RCU Forums - 4 stroke

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Setting up a 4 stroke for the first time( os fs91) looks like a extra fuel or vent hose ,any diagrms on setting one up?

Are you referring to the nipple on the bottom of the crankcase?

not excatly sure what your asking, four strokes will have three nipples on the motor, one on the carb for fuel to the carb from the tank, one on the muffler that connects to the tank for pressure, and a third nipple on the crankcase, that just vents out into the atmosphere, just run a piece fo fuel tubing on it and run it so it hangs below the plane, hope this helped

Caution - on that not all have vents some have a line from crankcase to the valve /push rods - best find out which motor he has

Yes, the newer four strokes have crankcases that vent back into the intake, I assumed that his was the older style.

If there is a fuel line that runs from the crankcase to the intake, that is a vent line to neutralize pressure and vacuum in the crank case. If there is just a nipple on the bottom of the case, it is still a vent line. Just put a fuel line on it and run it out the bottom of the cowl.

I prefer to attach the line to the fire wall rather than let it just hang out the cowl. This way it stays where I put it. I have not secured it in the past, and then the line worked it's way into the cowl. Then you can end up with a mess inside the cowl when the excess oil drains from the vent line.

sorry i should have been more specific its a older moldel fs 91. i just noticeed there was a extra nipple besides the 2 on a 2 stroke!

yea thats your crankcase vent, do as gaberber suggest, main thing to know is that nasty stuff will come out of that line, so you want to run it so it doesn't get all over your plane

Here's a link to OS's website, specifically to their "manual download"page. www.osengines.com/manuals/index.html

BTW- most are current model manuals. For your older FS91 (rather than the FS91 II) you might look at the manual for the FS 70S.

Here's another OSwebpage that includes all of the specs for discontinued OSengines ... www.osengines.com/engines/engine-specs-discontinued.html

How do you usually run it, back the entire length of the fuselodge or is there that much stuff come out?

Usually, there isn't much that comes out. I just drill a small hole in the bottom of my cowl and let the line stick out 3/4"- 1".

as gabarber said, there's not a lot that comes out, it's just that over a period of time that "small" will add up if not taken care of

There was a thread a while back and the conclusion was that shorter on the line is better.A long line to the rear of theplane my well cause some running problems. On ofour guy tried to put a catch bottle on his old O.S. 52 and it cause him a lot of problems. Whenhe pulled the bottle arangement off, and just vented it as described above,it went back to a good running engine.

Don

Think about what's going on inside the crankcase.

When the piston moves up the cylinder towards the head the volume inside the crankcase increases causing a low pressure inside the crankcase.

When the piston moves down the cylinder away from the head the volume inside the crankcase decreases compressing the air resulting in a high pressure area inside the crankcase.

The vent tube compensates for this change in pressure. When the pressure inside the crankcase increases it will be vented out through the tube. When the pressure decreases the vent allows outside air in balancing pressure through the vent tube.

During this "breathing" process fuel residue inside the crank will be pushed through the tube. If the tube is too long the fuel will create a plug inside the vent tube that will adversely effect this breathing.

Another affect of a "too long" tube is that this pressure buildup will push the fuel residue out the front bearing as it is not sealed. Result: one really, really slimy engine & engine compartment.

Thanks everyone for the replies!I learn something new everytime i get on this site!!!!!