Jab burping Update - issue resolved

[ldmill]

Svingen, funny you asked about the filter. Yesterday as I was putting the new #3 needle in, I decided to remove as many variables in the system as I could within reason. I ended up removing the filter and the modest 90 degree between it and the carb after it and went with high quality fuel hose (fire wrapped and no insulation) with a nice sweeping entry into the carb.

As I went back through my records, I did find a note that I had a moderate cough during throttle up on takeoff once after the original fuel line cleanup but when I still had the filter and original carved #3 needle.

Right now the only components in the fuel line are the ball valve and my MGL FlowScan transducer.

I intend on leaning the needle about 1/4 of a turn today/tomorrow and seeing what happens. Will report back.

Lorin

[ldmill]

Still rich at 2850rpm with #3 needle tonight after taking another 1/4 turn out. I then put in a 2.5 needle and set per factory initial setting - and it was still rich across the throttle spectrum up to 2850rpm- not quite as bad at idle as before, and not enough to cause the engine to cough during full throttle up. After leaning a full turn was down to about 120f spread from rich to Lean of Peak at 2850rpm. I am going to try a #2 needle tomorrow.

Ran WOT for about 2 minutes and almost hit 3200rpm. Oil temps never got above 185.

I'm definitely liking the direction this is heading at this point in time.

Lorin Miller
N81YX

[ldmill]

Changed to the #2 needle on Aug 20th and it works absolutely perfect. I had to lean the needle 1.5 full turns from stock factory setting to get it set correct with a 100-120f degree spread on the EGT's at 2850rpm. I hardly have to adjust the mixture setting at all from 2000rpm to 2850 rpm when at LoP. Flew the plane for about 8 hours like this and it worked flawlessly. I was running a high quality rubber based fuel line with firewrap on it and no filter.

So - I decided to modify my fuel line setup and put my fuel filter back in and run the braided fuel line. The engine ran slightly leaner and during taxi back it hiccup'd pretty well. So - the filter (Summit racing brand), is taking enough of a pressure drop when the fuel enters the body that the heat it is picking up is vaporizing the fuel. Also- it is restricting the flow a tad. Not much of a restriction, but enough to lean the engine a tad. Next step is to see if I can't find a different filter that will address this issue. Or, just go back to the standard high quality fire wrapped rubber line with no filter and call it good.

[ldmill]

Soooo, to update all my previous updates. At 130 hours of flight now, even though the plane is flying very well behind the Jab3300/Aerocarb, and all temps are spot on - I decided to make yet another fairly significant change after a comment from my wife and the number of incidents we've had this year in the Sonex community.

Please note that my flight profile also began to change in the last 6 months to include giving rides and flying to pancake breakfasts. This means that the plane would sit for about 1/2 - 3/4 hour after landing, then would be flown again.

You will remember in one of my previous posts that I commented that I started getting a takeoff "hiccup" that I hadn't really experienced previously. Well - this became a common occurrence with the new flight profile- and I was very uncomfortable with it. I'm pretty sure I know the root cause (not the Aerocarb). I believe it is a combination of the Flowscan fuel flow transducer for my MGL EFIS, and heated up auto fuel close to vapor pressure point. The restriction in the FlowScan is really small. Also, my wife started making complaints that the rich exhaust smell during taxi was giving here a headache (even though I would try to keep it leaned optimally) and that she couldn't do this anymore if this issue continued (she's very prone to migraines).

So - over the last several weeks I put my Bing/mechanical Jab fuel pump back on (gasp!!!). Even though the engine came with this setup and went through initial break in with it - I had never actually even tried it. Imagine my pleasant surprise when she cranked over and almost immediately started. Without having to lean the carb, it ran almost perfect mixture at 850rpm. WOT at 2850rpm static. WOT in air at 3200rpm with EGT's in the 1150 range. After multiple heat soakings and WOT takeoff's, I still haven't had an issue. So far, so good. Note - I do like the Bing throttle cable fail mode of taking the engine to full throttle. I never had tried to implement that setup with the Aerocarb.

My opinion - the Aerocarb is a good carb - but for some reason my fuel and cooling system setup just didn't seem to work right with it. So - if all goes well with the Bing during testing over the next 3-4 months, I may be selling my Aerocarb (with throttle cable still installed), needles #2,2.5,3, and 4), and the Aero Conversions throttle quadrant in the spring.

Cheers and happy flying!
Lorin

[fastj22]

The fuel pump and bowl on the bing make sense to solve the burp.
What is your fuel burn before and after the change?

[ldmill]

I don't have a lot of data yet, but right now it looks like I'm burning average about 1/2 gallon per hour more than I was with a fully leaned out Aerocarb. The one big surprise for me was that during extended WOT straight and level, I hit 3200+rpm at 3000ft and was showing about 9gph gulp rate (about 1.5gph higher than I ever got with the Aerocarb). My EGT's however were at 1150 or so with the Bing. CHT's never got over 290f, and oil never got over 185f after about 5 minutes of this. So far, I'm kind of liking this.

Keep in mind that the aftermarket Hacman setup does allow you to manually lean (only) the Bing carb if you want. Also, the Bing now has an electric carb heat aftermarket option as well.

Lorin

[ldmill]

It was 27f out today and I flew 1.5 hours in two equal legs. It was an ultra smooth/no wind day today. Flights were at 3500ft and 4500ft msl. I had installed the dual element electric carb heat from Jabiru USA this last week and it seems to work great. My E-Z Heat system (way cheeper than Tannis and works just as good) had the oil at 125f and the CHT's at 120f when I started the plane - with the choke on, it started on the first blade.
Again, as a reminder - I use premium auto fuel almost all the time. I only use 100LL when I have to.
During extended cruise, my EGT's settled in at an average of about 1240-1245f at 2750 rpm (150mph indicated). Fuel burn rate was 5.26gph. Peak EGT was at about 2700rpm and average temps were about 1255f. When I bumped RPM up to 2800, I could tell I was starting to hit the secondary taper in the needle as the fuel flow rate started kicking up quickly and the EGT temp averages dropped down into very low 1200's/upper 1100's. I've got the stock Bing jets (main jet = 255, needle jet is 2.85) for the Jab3300. Am going to order some smaller jets.
CHT' coldest was 226(#6), hottest one was at 262(#1) - but that was because I had a little too large of piece of tape blocking the inlet. #1/2/3/4/5 range was only 12-13f Usually coldest to hottest range is now 20-30f, #5/6 being the coldest and 3/4 the hottest. Oil temps stayed between 145 - 165f. I only had about 4 square inches of the oil cooler inlet open, the rest blocked off with tape.
I love being at idle and not gassing myself out/fiddling with the mixture, not having a burp any more, and my vernier throttle (used to be my mixture cable for the Aerocarb). Until you use the the Bing, you don't appreciate the amount of force it takes to move the Aerocarb with the Sonex throttle quadrant on a Jab3300. Now it's butter smooth, no creep, and I'm able to fine tune easily with the vernier setup.
Again, so far I'm liking this. At this point, I'm starting to wish I would have started with the Bing.
Lorin

[ldmill]

Latest flight - changed to a 278 needle jet and the EGT's are averaging right at 1290f. Coldest is about 1230f, hotest at 1320f. During climb out, my EGT's average slightly below 1200f, so am changing my main jet from 255 to 250. I doubt that will make much of a change on my cruise EGT's, but will see. I've got a 276 needle jet coming as well just in case - goal per Pete is to get EGT's to average around 1325f and fuel burn at around 5gph at cruise rpm (2750-2850rpm goal). I find my cruise needs to be at 2780 rpm, beyond that I hit the taper in the secondary needle and the fuel burn increases rapidly.

I've spent a grand total of 15 minutes changing needles in the Bing and I've about got the carb tuned now. Very satisfying.
Lorin

[mike.smith]

Latest flight - changed to a 278 needle jet and the EGT's are averaging right at 1290f. Coldest is about 1230f, hotest at 1320f. During climb out, my EGT's average slightly below 1200f, so am changing my main jet from 255 to 250. I doubt that will make much of a change on my cruise EGT's, but will see. I've got a 276 needle jet coming as well just in case - goal per Pete is to get EGT's to average around 1325f and fuel burn at around 5gph at cruise rpm (2750-2850rpm goal). I find my cruise needs to be at 2780 rpm, beyond that I hit the taper in the secondary needle and the fuel burn increases rapidly.

I've spent a grand total of 15 minutes changing needles in the Bing and I've about got the carb tuned now. Very satisfying.
Lorin

For a normally aspirated engine, EGTs really don't mean nearly as much as some would lead you to believe, and probably aren't a determining factor in how you set up and run your engine, unless you have fuel injection with something like GAMI injectors. I don't even look at mine any more, other than looking for continuing trends. This is a really good webinar on the subject:
http://www.eaavideo.org/video.aspx?v=1316946190001

[ldmill]

Thanks Mike - I've been building engines as a hobby for almost 35 years and that's clearest explanation I've ever heard - thanks!! I guess I didn't do justice to the full conversation with Pete on this. He actually didn't even mention trying to limit max EGT at all (which matches up with this video's message)- he was focussed on getting my fuel burn down to around 5 gph at 2800-2850 rpm so that I wasn't running engine too rich and possibly causing longer term issues. His comments on EGT were that the the 6 cylinders would vary between upper 1200's and quite possibly over 1400 which he saw as no issue - but at correct fuel flow rate at cruise rpm, they would probably average around 1325f. My CHT's just aren't an issue any more for me, so we didn't dig into that at all.
Lorin