Running a Rotax Engine with Pre-Mix Gas: Why Do People Do It?

[Frank_Hassa]

I've been reading a lot of forums over the last few weeks, here and a few others, and threads in Ski-Doo forums too, and I read a lot of posts where the OP is for some reason mixing his oil in the gas instead of operating the SeaDoo the way it was intended to operate at the factory. I get a vibe off the high-end pros here that they are going to say that this is dumb and that you should never pre-mix, given how focused people here are for OEM parts (and not crappy aftermarket), I assume the main belief here is that these machines should be run the way they were intended to be built at the factory.

I say all that so that someone doesn't think I actually WANT to run pre-mixed gas. I don't. Wouldn't want to. Not going to do it, etc...

But I'd like to know why all these other people are doing it. Does something expensive break and premixing the gas is a workaround? Do they think they are getting some other benefit? I just don't understand why a person would do that. What's the reason.

Also, because I just pulled my oil tank out last night and cleaned it, I have a question about the oil sensor. It's a
"T" shaped thing and the float at the bottom doesn't move up and down, so how does it know where the oil level is, and what's the other side of the "T" for? One side has the oil line going to the engine, and the other side has a short piece of grey tempo line and then a narrow nipple-looking thing. Is that a one-way valve for atmospheric pressure on top of the oil? If not, what's it for?

And finally, the oil line splits at the end of the oil line. One side goes into the engine and the other end goes somewhere else. Where does it go, and why? Is there some kind of "schematic" showing the oil lines for my 1997 GSX? And should I replace these lines. They're dirty and dark grey, but flexible and seem like they're in serviceable condition. It's just one more part on a long list of parts, and I'd rather not drop more money on this thing if it's not necessary.

 

[soccerdad]

Typically Seadoo oil pumps and the injection system work very well. So for recreational riders, it is a sound and safe way to go. But there are other brands out there that have a system is not a strong. So many Seadoo systems have been converted "to be safe". High end race motors often premix as they have different requirements.

The bottom line is that for a rec motor, you are usually safe with the oil injection. But if the system stops working.... that is why some premix. YMMV

 

[suke]

I premix cause it's cheaper than replacing a motor should an oil line come off. It's cheap insurance on an old motor and a little extra lubrication ain't a bad thing for a 20 yr old motor. Now would the oil injection pump fail or lines never come off? Possibly, but it's something I'll never have to worry about.

 

[Sportster-2001-951C-Stock]

In "defense" of pre-mix, I've never seen a motor damaged by having a "little too much" oil, my antiques (produced before needle bearings were introduced, thus these are Babbitt shell type bearings) run 16:1 non-detergent motor oil and no problem with fouling plugs. Zika eliminators, they are.

Books and entire careers, fortunes made and lost concerning the rest of your 2-stroke questions, just keep your pistons from becoming molten and be prepared to replace them when/before they do.

 

[jknightg]

For a schematic, try here
http://epc.brp.com/Index.aspx?lang=E&s1=49214e28-332d-4622-a098-f0ce3a4223a1

 

[Spimothy Leary]

In "defense" of pre-mix, I've never seen a motor damaged by having a "little too much" oil, my antiques (produced before needle bearings were introduced, thus these are Babbitt shell type bearings) run 16:1 non-detergent motor oil and no problem with fouling plugs. Zika eliminators, they are.

Books and entire careers, fortunes made and lost concerning the rest of your 2-stroke questions, just keep your pistons from becoming molten and be prepared to replace them when/before they do.

lmao.

we used to joke about that from time to time when a group of us 2 smokers headed out and someone would say, "you go fog the left side i'll fog the right"

my yamaha 1300r was the worst, yamalube @ 35-1 with triple cyl's. actually made my old xp appear to hardly smoke at all lol.

I premixed every 2 stroke I owned and never gave it much thought. I burned more oil, and it was inconvenient, but I was ok with that.

 

[TLH101]

When you pre-mix, you lean the fuel mixture. Only so much fluid will flow thru a given orifice. If some of it is oil, then that means less fuel.

 

[Sportster-2001-951C-Stock]

When you pre-mix, you lean the fuel mixture. Only so much fluid will flow thru a given orifice. If some of it is oil, then that means less fuel.

Theoretically correct, it depends on how generous your tune is to begin with, of course. So we can probably compensate for this by using the mixture adjusters and hopefully we're not awfully lean to begin with, right? That would be a tragedy.

http://www.bridgestonemotorcycle.com/documents/oilpremix6.pdf

 

[gerallison]

Ok, I had 2 blown 951 2002 rotax engines. Do not want another one. I always used Seadoo recommended oil, I personally rebuilt my last engine, I wounder if I can use both, the direct injection and extra premix? Any suggestions on the ratio? I am now breaking-in new engine with 100% synthetic oil, after reading a lot of information in how to break in the engine I had a 40:1 premix and oil in the direct injection, yes I had some extra smoke but the engine always started, park plugs and decent clean! So after finalizing the full tank break in procedure, any recommendations? I've been thinking on canceling the direct injection system and moving to premix, not sure what to do. Just don't want to spend over 500 dlls again!

 

[mikidymac]

Ok, I had 2 blown 951 2002 rotax engines. Do not want another one. I always used Seadoo recommended oil, I personally rebuilt my last engine, I wounder if I can use both, the direct injection and extra premix? Any suggestions on the ratio? I am now breaking-in new engine with 100% synthetic oil, after reading a lot of information in how to break in the engine I had a 40:1 premix and oil in the direct injection, yes I had some extra smoke but the engine always started, park plugs and decent clean! So after finalizing the full tank break in procedure, any recommendations? I've been thinking on canceling the direct injection system and moving to premix, not sure what to do. Just don't want to spend over 500 dlls again!

Never premix in a fuel injection ski. It is very bad for the injectors.

 

[gerallison]

Mine is not a DI, is a carburated one!

 

[mikidymac]

Mine is not a DI, is a carburated one!

Ok, you were referring to the oil injection, I thought you had fuel injection.

 

[gerallison]

Yes, I was! Sorry for the confusion, I forgot there is a rotax engine with Fuel DI, I am referring to the oil injection with has failed me in the past!

 

[mikidymac]

Are you sure the oil injection failed or did the carbs just go lean?
With new 3/32" injection lines there is almost nothing that fails on the factory seadoo oil injection. There have only been a handful of pumps actually go bad here with hundreds or even more without a single pump issue.
99% of the time a engine fails here it is due to the fuel system not the oil injection.

 

[gerallison]

Not sure what it failed, mechanic said one line was disconnected, maybe when I was getting power washed, how knows, I just want an extra layer of protection, I guess if oil is premix there shouldn't be a problem ever, I used to race 2 stroke bikes before the 450's came out and always premix, never had a problem.

 

[mikidymac]

Premix is a safe bet but you will use way more oil and it is not as convenient as just adding plain gas to the tank.

 

[gerallison]

So, anyone has a suggestion? I need help with ratio to use premix and oil injection system together!!

 

[gerallison]

I premix cause it's cheaper than replacing a motor should an oil line come off. It's cheap insurance on an old motor and a little extra lubrication ain't a bad thing for a 20 yr old motor. Now would the oil injection pump fail or lines never come off? Possibly, but it's something I'll never have to worry about.

I need help with ratio to use premix and oil injection system together!!

 

[suke]

I need help with ratio to use premix and oil injection system together!!

I would say either or. I wouldn't do both.

 

[Seadoosam]

I wouldn't do both personally. Too much oil makes it run to rich. Also you will go through spark plugs like mad. I like premixing mainly because it is insurance if your oil pump dies. And I am on a big lake so it would be a big headache. I mainly do it because the person I bought it from had already converted it though!

 

[gerallison]

I am using it in a lake too, Chapala Lake, what ratio do you use?

 

[Seadoosam]

Usually around 50:1 but it sometimes varies. No less than 40:1 though!

 

[Sportster-2001-951C-Stock]

What happens if it's more than 40:1 ?

 

[Seadoosam]

Well since I usually do 50:1, nothing bad has happened.

 

[Sportster-2001-951C-Stock]

Do your plugs ever foul? Not much smoke at low speed? There are a lot of people who run 50:1 with positive report.

Personally, I think it's a little light for WOT blasts but I haven't tried it myself, still using injection.

As far as running both injection and pre-mix 50:1 would save your engine if injection failed, not sure if plug fouling would be a problem.

The BR8ES seems to run pretty cool in my 951 and will foul in a season, so I'm testing BR7ES this year. I don't have any results to report yet but so far no problems.