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Permalink Reply by John Austin on November 5, 2021 at 8:45pm

Jerry,

Like you, I needed a project and love to experiment, so I switched from the Bing to an AeroInjector (latest version of AeroCarb).  I have 100's of hours experience with it in my STOL CH750/Jabiru 3300 and have a lengthy, detailed thread in the forum located here: AeroInjector TBI Carb

Not required, but I used a McFarlane "vernier assist" throttle and a "vernier assist" mixture control.  These allow you to make coarse adjustments without any sort of lock or button and then have a vernier action for fine adjustments.  However, you will have to have a throttle direction reversing bell crank or devise some sort of mechanism to operate the slide on the AeroInector "backwards" since the throttle action is reverse of conventional carbs.  I made my own reversing bell crank which is described here: Throttle Reversing Bell Crank

That's a lot of information to digest but I recommend you read the entirety of each thread.  But, to summarize the key points:

1. The Aeroinjector works best with gravity feed only - no problem with the STOL 750 since it's a high wing plane!
2. Since the AeroInjector doesn't have a fuel bowl, vapor bubbles will cause "burps" or hesitancy.  To avoid this, keep the fuel line as short as possible firewall-forward (to avoid heat soaking), insulate the fuel line with fire sleeve and a heat reflective line wrap, and the line must be routed always upwards toward the carb with no high spots to trap vapor bubbles.
3. The AeroInjector doesn't fully shut off even with the throttle closed and the mixture pulled full lean - it'll slowly drip after shut down - so develop the habit of killing the engine by shutting the fuel selector valve to "OFF."
4. As mentioned, you'll need either a throttle reversing bell crank or some other mechanism to operate the carb "backwards" so the throttle will operate conventionally with pull to close and push to open.

If done correctly, I've found it to be a very predictable and dependable carb and my EGT balance improved.  Installation allowed removal of the airbox and carb heat muff for a total weight savings of 8 lbs (that Bing is heavy!).  I like having a mixture so I can deliberately run the engine rich when additional cooling is needed in a hot and long climb, etc.  I get slightly better fuel economy in cruise.  I wouldn't consider going back to the Bing now that I have mine so well dialed-in!

John

N750A

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Permalink Reply by jerry nichols on November 6, 2021 at 10:54am

Great info; thanks

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Permalink Reply by jerry nichols on May 22, 2022 at 11:38am

I installed the Aeroinjector, did the tune procedure, and discovered it was within specs right out of the box!  100 degree drop from lean to rich at full power.  I didn't even open the adjustment tab but took off for a test flight.  At about 500 feet RPM began backing off and I was looking for a place to set it down.  I took a chance and started leaning; that brought the RPM back up to almost full power.  After a normal landing I retested the tuning and it was so rich it would hardly idle.  When I did remove the plastic cap on the needle adjustment, I discovered that there was no "set screw"; the needle carrier was free to move and had backed out to a rich position.  I found the "setscrew" in the throttle body.  I retuned but full power was less than before. 

 

I couldn't adjust the needle carrier to a leaner position. The  Aerocarb tech suggested I return the slide and carrier for their inspection.  They judged the carrier and slide as "incompatible".  A different slide worked with my carrier and a different carrier worked with my slide; but, they didn't work together.  They sent back a different carrier and adjustments were possible.

I was able to make adjustments but still couldn't get full power.  After a lot of head scratching, I took a close look at the Aerocarb air filter element.  It was almost fully blocked.  Even pressurized air blowing through the element could hardly be felt by a wet finger.  I don't know whether the filter came that way or if it was contaminated by the rich fuel mixture.  There was no soot in the manifold or carb body.

I guess it's too late to make a long story short but after weeks of trouble, I'm flying again!

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