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Engine basics => Engine set up tips => Topic started by: wwwarbird on June 01, 2010, 11:52:11 PM
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I've got three OS .35-S's that all seem to have the same run characteristic for me on any model I mount them on. They only want to run consistently if they are on a "Full Honk" two cycle. Although it would be nice I'm not expecting a perfect 2/4 out of them, but what combo will provide a consistent slightly wet two cycle run? What combos are working well for some of you? D>K
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I've got three OS .35-S's that all seem to have the same run characteristic for me on any model I mount them on. They only want to run consistently if they are on a "Full Honk" two cycle. Although it would be nice I'm not expecting a perfect 2/4 out of them, but what combo will provide a consistent slightly wet two cycle run? What combos are working well for some of you? D>K
This is a well-known problem from the good old days. We all used the *small* (of the two supplied) os-25S venturi. Unfortunately I can't recall the dimensions. Now, I would get a series of them about .005" apart, and select from those by experiment. Actually, I am sure that someone has one that they can measure, or they just know it off the tops of their heads.
Brett
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Brett, maybe I should just go electric? LL~ LL~ LL~ LL~ LL~
Seriously, thanks for the tip. That's what I was thinking, start shrinking the venturi.
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I've got three OS .35-S's that all seem to have the same run characteristic for me on any model I mount them on. They only want to run consistently if they are on a "Full Honk" two cycle. Although it would be nice I'm not expecting a perfect 2/4 out of them, but what combo will provide a consistent slightly wet two cycle run? What combos are working well for some of you? D>K
If you are using the Stock venturie it is about .305 diameter, Too Big try a 275 or so size,
Randy
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Yeah, the stock venturis are definitely too big I think. I've got Jim Lee's venturis on all of mine. I'm pretty sure they are .280's, I'll have to double check.
What props and fuel are some of you using? I'm using Sig 10% nitro with 20% all castor and have tried most every 10x4 thru 10x6 prop.
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Big Art told me some time back that the best venturi size for the OS Max S was .280. And I'm not gonna second guess Big Art !!
So I sell a .280 venturi for the Max S.... The stock one is about .305....
thanks
Jim
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Yeah, the stock venturis are definitely too big I think. I've got Jim Lee's venturis on all of mine. I'm pretty sure they are .280's, I'll have to double check.
What props and fuel are some of you using? I'm using Sig 10% nitro with 20% all castor and have tried most every 10x4 thru 10x6 prop.
I always used 25% oil content in mine, 20% was never enough for the motor to cool and heat quickly. My OS 30 and 35 used half castor half synth. Still have about 6 of them from the 70s, still in great shape.
The venturies on motors will "act" larger or smaller depending on how open or restrictive the muffler is, That is why many could use the stock 305 with the stock muffler that had the tiny exhaust hole in it
Randy
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Big Art told me some time back that the best venturi size for the OS Max S was .280. And I'm not gonna second guess Big Art !!
So I sell a .280 venturi for the Max S.... The stock one is about .305....
thanks
Jim
Spot on Jim with a 0.155" dia needle body like a ST or one of randy's excellent products. If you are running the Max valve ~0.135" od body look for one of the .265 or smaller (they came in MANY different) If you've got a 0.272" the Max valve sometimes will work on muffler pressure. I say sometimes based on how worn the Max valve is. It will leak and break your heart. Get the ST or prefferably the Randy valve. and a 0.280 and you will be in a good place to start.
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Spot on Jim with a 0.155" dia needle body like a ST or one of randy's excellent products. If you are running the Max valve ~0.135" od body look for one of the .265 or smaller (they came in MANY different) If you've got a 0.272" the Max valve sometimes will work on muffler pressure. I say sometimes based on how worn the Max valve is. It will leak and break your heart. Get the ST or prefferably the Randy valve. and a 0.280 and you will be in a good place to start.
Hmm, will a 25LA venturi work? It's ~.257, which sounds about right with a stock spraybar.
Brett
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If you are using the Stock venturie it is about .305 diameter, Too Big try a 275 or so size,
Randy
The stock NVA size is approx. .157 diameter, the ..new.. OS 35 FP uses the 25 NVA and is much thinner , so be careful that you don.t ix the sizes up and use a .275 venturie with the New thinner spray bar. If you use a new thin one you will need a .250
Regards
Randy
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I double checked and my venturis are .280. I'm also using the standard O.S. NVA. On the plane I'm currently dealing with I'm using a Hobby Fasteners tongue muffler. Sounds like I need to go smaller on the venturi.
I'll be looking for ya at Sig Jim! ;D
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I double checked and my venturis are .280. I'm also using the standard O.S. NVA. On the plane I'm currently dealing with I'm using a Hobby Fasteners tongue muffler. Sounds like I need to go smaller on the venturi.
I'll be looking for ya at Sig Jim! ;D
If you are using the standard "Today" size (.134) spraybar that OS uses ,which is a 25 size you will need to go down to a .250 or so venturie, or the one that Brett mentioned that was for the OS 25 may work too, If you put in a .157 diameter spraybar , that came with the OS Max 35S , or equivilant,you can use the .280 sized ones
Regards
Randy
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Big Art's prop suggestions to me were 10 X 6 Wide or 10 X 6 Extra Wide Rev-ups. (FWIW)!
W.
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There's a Thunder Tiger Cyclone 10 x 5.5 (and a 10 x 6). Pete Ferguson's brother in NJ tried one and liked it. I got one of each for Pete when I sent in a "club order", and he shipped them to NJ. I'm glad to hear that the prop worked, because I have an OS .35S ABC project waiting on me. I got the Jim Lee venturi inserts. It's gonna go into a WU Excalibur that's also waiting... :'( Steve
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I don't have a caliper for an accurate measurement, but the NVA assembly I'm using is O.S. part number 22311000. It's what I use on all of my .25 and larger O.S. engines.
Does anyone ever bother with adding or taking away head gaskets on these? How many would have been standard in the .35-S?
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1 head gasket, Randy or ST needle valve, .280 venturi, Excaliber 25% castor, 3% synthetic, 10 or 15% nitro fuel,
RSM 10X6 prop and go fly. Mine pretty much 4 stroke throughout the flight. Great classic engine. 8)
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I don't have a caliper for an accurate measurement, but the NVA assembly I'm using is O.S. part number 22311000. It's what I use on all of my .25 and larger O.S. engines.
Is that the current 25LA version? If so, and I can find them, I have a big pile of them somewhere and can measure them.
Does anyone ever bother with adding or taking away head gaskets on these? How many would have been standard in the .35-S?
One, as I recall. I think the "add head gaskets" plan was pretty well invented about the time people tried using 40FSRs for stunt. We used to get good and reliable runs changing only the venturi. The compression ratio is higher than a Fox but still not particularly high.
Brett
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For informations sake the LA's come out of the box with the rear mounted remote NVA. I'm pretty sure the proper application by the book for the "accessory" NVA that I'm using here is the same for all of the .25 through .40 FP'S and LA's.
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For informations sake the LA's come out of the box with the rear mounted remote NVA. I'm pretty sure the proper application by the book for the "accessory" NVA that I'm using here is the same for all of the .25 through .40 FP'S and LA's.
Correct OS uses the 20 25 NVA for all of the motors 20 25 35 40 46 FP and LA series. The spray bar is a much smaller diameter than the Older OS 35 S engines
Randy
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Thanks for the confirmation Randy. y1