Jabiru3300/Aerocarb Vapor lock?

[BenCharvet]

I've only been flying my newly purchased Tri-gear Sonex for 6 hours so far, but I'm having some trouble with what I believe is vapor lock. I've searched the archives extensively and implemented most of the suggestions I've seen. N809SX was finished in 2012 and had only 143 hours on it when I got it. The fuel system is very simple with a bulkhead AN elbow fitting going through the fuel flow sensor and a Jegs Fuel filter. A braided stainless fuel line enclosed in fire sleeve curves slightly downhill to the fuel inlet on the Aerocarb. I'm located in Central Florida, so the temps and DA's here are generally high. On my first two flights with my transition coach we experienced a few in-flight burps, and an RPM lag occasionally on takeoff. On my first solo flight I went to a nearby airport for fuel (its always had 100LL), and after a shut-down over 10-15 minutes the engine started and taxied to the runway normally. When I slowly added throttle to take off the engine quit. Again I assumed it had swallowed a big bubble. It restarted and ran fine, and with added throttle took off normally
for the short flight home. On another flight the next day I added more fuel at the same airport, it restarted and took off normally, and when I got back to my home airport the engine quit as I taxied off the runway. At this point for some reason the electric starter would not operate and I pushed it back to my hangar. After sitting for 20 minutes or so the electric starter worked (I could hear the solenoid clicking even when the starter didn't work), and engine started and ran normally.

After searching the archives and Sonex/Jabiru installation manuals I did the following:
Wrapped my exhaust system with DEI Titanium wrap (used about 2/3 ofthe 50 ft roll)
Covered my fuel line, fuel flow sensor, fuel filter, and the lower part of the Aerocarb with pipe insulation
I discovered that the builder had never trimmed the cowl cylinder inlets per the installation manual, so I did that
Enlarged the cowl outlets approximately 8-10 sq inch as Jeff Schultz's website.
Did the FWF part of the annual, comps good, spark plugs looked light tan

I put it all back together and flew it yesterday. No problems on taxi, smooth burp free takeoff! I took it up to 3000 ft, OAT was still 86-88F. Throttled back to do a clean stall with mixture full rich, and before it got slow enough to stall the engine started to quit, so I dropped the nose and added throttle. Trying the same stall again with the mixture leaned at the same position as cruise flight I was able to get it slowed down to the buffet with no noticable engine stumble. I kept the mixture leaned to the cruise setting to a normal landing, and it idled noticably smoother than it had prior to my changes above, but 100 ft from my hangar the engine quit again without any warning. It restarted normally and I taxied it back. I let it idle at around 1000-1100 rpm and tried messing with the mixture control, and it didn't seem to have much effect. I could pull the mixture within 3/8 inch of shutoff, and it still idled nicely, with the same effect at full rich.
Today I taxied it around a bit with no problem (had a buddy watch my exhaust to see if it was blowing black smoke like it was rich, it wasn't) and got everything up to temp, and did a takeoff. It had a brief lag on acceleration, but a normal takeoff, came back to land and it idled well all the way back to my hangar and idled there 5 minutes with mixture full rich with no stumbles. 30 minutes later I hit the Aerocarb with an infrared thermometer and it was still at 135F.

In my installation the Aerocarb sits right behind the oil cooler. Has anyone made a deflector to direct that heat down and out and away from the Aerocarb/Aeroinjector? There is nothing left to insulate. Anyone else had a problem with the starter when it's hot? Next flight I'll check the temp on the Aerocarb right after shut-down. Sorry for the long post, but I know there is a lot of expertise on this forum, and I need some fresh ideas.

[Sonex1517]

Hi Ben

I’m glad to see you asking in such detail. I’m sure others have much more wisdom to offer, but there’s a couple of things I’ll offer up.

1. Have you tuned the AeroInjector? I’m not sure where the airplane was based previously or if you’ve adjusted anything, but there are sometimes seasonal adjustments required. If there is a difference in where it was based to your current location it’s worth looking into.

2. It is possible the injector needle is not staying put. On mine I had to very lightly peen the threads so when I made adjustments it stayed where I put it. I had less worrisome issues but once I peened the threads and retuned it, I didn’t have any more problems.

Be sure to carefully follow the directions in the manual if you do re-tune it. The rest of what you describe sounds like the burps.

Kudos for reaching out!

[caveman371]

I’m by far an expert but where/ what altitude did you’re plane come from. If your carb was set at a higher field elevation it might be running lean where your at . Someone else may chime in here but you might need to re- a just your carb . Find out what needle is in there also
As for the heat, every time I stop the only thing extra I do is get your oil access door open immediately and let the hot air out. That really helps with mine. Have you asked about a burp tube ( John Gillis made mine). The starter issues could be heat buildup but someone that has more information could chime in on that one.

Mike


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[tx_swordguy]

I have the same basic setup. I have no gascolator or fuel flow indicator. I have my FW forward fuel line heavily insulated and wrapped in aluminum hvac tape. I also have a deflector behind the oil cooler that directs air down toward the exit holes.. I have a heat shielding over the exhaust pipes and fiberglass heat wrap on the pipes as well. I have never had the burps that you are talking about. I run 91 non ethanol auto gas. I do not know what needle you have, but at the very least I would clean the carb and perhaps start at the recommended needle setting to start. That would most commonly be a 3 for the jab with the start of the needle bevel just at the bottom of the slide. There are numerous post about this Jeff Schultz being more or less an authority on this. Give that a start and see what happens.
The starter may or may not have issues. Although it is hard to do, if the starter won’t move tap the starter casing with a hammer. Not beating the crap out of it but a fairly good wack. That causes any dust on the brushes etc to fall and conduct the electricity. If that works the starter might need rebuilding. You may also need a better ground for the starter ( sounds weird I know with the starter bolted to the engine block) aluminum gets corrosion and sometimes won’t conduct . A second ground can sometimes help that. Anyway hope that gets you started.

[BenCharvet]

This airplanes built and flown locally, so altitude changes probably aren't the problem

[GraemeSmith]

As a general statement about ANY setup - experimental or certificated. I'd be looking at the environment. 3,000ft over mid Florida with temps in the high 80's (was that on the ground or OAT?). Without the pressure I can only guestimate you might have been 3,000ft MSL but anything from 5-7,000ft DA. So you are almost certainly too rich. Full Rich for stall practice may not be appropriate - even in a good set up. And that fits your description of how you did get the engine to run for the stall practice. Lean for take off and altitude to suit environment. Automatically picking full rich works for CFI's getting students succesfully airborne MOST days. But it's not always approriate.

Try the opposite. Up here in New England in the winter in really cold dense air - it's hard to get rich enough!

--

Specific to your setup - I'd be looking to get some cold(er) dense outside air onto that carb rather than running on the hot left overs from the oil cooler.

This car has a Hood Scoop for a reason (at least if there is a real performance engine under the hood and it's not just for show)....

[OneTallShort]

Have you done a fuel flow rate test at the carb?

How is the tank vent plumbed?

[Onex107]

My AeroInjector is on an Aerovee but I think we have had the same problem. Heat. In my case in order to cure the burps I removed the gascolator and insulated everything else. Wrapped the pipes, and it worked fine until a hot day last summer. After flying the engine would surge. Like it was running lean then rich. wouldn't idle at all. This had been going on for a long time but I thought it was just a bad needle set up. I had a hole in the front baffle that had been used in an early attempt to solve the burps, and had been abandoned. So I added a scat tube to the front of the AeroInjector, the mixture valve end, and it was like day and night. The next flight the engine idled great at 950 - 1000. My system is insulated, all but the alum body of the AeroInjector. I have to presume I was getting vapor at the mixture end of the slide. It was not a burp, It was a surge. The rpm changed. Lean then rich. In 300 hours I have had two other failures I attribute to heat. One ignition coil and the voltage regulator. Both mounted on the fire wall. My oil cooler is mounted on top of the engine and there is no fresh air intake in the bottom of the cowl. Your oil cooler is probably adding to the problem like mine is on top. The oil temp is running in the 180 degree range on a hot day and, in my case, the only air flow to the rear of the engine and the AeroInjector is through the cylinders and oil cooler. Hope this gives you a different look at the problem.

[sonex1374]

A few general thoughts first, then some specifics to the original post....

I think the first thing people need to recognize is that when the outside air temps are hot, the entire system under the cowl of a Sonex or Onex is pretty stressed. The installation is tight, and heat tends to build up over time. It's a torture test to fly the plane for an hour on a hot day, then park the plane in the sun for an hour, then fire up and go fly again. The heat from the flight and the baking in the sun heat-soaks everything. Those conditions can be a challenge for even the best installations.

The methods to resist these harsh conditions is a menu of options. You can use a few of these techniques and get some benefit, and a few might be enough to keep the engine performing well in your typical conditions. But, you might need more in the harshest of conditions. You'll just have to experiment to see.

Insulating the fuel system is a great first step to keep the heat out, but if that doesn't work, there are a few other things to try. You can install heat shield/heat deflectors between the hot exhaust pipes and your carb/fuel lines, you can use header wrap on the exhaust to keep the heat inside the pipes and going out the tailpipe, and you can supply the carb body with fresh outside (cold) air. Fresh air to the carb can be a simple as some cool baffle air routed to blow on the carb, or as complicated as an enclosed filter box supplied exclusively with cold outside air that is then routed to the carb. Using either approach will certainly help.

The carb has a pretty good chunk of metal that can absorb a good deal of heat. This means that it will take time to thoroughly heat soak, and it will take time to cool back down again. Keeping the heat out in the first place is a good preventive measure. From my own experiments, I concluded (my thoughts only here...) that my AeroVee just seemed happier and smoother with cool air intake, and that it was worth the effort to install. However, my Jabiru has run ok without cool air largely because it is always flying faster and working less-hard to do so, so the heat soak under the cowl just isn't occurring. Cold air would certainly give me even more margin, but it just hasn't been an issue for me (not to say it couldn't, or it wouldn't for someone else).

Now to the specifics.

At this point for some reason the electric starter would not operate and I pushed it back to my hangar. After sitting for 20 minutes or so the electric starter worked (I could hear the solenoid clicking even when the starter didn't work), and engine started and ran normally.

This certainly seems heat-soak related. Maybe the starter is binding up internally when hot and expanded, but this goes away when cool. You could try two things. If the starter doesn't turn when hot, determine how easy/hard it is to turn the engine by hand using the prop. If the engine is really tight, this could be a clue. Second, you could put a volt meter on the starter and see what the voltage is at the starter terminal before and during a start attempt. A jammed starter should be pulling a lot of current to try to turn it, and you'd see some voltage sag. Some test data might shed some light.

I let it idle at around 1000-1100 rpm and tried messing with the mixture control, and it didn't seem to have much effect. I could pull the mixture within 3/8 inch of shutoff, and it still idled nicely, with the same effect at full rich.

It sounds like the mixture is pretty rich at idle rpm setting. Being rich at idle will allow you to lean quite a lot before the engine stumbles. It's common at idle to pull the mixture knob out halfway without any real indication of leaning, then pull some more and it starts to actually lean out, then continue to lean and it runs better and better until you finally go too lean and it quits (all within the last little bit of knob movement). It's just they way it is with the low fuel demands of the engine at idle.

It had a brief lag on acceleration, but a normal takeoff

Rapid throttle movement on takeoff will commonly cause a brief lag in acceleration. The slide is quickly moved to full open, then the airflow to the engine increases all at once but the fuel flow hasn't quite caught up yet (the fuel droplets have a bit of inertia and don't speed up for a fraction of a second). This causes a temporary lean condition that goes away almost immediately. Slow movements will prevent this. This dynamic is why carbs often have accelerator pumps.

30 minutes later I hit the Aerocarb with an infrared thermometer and it was still at 135F.

Sounds like the body is retaining a lot of heat. I think you'd benefit with some cool air directed on the carb itself.

Has anyone made a deflector to direct that heat down and out and away from the Aerocarb/Aeroinjector?

Although I can't recall anyone mentioning an oil cooler heat deflector, it could help. If the air exiting the cooler is bathing the carb body in warm air and heat soaking it, deflecting that air to the outlet and not onto the carb body should help. What are your typical oil temps? The hotter the oil temps the hotter this discharge air will be.

I think you're doing all the right things and on the right track. Keep at it and I think you'll get this iron out. If you have any pictures of the area and your engine installation that might help generate some additional thoughts or ideas as well.

Jeff

[sonex1374]

Some additional searching on an oil cooler exhaust air deflector yielded the following thread from a few years ago.

viewtopic.php?f=8&t=1274&p=9040&hilit=lesson#p9040

Jeff