Leaky Fuel Tanks and priming problems
Miniplane and other manufacturers have trouble with properly
finishing their fuel tanks and connections after they are molded. Not
sure why this is. It would take them a minute to fix it and then
test the tank for leaks. Oh well....
In particular, they fail to smooth out the edges of the tanks where they
contact the caps and the openings for the various tubes. The result is
that the tanks leak not only fuel but they are difficult to pressurize
(with one's breath) = trouble with priming. At least half of the
Miniplanes, for example, I have ordered have fuel tank leaks.
There is nothing wrong with the concept of a priming system using a tube
to pressurize the fuel tank A primer bulb, however, adds weight
and is another unnecessary point of failure in your fuel system.
First of all, make SURE your fuel tank does not leak. The best way is to
immerse it in water (just the top of the tank) and blow in the primer
tube to see where the leaks are. If there are leaks (and there will be),
1. With a wide file, finish the cap openings until they are
perfectly flat and smooth.
2. With brake cleaner or mineral spirits, thoroughly clean the tube
inserts and their openings.
3. Using RTV ("blue") from the auto parts store, LIGHTLY coat the
inside of openings and the outside of the tubes and insert them into
their respective openings. If you use too much RTV you will plug the
openings. Make sure the primer tube is lined up properly.
4. Let things sit for a day in order to thoroughly cure.
5. Retest your tank for leaks. Make sure the primer tube is not
restricted or blocked with RTV or bits of tank material.
If all is OK, reassemble everything. Without leaks, the tank will
easily pressurize and the carburetor will prime. When priming, it
helps to rotate the engine so that excess fuel will run out of the
carburetor and not into the engine and flood it.
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