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For several weeks I've been chasing high CHT's. I've moved the oil cooler and it's air intake. I've removed
the baffle under the oil pan and closed off the front hoping to get more pressure difference above and
below the engine. Nothing I did made a difference. In addition I was gradually richening up the needle
position .. or so I thought.
Then I removed the carb to look it over and noticed that whenever I tightened the set screw against
the needle carrier it was also screwing the needle carrier in leaning out the mixture. Because of the
simplicity of the aeroinjector it never occured to me that the needle position could be changing.
Now the scarey part. This morning while I had the carb off and could watch it I reset the needle to
the starting point and while holding the needle so it couldn't move tightened the set screw.
I went flying to test. About 2 miles from the airport my CHTs hit 400, then my EGT's shot up over 1400.
At the same time the plane was losing RPM and wouldn't run at other than full throttle. I managed to make it back to the airport at full throttle position with the declinging RPM. I'm attaching a pic of what I found afterward. The needle carrier had vibrated loose and worked it's way IN in the course of the 5 min or so I had been flying. I made sure the set screw was tight against the carrier screw before I fired it up.
The board won't let me upload the file. I'll try to reduce it later when I get home. But the needle had worked it's way in by about 1/2 inch or more nearly shutting off the fuel completely. Had I not been close to the airport I would have ended up in the swamp.
I won't fly behind an Aeroinjector again. Does anyone have any other carbs they've had good luck with?

RT

Roger,

The threads on the needle carrier and set screw are fairly coarse, and subject to loosening with vibration. If your needle carrier moves very freely you may consider deforming the threads slightly to reduce the tendency to move. "Peening" the threads slightly with light taps from a hammer will deform them sufficiently to stay put. Essentially, you're mimicking the action of a locknut by doing this. Also keep in mind that over the course of time vibration can cause wear and change things within the carb body and threads, leading to a gradual change. This is something that should be inspected periodically as there's no set pattern to the wear.

Jeff

Hi Rt,
We started out with a aeroinjector, but promptly switched to a rotec. Very happy with it on a jab3300
If u purchase a used one make sure u upgrade to the new diaphram design , about $200.
Good luck!!

WaiexN143NM
Michael

WaiexN143NM wrote:Hi Rt,
We started out with a aeroinjector, but promptly switched to a rotec. Very happy with it on a jab3300
If u purchase a used one make sure u upgrade to the new diaphram design , about $200.
Good luck!!

WaiexN143NM
Michael

My Rotec carb put me in a field due to the diaphragm design.
Rotec offered no assistance besides requesting a large charge to upgrade it. Buyer beware.
I have a slightly used Rotec on my desk (paper weight) that I wouldn't sell to my worst enemy.

Hopefully the pic came across. How I found the needle position after my incident.

Rt

I had the same issue. If you put a ball bearing inbetween the needle and lock but and your problem will be solved.

hi all,
we started out with an aero injector, but had very bad experience with it. we have a jab 3300, we contacted tech support for advice. we upgraded to the larger diameter throttle cable, cable and aeroinjector orientated properly. worked ok when engine was not running, but with the engine running
the induction suction caused the tbi to lock up. you couldnt move the throttle. we installed the rotec, 5 min to adjust the idle mixture and has been working great. we upgraded to the newer diaphram design ,
about $200. has been trouble free. we have a slighty used aeroinjector for a jab 3300. sitting on the shelf. $395 new, make an offer, first reasonable offer gets it. would be happy to sell it, to anyone friend or foe. good luck.
added:while i agree with john that rotec should be giving these diaphram upgrade kits out for free, i didnt want to risk myself or plane over $200. rotec will have some diaphram upgrade kits at oshkosh , suggest to anyone with a rotec to pick one up, save on shipping costs. you may even barter with paul for a better price. with the upgraded diaphram i have full confidence in our rotec tbi.

WaiexN143NM
Michael

RT.......another option would be the Zenith carburetor. This is what I have on my Hummel 2400 powered Onex. Not sure where you would buy one.....it came with my engine from Scott Casler in Arizona.

In this hot weather there has been NO problems with burping or vapor lock.....(all fuel lines are fire sleeved). The engine runs great although I am very early in the "test phase" so the jury is still out.

A downside is you must have a carb heat box to address carb icing.

Gordon....Onex....First flight June 17, 2018

I'm going to look at all the carb options. I'd just as soon not have to deal with plumbing carb
heat if I can get away with it.
I'm concerned that apparently Sonex is aware of this happening and hasn't addressed it. At a
minimum the slide should have a pin going thru it to keep the needle carrier from moving out
to the lean position like it did with me. This a huge safety issue. The idea of peening the
threads isn't that attractive because it will gall up the threads inside the slide.

I appreciate all the input.

RT

You have a tapered end of one set screw bottoming out on the hex opening of the second one. Take a close look at the two surfaces. The contact area can be very small. The ball bearing idea over comes the problem, but tight is tight and mine hasn't moved in 250 hours. No peening required.