While flying my gas model on the weekend I noticed bubbles in the carb's feed line and decided to redo the tank plumbing. On inspection of the tank etc I found that the brass clunk used as a weight on the fill line in my 3 line system was covered in a dark sticky oil like goo, which was also in spotty patches on the sides and bottom of the tank.

My first impression was that the tank stopper was disentegrating, but on removal I found it to be intact. No where else in the tank was affected including the felt clunk. Thank goodness I used one which I'm sure is what kept the goo out of the carb.

I am wondering if the Bel Ray MC-1 oil/ gas combination I use could in any way be contributing to this happening. Of note is the fact that the goo washed off fairly easily with gas. What are your thoughts on this.

Karol

do not use a brass clunk. Use only felt clunks or other fine mesh filters.
Not because brass is no good, but because you should filter all fuel that goes to the carb well. (rule #1 in gas engines)

Concur

Other than that, your fuel probably has alcohol in it. It attracts water and then the brass starts to grow the crud you mentioned. When folks start rioting over the price of corn tortillas and suger they'll stop putting it in our gas. But then older big block engines run well on it and so do our gas engines. Put a good filter anywhere you want it as long as you have one. The paper filtered clunks are nice though, they are heavy enough to follow the gas around, but are limited to a 3 line system and they present their own set of problems.

Pe,

If you read my post carefully you will see that the brass clunk is used only as a weight on the fill line in the tank, and that I do in fact use a felt filter on the feed line to the carb.

Pat,

I was hoping for a more indepth response from you.

So far no one has addressed my only concern, which is simply what are the possibilities as to what might have caused the goo on the clunk and on the sides of the tank.

Karol

Methanol attracts water, the brass probably has impurities in it that react to water. the spots around the tank are from the brass sitting in one place for extended periods of time. Solution> FLY MORE!!!

What sort or type of weighted clunk would you suggest as a replacement for the brass.

Karol

""Pat, I was hoping for a more indepth response from you. ""


Pat,

Apparently your public demands MORE!!

(too good to pass up)!!

Seriously, thanks for all the posts that you share your experiences on - I am impressed that you get to as many as you do.

tom

If it were me, I would go with a two line system. Use a small automotive paper filter on filling jug out put line and a felt clunk for the tank. Has worked well for me over the years, KISS

Something with chrome plating should do it.

Sorry but the photo I needed for more input was on a different laptop and I wasn't where it was at the time. Brass reacting with residual oil after a prolonged period sitting in an empty tank does that. I use what's in the picture. It will work up to at least a 115cc engine and probably a lot more. You can't get any more fuel in a carb than what the size of the carb inlet permits and this filter equals or exceeds the size of most carb inlets. Just like fuel tubing, where anything larger than the medium stuff is a waste of money.

This filter has a nasty habit of eliminating bubbles in the fuel line and picking up every last drop of gas before the engine runs dry I use one in the gas can and one in the plane. Don't need no stinking paper filters[8D]

That's what I use too

Thanks to all who responded.


Pat,

My faith has been restored

Karol

That's the same felt filter that I've always used as well.

I can back Pat's statement up about this type of clunk eliminating bubbles and sucking ALL the fuel out of your tank. You get no warning when the engine is going to run dry. It's ugly when you're in a TR at 50 ft. [:@]

Decided to use a felt clunk on the fill line so hopefully that will be the end of that particular problem. Now I gotta go check that 'other' tank with a similar arrangement. Any bets on what I will find ?? Thanks all.

Karol

If it is a problem with your fuel attacking the brass then what are you going to do about the brass tubes in the tank? I have always ran a heavy clunk that will follow the fuel in the tank and never had any funky growth in the tank.. Maybe I am just lucky.. I run two lines. A vent to the top and a clunk line. I put a large ID brass "T" in the fuel line in route to the carb and off the "T" run a fuel DOT or a line with a plug in it.. Fuel and defuel all through that line...

K.I.S.S.

Rick

He's in Jamaica, the humidity there is 100% all the time. As his tank empties, the warm moist air replacing the fuel has probably 1/4 teaspoon of water in it. Do that over and over and some things gona start growing. Add to that, methanol in the gas that absorbs the water.
I imagine Karolh has chosen an oil that has after run protection built in.

You are so right about the humidity here. For oil I did the usual Q & A routine, and then opted for a brand that is quite popular in our sport, that is easily obtained and reasnably priced. For me that is Bel Ray MC-1 which I use mixed at 50:1.

Karol

I am curious, why are you using a clunk at all on a "fill line" inside the gasoline fuel tank?
I understand the "to the carb line" felt clunk, but not the "fill line" clunk.
What is the reason for the "fill" clunk?

The felt clunk was the handiest thing available and is simply a 'weight' to replace the brass clunk I used on the fill line that grew goo.

Karol

You do not need a clunk on the "fill" line.
After the tank is filled, this line serves no other purpose.
just on the line to the carb.
The way I understand your system, you have a 3-line system.
1-line to fill tank (no clunk needed, unless you use this line to pump fuel out at end of the flying day).
1-line from tank to carb (felt clunk needed here).
1-line used as a vent (no clunk needed).

There you go, I use the fill line to empty the tank after a flying session and the felt clunk is just a weight to keep the fill line close to or on the bottom of the tank.

Karol

If you think the brass clunk is causing the crud, try using a nickle or chrome plated one instead of an expensive felt clunk.
Or cheaper yet, use a long curved copper or brass tube, same as your other tubes used for the vent and carb feed tubes, aimed at the bottom of the tank.

I agree with you but I simply used what I had on hand.

Karol

More likely the crud was condensed mositure in the tank that settled around the cluk, which was also probably the low point in the tank. The high humidity levels were already mentioned, drawing moisture in from the vent. As in full scale, water will "sump" in a gas tank and remains separate from the gas. It generally has a cruddy brown appearence but that color could change with some of the oil colors out there.

In a three line tank, where the fill is used to de-fuel, you need an additional clunk to keep the fill line in the fuel. Otherwise you won't be able to remove all the gas from the tank. That's one of the problems with a three line, the extra clunk, which has been a problem at times interfering with the primary fuel supply line. Three line systems look neat but truly don't do any more than add complexity over a two line system.