mufflers for OS fs-70 ultimate - RC Groups
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Jan 15, 2013, 05:46 AM
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mufflers for OS fs-70 ultimate

I've got a question regarding fs-70ultimate's muffler.

I know that the fs-70u has a fuel pressure system so it does not need fuel tank pressurisation from exhaust pressure like most non-pumped engines.

earlier today I found a shop selling fs-70u mufflers ( f4020u 45925050) but I couldn't remember if there was a pressure nipple on the muffler.

anyone have a clue on this?
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Jan 15, 2013, 07:19 AM
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DarZeelon's Avatar

Your assumption is correct.
Engines that use a fuel-pump, like the OS.70 Ultimate, neither need nor use a pressurized fuel-tank.

The only reasons a pressure fitting might exist on the Ultimate's muffler, is if it is use to burn-off excess oil (connected to the crankcase breather), or if it is a carry-over from earlier Surpass engines.

Earlier YS (Yamada) engines differ, since their pressurized fuel-system requires the tank to be highly pressurized (over 5 psi, compared to ~.3-.6 psi for muffler pressure).
This is done by timed pressure from the crankcase - not from the muffler.

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