Aero-injector slide binding

[GWMotley]

I have been having trouble tuning my aero injector lately. So far I have ordered a new stainless steel needle as my old brass one seems to have become quite loose in the metering hole of the carb body. I also decided to dismantle the whole carb today just to make sure that no trash had been caught up inside. I noted the the slide had been a little difficult to move. As I took it apart I did note some small bends in the old solid wire control and thought that that was the cause for the friction. However, after installing the new very flexible braided steel wire it was still stiff. What I see happening is that when the cable is pulled to open the slide, it looks like the slide cocks over to the side a little and causes the friction. As you know, the cable is not attached to the center of the slide but over to the side. I cleaned all surfaces without any improvement. I have about 350 hours on this unit. I did not notice any major wear or scuffing on the parts except the Derilin gasket. But even with the top off you can see and feel the binding so I don't think the gasket made any difference. Do you guys think that perhaps the slide has worn some on the sides allowing more side to side movement than when new causing this problem?

[MichaelFarley56]

Sorry to hear this Gary. Is there a lot of play in the slide as you move it inside the carb body? I've never heard of one wearing to the point it causes excessive play but anything is possible.

Do you think it's the carb or the cable? I've heard of people having issues with sharp bends in the cable casuing issues, but if yours was fine for a while I have my doubts that's the problem. Hopefully when you reassmebled the carb you kept all the parts dry. I don't believe we're supposed to use LPS or anything else as that can cause dirt to eventually jam up the slide.

Other than making sure the Derilin gasket is cleaned up (flip it if needed) and making sure everything is nice and dry, I'm at a loss on this one. Hopefully others who have ran into the same issues can comment.

Best of luck getting it fixed sir!

[mike.smith]

I swore up and down for a long time that my slide was binding. I took it apart a couple of times, cleaned everything, checked for signs of wear, but still my throttle was sticking terribly. In the end, the culprit was the routing of the throttle cable. I rerouted like the factory Sonexes, and the problem was instantly solved.

http://www.mykitlog.com/users/display_l ... 3250&row=6
http://www.mykitlog.com/users/display_l ... 3251&row=5
http://www.mykitlog.com/users/display_l ... 3253&row=4

[GWMotley]

Thanks for the thought. However I had also removed the aero injector, opened it up, extended the cable so that it was straight and then pulled with the new cable. It was very evident that the slide is not pulled straight. The inherent problem is the side attach point to the slide. It will push close much easier than being pulled open. I have a message out to Sonex tech to see if they can provide any slide clearance design measurements.

[SonexN76ET]

Have you considered putting a very light coat of fuel lube on the side of the slide that is binding? This is the stuff that Sonex puts on the O rings on the fuel metering valve. There was also an article on it in Sport Aviation last month in using it on fuel drain cocks and as a thread sealant. I bought some from Aircraft Spruce. I put it a very thin coat on the rubber on my fuel cap as a protectant (something it is advertised for) and on my fuel metering valve o rings as specified in the AeroInjector manual when I cleaned my AeroInjector. You may want to do some research on fuel lube if this sounds like something that may work for you. I would be very careful where you put it, however. It does not dissolve in fuel and can build up and potentially plug things up.

[GWMotley]

This is a follow up on my investigation. First, apparently the slides are matched to the bodies according to Sonex tech support and they do not sell them individually. I went back to the hangar today to continue trouble shooting. Again, with the carb opened up, it does appear that the slide shifts when pulling the cable out in a straight line fashion. I lightly polished the edges of the slide with fine grit sand paper just to make sure it was smooth. This helped a little. As I continued to work I noticed that if the mixture needle set screw was not tightened against the needle carrier, the slide moved much easier. I then lightly polished the sharp edges of the flat taper and found that this fixed the issue. Overall, I find the new stainless steel needle to be a much tighter fit that my old brass needle. Now to see if the new needle will help in tuning as I have been having trouble getting a good mixture as when new.

[MichaelFarley56]

Glad you figured things out Gary! Best of luck on tuning; let us know how things go!