AFP Injected 360 stumbles on rapid throttle-up

I searched through the archives and couldn't seem to find an answer or similar issue.

The engine starts OK with the throttle cracked and moving the mixture from lean to rich as it catches, boost pump on.

I can run the engine, and it's smooth at any rpm above 700, but if I advance the throttle "smartly," the engine quits. "Smartly," in this case is not abruptly, but no more than a 2-count from idle to runup RPM. I advance the throttle at the same rate I was taught during flight instruction.

The slower I advance the throttle, the better the chances of it continuing to run.

The problem seems to occur somewhere in the transition through 700 to 1100 RPM.

If I advance the throttle slowly enough, it gets it together and runs fine at 1800 RPM, with 100RPM mag drops on each side, as far as I can tell: I'm still getting used to the rpm lag on the digital tach.

Here's the equipment:

I have an O-360-F1A6 converted to fuel injection using a Superior Cold Air sump and Airflow Performance FM200 injection system. Ignition is from 2 Slick 4371 mags. The AFP system and sump was installed during an IRAN performed in early 2011 and the engine was run in the test cell, where no problems were reported, but I don't have detailed information on the test cell run.

I'm using the AFP electric boost pump and FloScan flow sensor. I tested the fuel flow from the boost pump just after wing install and it worked fine. The situation occurs whether the boost pump is on or not.

My mags are timed at 20 degrees, as indicated on the mag housing.

I hope someone can help me out on this one. I'm getting ready for inspection!

Idle Mixture too lean

Sounds like your idle mixture is a bit lean. Check the manual under Field Adjustments to set the idle mixture.

My superior 0360 is timed at 25 BTC on both mags and only get 60-70 rpm drop on mag test

injection

John,

It seems to me that you need to richen it up. Get your manual and follow the instructions for setting it up. When it is correct, it will not stumble and your EGTs should not exceed 1250 degrees in a full power climb at sea level. Anything hotter than that indicates a lean setting. (That's what I was taught and mine has been working beautifully for three years now.)

Thanks!

Thanks for the advice.

Another data point: I found the data plate for the engine attached to the old rear-facing sump, and it says the timing should be set to 25 degrees.

When I head up to the airport on Thursday, I'll take my AFP manual with me and do the adjustments to the timing and the idle.

Markings on Slick/Unison Mags

Hey John,

Merry Christmas to you and yours. Just thought I would let you know about that data plate on your mags. If your mag model is 4371 that indicates an impulse coupled mag and the 20 deg marking is indicative of the "lag angle" for that mag during cranking for engine start. The magneto will retard those 20 degrees during engine cranking for easier start and to avoid kickback. After engine comes to life, the impulse coupling disengages and mag timing will resume whatever you have the mag timed to, based on the ENGINE data plate which is probably 25 deg BTDC. Why do I know this? I have the same mags on my Superior IO-360. My engine is timed to 25 deg BTDC per the data plate. During engine crank, that means the mag will fire at 5 deg BTDC. Why? Because during cranking the engine RPM is only like 300 RPM I think. The impulse coupling does that for us plus gives the mag a little zing for engine start due to low cranking RPM. There you have it.

I read way to much about slick mags and have the service/overhaul manual from Unison. Enjoy the holidays and double check that timing on those little rascals with a buzz box.