Problems Tuning Hp 21 Nitro Engine (Foaming fuel) - RC Groups
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Feb 03, 2009, 12:41 AM
disabled and broke

Problems Tuning Hp 21 Nitro Engine (Foaming fuel)

Does anyone have or ever had an HP (german made) small nitro engine? I got it started but doesnt want to transition very well. Also seems to be getting air in the fuel line probably due to fuel foaming. Seem to have alot of vibration with this small engine vs a 46 size engine. Any way to avoid the foaming situation? Any tips on this engine that may be different from the OS series? Anything would be helpful as I am new to the smaller nitro engines. Thanks F2F
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Feb 03, 2009, 03:42 AM
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No experience with that particular engine, but have you balanced the prop?

As for fuel foaming, that's usually caused by the fuel tank not being isolated from the fuselage. You should wrap it in foam, if you haven't already done so. But air in the fuel line is more usually caused by a leak in the silicone tubes -- often it's very difficult to see a pinhole or a nick in the line unless you disassembe the whole thing and then stretch the tubing.
Feb 03, 2009, 04:41 AM
Registered User
the foaming fuel need to be addressed first...try and isolate the problem to a line leaking or foam due to vibration...defuel the tank remove it from the plane and leak check the tank by blocking off a line..submerge the tank in water and blow in the remaining line and watch for bubbles....if that is all good..then isolate the tank from the aircraft structure with foam. I don't know this to be fact but I've heard that you can cut down on the foaming by adding a drop of dishwahing soap to a gallon of fuel...
Feb 03, 2009, 11:20 AM
disabled and broke
Thanks fellas, was wondering about the prop myself so I balanced one and bought two others yesterday to experiment with. As far as foam around the tank I have done that but the problem is there is absolutely no room to do it the way I consider to be correctly. I am going to try a couple of other alternatives today if I can get time. I did pull the tank and block off one line and blow into the other and appears to be no leaks. Dishwashing soap and armor all have both been suggested on other sites too but it is my belief that this couldnt be too good for the carbs could it? Last resort there. May also try rubber band rings around the tank instead of solid packing of foam or maybe rubber gasket between the motor mount and firewall. Possibly rubber washers under the motor where it meets the motor mount. Just cant believe how this thing vibrates but man when it runs it RUNS!! Thanks for the suggestions again and will keep posted

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