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Os ft 300

Old 08-12-2015, 10:11 AM
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bob62
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Cool Os ft 300

Can anyone tell me if this engine needs fuel tank pressure to run. There are no connection to put pressure to tank. If it does not need pressure do you still have to vent tank and if so won't the tank leak if plane is inverted

Thanks Bob
Old 08-12-2015, 04:56 PM
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JohnBuckner
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Hi Bob my apologies I do not know anything about that particular engine but I can answer your second question and that is Yes if there is no pressure lines applied to the tank then absolutely the tank must be vented. With no vent to atmosphere then as the engine ran a negative pressure slowly builds in the tank until fuel supply is totally cut off.

So if you are worried about a little fuel loss the run a loop of hose on the tanks vent down below the lower level of the tank then up above the top level of the tank where it is vented to atmosphere. On most of my gassers I do not really bother and just leave a vent line hanging or mounted in the cowling cooling out flow in the bottom.

John
Old 08-12-2015, 06:08 PM
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Thanks John, I appreciate the reply. We are going to run engine tomorrow
Old 08-13-2015, 06:15 AM
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The tank should be set up so that the vent line goes from top-forward inside the tank and then exits through the bottom of the fuselage/cowl. That way, fuel cannot siphon out. Yes, in some maneuvers you'll lose the fuel that in that small length of fuel line, but it won't be enough to matter. Since many maneuvers will have positive "G's", fuel won't come out at all.

The correct fuel tank placement should be such that the centerline of the fuel tank is level with the center of the carburetor or slightly lower. It is common for the tank to be too high.
Old 08-13-2015, 07:26 AM
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Thanks Bax's
Old 08-14-2015, 10:39 AM
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RBACONS
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I have several of the OS FT-160 Geminis, little brother to the FT-300. I've found they do run better with muffler pressure and assume the FT-300 would as well. In addition, an on-board glow driver is worthwhile as they tend to drop a cylinder now and then. You can purchase them or make your own (my preferred method for both cost and reliability). Also, although OS recommends the OS-F plug for the FT-160, experience has shown them to run better on the Fox Miracle Plug which also allows you to lean them out more and significantly reduce fuel consumption.
Old 08-14-2015, 02:57 PM
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Thanks for the info, I ran the engine today and I notice that it does drop a cyl. I put the glow driver back on and the cly would come right back. Was doing good until it threw the prop off, need to get the lock nut assy as it did not come with one. I have ordered the Ram glow assy as I have a few of the singles and they seem to work good. Thanks for the comment and info

Bob
Old 08-15-2015, 05:20 AM
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bob62
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Originally Posted by RBACONS View Post
I have several of the OS FT-160 Geminis, little brother to the FT-300. I've found they do run better with muffler pressure and assume the FT-300 would as well. In addition, an on-board glow driver is worthwhile as they tend to drop a cylinder now and then. You can purchase them or make your own (my preferred method for both cost and reliability). Also, although OS recommends the OS-F plug for the FT-160, experience has shown them to run better on the Fox Miracle Plug which also allows you to lean them out more and significantly reduce fuel consumption.
How did you go about putting muffler pressure to yank

Thanks Bob
Old 08-15-2015, 10:21 AM
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RBACONS
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I use slip-fit lengths of K&S brass tubing over the short exhaust tubes that come with the FT-160 (and I assume FT-300). I don't remember the size but it fits like a glove. I anneal and bend the K&S to exit the cowl where I want it. The exhaust tubes on the OS point inward and downward so you end up with the K&S forming kind of a "Y" and I make a simple bracket out of flat brass stock and screws to secure the lower end of the "Y" to the firewall.

To make the vent line, I take a short piece of K&S 1/16" brass tube (about 3/4" - 1"), cut one end on a 45 degree angle and solder a 1/8" or so piece of the next larger K&S brass tubing on the other end to make the equivalent of a fuel barb. Drill a 1/6" hole in the whichever brass exhaust extension tube you want vent line on. Roughen up and clean with alcohol both the exhaust tube around the hole and the vent tube, insert the vent tube halfway through the exhaust tube, with the slanted face of the 45 deg end facing forward. Secure with a nice dollop of JB Weld (make a healthy fillet both up the vent tube and on the exhaust tube).

I find it best to also put a 90 deg bend in the vent tube piece (before you cut it) so that when the vent tube is inserted into the exhaust tube, the fuel barb points straight back along the exhaust tube.

Doesn't seem like it would hold up well but I haven't had one fail yet.

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