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super rich, overfueled CJ

 
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JL2A



Joined: 07 Apr 2015
Posts: 110
Location: Australia

PostPosted: Tue Jul 28, 2020 11:47 pm    Post subject: super rich, overfueled CJ Reply with quote

Does anyone know if the fuel pump used on the HS6A has a minimum pressure shut off to prevent over pressure situation between it and the carburettor's fuel shutoff valve?

I got one of our carbs overhauled, when we installed it it ran extremely rich and would pour 1/4 cup of fuel out of carb on shut down.

We then put the original (working) carb back on and now it does the same thing.

Starting to think it is not the carb...

So we replaced the primer (thinking it could have been leaking and sucking excess fuel through the prime system). No difference, even disconnected the primer line, still got fuel pouring out.

At a loss...


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dsavarese0812(at)bellsout
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PostPosted: Thu Jul 30, 2020 12:04 pm    Post subject: super rich, overfueled CJ Reply with quote

Try pulling the fuel shut off lever in the cockpit just prior to shut
down and see if the carburetor still leaks after shut down. That will
shut the fuel off from fuel pump and thus, the carburetor.  Hopefully,
the shut off valve arm, which is physically attached to and above the
main fuel screen on the firewall, is adjusted properly.  Let us know
what happens when you do that.

Don't forget to push the fuel shut off lever forward before the next
engine start.

A. Dennis Savarese
334-546-8182
www.yak-52.com

On 7/29/2020 2:46 PM, Walter Lannon wrote:
[quote]

Can't say I know what your problem is but some info and speculation on
the fuel system may be in order.

1.  Carb. fuel shut-off valve?  Not aware of any such valve in the
carburettor  but not an expert on pressure carbs.

2.  The fuel pump is operationally identical to all rotary style
aviation fuel pumps complete with an internal by-pass and an
adjustable pressure relief valve that allows excess fuel to circulate
internally.  The pressure will be set to 5 +/- 1 psi (or equiv. in 
metric) ---  Any possibility the setting has been compromised ??

3.  The fuel pump installation includes a restrictor installed in the
outlet port as a safety feature in the event of a hose failure (and
major fire hazard!) by reducing the output volume.  The hole in this
restrictor is in the order of 0.010".   Having  seen numerous
instances where this restrictor has been unknowingly lost with no
evident effect on carb. function that would not appear to be your
problem but I suggest you check that in any case.

Cheers;
Walt


--


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JL2A



Joined: 07 Apr 2015
Posts: 110
Location: Australia

PostPosted: Sun Aug 02, 2020 5:54 pm    Post subject: Re: super rich, overfueled CJ Reply with quote

Hi Dennis, yes pulled shut off valve and engine ran beautifully for about three seconds before shutting down.

Have swapped carburettors fuel pump, carburettor shut off valve, isolated priming system and oil dilution system. All to no change.

Is there something about the fuel shut off valve arm position that affects how much fuel the carburettor receives?


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