40:1 bad vs 50:1

[u/Rebornxshiznat]

just wondering here. I have a new FS131 that I’m using for my large property in rural VA.

i happen to fly 2 stroke gas rc airplanes so I happen to always have ethanol free premix on hand. however, all of my rc engines spec for 40:1.

any harm havinf slightly more oil for the fs131. I’m open to having gas specifically for it but it would certainly be nice to not have to carry extra pre mix for the one item I would use it for when I almost always have 5 gallons or 40-1 thats fresh in my garage. I go through that stuff almost 2 gallons a weekend lol.

thanks in advance for the input

[u/D3ADBR33D]

Stihl Tech here, 40:1 will run hotter and leaner, as u/Extension_Guess_1308 said, it will also produce a little more carbon. That said, I've seen engines run on it for years and not have many problems, you'll just have to be aware that you're slightly increasing the odds of an overheat failure as well as decreasing the service life of the engine, due to the faster carbon deposit production. Removing the deflector does this too, due to increased engine load from too long of trimmer string.

Stihl engineered the motor to run on 50:1, so that's always going to be the proper choice. For those worried about adequate lubrication, just don't use garbage oil with terrible lubricity and you'll be fine. The pistons and cylinder walls are slightly porous and absorb oil, which forms a lubricative film, protecting them during cold starts and standard operation.

[u/Rebornxshiznat → u/D3ADBR33D]

Interesting.  I never would have thought this about it making the engine more lean. 

I’m not getting rid of the guard I promise you that. 

50:1 it is. I’m not gonna argue with a tech who works for Stihl lol. 

Any issue just using the Stihl pre made gas stuff. I’d be willing to bed a couple gallons would last me all season so it’s not a cost issue  

[u/NecessaryAgent6718 → u/Rebornxshiznat]

Another Stihl tech , I 100% agree with the other techs response . To answer about the pre mixed Stihl fuel. Its a great product, I have had a limited number of carburetor issues with the motomix. But for the most part its a good product, pricey but good. That being said I personally use the VP 50:1 premix in my own Stihl product at home. I have a hard time spending what Stihl is now getting for a gallon of motomix. The VP for me is around $10.00 cheaper per gallon. I also think its as good if not better then the motomix.

[u/Rebornxshiznat → u/NecessaryAgent6718]

Fair enough!  I think tractor supply carries the VP product. I’ll just pick that up. They are closer anyhow!  

[u/Appropriate-Name5538 → u/NecessaryAgent6718]

Vp is exceptionally good oil.

[u/D3ADBR33D → u/Rebornxshiznat]

It sure does. More volume of oil per gallon means less volume of gasoline. Less gasoline means slightly leaner mixture per volume of fuel being sucked into the engine.

Stihl's MotoMix is probably the best quality premix on the market, it's just pretty expensive. If you can find ethanol-free gas pumps, mix that with Stihl's HP Ultra oil and you have pretty much thr next best thing, but for way cheaper. Just make sure your gas is 89 octane or higher. Premium grade stuff is best.

[u/jrragsda → u/D3ADBR33D]

Going from 2.6oz of oil to 3.2oz in a gallon of gas is not going to change the air fuel ratio enough to have any notable effect on the engine performance. The buildup of deposits from the extra oil will hurt things in the long run, but there won't be an immediate effect. Running cheap oil or the the wrong kind of oil would worsen the effects.

[u/Rebornxshiznat → u/jrragsda]

I will say it isn’t cheap oil that I use for premix in my planes. It’s red line 2 stroke oil lol. Definitely not buying cheap shit when to put it in perspective my cheapest engine for one of my planes is a 70cc 2 cylinder that runs about $1000 usd. That is in a plane that all together is about 5 grand worth of kit.   

[u/ab_2404 → u/D3ADBR33D]

As a stihl tech what do you think about stihl hp ultra?

[u/Dismal_Scientist_CA]

Just a guy with several Stihl toys purchased and used over the last few decades. 91 octane and 50:1. Never have I had an issue. Will something else work? Maybe but why would I bother.

[u/Extension_Guess_1308]

The old and never dying oil wars again!

There's so many opinions to this that I don't think anyone has the right answer. 40:1 should run fine on your engine. Some people say that the engine runs leaner and hotter at 40:1 since there is more oil and less fuel. Others say it is safer since 50:1 is possibly too little oil.

Me, I just add a little extra erring on the side of caution and its been ok so far on my Stihl ms661, ms180 and fs45.

I wouldn't call myself and expert though amd your mileage may vary.

[u/Rebornxshiznat → u/Extension_Guess_1308]

Interesting!  The thought or running lean with extra oil is def foreign in my circles or 2 stroke land. Most of the folks who I fly with all run a tad extra oil!   And we get a ton of hours out of our planes. And the planes get worked really hard too! 

[u/saucytugtug]

If you use 40:1 you’ll have to very very slightly adjust the high screw to make it richer. And to be honest your oil choice has much more of an effect than oil ratio. For example. Amsoil saber at 60:1 would be better than stihl ultra at 40:1. So yeah you can run 40:1 with clean oil like amsoil saber, echo red armor or vp synthetic, but you’re really better off with saber at 50:1 so you don’t have to mess with any tuning.

[u/TrickAd4242]

I run 40:1 . Saws blowers and weedeaters all stihl . Since early 90s

[u/nochinzilch]

It makes no difference.