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Engine runs rich

pgtuck

Active Member
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!
 
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.
 
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).
 
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.
 
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.
 
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.
 
Engine runs rich at idle, taxi and, run up if I don?t 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. I?ve had two different A&P?s tune it with the same result.
 
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!
 
Engine runs rich at idle, taxi and, run up if I don’t 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. I’ve had two different A&P’s tune it with the same result.

idle circuit/mixture has virtually no influence at 1800 rpm (run-up) therefore you should be looking for a different source. Could be an inssue with the FM-150. Call Don for ideas. Do you have a fuel pressure sensor? 50+ PSI could cause an issue. A spider that is stuck in the up position could possibly be a reason, but not sure how much it is an influence at `1800. I don't have enough experience with them. They are mostly for controlling fuel flow at idle pressures, but not sure what RPM they taper off at. It would definately cause issues for idle and taxi RPMs.

Larry
 
From the manufacturer:

Bring the engine up to operating temperature.
Put the mixture control to the FULL RICH position. Advance the throttle to wide open.
Observe the RPM and EGT. These parameters must be within the engine manufactures specifications. Typical full throttle EGT for Lycoming engines is 1300 to 1375 degrees Fahrenheit. On most 4-stroke engines, correct full rich mixture is indicated by an increase of 25 to 50 RPM when the mixture is manually leaned while at full throttle. This is with a fixed pitch prop. On engines with constant speed props, correct mixture can be determined by EGT change from full rich to peak EGT. To determine mixture using this method power must be set 22-24? MAP at no higher than 3500 ft. MSL. Record peak EGT on one cylinder then record full rich EGT on the same cylinder. The difference in EGT between peak and full rich should be 185 to 225 degrees F.
If the full rich full throttle mixture is not correct, it can be adjusted by changing the main jet located inside the fuel controller.
 
Thanks for the great information! I did install the .024 nozzles. That helped!
Found that mixture about half out on the ground and during run up works great. On the go mixture is returned to full rich.
 
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