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Old 07-24-2019, 10:10 PM
pgtuck pgtuck is offline
Join Date: May 2019
Location: Keller TX
Posts: 26
Default Engine runs rich

I have a air flow fuel injection system fm-150 system on a 360. RV-6A. Constantly having issues with the engine running rich on the ground. Once in the air engine runs great. For a smooth running engine on the ground a need three mixture settings.
One for taxi. One for engine tun up and a third for down the runway. Local A&P adjusted idle circuit to optimize. When engine cold it works prett good. Hot engine is where I have the rich/ rough running engine.
Enjiction system was sent to air flow products for testing. They claim injector is in great shape. Mags and, mag timing have been checked.

Any though aor input would be great! Thanks in advance!
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Old 07-25-2019, 09:03 AM
Jpm757 Jpm757 is offline
Join Date: May 2013
Location: Sherman, CT
Posts: 556

What type of intake/filter are you running? Airflow may be restricted on the ground, but in flight you are getting sufficient ram airflow. Just a thought.
RV6 #20477 completed 1991 sold.
RV7 #72018 N767T first flight 11/21/2017 300+ hrs.
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Old 07-25-2019, 09:08 AM
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DanH DanH is offline
Join Date: Oct 2005
Location: 08A
Posts: 9,022

How do you know you are rich?

That question aside....

Rough running at ground idle with any brand of constant flow injection is a function of either or both (1) fuel heating (vapor formation) and (2) poor atomization at the nozzle.

Vapor doesn't meter well. Reduce fuel heating by insulating engine compartment lines and keeping them as short as possible. Running the boost pump can help the fuel heating issue by pressurizing the fuel prior to the engine driven pump. If it idles better with the boost pump on, the fuel heating (or a possible flow restriction) is upstream of the engine driven pump.

Nozzle flow at idle is very small and at very low pressure. There also isn't much bleed air pressure to break up the stream from the nozzle, so the fuel enters the intake port as a series of blobs. Atomization is thus dependent on port heat (CHT) and the pressure drop when the intake valve opens.

Superior idle is a key advantage for the electronic injections, which recirculate fuel (low heating) and maintain high line pressure all the way to the injector nozzle (fine spray).
Dan Horton
Barrett IO-390
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Old 07-25-2019, 09:27 AM
pgtuck pgtuck is offline
Join Date: May 2019
Location: Keller TX
Posts: 26

Identified as rich due the black sout on plugs and, the rich smell of exhaust! I use K&N filter. Brand new and, very clean.
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Old 07-25-2019, 09:29 AM
pgtuck pgtuck is offline
Join Date: May 2019
Location: Keller TX
Posts: 26

Any recommendations on where to get insulation for fuel injection lines and flow divider?
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Old 07-25-2019, 09:37 AM
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airguy airguy is offline
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 4,856

I ran a double layer of firesleeve over my FWF fuel lines to insulate them, works great. The fuel lines were ordered with the standard firesleeve attached to them, and then I ordered additional larger sized firesleeve which I cut lengthwise, wrapped around the hose after it was installed on the engine, and used safety wire every few inches to hold it in place wrapped around the hose.
Greg Niehues - PPSEL, IFR, Repairman Cert.
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N16GN flying 560 hrs and counting! Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.
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Old 07-25-2019, 09:44 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 4,561

Is it running rich at idle RPMs or just at taxi RPMs?

RV-6A / IO-320, Flying as of 8/2015
RV-10 in Phase I
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Old 07-25-2019, 09:46 AM
Bavafa Bavafa is offline
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,094

Beside Dan's recommendation, there is a very specific instruction for checking and adjusting the mixture setting at idle.

If I remember this correctly;
At idle, pull the mixture half way out and then start leaning slowly. If your manifold pressure raises more than .5"-1" or so, then you will need to adjust your mixture.

For Airflow/FM-150 if too rich, shortening the hex rod arm by the way of turning two flats max and retest.
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Old 07-25-2019, 05:12 PM
pgtuck pgtuck is offline
Join Date: May 2019
Location: Keller TX
Posts: 26

Engine runs rich at idle, taxi and, run up if I donít manually lean it. Mixture control about half way out for all three conditions. After run up. Rol out on the runway mixture full rich with full throttle and, it runs great. Boost pump on or off does not change the rich situation. Iíve had two different A&Pís tune it with the same result.
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Old 07-27-2019, 12:59 PM
Gisnar Gisnar is offline
Join Date: Nov 2012
Location: Northern Nevada
Posts: 136

What is your rpm rise when engine warm, idle when you you lean to stop? It should be 10-50 rpm rise. If greater shorten the linkage until it is. It is a real pain to get it correct. Also when you tighten the stop nut it changes.
Good luck and persevere!
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