Can I use the same fuel for my OS .46 vr-m and my OS .40 fs-m? I currently use Wildcat 15% nitro with 18% oil with the two stroke engines and haven't started the four stroke up yet. I am hoping to use the same fuel for the 4st.

Sure, why not? Ive had great luck w/ 2 stroke fuel in 4 strokes, and better fuel economy w/a loy of low end tork.

Just remember to break it in really really ritch,and dont try to lean it out like a 2 stroke.

Just my 2 cents worth, but Im sure if Im wrong some will tell us both.

good luck and have fun.

what is the difference between the two fuels?
I just got the 4 st engine this week and only ran two cycles in the past. I got a good deal on a vintage new in box marine 4 st and couldn't pass it up. Plus a fellow boating buddy said he always wanted one and it will be fun showing it off to him. He dosen't beleve in E-bay!

Fuel difference? When 4-strokes first became popular, 4-stroke fuel had less oil because they turn fewer rev's and the lower oil content helped prevent the engine from loading up at low throttle settings. Now the trend is the opposite. 4-stroke fuel "generally" has more oil because they rely on blow by from the piston to lube the bottom end and cam(s).

In the 18 years I've been in this hobby, I've never heard of a 4-stroke failing due to lack of lubrication, with the exception of the newer YS's. Most have bearing failure because people do not squirt a little after run oil into the crank case when they are finished for the day.

I personally run Magnum 2-stroke #1 in everything I own from an OS .25 VF to a pair of OS BGX 35cc's with several different 4-strokes in the middle including a YS .91 AC. All run equally excellent. I don't know what the oil content is and don't care. Oil content is not as important as oil quality. You can have 50% oil and still ruin an engine because the oil is pure garbage. Or, you can run 10% and never have a problem if the oil is absolute premium quality for the task at hand. Of course that premium oil must be present in the right quantity, but you get the idea.

Thank you Don Nix for that lesson in fuels several years ago.

YMMV,
John

Thats what I wanted to hear. I diden't like the idea of having to buy special fuel for just one of my six boats. Now just one more question. Can I use the breather vent on the back of the engine to pressurize the fuel tank? Thanks for the help!

You can buy pur csator oil from wal mart in 4 oz bottles for about 2 bucks each. I usually add 8ozs of casor oil to every gallon of fuel. Sure its a little messier but i dont mind cleaning up the mess. The larger the engine the more oil it needs to run better. Ive got an os wankel and i boost the oil content in the fuel i run in it to 25% it helps keep it cool and it runs better.

I am now using the same fuel in both 2 and 4 strokes, I have an older VRM .46 boat and 40FX,91Surpass, and Saito100, I now use cool power pro pattern 20. it is 20%nitro/20% oil. nice not having a slew 'o' fuels.

Hydroguy,
No, you cannot use the crank vent to pressurize the tank. It is after all, a vent, not a pressure tap. The vent is needed to vent off excess oil from the crank. If you use it to pressurized the tank, you will accumulate too much oil in the crank and performance will suffer drastically.

Also, the idea of needing more oil for larger engines is not true. If it were, then why to the big Supertigers like LESS oil? With a larger engine comes higher fuel consumption. With higher fuel consumption comes more oil.

John

Thanks... I will just have to run the tap off from the exaust. So what type of fuel do you recomend to use in both engines?

I personally run Magnum #1 2-stroke in all of my engines. Big, small, 2-stroke of 4. Doesn't matter.

I'm not familiar with marine engine use so all I could recommend is try what you're running in your 2-stroke in the 4 and see how happy it is. If it runs fine, then go with it.

BTW, don't forget to inject some after run oil in the crank breather when you are done for the day. Don't want any water sitting in the bottom end.

John

Sounds good thanks!

Some 4stroke engines don't like 2stroke fuel with 20% oil. The "excessive" oil cools the glow plug too much. You can easily tell if this is the case when you remove the glow clip. If the RPM drops substantially and the engine does not idle and transition well, then you need to reduce the oil content (i.e. use a "4stroke" fuel). Otherwise, use the same 2stroke fuel on your 4strokes.

The only problem with this is most 4 stroke fuel actually claims MORE oil than 2 strokes. I don't know why this is done, or when the change took place, because it didn't used to be this way, it's just my observation looking at fuel lables lately.

John

I drilled a hole in my carb intake and put a nipple in it and ran my crank breather hose there. It does great. OS does that now.

Thats a good idea. I was just thinking where I was going to run the hose, since I cant put a hole in the bottom of the boat to vent it out. I thought I was going to have to add a small vented tank to it for it to drain to. I will check out OS's web site to see exactaly where they put it. Thanks

I've talked to Byron about this very subject. It seems that they sell their 10/18 sport fuel and a 10/18 four stroke fuel. I asked if there was any difference in the two. they said the only difference was the label on the container. Some people apparently feel more comfortable running "special 4 stroke fuel".
Well, they're the same...
So don't worry.

It's final then! I am going to find a good fuel with around 20% oil and use the same on both engines. Thanks for all the help guys!