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lutorm wrote:I added a very small O-ring between the adjustment screw and needle carrier. The intent was to get rid of the play where the carrier is held in the screw, but it also had the unintentional side effect of acting as a "thread locker" of sorts since the friction against the O-ring prevents the screw from turning freely. I don't think it would move under vibration even if the set screw came loose.

Based on my experience I think that would provide a grip which would screw the carrier in with the set screw as it was tightened. It may keep the carrier from vibrating loose from the set screw and coming out of the slide all the way like mine did. That is the dangerous situation that I had.

RT

lutorm suggested putting a small O-ring behind the needle holder. Excellent idea. It not only eliminates the play in the ball/socket but acts as a thread locker. We, I and another builder, elected to have made a new needle holder and set screw with a disk/slot instead of the ball/socket. Play eliminated. Maybe the new set screw with a disk is tighter than the original, I don't know, but mine hasn't been a problem for 250 hours. If I had it to do again I'd go the o-ring route. That's something to think about. The set screws are 3/8 X 16 threads. One turn equals about .060 linear movement. Mine had about .020 slop in the ball joint. That's almost 1/2 a turn. You can't make repeatable adjustments with a needle holder that loose.

So here are your options ....
If flying a Jab, you can hang with the Bing. Lots of Sonex drivers have done this, gotta figure out carb heat and mixture control if you want it. But good results, no burbs due to the bowl. I've disassembled a Bing and it ain't a simple carb. Good atomozation of the fuel = good spread of fuel to all cylinders.

Fly behind a Rotec. Really pretty TBI with a very delicate pressure regulator required to make it work. If it sticks, you go down. Do you really want to rely on a device firewall forward that can shut off fuel flow because it gets sticky? Good atomization of the fuel = good spread of fuel to all cylinders.

Fly behind an Ellison TBI, are they still being made and supported? Unknown on how efficient it atomizes fuel.

Fly behind an AeroInjector. Lots of drivers are doing this. Sure it has some tuning issues but its wicked simple. Failure points are basically the walking needle if the set screw isn't properly set. Work that out, and it won't fail you and put you in the mud. Poor atomization of fuel, by rear cylinders are richer than the fronts on climb out.

I've moved back to the AeroInjector. I've really torqued the set screw on the needle as I have had it walk lean. I set it pretty rich. I then use the mixture to adjust the mixture. I'm based at 7000ft MSL. I have to lean it quite a bit here, near idle cut off. But when I head south to Texas, I have plenty of richness to keep in spec at 800ft. I enjoy the fact I don't need a fuel pump or rely on a very complicated pressure regulator.

Thanks, John, for your summary. There's also Zenith or Revflow.
The thought of having to add a fuel pump or regulator doesn't appeal to me that much,
since it adds another point of failure.
The main safety issue is the ability of the needle to walk out of the slide and go way lean,
causing the engine to not run. That's the biggest concern. The slide should have been designed
so the needle can't go all the way thru and has a maximum lean position. So that's what
I'm thinking about .. a fix for that. A couple things come to mind. Putting a pin or rivet
in the path of the needle/carrier so it can only go in so far. The underlying issue is that
the hard stainless screws are wearing the aluminum and loosening. I'm wondering about
putting in a threaded sleeve much like a Time-Sert or Helicoil plug repair insert. I'll probably
try some threadlocker on the carrier screw too.

RT

So the Rotec tbi ,

If there is an issue its supposed to supply fuel when the primer is manually opened.. adjust the mixture so it runs ok then limp home? The ppl that have had failures with them did this not work?

I've had the aerocarb and rotec tbi version one and two on my engines and believe I prefer the Rotec hands down.

Just a point of clarification on the carb comparison. None of the ones listed require a fuel pump. They will all work with a gravity feed system. Some like the rotec and zenith can work with a fuel pump if you dont have a gravity feed system like the sonex does and some like the aerocarb and the revflow wont work with a fuel pump at all. For a typical sonex setup any of the carbs listed will work.

Keith
#554

floridasonex wrote:

lutorm wrote:I added a very small O-ring between the adjustment screw and needle carrier. The intent was to get rid of the play where the carrier is held in the screw, but it also had the unintentional side effect of acting as a "thread locker" of sorts since the friction against the O-ring prevents the screw from turning freely. I don't think it would move under vibration even if the set screw came loose.

Based on my experience I think that would provide a grip which would screw the carrier in with the set screw as it was tightened. It may keep the carrier from vibrating loose from the set screw and coming out of the slide all the way like mine did. That is the dangerous situation that I had.

The O-ring is between the adjustment screw and the needle carrier, preloading the ball joint between the two. It does not affect the set screw, it merely makes the adjustment screw harder to turn.

Brett wrote:So the Rotec tbi ,

If there is an issue its supposed to supply fuel when the primer is manually opened.. adjust the mixture so it runs ok then limp home? The ppl that have had failures with them did this not work?

I've had the aerocarb and rotec tbi version one and two on my engines and believe I prefer the Rotec hands down.

When my regulator shut off fuel, even pushing the primer button didn't help. Once I took it off the airframe and was blowing through it, wiggling the primer button as I pushed it, it finally opened. Disassembly found nothing out of the norm. Reassembled and it worked fine. Not knowing and no help from Rotec has left me with an expensive paper weight.

The RV guy I emailed with had the same experience as John. The primer button didn't work for him, but he was high enough to make a 180 and land on the runway.

He also told me that he got Rotec to buy it back from him, and is now using the Ellison TBI, and is happy with it. He says the Ellison is way better quality.

Well that's a bit unreasuring.. I have always had that happy thought that the primer button would be my saving grace in an issue....

Certainly know what you mean about the help from the Rotec factory...... Paul has never been any help and usually quite condescending if I've actually needed to ask anything.. but I do really like how that TBI makes the engine run...


As much as I absolutely hate the Aerocarb I could probably think about refitting it for the sole reason to a add fuel injection system like Chris's one from Australia and have it as a back up...

Prob is my plane is finally going sooooo well now, I am hesitant to touch anything... only prob is I have to keep putting fuel in it now :)