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Old 29-03-2010, 16:52   #1
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Two-Stroke on Propane

I know there are kits to change a 4 stroke over to propane but a 2-stroke is oiled by the fuel... Anyone have any great ideas on how to set up a 2-stroke with an oil system to allow it to be run on propane..
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Old 29-03-2010, 17:09   #2
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Propane takes a special carb. Doubt if you can find any small sidedraft carbs for propaane. That would be the main issue. Why, other than propane does not go stale like gasoline?

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Old 29-03-2010, 18:31   #3
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G'DAy Randy,

Don't know about the carb issue, but lots of small o/b motors are offered with oil injection rather than relying on premix fuel/oil, so lubrication shouldn't be a problem.

Cheers,

Jim and Ann s/v Insatiable II lying Morning Cove, NSW, Oz
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Old 29-03-2010, 19:33   #4
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The carb issue is not a problem, I have access to one,.. its the oil for the bottom end that I'm worried about..
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Old 29-03-2010, 20:47   #5
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Sounds like a fun project. The first thought I had was"simple and small", possibly a small low pressure tank with a flexible line to a very small Jet positioned in the upper inside of the carburetor bell. Metering the proper rato of oil to intake charge would be the trickiest and most critical part. I like your thinking, please keep us posted.
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Old 30-03-2010, 09:19   #6
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You guys are going off track on this one..
as I said in the first place, and IS NOT an issue, the carb, many kits are avalable, and many small motors have been run on them for years including almost every forklift on the market..
The question was and still is,
How to OIL the bottom end on a two stroke without pre-mix?
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Old 30-03-2010, 10:09   #7
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The problem is a complicated one. if you know the fuel oil ratio, say 40:1 you know that this is per revolution of the crankshaft, without premixing the fuel (impossible with propane) you need to go to oil injection. a pump driven off the crank is your only option, this way as the engine rpm increases the oil added in increases as well. Unless your an engineer and a machinist, this is going to be tricky, as the engine increases its rpm, the carburator will introduce more fuel and air into the engine, the oil injection system must increase its capacity for flow to match the increase in amount of fuel to keep the 40:1 ratio. It's not a flat line of increase, as you can see, at idle the engine uses 40:1 fuel to oil, but the fuel oil to air is 15:1 changing the throttle setting introduces more air/fuel per revolution, the pump must adjust for this. By premixing, you eliminate the need to increase oil as rpm increase, because the appropriate ratio is already in the tank, no mater what the rpm.

sorry for the rambling...

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Old 30-03-2010, 10:18   #8
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Alright, thought about it a little, maybe this is clearer, as your throttle setting is increased, the fuel and air are increased, the oil is still pumping at a set ratio, per revolution of the engine. But the higher the throttle setting, the more fuel/oil is needed per revolution to produce the horse power required to sustain the RPM. unless the pump increases the volume of flow of oil as the rpm increases, the proper fuel/oil ratio is lost as soon as you come off idle, and heads straight for seizure.


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Old 30-03-2010, 10:34   #9
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Unless you have a motor with oil injection I can't see how this would be worthwhile. I believe most small outboards (under 25hp) do not have oil injection
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Old 30-03-2010, 10:36   #10
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Suzuki did produce small obs including a 9.9 and a 8hp 2stroke w oil injection
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Old 30-03-2010, 12:07   #11
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I still would be interested in the carbutation.
There are three components that all work together on the 2stroke boat engine, not two. The third is timing. Most motors change the timing radically as they increase throttle opening rather than rpm and that also must be a part of the equation. As to the injection, I donít see a big problem if you start with an injection type engine and modify to meet the parameters of the drier fuel. Also have to look at fuel (propane) and oil compatibility. I donít foresee any issue but there could be.

The best injection systems work on a combination of engine load (throttle opening) combined with engine speed (rpm). This injects more oil per revolution at high engine load and less at lower loads no matter what the engine speed. So over the entire rpm/engine load scenario the bearings and rings get enough oil and no more.

Was done with a metering pump off the crank with an auxiliary throttle cable on 2stroke dirt bikes.

Again, I ask the question of why? The two stroke is a very inefficient design with about 1/3 of the fuel going through unburned. That is the big pollution issue with the two stroke, not the burning of the oil. Would it somehow burn the propane more completely? It might. I donít know.

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Old 30-03-2010, 12:39   #12
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Quote:
Originally Posted by um saudade View Post

Again, I ask the question of why? The two stroke is a very inefficient design with about 1/3 of the fuel going through unburned. That is the big pollution issue with the two stroke, not the burning of the oil. Would it somehow burn the propane more completely? It might. I donít know.

Um Saudade
There are a couple different issues I'd like to get over.. One being its a third fuel to carry on board and our dink is used daily like a family car.. Our Propane is stored in One 20lb fiberglass bottle and transfered to 1 gal units for use.. A 1 gallon tank hangs off our rear pit for the use of the stove.. It would be more convent to have another 1 gal tank for use of the dink..
The second issue it the weight of the motor.. we have a small 2hp 2 stroke now and its very lite to be passing off and on the boat when used in the dink.
The use of regular gas and having to mix it befor use gets to be a pain and the thought of having a lite weight motor using the same fuel we use on the boat sounded like a good Idea..
The carb issue is not a problem as fork lift companies sell a conversion kit that bolts under the carb to change over to propane.. I could easily modify the plate to work on an outboard..
I had hopes of using the 2 stroke I have to convert but it looks like I'll have to fork out the bucks for a new 4 stroke if I want to set it up for propane use..
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Old 06-04-2010, 20:39   #13
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I thought about running a 2 stroke on hydrogen, but I have concluded that 2 stroke engines are crap compared to 4 stroke... noisy, less efficient, higher pollution, and only to save a little weight...

I think they ought to be outlawed, since 4 stroke are better, do yourself a favor (and everyone else) and get a 4 stroke.
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Old 06-04-2010, 21:03   #14
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It is not likely that you will get this to work.

2 stroke oil does not atomize well. It relies on the fuel to transport it through out the motor. If you injected it in the intake, it would mostly just drizzle down and puddle in the bottom of the crank case.

You are not likely to get the right quantity of oil to the right places to protect the motor without gasoline.

It is not just the "lower end" that requires lubrication, but everything from the reed valve seats to the rings, and lower end....

Also, the 'special carb' is often (usually) just the normal carb with a small line added before the intake in front of the butterfly.... that is what you find on most converted vehicles like fork lifts, cars, and other motors.
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Old 06-04-2010, 21:44   #15
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So how do I convert my Yamaha 9.9 4 stroke to propane then?
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