(All) YS170 Fuel Lines

[Pittsartist]

Question ....................

Why do YS choose to fit such a thin piece of silicone pipe on the fuel line that runs from underneath the regulator to the nipple on top of the front bearing ?.

All the other pipes as supplied are of the best quality silicone I have ever seen, but this particular one is the thinnest wall I've ever seen.

I'm hatching a theory that it could be to cool the fuel as much as possible ?. If so, how about replacing it with a section of the K&S type alloy tube ?.

Anyone know the answer ?.

Meanwhile, having just split the original I'm on to some "vanilla" replacement for the time being.

[Stuart Mellor]

Hi Richard,
you beat me to it................ may have the answer.
The line is for pressure only  - its a reference pressure from the crankcase that plays on the 'dry' side of the diaphragm i.e does not pass fuel.
I did a calc - YS fitted front clear tubing is 7.2 sq. mm , other blue tubing is 4.2 sq. mm.
So I assume the larger bore causes less restriction on pressure.
Don't see any reason why it can't be replaced with 3mm ali tube though since the supplied tubing is the first to split....
Can't see the tubing passing any heat since there would be no flow in the pipe - i.e. just pressure.
Stuart

[Adrian Mansell]

Most model suppliers do two internal diameters of silicone fuel tube: 3/32" and 1/8"  e.g.,

http://www.inwoodmodels.com/index.php?cPath=46_47_226&sort=2a&page=4&osCsid=e73d825b1692a0bed7f0a8462fe2614f

These match the internal diameters that stuart has measured, but (unlike the YS tubing) the 1/8" I.D. fuel tube supplied is bigger overall and has a decent wall thickness.  This is what I've been uysing to replace the crankcase pressure feed tube on YS's (with a turn of lock-wire at each end).

:-)

[Ashley Hoyland]

As this is "a pressure only line" and I assume it is around 6lbs psi, which would be typical of crankcase pressure, the pulses might be absorbed by the tubing if the wall is not strong enough resulting is very little reaction at the critical end.

I will leave those thoughts with you.

Ashley 

[Stuart Mellor]

Hi all,
Ash - you are right, but at the risk of being pedantic - the supplied ys tubing is more flexible than standard silicione & you're right that too flexible a wall thickness will lose pressure- but ys obviously believe these losses are more than made up for by the increased diameter I.D. I know most people just replace ys split tubing with UK brand stuff & have no problems - but if ys use big bore then who can argue?
ps  - on the crankcase operated Perry pumps, a strong piece of non flexible tubing is supplied for the very reason you describe  i.e. flexible tubing will absorb pressure - not what is reaquired.
Stuart

[Stuart Mellor]

Hi all,
Perhaps this belongs in the oo-er dept. - a club colleague was flying a ys170 powered model at the weekend. No problems, engine throttled & ran OK. Landed. Take canopy off to refill, oo-er - sides of tank sucked in & nearly touching! He had forgotten to unblock the tank vent before take off! It just shows how powerful the mechanical pump is on a YS. It took 20 minutes for the tank to regain its shape. If the tank had been too rigid - the engine may well have cut.
Stuart