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Old 05-01-2019, 07:30 PM   #1
RSVenture
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Excessive exhaust residue


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Hi. I have a RCGF Twin 30cc and, in my opinion, it is spitting out an excessive amount of exhaust residue, as bad as my nitro's used to be.
I am using Stihl oil, mixed at 40:1, as recommended in the RCGF manual. However Stihl recommends a mix ratio of 50:1.
So, what do you think? Should I go to 50:1 as Stihl states on the bottle? Would less oil in the mix reduce the residue, and yet not cause harm to the engine? Engine is past any warranty.
I tried a couple tanks of 40:1 Redline oil with the same result. Excessive exhaust residue.
I also tried, but was not abe to run carb any leaner than now set.
Any suggestions/advice will be greatly appreciated.
Thanks,
Arnold
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Old 05-01-2019, 07:52 PM   #2
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Re: Excessive exhaust residue

what do you mean by excessive , some oils don't run very clean and leave a black residue , some oils run clean and leave a clear or cleaner residue . it's a good sign when you have some residue as it show you have enough lubrication. I run 40:1 and always see some oil on the belly of the plane .. you can reduce lubrication so it shows none but that will increase wear , some guys don't care about the increased wear as they feel they still get enough life from the engine even if it is shortened and they just want a clean plane . likely the difference between rebuilding after 3 or 4 years or 10 ..
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Old 05-01-2019, 08:31 PM   #3
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Re: Excessive exhaust residue

By Excessive Residue: flights of 5-7 minutes, black, oily residue drips from cowl, landing gear, and back to mid fuselage.
Flights of 10 minutes plus has residue dripping as above, plus, all the fuselage bottom, as wel as horizontal stab, elevator, bottom of rudder.
My other gasser have some residue which I expect but this seems, at least to me, like way to much!
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Old 05-01-2019, 08:34 PM   #4
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Re: Excessive exhaust residue

Quote:
Originally Posted by RAMJET View Post
what do you mean by excessive , some oils don't run very clean and leave a black residue , some oils run clean and leave a clear or cleaner residue . it's a good sign when you have some residue as it show you have enough lubrication. I run 40:1 and always see some oil on the belly of the plane .. you can reduce lubrication so it shows none but that will increase wear , some guys don't care about the increased wear as they feel they still get enough life from the engine even if it is shortened and they just want a clean plane . likely the difference between rebuilding after 3 or 4 years or 10 ..
For the most part I would agree.. I don't think Stihl oil is the all that great.. but I do look at the residue left on the plane , and I want to see it there.. and I want to see the colour of it.. this gives me one indication of how the engine is running and if there is enough lubrication..

At a 40:1 mix and you are getting residue like a nitro motor.. then I would have to say there is something wrong with your engine.. maybe a damaged ring allowing to much blow by..

Or you have your mixtures way out of wack..
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Old 05-01-2019, 09:58 PM   #5
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Re: Excessive exhaust residue

I don't fly any gas engines but my chainsaw which recommends 32:1 mix and my blower and weed wacker all use the Stihl 50:1 oil with no issues for the last ten years. I was worried about my chainsaw not getting enough oil but its been fine since I switched over. Why not try the Stihl 50:1 mix and see how the engine runs. Cheers Floyd
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Old 05-01-2019, 10:17 PM   #6
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Re: Excessive exhaust residue

Thanks for that info Floyd. I was leaning towards doing the 50:1 mix. Spitting out as much oil residue as it is, should be fine with a little less.
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Old 05-02-2019, 01:09 AM   #7
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Re: Excessive exhaust residue

Unless I am missing something, when Stihl recommends a specific mix ; I would presume they are referring to Stihl equipment . I would stick with what each motor manufacturer recommends. As for weed wackers or any other non-aircraft use motors operate under differing loads or operating conditions and have to dissipate differing amounts of heat. Sure they are all gasoline powered engines but that’s where it ends.
Jeff brought out a good point : could be some blowback past the ring or if a reed type intake ; might not be making a good seal and could be blowback thru the carb.

Reminds me , many years ago when Byron sold their fuel they had instructions in each case of fuel advising users to adjust their carbs a little different than other fuel manufactures . Yet there was always a few that wouldn’t follow their instructions and wanted to do it their way and then bitched because they couldn’t get a good run. Similar comparison ; would you go with the motor manufacturers recommendations or the oil companies ? Always other brands out there to try .
Just some food for thought in my opinion. Sure, Some will pick apart my suggestions so go right ahead....

Last edited by stegl; 05-02-2019 at 01:30 AM.
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Old 05-02-2019, 04:53 AM   #8
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Re: Excessive exhaust residue

Quote:
Originally Posted by RSVenture View Post
By Excessive Residue: flights of 5-7 minutes, black, oily residue drips from cowl, landing gear, and back to mid fuselage.
Flights of 10 minutes plus has residue dripping as above, plus, all the fuselage bottom, as wel as horizontal stab, elevator, bottom of rudder.
My other gasser have some residue which I expect but this seems, at least to me, like way to much!
First be sure you are mixing your oil correctly , at 40:1 you should get some spitting down the belly and maybe a bit on the gear but I have never seen anything dripping . the comment about the catb spitting back is a real possibility ,also make sure the carb is not leaking ..you may need a velocity stack on the carb. Sounds like the oil is coming mostly from the intake if it's dripping from the cowl ,starving the engine for oil will do little to help if this is the problem . Another possibility is the engine baffling ,if the engine is not baffled correctly you will have to run the engine much more rich then should be necessary to control the heat of the engine .also if the engine is not broken in it need much more fuel to stay cool .. just a few thoughts
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Old 05-02-2019, 08:50 AM   #9
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Re: Excessive exhaust residue

A dark colour in the exhaust oil usually means excessive wear of the engine. In the ultra-light aircraft world many of the popular brand name oils were not recommended. I found the best was the Bombardier synthetic. It prolonged the life of several engines that were known to to have a short life.
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Old 05-02-2019, 09:00 AM   #10
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Re: Excessive exhaust residue

Quote:
Originally Posted by stegl View Post
Unless I am missing something, when Stihl recommends a specific mix ; I would presume they are referring to Stihl equipment . Just some food for thought in my opinion. Sure, Some will pick apart my suggestions so go right ahead....
When I sold Amsoil we had a 2-Stroke oil that could be ran as high as 100:1. It all depends on the quality of oil you use. The Stihl oil is a high quality oil with the fuel stabilizer already in the oil for all the alcohol in our fuel. My chainsaw is 20 years old, it starts perfect each time I use it and I've never had to touch the carb, even after changing my ratio to 50:1. Cheers Floyd
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