1QwkSport2.5r

One problem I have ran into with some of my boats is bubbly fuel. Bubbles in the fuel line is bad news. There are a number of manufacturers that sell bubbleless tanks but they are expensive. Being on a very tight budget, I needed a homebrew method to have bubble free fuel systems, so I came up with the "boost bottle". Here's a little write up on what I came up with.

I used Boost protein shake bottles. They are clear 8oz bottles with a really good sealing cap. The rest of the parts list consists of 2 bolt-on pressure fittings, 8oz disposable baby bottle liners, and permatex ultra copper or black RTV silicone gasket sealant.

Drill a hole in the bottle for the pressure fitting.

Install pressure fitting. RTV the threads of the fitting, install the gasket and tighten the nut.

Drill a hole in the cap and install the other fitting in the same fashion. It works best if the fitting is offset to one side of the cap.



Goop the threads of the bottle with RTV sealant and install the baby bottle liner in the bottle. Cut the little collar off the bottle liner and fold the liner over the top of the bottle just enough so when the cap goes on no liner plastic sticks out.

Goop the inside of the cap where the little lip seals around the top of the bottle. Keep the sealant off of the part of the cap that will be in direct contact with the fuel.

Screw the cap onto the bottle over the bottle liner, get the cap as tight as possible. Let the RTV sealant cure overnight at least, 24hrs is best.


This will give you about 6oz of fuel. I use an 8oz fuel bulb to fill the tank with a fuel line clamp on the tank fuel line so it can be clamped off when full to prevent any air from getting into the tank. Suck out any bubbles before hooking up the tank to the carb.

Small engines will do okay on 6oz of fuel, anything over a .61 should use 2 tanks using "T" fittings to join the feed and pressure lines together.

The fittings are about $3/each, the RTV sealant is $5-6/tube, and the bottle liners are about $5 for a box of 50 or so. I figure it costs about $7-8 per tank build cost. A lot cheaper than the $15-$25 tanks you find online. The liners hold up pretty well but will need periodic replacement as the fuel is pretty harsh on the thin plastic. For glow fuel only, no gasoline.

Altered1

Saw this on RCAW - great idea

1QwkSport2.5r

I have to find a better method for sealing the liner to the bottle. I've had 2 of the 4 tanks I made get fuel outside the liner but inside the bottle. I'll revise my method and repost the results.

crispyspa

Does the liner itself start leaking? Maybe the plastic is breaking down from the Nitro or the methanol?

1QwkSport2.5r

I don't know. I don't believe so. I think it's the friction of the cap against the liner against the bottle as the cap gets twisted on. I have to pull my other leaker apart to see what happened.

1QwkSport2.5r

YouTube video of the leaky tank teardown. http://youtu.be/Yf3e6mO_ibs

I resealed the tank and will let it cure before fueling it up again.

aspeed

If the friction is tearing the plastic, maybe a washer should be made up so at least it will seal before the threads tear it.  I bought a bunch of bottle bags a while ago to try this too.  Never got around to it yet.  I got 4 oz. bags though.

1QwkSport2.5r

What I did this time was use more RTV sealant on the bottle threads, cap threads, and the outside of the bottle liner. The cap twisted on much better this time.

My liners are 8oz with 6oz of fuel being usable. Once the bladder runs down to nearly collapsed, the engine goes lean and quits. I get a little warning when it's getting low but not much. I'll test the repaired tank later this week and see how it goes.