Cox .049 won't start - Page 2 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 11-15-2007, 09:43 AM   #11
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In my experience which holds all else said here to be true, if there are no fuel obstructions and the reed is operating, o ring sealing properly then "Air Leaks" can still be a problem.

Is the gasket between the tank and crankcase in good shape? The other possible spot that I didn't see mentioned yet is the Needle valve stem itself in backplate. If a needle valve needs corrosion cleaned off or the insert looses integrity through corrosion then air can get by the Needle valve.

Removing the spring and replacing it with a piece of silicon tube the same inside dia. as the NV cleanly cut square at each end and of a height that will provide a pressure seal, for lack of a better word as well as an appropriate friction fit to maintain the needle setting.

This has worked in the past for me.
My Dog lived to be walked.
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Old 11-15-2007, 10:46 AM   #12
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One thing that could cause your problem is the spring clip that holds the reed valve could be in backwards. The reed must have room to pulse so the center post of the spring should stand off the center of the reed.
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Old 11-15-2007, 02:24 PM   #13
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The engine is now running nicely but I'm getting considerable fuel leaking from the screws in the back plate. my run time is about 30 seconds per tank. I'll need to find a way of sealing the screw heads. Any Ideas?
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Old 11-16-2007, 05:17 PM   #14
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You might try the following:

Apply a small amount of Blue locktite to clean screws when assembling the engine tank to the crankcase. Once the screws are tight, use a silicone sealant glue over the screw heads flush with the crankcase.
Then stick clear tape (I use mylar) over the entire backplate. Cut the tape away in the venturi air inlet area. This gives a double seal in the area.
Good Luck, Paul
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