Temperature Balancing by Turning/Twisting the Carb

[MichaelFarley56]

Greetings Everyone,

I know this subject has been discussed many times in the past, and it seems to be one of those eternally debated topics of conversation, but what the heck, I'm curious...

I'm curious to hear feedback and information from those who are flying behind an AeroCarb/AeroInjector and successfully was able to balance engine temps (EGT and/or CHT) by somehow offsetting the carb. We all know and understand the goal here; if we can somehow favor the mixture towards one intake side or the other, this may possibly help temps by promoting one side of the engine to run a little richer or leaner. The common method is to either twist or tilt the carb to favor fuel delivery towards one side of the intake system slightly. Easy in theory, but I'm curious who all has actually tried this.

If you've ever fiddled with carb orientation for this purpose, could you please reply and let us know what the issue was, what you specifically did to the carb, and how it worked out.

I do admit that I want to (probably) fiddle with mine a little bit; on mine, both the EGTs and CHTs tend to run coolest on the front-pilot side cylinder (#4 I believe) to the hottest being the rear, copilot side (#3). In general though, on my AeroVee the pilot side cylinders tend to run richer than the copilot side, so if there's a solution such as a carb twist to help balance things out, I'd be happy and willing to try. But I hate to run into this blindly, hence the thread.

If anyone has any experience here, please share!

Thanks Everyone!

Mike

[gammaxy]

On my Aerovee, I rotated it about 15 degrees and didn't notice any change, so I rotated it back to the initial orientation. My left cylinders also seem to run cooler than the right ones.

[MichaelFarley56]

That's interesting Chris. I know these engines aren't fuel injected so they won't be perfectly balanced, but I do run into CHT issues on high performance climbs. My right rear cylinder gets warm but it's also the leanest so it would be nice to get that cylinder some more fuel at full throttle.

[fastj22]

I think its more of an issue on the Jabiru. The intake is very close to the back two cylinders. So there isn't much run to atomize. A small change in the orientation on mine can make big changes on how lean #6 and #5 in comparison. The forward four don't seem to care. #6 is always my leanest on climb out. Its closest to the intake. Turbo guys shouldn't matter a nit. And even aerovee with your long intake run.

[sonex892.]

I think its more of an issue on the Jabiru. The intake is very close to the back two cylinders. So there isn't much run to atomize. A small change in the orientation on mine can make big changes on how lean #6 and #5 in comparison. The forward four don't seem to care. #6 is always my leanest on climb out. Its closest to the intake. Turbo guys shouldn't matter a nit. And even aerovee with your long intake run.

I realise this thread is about aerocarb. My experience is only with a bing on my 3300. When it comes to balancing the mixture by rotating the carb, I find that less rotation is actually more. When tuned so both left and right banks are reading pretty even. A matter of just a degree or 2, maybe even less, will spread the left vs right cruise EGTs by 50 degree C.

[jeff0196]

My experience with the naturally aspirated AeroVee and cht and egt is the same as yours. The front run richer then the rears, and the left cooler then the right. My friend and I tried twisting the carb. First 15 degrees, no change, then 30, no change, then 90, no change, then 90 the other side to see if we could make it worse. No change. We gave up with moving it. I have a theory that fuel is dropped into the airstream in large slugs/droplets with the aeroinjector. When they make it to the intake manifold on the head, the inertia carries the heavier still liquid fuel drops to the front cylinders due to the design of the intakes. The left/ right balance must be more like pulses in the manifold and moving the injector one way or the other doesn't seem to help. I think the both left then both right cylinder firing order contributes to this. The uneven running of this system was one of the biggest draws toward the turbo that in my opinion being a draw through turbo can make a homogeneous mixture under pressure that is much less sensitive to the effects of inertia and runs more evenly.

[sonex1374]

I have a theory that fuel is dropped into the airstream in large slugs/droplets with the aeroinjector. When they make it to the intake manifold on the head, the inertia carries the heavier still liquid fuel drops to the front cylinders due to the design of the intakes.

This is exactly the conclusion I have come to as well. The intake design of the AeroVee is simple and compact, and has a lot going for it. However, getting perfect mixture distribution into the front/back cylinders is a bit harder because of this design. I have experimented with various means to better mix the fuel/air charge in the intake, but all the methods I tried were unpredictable and ultimately not worth keeping. I've often thought of continuing the experimentation with vanes installed in the intake runners to better split the intake flow to the front and rear cylinders, but haven't done this yet. The turbo, however, is clearly the best mixture-homogenizer out there!

I have also experimented with twisting the carb, and I have also found that a few degrees one way or another will have an impact. However, if you are running overly-rich to begin with, you probably won't notice the change (it will be obscured in the data). Try leaning to a very efficient mixture setting in flight and you should see the effect.

Jeff

[rizzz]

I have a theory that fuel is dropped into the airstream in large slugs/droplets with the aeroinjector. When they make it to the intake manifold on the head, the inertia carries the heavier still liquid fuel drops to the front cylinders due to the design of the intakes.

It's a shame I only measure EGT's on my rear cylinders (my MGL E1 only has 2 EGT inputs), as I believe the revmaster style intake manifold I have on my VW would fix this issue if your theory is correct. We would have some data to confirm it:

[rizzz]

And on that topic,

Here’s a recent learning I have to share, it may help others.
I recently did quite a bit of work on my engine including replacing the air filter on my AeroInjector.

When I went flying I noticed a serious imbalance in EGT’s left vs. right, well over 100 degrees C! The engine was also not running very well and I had to get the mixture setting just right to get it to run at all.
Obviously that flight wasn’t a very long one.

Comparing the data too older EGT data recorded during phase 1, it seemed EGT’s just went way lower than before on the left and way higher than usual on the right.
I had a serious mixture imbalance all of the sudden.

Because of all the work I had done on the engine it did not immediately come to me what the cause of this sudden problem was but to cut a long story short, it turned out to be the new air filter.
Once I replaced that again with another one all problems went away. Nothing looked obviously wrong with the bad one but I must admit I did not inspect it in detail, it must have had a tear or something which would perhaps “swirl” the air intake much more than usual and thus getting it pushed more towards one side than the other.

Anyway, this might be something to look at if you’re struggling with left/right EGT imbalance.

[Doron]

It looks like the Jabiru main problem is the carburetor is very close the the manifold.
Is anyone ever try to extend the distance by adding a tube between the carburetor and the the manifold ?

Doron