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RotaxEngines-List Digest: 1 Msgs - 09/05/17

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PostPosted: Mon Sep 11, 2017 8:32 pm    Post subject: RotaxEngines-List Digest: 1 Msgs - 09/05/17 Reply with quote

Thanks for the couple of replies on the fuel tank and fuel pump problem. It was a fuel flow problem as was evidenced by the need for choke and not able to get full RPMs. The fuel had not sat in that tank very long as it was a new tank that I had built. This Rotax engine was one of the ones that  came under the SB-912-063 requiring a fuel pump replacement. They must have had a batch that had a short service life. The fuel pressure with only the engine mechanical pump on was about 0.5 psi, it took awhile to find this as with both pumps on the fuel pressure was ~2.5 psi. With a new mechanical pump only fuel pressure is ~4.5 psi and with both pumps on it rises to ~5.4 psi. The engine now starts and runs fine.
Thanks again.
On Wed, Sep 6, 2017 at 1:03 AM, RotaxEngines-List Digest Server <rotaxengines-list(at) (rotaxengines-list(at)> wrote:

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   EMail Version of Today's List Digest Archive

                           RotaxEngines-List Digest Archive
                     Total Messages Posted Tue 09/05/17: 1

Today's Message Index:

     1. 10:43 AM - Re: 912 fuel problems  (Guy Buchanan)

________________________________  Message 1  _____________________________________

Time: 10:43:26 AM PST US
Subject: Re: 912 fuel problems
From: Guy Buchanan <gebuchanan(at) (gebuchanan(at)>

75 hours over three years means auto fuel sat in the tank unused for
some long periods. From what I've heard auto fuel only has about a two
week shelf life. I worked on a Kitfox that had sat for long periods with
auto fuel in its tanks, and the fuel left deposits in the tanks which,
when re-filled, would soften and migrate to the filters, plugging them.
It took only minutes for the filters to become plugged enough to kill
the engine. The challenge was that you couldn't /see /the deposits, but
you could sure feel it when you tried to drive fuel through them. Your
two symptoms of requiring choke to run and inability to attain full rpm
indicate a fuel flow problem, as you've already guessed and proven. If
your tanks have become "varnished", you'll have to clean them
thoroughly. On the Kitfox we rigged a fuel pump and circulated fuel
through the tanks continuously for two weeks, replacing the cycled fuel
daily, until the varnish was eliminated enough for it to run continuously.

Guy Buchanan
Ramona, CA
Kitfox IV-1200 / 912-S / Warp 3cs / 600 hrs
Glider pilot, too

On 9/1/2017 7:37 AM, Henry Roden wrote:
> 1) Is this a normal throw for this cam?
> 2) Why does it need so much choke when it did not do so before all the
> fuel problems.
> 3) Is there something else I am missing that would cause these symptoms?
> Since pulling off the fuel pump off another mechanic remarked that the
> engine seemed very stiff to pull over with the prop, it had always
> been that way since new and I had attributed it to the engine gearbox
> combination. I removed the top plugs and the gearbox and the engine
> and the gearbox are each quite smooth but not when the gearbox is
> mounted back on the engine. It feels like the plugs are still in and
> there is compression pressure causing resistance?
> I apologize for the long description.
> Henry

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