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OS FS 70 muffler pressure

Old 04-27-2005, 03:45 PM
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Default OS FS 70 muffler pressure

Hey Bax, settle an argument between my dad and I ...

IS an OS 70 supposed to use muffler pressure or not?
Old 04-27-2005, 04:38 PM
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Default RE: OS FS 70 muffler pressure

It all depends. A nipple is on the muffler so you can use muffler pressure if you wish, but it's not necessary. The carb will be able to draw fuel without muffler pressure...you'll just have a different needle setting w/o pressure as opposed to w/pressure. W/O pressure, you'll have to keep the tank close to the engine, and the up/down positioning of the tank is more critical.

A better question is, "Does the FS-70 require muffler pressure?"

NO.
Old 04-27-2005, 05:08 PM
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Default RE: OS FS 70 muffler pressure

Ok,thanks!
Old 04-28-2005, 10:09 PM
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Default RE: OS FS 70 muffler pressure

Mike, I have been through this as well, and found an interesting solution. If you run without muffler pressure, and run your tank vent to just hang out the top or side of a cowl, chances are it will get negative pressure on the end, which will depend on speed, and give inconsistent running. We found that we can get good reliable runs to near end of tank just by running the vent line (with a small brass tube in the end) so that it faces directly into to prop wash, straight forward to the front (assuming tractor prop of course). This means it will NEVER get negative pressure, even if it only gets VERY low psi pressure. Seems to work for us - every time I tried to use an OS 4 stroke muffler, it got spat off in flight, as the threads are very fine, and get worn out by vibration eventually. Hope the new ones are better in this area.
HTH
jp
FS120 twin rocker
FS120 SP

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