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Fuel foaming?

Old 03-28-2004, 05:43 PM
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Default Fuel foaming?

Hi all , I would like to know if the problem I am having is fuel foaming or something different. I have normally used Cool Power 15% fuel in all the engines I ran up untill 2 weeks ago without any problem in my engines. I switched to Wildcat 15% with 80/20 oil mix. My problem started when I tried to fly my giles 202 with a used ST 90 with new carb on it. The ST would run for approximately 3 minutes and then start bogging and eventually stop. I discovered it was extremely hot and assumed it didnt have enough cowling removed. I then ran the engine on the the ground with the cowl removed but ended with the same results. I replaced the tank and lines and made sure of no air leaks (water tested in sink) and checked for carb leaks. After 3 unsuccesfull attempts at getting the engine to run cool I extra wrapped the tank with foam. This did not help the situation it still heated up and quit. I am running the engine to the max fuel rich setting. I got tired of fiddling with the engine so I installed a NEW ST 90 ......same problem with the new engine. In the proccess of trying to figure out my problem I was also helping my girlfriends son finish up a airplane with a NEW GMS 32 engine on it. We took it to the backyard and was attempting to break it in when it had the same affect that the two ST90's (heated up and quit). It seems that the vibration from the engines had some foam inside the tank on his airplane but I could not see the tank on the giles so I was not sure if this fuel foamed on the giles also. My question is does this fuel foam easier than the cool power and if so why can I fly two other airplanes (t-34 and patriot jet) without any problems? All tanks are foam covered and fit tight within the fuse. I am goign to purchase a gallon of cool power and run that again this weekend coming up. I purchased the wildcat thinking the 80/20 mix would be better than a 100% synthetic mix. Thanks
Old 03-29-2004, 09:43 AM
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Default RE: Fuel foaming?

Dont know about the specific fuel you are using but I always put in a couple of squirts of Armor All into my fuel I mix and do not seem to have any problems with Foaming, might want to try this see if it helps.

Old 03-29-2004, 10:08 AM
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Default RE: Fuel foaming?

I always put two drops of Armorall in a fresh gallon of fuel.
That's all it takes. Never had any probs doing this, done it
for yrs. It really stops the foaming. However the best
solution is a fuel tank that is lightly held in by foam padding.
I know this is not always possible.
Good luck with it, hope you can resolve the prob.
Old 03-30-2004, 05:05 PM
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Default RE: Fuel foaming?

Fuel foaming can usually be determined by the fact that the engine's running very lean. You can open the high-speed needle a LOT before the engine will go rich...and then it will go rich with a vengeance, becoming extremely rich. You'll then start to lean the engine and then it will suddenly go very lean, and you'll have to open the needle a lot again to get it rich. No smooth needling.

This happens because the engine builds up to the RPM where the air starts to get agitated into the fuel. At that point, the engine goes lean at high speed. Then it stays at that high speed until the needle's so far open that the engine just falls to almost choking rich.

Fuel foaming can happen in the air but not on the ground. The plane's free to vibrate in all directions in the air, but is restrained by the ground and the modeler's hand when not flying. The engine will also unload in the air, and increase in RPM.

You can have too little or too much foam padding around the tank. Too little, of course, provides no vibration isolation, but too much can result if you've packed in the foam rubber to help hold the tank in place. In that case, you may just as well have used unpadded wood to hold the tank.

Fuel foaming can be a "bear" to track down and eliminate. Sometimes, you wind up having to replace the entire fuel system with a different type of tank to cure it. Sometimes, the model is such that you just can't totally get rid of it.


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