I just recently got a Saito fa72 4 stroke for a Sig 4star 60 I'm building. My concern is the type of fuel it requires. I have a gallon of Wildcat 10% that shows 18% synthetic. Should I add castor or can I run with this? All my other engines are 2 stroke os and evolution. Never had a problem with those that wasn't other issues. I just don't want to make a mistake with this engine.

I run my OsFs91 on 18% synthetic oil. Should have the fuel % in the manual if you have one.

It will run fine. 4 strokes can handle fuel with less oil in them, but they don't require it. One thing that could become an issue is that congealing castor can make your valves stick or not seal properly if the engine sits for a long time. Synthetic castor won't congeal like that, so many 4 stroke owners use a full synthetic fuel instead of a blend.

Over the years I have run 4 different fuels through Saito 72's. Three of those had castor in them. Nitro was anywhere from 15% to 30%. While the tune was effected by the higher nitro I pretty much ran what was in the jug with no issues. I never had any valve issues with the castor blended fuels, but it will tirn the mufflers and headers dark brown. BTW the APC 13x6 is a the benchmark prop for these.

david

As the fellows have already indicated your existing fuel is perfectly fine. In years past especially when the four strokes engines became more commonly used the so called four stroke fuels became popular. There really was very little difference other than the total oil content was less, considerably less. Not all but many of the four stroke fuels had a total oil content as little as 14%. This at a time when most fuel blenders considered oil content and sometimes nitro content proprietary information and would not divulge this information to the customers.

Now it seems the first generation of widely marketed four strokes which were quite frankly not very powerful, These early engines did OK with the low oil content but that left a rather narrow margin for tuning error, plus the fact that needling a four stroke is not so obvious as it is with a two stroke, made these fuels not a very happy situation.

Later on when folks started pushing for disclosure of there fuels nitro and oil blends major industry wide wars started in the modeling press that lasted for some years but finally the consumer (that's us) won out and today most blenders do disclose nitro content, total oil content, oil type and sometime even the ratio of oil types if a blend.

One last thought on the newer generation of four strokes most do tolerate a much higher nitro content and some even recommend higher nitro as well as a higher oil content as high as 20% total oil and nitro. Hence the expression you will here 20/20 fuel for four stokes.

So yup your existing fuel is just fine in you little Saito

John

Many thanks on the replies. Will use what I have.

Generally speaking, the only engines that require castor oil are the plain bearing engines (bronze bushings instead of ball bearings supporting the crankshaft) like the O.S. Max La-series, the K&B Sportster engines, or the Thunder Tiger GP-series engines.

Castor oil's thick viscosity helps float the crank shaft inside the case and helps seals any minor gaps or spaces. Castor oil offers ideal lubrication and protection for almost all kinds of glow engines (YS engines being the exception), but most pilots prefer synthetic oils in their glow fuel because the exhaust residue is lighter and easier to clean up.

I run 10% nitro fuel with 80/20 synthetic/castor lubrication through my Saito 4-strokes just like I do with the rest of my glow engines. It's still running like a champ after half a decade of regular flying with castor oil in the fuel mix.

Thanks Big. I do have a old 46 blu osmaxla engine that is still going strong.

You have an OS LA series that runs "strong"?? Never seen one of those :-)

Sorry could not resist.

It all depends on what it's on. If you put a .46 LA onto a plane that was designed for a hot .35 or so, they weight will be about the same and the plane will have plenty of power. But if you put it on a plane designed for a bearing type .46, it will be a bit puny.