com/en/products/ro...850-e-tec.html


165 hp out of 42.2kg -- that's 0.56 pounds per hp!


I own the 120hp , 600cc version of this:


https://www.rotax.com/en/products/ro...600-e-tec.html


What is crazy is that despite 200hp/liter specific power, these engines are torquey, smooth, and as docile as lambs, nothing like high performance four-stroke motorcycle engines.



It looks like some car manufacturers are still working on two strokes:


https://www.roadandtrack.com/new-car...-turbo-diesel/


Some bedtime reading on the subject:


https://www.intechopen.com/books/adv...nition-engines
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Old 03-11-2018, 16:20   #71
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Re: Two stroke or four stroke

2.6m=Torqueedo! No regrets here.
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Old 03-11-2018, 17:32   #72
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Re: Two stroke or four stroke

In all of these helpful comments, it appears that no one mentioned the issues with carbs on the four strokes. In much of my reading on smaller sailboat forums, many in the range of 7.5 to 9.9 hp 4 strokes have had recurring issues with starting due to small jets. Might be something for you do so some more research on. Start with a Google on Honda carbs. Good luck, either way you choose.
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Old 04-11-2018, 10:46   #73
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Re: Two stroke or four stroke

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The TZ-750 made 120 HP at the peak of its development, the H2R at 998 cc makes over 300. 25% displacement increase, about %300 power increase. Mass produced street bike that meets all emissions standards and of course meets reliability requirements, makes “Only” 200 HP.
So there you are.

Meanwhile back on the tender, a two stroke will be about 2/3rds of the weight whilst using 5/3rds of the fuel of a four stroke. It will also start easier if it hasn't been run for a while and run all day. You won't have to worry so much about gum or fuel stabiliser because it doesn't use a micro jet in the carb so clogging is not so much of a problem.

2 Strokes are smelly, smokey and inefficient. They are light and reliable.

For tenders used infrequently they are ideal. Other uses not so much.
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Old 04-11-2018, 11:01   #74
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Re: Two stroke or four stroke

I've got two words for you...the only two word you need when making a decision on an outboard....FUEL INJECTION

Carburetors are the Devil!
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Old 04-11-2018, 11:48   #75
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Re: Two stroke or four stroke

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I've got two words for you...the only two word you need when making a decision on an outboard....FUEL INJECTION

Carburetors are the Devil!
What the smallest fuel injected outboard? 9.9 is smallest I've seen. If the OP wants something smaller he's stuck with carbs.

I am a big EFI fan myself. Carbs are cheap and just about work so unfortunately haven't trickled down the range.
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