TCraft Lover

My Feedback: (1)

I ordered a new OS 1.20 AX yesterday and have not been able to find the correct fuel line size to use with it. Can anyone out there steer me in the right direction? Thanks.

1QwkSport2.5r

I'll almost bet medium size fuel line will suffice for that engine just fine.

TCraft Lover

My Feedback: (1)

Yep, that's what I'm thinking as well but I have been unable to verify it either from OS or the engine manual from Tower.

Hobbsy

My Feedback: (102)

I have used medium for everything from an LA .10 to a SuperTigre 4500/2.76 cu in, it's sort of one size fits all.

TCraft Lover

My Feedback: (1)

Good enough for me Hobbsy.

1QwkSport2.5r

Sometimes ya just go with a hunch.

TCraft Lover

My Feedback: (1)

HaHaHahahaha!!

1QwkSport2.5r

Can't always rely on manuals to show you the way... I have an engine manual that calls the head button a "burn room" and says "do not screw up the cylinder too tight" when installing the head and head button. LoL!

elmshoot

My Feedback: (6)

I would go with a Large fuel line but I have a selection of all sizes. If you can't get the engine to richen up then you have too small a fuel line all other issues being the same.
I prefer the Prather products of fuel line.
Sparky

flycatch

My Feedback: (26)

The ID of the nipple on the carburetor determines fuel flow intake. Match the ID of the fuel tubing and you have answered your question. For those who disagree please explain to me and others why I'm wrong.

raptureboy

+1 what fits snug on the nipple stays on the nipple

microdon2

My Feedback: (47)

I've got standard size fuel tubing on my OS 1.60 2s and Saito 170 4s. It's fine.

airraptor

My Feedback: (66)

larger fuel tubing is way to big. i have had many of the 120AX engines and run them on tuned pipes to stock and regular medium is the line of choice.

drac1

My Feedback: (4)

I use the Prather fuel tube on everything.

32 2 strokes up to 185 4 strokes and Super Tigre 4500's. No problems.

elmshoot

My Feedback: (6)

there is surface friction from the liquid flowing in the tube so I disagree on your premise. I would have to dig out my fluid dynamics books but suffice it to say, use what works for the application.
I personally would use the the large to avoid any potential issues.
Sparky

microdon2

My Feedback: (47)

It does seem that engine fuel nipple size would dictate tubing diameter. I haven't ever seen larger Nitro tubing, but with gas the larger tubing will not be snug enough. I'd imagine the same for the Nitro tubing. Are there any size of Nitro engines that call for larger (1/8") tubing?

airraptor

My Feedback: (66)

the large dia. tubing will cause issues with this engine as it will not be tight enough on the nipple. regular medium fuel line is fine. oh elm I pulled out my fluid dynamic book also and calculated that medium sized fuel line will feed an engine up to 5.21831 HP on a glow engine. so plenty large enough for the 120AX

Hobbsy

My Feedback: (102)

The majority here say that the medium works issue free on engines from LA .10s to SuperTigre 4500s, the fuid dynamics book is not going to change that. Agreed AR.

blw

My Feedback: (3)

Me too and I still have half of a spool that I bought a few years back. I heard they quit making it though. The blue Great Plaines stuff is cheap, imo. Too easy to get holes and leak. The Prather pink fuel tubing it tough stuff.

elmshoot

My Feedback: (6)

A RC boat shop carries the stuff out on the left coast they say they are using the same equipment and formulas as when Prather made the stuff. It is the best for our applications regardless of the size used.
Sparky

drac1

My Feedback: (4)

Yeah I heard they were stopping making too, so I bought 2 rolls. Should have enough for a long time.

flybyjohn

My Feedback: (2)

Fuel flow rate is not only a function of diameter but also the length and pressure. So even though you have a small fuel nipple, a larger line can still be beneficial. There are also other factors here. One is that different engines and mufflers create different tank pressures , so what works with one engine model and muffler might not work with a different engine model and muffler. I have an os 91 fx that starves on medium fuel tubing and so I had to go with the large (that solved my problem). Another is how large of a prop you intend to run. A higher revving prop will use more fuel than a lower revving prop. Perhaps my os 91 fx might have less muffler pressure or I am running faster rpms, so depending on the circumstances, your 120 might run just fine on the medium tubing. Since the tank is under pressure, as long as the tubing has a good fit on the fuel nipple, you cannot be too big but you can be too small.

Just as a side note: I have never had a problem with medium tubing until I bought my 91.... but then again it is the largest engine I have had.

airraptor

My Feedback: (66)

to large of a fuel line on an engine will have a leaning effect when accelerating or in the vertical so you will have to run it richer to take off and climb so that it doesnt go lean.