Fuel setup.
Posted: Thu Oct 15, 2015 2:54 pm
by vwglenn
So I’ve decided my 3300 has got a case of the burps. My machine has a Jabiru 3300 running an aerocarb which still has a gascolator and all the associated plumbing. My intention is to run a straight shot to the aerocarb and install an inline filter.
Summit Racing (not far from my house) has some inline filters with male AN fittings but I don’t see any that are clear (visual inspection) on their site. Also, none seem to mention whether they have replaceable elements which leads me to believe they are throw away filters? Since the AN fitted filters seem to be running around 80 bucks (a lot of cheddar for a throw away part). I wanted to know what you guys who have done this mod have used.
Re: Fuel setup.
Posted: Thu Oct 15, 2015 3:27 pm
by marsolgp
Just my opinion…. of all the posts on ‘burps’ the common denominator is the aerocarb/aeroinjector…… some people run them without issue, others not so lucky…… I ran one and had burps. Changed to another type of carb, kept my fuel flow sensor and gascolator (uninsulated) and even with the extra heat generated by the turbo, I have not had a single stumble or burp since and that’s been over a year now.
Re: Fuel setup.
Posted: Thu Oct 15, 2015 3:53 pm
by mike20sm
Interesting. What type did you change to and have success with? I’m still in the ealry learning phase of deciding which engine/carb to go with. I attended the Contact magazine alternative engine seminar last month and learned alot. I saw a slow motion video of the spray bar of this carburetor http://www.ellison-fluid-systems.com/articles-notaposa.shtml which I thought looked like an intriguing possibility.
Re: Fuel setup.
Posted: Thu Oct 15, 2015 4:18 pm
by marsolgp
It’s a Rotec, which, by there own admission is an improved upon Ellison.
Re: Fuel setup.
Posted: Thu Oct 15, 2015 5:28 pm
by wlarson861
The in line filters have very fine screens that are removed and cleaned at annual inspection. Have been running mine a few years and never found anything other than a couple of plastic shavings from a gas tank repair. Removing the gascollator removed the burps.
Re: Fuel setup.
Posted: Fri Oct 16, 2015 8:34 am
by vwglenn
I understand the common denominator with the burps is the Aerocarb. I also understand the problem comes from heat soaked fuel system on the engine side of the firewall. The easiest, cheapest, and lightest repair seems to be to simply make a shorter run to the carb and insulate what I can. There have been some concerns about water in the system. I haven’t ever seen a drop of H2O when sumping the fuel and the carb will be the lowest point in the system. Since there is no bowl in the Aerocarb there is no place for that water to collect and any at the base of the run will get vaporized on startup if any accumulates. I’m going to make the mod, I was really just asking about inline filters and those have done the mod are using.
Here’s my opinion about the filter…Would I like to see if it’s dirty? Sure but how often is that going to happen? Only when I have the cowling off. I’m more comfortable with an filter where I can’t see the element (AN fittings) than a clear one which has to be clamped into place.
Thanks Bill for weighing in. I was thinking the same thing. If the filters have a cleanable element, just be sure to clean it every time the plane is in annual or when I have the cowl off.
Re: Fuel setup.
Posted: Fri Oct 16, 2015 10:50 am
by fastj22
I’ve got around 200 hours behind my Aerocarb and here are my observations.
This summer 4 Sonex flew to an airshow in Colorado. All Aerocarb equipped. The planes sat on the line for 5 hours heat soaking in the 100 degree sun. My cowl allows the top to hinge open and I left it open to allow the crowd to peer inside. It also let all the heat out. The other Sonex stayed buttoned up. One sonex was based there and didn’t depart after the show.
I was first in line to depart and after a fairly long taxi, was finally cleared. I as running AvGas, gascolator. I had burped my system (burp tube) before taxi yet was still feeling some burps as I launched but it cleared before the end of the runway.
The second sonex, also with burp tube, launched behind me. AvGas, gascolator. He burped all the way down the runway and for a few miles after too. He radioed to me that he was considering turning back but then it cleared.
The third sonex, no burp tube and running auto gas, no gascolator, was burping so bad on departure he returned to the airport immediately. He ended up spending the night with the other sonex flyer and departing the next morning.
Burping is clearly related to heat soaking and fuel type. Auto gas burps more than AV Gas. If you are doing multiple stops, you will accumulate heat in the system on every stop. You can mitigate many factors, but in the end, without a circulating system, a pressurized system or carburetor fuel bowl to absorb the bubbles, you will burp.
For a number of reasons, I’m installing a Rotec with a circulating system.
Re: Fuel setup.
Posted: Fri Oct 16, 2015 12:29 pm
by vwglenn
Interesting John. I run AVgas and my first experience with burps in flight was two days before the Crossville gathering. It was a test run to see how the plane would handle some cross country work and get an idea of what my fuel burn would be. It wasn’t a particularly hot day. 75 degrees at field elevation and cooler at my initial cruise altitude of 3500ft. I had a burp as I brought the power on for takeoff (something I’ve experienced before). I climbed pretty aggressively but none of my CHTs got in the yellow. Then I leveled off and set up a 2900rpm cruise. About a minute later I started burping and it did so about three or four times. Luckily I was over a relatively close airport and was about to land there when they stopped. I decided to head home. No burps on the way back or in the pattern. Although none of the gauges were in the red when I landed, the engine smelled hot when I shut down. I’ve considered the burp tube, piping air to the gascolator but the straight run seems like the most effective for now. I realize some people have had luck with it and some haven’t. I’m just hoping I’m one of the lucky ones. At this point I’m going to start with the easy/cheap stuff and work my way up. I can always put the gascolator back on and start over if I decide to switch to a more conventional carb or TBI.
Re: Fuel setup.
Posted: Fri Oct 16, 2015 8:48 pm
by fastj22
I’ve never had a burp after the initial ones cleared during the takeoff roll. Acceleration may be a factor too.
Re: Fuel setup.
Posted: Sat Oct 17, 2015 12:06 am
by ldmill
John is absolutely correct above :“Burping is clearly related to heat soaking and fuel type. Auto gas burps more than AV Gas. If you are doing multiple stops, you will accumulate heat in the system on every stop. You can mitigate many factors, but in the end, without a circulating system, a pressurized system or carburetor fuel bowl to absorb the bubbles, you will burp.”
I fought the burping for the first 130 hours on my plane and finally grounded it after an extended flight down to Kansas City from Central Iowa when the engine began burping continuously last 20 minutes of a 1.8 hour flight (scared me and passenger badly) - the engine compartment was thoroughly heat soaked. This was after removing gascolator and going to a high quality in-line fuel filter and a modified fuel line system where it ran straight from the tank downward directly to the Aerocarb.
Final solution was to put the original Jab fuel pump and Bing carb back on. As of 60 hours later I’ve had not a single hiccup or burp. It took me 1/2 hour to get the correct jets in it and install an electric carb heat system. I think that as tightly cowled as the big-6 Jab engine is in the Sonex, and if you are running auto fuel, you are much more susceptible to burping. Also - keep in mind that unless you install a heat deflector behind the oil cooler that; 1) you are pre-heating the carb because you’ve got hot air coming out of the back of the oil cooler and dumping straight back onto the carb, 2) your exhaust pipes are about 4"-6" from the sides of the carb. Lot’s of heat on the back end of the big-6 Jab.
Lorin Miller
N81YX
Re: Fuel setup.
Posted: Sat Oct 17, 2015 12:25 am
by gammaxy
vwglenn wrote:About a minute later I started burping and it did so about three or four times.
Are you sure its burps and not a mixture problem? I don’t think I’ve ever experienced burps although I do regularly experience a “miss” if I advance the throttle rapidly during the takeoff roll–I don’t know if this is what others call a burp or not. I blame my “miss” on the lack of an accelerator pump. Anecdotally, this seems to happen less the richer I have the needle adjusted.
I have also experienced surging near idle settings when in a descent (my working theory is at a fixed throttle setting, the propeller spins faster in a descent than on the ground so the same amount of fuel is metered into a larger amount of air causing the mixture to become leaner. If the setting is pretty marginal on the ground, it might become impossible to adjust the mixture rich enough while in the descent and it surges).
I also regularly pull the mixture lean during climb-out for additional power, but if I level out and leave the throttle at WOT, I need to richen the mixture to keep it running smoothly. This seemed counter-intuitive at first, since I expect to lean at altitude, but I also never fly other airplanes at WOT in cruise 
None of these sound quite like what you describe, but have you overruled a mixture problem at 2900 rpm? Intuitively, I would expect you to be moving fuel (and air) through the cowl fast enough at that power setting not to have to worry much about vapor issues. I also admit that the Jabiru 3300 is probably completely different than the Aerovee I fly.
Re: Fuel setup.
Posted: Sat Oct 17, 2015 4:57 pm
by RodgerC
For years I’ve read about the infamous burb in this forum, and its predecessor, along with the guaranteed fixes that include tossing the Aerocarb, change/tune needles, burb tubes, insulation, gascolator removal, cowling mods, fuel pumps, Rotec TBI/Bing carb etc etc. The list goes on. At the risk of extending the debate indefinitely, I’d like to add another possible modification that might be worth adding to the list. Although I’m not certain I’ve ever experienced a true burb (Other than those induced by Coca Cola) I’ve certainly had engine misses, though usually during partially closed throttle settings…Decents, taxiing etc. After doing all the usual fuel line fire sleeving and insulating with that nifty self-adhesive reflective fibreglass sheet/tape, it occurred to me that the clearance distance between my exhaust pipe and fuel line was only 1/2 to 3/4". Not a lot when fuel is slowly passing by it due to partial throttle setting. After considering and rejecting the idea of wrapping the exhausts in glass tape, I fabricated a concave heat deflector and strapped it to the exhaust just below where the fuel line crossed overhead. Now it could be pure coincidence, but my engine misses have gone away. So perhaps, before throwing out the baby with the bath water, maybe check fuel line to exhaust pipe clearance and if it seems too close, spend a couple of hours making a heat deflector and see if things don’t improve for you too.
Re: Fuel setup.
Posted: Sat Oct 17, 2015 7:59 pm
by vwglenn
I’m not certain about anything but the inconsistency of the aerocarb from plane to plane. Some people have no issues running a gascolator. Some have fixed the problem removing it. Some have piped fresh air in. Some have given up and moved on to something else.
My plane didn’t come with a pump or a Bing so I’m going in order from the easiest/cheapest fix on up.