Not throwin' any jabs here, or intending to upset anyone. Feel free to sound off, because I don't have all the facts at hand that I would prefer. I have been perplexed with this "pre-mix" issue in conjunction with oil injection, after reading posts on several snowmobile sites.
30 some years ago, I popped the carbs off of my Invader and my Sno Jet in the fall to clean them. I didn't have the intelligence to use any type of fuel stabilizer (back then) in the spring. The Invaders carbs, using straight gas, had the most disgusting build up of green "pond scum" in the float bowls. The Sno Jet used 40/1 pre-mix, and the float bowl was absolutely pristine.
Pretty much ever since, I have added about 3 oz. of oil to 5 gal. of gas (3.2 oz. is a 200/1 ratio) to all of my injected sleds, and continued to use the injection system.
I like the fact that this provides a tiny bit of lubrication to the throttle slides, and may help prevent corrosion in the float bowl when you inevitably get some water in the tank. I see Dandby7 is mixing at 100/1, Tory is going 70/1. I say pick your poison. I know, it defeats the "gas and go" convenience of injection, but I don't mind.
We could all agree that there is some "perfect" oil/fuel ratio that exists at a given moment in time. An Invader, cruising at 40 mph...maybe it's 70/1. There has to be enough oil, under varying loads, to adequately protect the motor.
I hear ya' when you say adding oil to the tank displaces some of the fuel. Lesse', if I have a regular Mikuni with a 300 main jet, and I pre-mix the tank at 50/1 (a 2 percent solution) I have effectively displaced 2 percent of the gas, or reduced the main jet "effectively" to a 294 jet. If I'm borderline lean, I just seized a piston.
BUT...2 stroke oil burns....it COMBUSTS in the combustion chamber, along with the gas. I don't know this, but I bet the oil burns at a lower flash point temperature than gas. So, your perfect EGT of 1100 degrees just dropped to 1090. HOW can the addition of a tiny, additional amount of oil to the mixture contribute to what we consider the classic "lean burn down"?
I will leave it up to you to discuss the miniscule change in the viscosity of the fluids and any effect on the flow thru the jets.
There is some "perfect" fuel/oil mix that exists...it depends on your goals. What may be the most sensible for emissions may not be best for engine longevity, or maximum HP. I think most of us would agree, a LIL' bit extra oil promotes engine life and probably frees up the motor a tiny bit. Frankly, we adjust the oil injection pumps and cables and we're probably lucky if we are within 10 percent of IDEAL. Gas mixture is a little more dicey. But, it's up to us to discover what mixture, jetting, etc. works best.
So, have at it. I'm all ears. I learn sumthin' every day. Trouble is I forget more these days.
Sorry, back to unfortunate 440RX and the piston failure. It sure sounds like you did everything correctly and competently to expect a motor that ran well, and then this happened. I wouldn't worry about an oil problem. The intake side of the piston would have been all scarred up from lack of oil. It sure looks like that PTO piston got hot. I see a guy responded to your post on "Vintagesleds" discussing a bent connecting rod causing him grief. Certainly possible. I rather think you need to re-visit why the PTO side probably ran lean...hey, we have all been there and done that, despite trying to be careful. Some tiny air leak on that side, or, tear into that carb again to make sure all is well....no speck of debris found its way into a jet, no float hanging up, etc. Hang in there!
Topic: Invader problems (Read 21716 times)