RE: 2stroke vs 4stroke
 

i dont have a 70 4 stroke.
yes you can run a 4 stroke on 5% nitro, i have done it, it works ok. however your top end takes a hit as well as your idle.
i run my .91 on 10% because i have plenty of 10% and dont want to go buy 15% and lug two jugs around. it works, the idle isnt as great compared to ys20/20 fuel. and i loose 500 rpm on the top end. however i dont care, i bought a bigger engine so i wouldnt have to worry about fuel.
however most people here, and at my field, run 15+ nitro in 4 strokes.

RE: 2stroke vs 4stroke
 

Okay thank you.

I know that my friend, who has this 70 Four Stroke, complains that the plane isn't very fast and I know the plane doesn't idle well. I think I'm going to recommend him to try out 15% fuel then. Perhaps this will solve the problem.

RE: 2stroke vs 4stroke
 

If the fuel is blended for 2 strokes, you may find the excess oil causes the motor to quit at low rpm due to plug fouling and the low nitro content will give you detonation (pre-ignition or pinking) at high rpm, so you'll wind up running rich to avoid that, making your low rpm problems worse.

RE: 2stroke vs 4stroke
 

They are popular at my club in the UK, but their chief proponent has his YS engines serviced regularly every winter because he claims they "go off" due to wear.
The only engine I've ever had serviced was the Laser 90 I bought from an estate sale in 1990 because obviously it had been abused. Maybe I just don't do enough flying.

RE: 2stroke vs 4stroke
 

uhhhhh no. you would have predetonation problems if you are useing higher nitro, not lower. 2 and 4 strokes can and do use the same fuel (and it wount foul your plug). 4 strokes need to be set a little richer than two strokes because they have more moving parts.
if the .70 is new the idle is set wayyyy rich from the factory. if he hasnt messed with it that would be his problem. my .91 would idle reliably on 5% just at a higher rpm than 10-20%

as for the slow plane. if he is useing a 13x6 tell him to try a 12x8
what plane is it on?

RE: 2stroke vs 4stroke
 

Fours produce more useable thrust from tourqe, two strokes produce torque at a higher rpm when you enter the power band curve, but unfortunately, the prop slip will eat thrust when that happens. The most efficent prop is going to be a slower turning high pitch prop over a high speed low pitch prop. As far as the four stroke debate, they all operate in the same principal, the only one's that deviates from this traditional setup is RCV and HP, Hp used a rotary valve for intake and exhaust, called the VT series, and RCV does the same thing, but spinning the cylinder to acomplish it. RCV made a early design that ran off the cylinder or as we americans call it the "camshaft" that runs the valve train, but since the port for intake was the cylinder rotating, there are no camshafts or valve's, just a spinning port. The latest design is the same, but they use the crank as a output like a conventional engine, and I have one in my skybolt, it runs like a top and is very reliable due to the plug being shielded from fuel and oil till it's ready to fire via the port timing of the spinning cylinder. The low profile design is a perk but the weight is a negative, alot heavier than an conventional 4 stroke engine. Adding excess oil to a fourstroke prolongs life, but kills plugs and causes loading-up issues, running too low a nitro will not produce enough heat to keep engine at running temps, nitro adds heat, keeps elements red/white hot and since there is a longer duration between combustion cycles, the more heat the better it will stay lit for the next cycle. Generally low nitro will cause idle issues and loss of rpm, extremely high nitro will cause predetonation and excess heat buildup that the engine can't and wasn't designed to get rid of. Most 4's will run fine on 10% and much better on 15% nitro, only power junkies really see the difference using 20 to 30 % nitro. For most field flying, 10-15% will suffice, another aspect that I'm not looking to start a fire on is oil, I've been running everything with a little castor oil in the fuel or at least 50% castor, I look at it this way, if I have to wipe it off the plane, then it's lubercating the engine, if it vanishes, it was burned off in combustion and provided little or no help to the engine.

RE: 2stroke vs 4stroke
 

I'm sorry, but you have got this completely the wrong way round.
Adding nitro is the glow fuel equivalent of using a higher octane number. Everyone who drives knows that if you use too low an octane number (RON) fuel in your car, it can "pink" or knock because of pre-ignition. Modern engines compensate for this with knock sensors that adjust the mixture and the ignition advance/retard. higher Octane numbers permit higher compression ratios without ignition due to compression heating (pre-ignition).
My own experience of this in my four strokes is that the only engine of the set I have (Enya 60-4C, Enya 40-4C, OS40 surpass, saito 45, saito 90TD, Laser 90) is that the only one that will run on straight fuel is the laser 90. Everything else needs at least 10% to give good behaviour throughout the range and even the Laser runs better on 10% because it runs leaner and therfore has less plug fouling. The "Laser" will knock on straight fuel if it is too lean.
The needle valve isn't used to set the lubrication in the engine, it's used to set the fuel/air ratio so that you get correct ignition. If you think your engines aren't being lubricated enough you should buy a fuel with more oil in it.

RE: 2stroke vs 4stroke
 

While correct on the auto fuel, very wrong on the effect of nitro in model engines. Operation with increased nitro requires lower compression on the engine, not higher compression.

RE: 2stroke vs 4stroke
 

Oh-man, we started the fuel debate again,.......just find a fuel that runs the engine well and fit's your preference and budget. I'll burn a gallon a day running about 8-9 flights on my skybolt or TF P-47, so cost per a gallon is important, on 40 sized planes, performance is more of a factor, so they get the better fuel because I can get twice the number of flights out of a gallon. All my fourstrokes have been treated normally, I forget to put afterrun oil in them every now and then, I try to mix the little bit of old fuel with the new gallon and when I run out of 15% I will run it on 10% for some of my other planes, I just realize that it's not going to run the same as the other fuel and tune it accordingly. I'm more interested in flying on the wing rather than the prop so that is where I stand on tweaking engines to get every last drop of power out of them. The wear of an engine can be offset by running a lower nitro, if compression decreases the lower nitro will make the engine run cooler, this will keep the interfearence fit between the piston and cylinder tighter, hence extending the usable life out of a worn engine, also adding castor will help seal the fit at top dead center. So with that bit of knowledge, if you normally run your engine on 15-20% nitro and decide to run on 10%, imeaditaly, plan on breaking it in again because the fit will be tighter due to the lack of thermal expansion.

RE: 2stroke vs 4stroke
 

Aint this pretty! :)

RE: 2stroke vs 4stroke
 

4stroker in a drag car!!!... yours???

RE: 2stroke vs 4stroke
 

awww i love my lil 2 strokes! super tigre G90 makes me smile! but 4 strokes are Very nice!!

RE: 2stroke vs 4stroke
 

Naw, I think its iin Austrailia. Somebody posted it on my site awhile back.

Notice the blower?