Thread: Oil injection or pre-mix?
09-29-2009, 08:23 PM #1
- Join Date
- Sep 2009
Oil injection or pre-mix?
I just got my 1993 SL 750 ski running. I bought the ski with the motor disassembled and now have it running with alot of help from everyone in the forum. I just wanted to say thanks to all who answered the questions I have posted. With that said I'll get to my next question. Being an old school kind of guy I don't really trust oil injection. Should I remove the pump and cap the line's and run pre-mix or keep it as is? Does anyone have any experience with Oil pump failure or are they reliable. Thanks again
09-29-2009, 08:27 PM #2
Very reliable. Lines are the weak link. Replace w/ high quality blue tygon fuel line.
09-29-2009, 09:00 PM #3
premix VS injection
I walked away from buying an Ultra which was converted to premix instead of the injection. It has 30 hours on it and they did this because the injection failed. I find it hard to believe. Maybe they forgot to fill up the oil tank?! My worry is mostly with low rpm running and fouling plugs.....imagine having to deal with that off shore!
09-29-2009, 09:44 PM #4
09-29-2009, 10:27 PM #5
- Join Date
- Oct 2006
- Cleveland OH
I personally prefer premix.
I've NEVER oil fouled spark plugs in 4 years, and replace them yearly.
How do you know when your oil pump has failed you??????
When the engine seizes........
09-29-2009, 10:41 PM #6
09-30-2009, 11:01 AM #7
09-30-2009, 11:40 AM #8
09-30-2009, 11:44 AM #9
- Join Date
- Jul 2007
- near Toronto, Canada
Not that I have a choice, on my Ficht engines
I also like the idea of using 1/2 the oil consumption for the same amount of riding, minimal exhaust smoke, re-fueling with straight gasoline anywhere, and not needing to carry any extra oil in containers in either the car or the ski.
I fill both ski's oil tanks before leaving home, and don't have to think much more about it for the next four-five tank refills of fuel. And my fuel tanks hold 17 gallons. That allows for a lot of riding between oil tank refills.
On a carb'ed version of the same engine, which I would expect uses more fuel to go the same distance, the oil tank capacity should last through even more re-fuelings.
Keep in mind that the oil pump output rate is only affected by engine RPM and throttle position. It doesn't know about the actual fuel flow through the engine. Oil flow into the engine is consistent, regardless of carb tuning.
Looking at it the other way around, leaner fuel delivery increases the effective oil-fuel ratio, while richer fuel deliver reduces the oil-fuel ratio (when using the oil pump system).
I suspect that as long as the crank case bearings and cylinder walls are getting enough oil to stay lubricated, the actual oil to fuel ratio inside the engine doesn't matter much.
In the past I suggested to someone else with a carb'ed who seemed really worried about the oil pump system, that they leave it functioning, and use an oil rated for 100:1 dilution in the fuel tank. In the event of an actual oil injection system failure, the pre-mix oil in the tank would still provide lubrication to the engine.
If the rider refueled with straight gasoline (on purpose or accidentally), nothing would be damaged, since the stock oil injection system is still in place (and probably working just fine).
For the pre-mix die-hards, something I have not seen (maybe I just missed it) is using the stock oil tank to hold pre-mix oil, and adapt a fuel primer pump system to transfer the oil into the fuel tank when refueling.
The volume of oil pumped per primer stroke could be measured, and a simple ratio of how many strokes per fuel gallon could be printed on the ski. No need to carry a separate oil container, or a measuring cup.
Estimate how many gallons will be needed, pump oil for roughly that amount. Fill the tank, look at the total volume of fuel purchased, and add enough 'oil strokes' to bring the total to the right number.
09-30-2009, 12:25 PM #10
- Join Date
- Aug 2006
- Pittsfield, MA
so mechanical error with injection or human error with pre-mix, either way there is no guarantee. The injection is the most reliable just keep the tank full. You can replace the oil pump gear just make sure it is shimmed correctly. If you pre-mix make sure you are the only one putting gas in every time as your friends and relatives may not do it correctly or mix to the same ratio you use. Injection is nice when traveling and filling up on a river or elsewhere. pre-mixing you better carry oil and a ratio rite with you so there are no accidents.
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