REFLECTOR: Fuel pumps on my Franklin

Brian Michalk michalk at awpi.com
Sun Nov 27 15:07:16 CST 2005


Since there was some discussion about fuel pumps, I thought I'd share my 
latest news.

If you recall, I'm using an Autronic EFI system, and a backup that I 
designed myself.

I have two fuel pumps.  One is a Bosch electric pump.  This long weekend 
was the first time I ran any liquids through the system.  The electric 
pump put out 140 PSI.  The mechanical pump is from Waterman Racing, 
which is a sprint car racing pump.  I machined an adapter to fit this 
pump to a standard AND20000 accessory pad.  While cranking at 200 RPMs, 
the Waterman pump gives me 71 PSI.  Both of these pressures are good.  I 
was planning on a 90PSI fuel rail pressure, with 45 PSI as an 
alternative.  If I go with 90, I can save some electrical power on the 
injectors.  I'll have to do some flight testing to work these details 
out, but for now I adjusted the pressure regulator for 45PSI, and set up 
my fuel tables for 45 PSI.

My backup injectors are "mister nozzles" from Mcmaster Carr.  I have one 
per cylinder, but I might go to a single injector per manifold, because 
the higher pressure will give me better atomization.  The spray pattern 
is a fine spray pattern that at least looks good.

The backup injector system is giving me some problems.  I designed it 
after the barrel valve systems used on racing cars.  The first leak 
test, I had some fuel leaking out towards the stepper motor side.  I 
pulled the barrel, machined a groove and put on a cheapo o-ring from my 
cheapo kit that fit.  The external leak is gone.  I ordered the correct 
metric viton o-rings that will fit with the correct crush.  When the 
barrel valve is closed, against 45PSI of fuel I get two drops of fuel 
per second leakage to the injector nozzles.  I'm satisfied with this as 
well.  The last problem is that I drilled the center pilot hole .007 
inches off center.  This is the hole that the stepper motor shaft seats 
in, and this offset is enough to bind the stepper when all of the screws 
are tightened down.  I ordered some cheap iron spider couplings, and am 
going to machine one down to fit inside the valve block that will allow 
for this offset.

I'll bet Kurt has similar experiences building up his engine.


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