I built my Corvair to WW specs but thought that an alternative carb was an attractive option. I test ran and flew with a Sonex Aeroinjector 35 initially, Like some I found it hard to tune and difficult to start in different weather conditions. My cable jammed on startup last week and quickly I was done with that crap. I installed a MA-3SPA carb the last couple days and I have never been HAPPIER! Today I flew with confidence - the new carb started perfectly, was responsive thru the whole range, never burped or hiccuped and was much smoother feeling. Spending $1450 on a carb is a jolt - I have never spent better money than this. I think if your engine is EXPERIMENTAL - your carb should NOT BE!

Views: 761

Reply to This

Replies to This Discussion

I've had a really good experience with an AeroInjector on a Jabiru 3300, but it definitely took some experimentation and meticulous attention to detail in the installation to eliminate the "burps" or slight hesitation due to fuel vapor.  Since the AeroInjector has no float bowl, I think it is critical to ensure that the fuel line always slopes upward to the carb from firewall-forward so there are no traps where fuel vapor bubbles can accumulate and then pass to the carb - this is what causes the "burps." I also re-routed my fuel line to make it as short as possible firewall-forward and put a radiant heat-reflecting wrap around my fire-sleeved fuel line to further insulate and reduce the possibility of vapor formation.

I now have a reliable "burp-free" installation.  I've never had any starting problems - perhaps it's because I use an EarthX lithium battery - it turns the engine over so fast that I can't hardly count any blades before it has started no matter whether it's hot/cold weather or a hot/cold engine.  The fast spin helps the mags make plenty of ignition current and likely the fast spin induces a more vigorous flow of fuel/air mixture from the carb.

The biggest negative is that the carb will drip fuel after shut-down, even with the throttle completely off and the mixture pulled all the way.  One quickly learns to develop a habit of killing the engine by shutting off the fuel selector valve to ensure there is no fuel available to the carb after shut-down. It is remarkable that despite the technique of killing the engine by cutting off the fuel, it starts next time near-instantly ... and this with gravity-flow and no fuel pump!

I agree that it definitely is not a "plug and play" carb!  I do like the simplicity (and the relatively low cost) of the AeroInjector, but in my case, the experimental trial and error of perfecting the installation became a challenge for me which I enjoyed ... probably because I finally had success!  ;>)



Let me give a few more details for posterity. Originally I ran the Aeroinjector on my test stand with honestly poor instrumentation - because it was a test stand and I just wanted the engine to run well. My EGT and CHT were not accurate and not set up well so I did not do the exact tuning procedure that was documented. My exhaust was a little grey so I thought I would try the 2.5 needle. With that needle my engine started fantastically in the colder temps but bogged down over 2200 rpm - too rich, no power. OK - back to the 2 needle.It ran ok in the cooler weather of the early spring but on restarting it was very easy to flood the engine and have a little extended cranking session to get it going. It did not feel smooth with throttle changes but i do believe I got the same full power and static rpm. I read a lot of comments on pilots getting very used to changing the mixture all the time for the circumstances - NOT what I am interested in. 

Since my engine was already installed in the plane, I had my 6 cylinder EGT and CHT monitoring (MGL EMS), which is a must-have for a 6 cylinder engine.  I wound up with a #3 needle (which apparently most Jab 3300's require). With that set-up, I  was able to tune it so it was rich enough for easy starting and keeping EGT's in-check during take-off and climb-out, and then I can use the mixture control as one would with any other plane with a mixture control - leaning in cruise for economy and aggressively leaning during taxi, etc.  It's nice also to be able to deliberately enrich the mixture on a long climb to help with cooling on a really hot day.

I read those same comments as you and it confused me - people were talking about re-tuning the carb for summer vs winter, etc.  I've never had to re-tune the carb since initial set-up. I got the impression they didn't understand what that mixture knob was for on the instrument panel and were afraid to touch it!  ;>)  For me, the whole point of installing the AeroInjector was to gain that mixture control (vs none with the original Bing carb) so the engine could be more precisely operated for best power, best economy, etc.

By the way, McFarlane Aviation makes a mixture control called "Vernier Assist" that is very nice.  You can push-pull the mixture just as you would with any mixture control, then it has a vernier feature so that you can simply rotate the knob to fine-tune the fuel flow - I'm able to adjust the mixture up or down in 0.1 gph increments to really dial-in where I want my EGT's. Works great!


Hi all, I have an Azalea Aviation 120 HP Corvair conversion engine in my Cruzer.  We installed a revmaster 40mm slide carb that has worked flawlessly through the first 55 hours of flight.  Engine turns right over but I select points to start the engine rather than the electronic points, then I switch to the electronic points before takeoff. Loads of power.  Incidentally the best way to start my engine is to pull the mixture all the way out, set throttle for 1500 rpm and turn of the fuel selector valve.  Begin cranking while slowly pushing in the mixture control.  The revmaster carb does not leak fuel on the ground as long as the mixture is at idle cutoff, never the less like John I do turn of the selector valve after cutting off the fuel supply by pulling the mixture control to idle cutoff.  This procedure works well in hot and cold weather and importantly when restarting a hot engine.


John Minatelli


New from Zenith:

Zenith Planes For Sale 

Classified listing for buying or selling your Zenith building or flying related stuff...

Custom Instrument Panels
for your Zenith

Custom instrument panels are now available directly from Zenith Aircraft Company exclusively for Zenith builders and owners. Pre-cut panel, Dynon and Garmin avionics, and more.

Custom Upholstery Kits for your Zenith Aircraft:

Zenith Vinyl Upholstery Kits

Zenith Apparel from EAA:

Zenair Floats

Flying On Your Own Wings:
A Complete Guide to Understanding Light Airplane Design, by Chris Heintz

Builder & Pilot Supplies:

How to videos from HomebuiltHELP.com

Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit HomebuiltHelp.com for the latest DVD titles.

Aircraft Insurance:


West Coast USA:

Pro Builder Assistance:


Transition training:

Golden Eagle Aviation

Pianosa Flying Farm

Aircraft Spruce & Specialty for all your building and pilot supplies!

© 2021   Created by Zenith.Aero.   Powered by

Badges  |  Report an Issue  |  Terms of Service