I recently took out a G20 powered model that had not been flown in about five months and decided to give the engine a run before taking it to the flying field the following day. The engine started up as usual but would not go past a fast idle and any attempt to incresase the throttle resulted in very raggedy running or an abrupt shut down. I drained the tank of the old fuel that was left in in from the last flying day and used fresh fuel, but still no go.

I inspected the carb, and though finding nothing out of place dismantled it and replaced all gaskets and diaphrams but still no better. I checked the ignition system complete and found no problems there. Looking through the fuel system showed nothing amiss ,but on a whim I tried blowing through the carb's feed line and felt clunk and found it extremely difficult to do.

So after two full weeks of hair pulling and head scratching it turned out that a partially clogged felt filtered clunk was the culprit.

Karol

Very interesting Karol. I need to keep that one in memory for future reference.

Filter your gas can and not the planes tank. Theres a last chance filter in the carb to catch any airplane tank junk. The little clear see thru filters at the auto parts stores wok great. Just drop it in your gas can and every new flying season replace it, problem solved.

Hey Barry, great idea. You all got a brand, part number, or picture of that gas can filter ?

Ed

Just use the felt filter you can get for less than $3.00 at any trimmer/chain saw shop. I use the same in my plane's tank. Works great and allows full drain of the tank every time and no bubbles.

Yes I do agree as the very same thing worked great for me too until now. Considering that I have a felt filter on the end of the pickup line in my gas bottle, and an automotive type paper filter in the discharge line from my manual fuel pump, maybe I really don't need the in tank felt filtered clunk on the carb's feed line.

Karol

I have experienced crud in the vent liine to the tank from the air replacing the used fuel. The filter in the clunk line prevents this crud from getting into the engine. I guess a filter in the vent line would also keep this crud from the engine. Sincerely, Richard

I fly from mostly grass field and have noticed that condition with my models but overlooked that fact just now.

Karol

But with a felt clunk, your carb will never suck a bubble

So true, I guess the real answer is to replace the felt clunk every so often before it starts acting up.

Karol.

At the local chainsaw dealer, i can get just the felts. it is a little cheaper to keep them up.

On average, how often do you replace the felt?

Karol

I usually go a couple years or if it is a plane that has had fuel in the tank and been setting around a few years before i run it, I change the felts.

The felt has been know to gum up, depending on fuel/oil combination quality.  You can either fit a spare felt, or remove the felt and knead it in clean fuel to get rid of all crud and gum. When using a glass bowl for that, be surprised of the residue that is washed out, despite using a felt in your fill bottle.
After washing and a good rinse after fitting back, the clunk is ready for another year or two.

Thanks guys.

Karol

Is that all??? Awwww... I thought you were going to share your money or lottery winnings with us.