Tuning the Bing CAMit 3300

[kmwoody]

Hi all,

I am attempting to tune the bing. The EGTs, in cruise, 2850 rpm, are only registering in the upper 1100F range. I have changed from the 280 main jet that came with Bing, to 250 and the 2.80 needle jet that came with the Bing, to 2.76 and the EGTs went up 50F. I changed the needle jet again to 2.68 and the engine would not stay running. I then changed the needle jet to 2.72 and the main to 245, the EGTs did not change. The engine still runs great.

Today I opened the Bing to adjust the jet needle leaner but there was only one circlip position. I am not sure where to go from here.

I was quite surprised to see the 280 main jet, I believe Jabiru USA sends a 255 main with Sonex applications. I have heard that Jabiru USA has their own jet needle they put in for Sonex, is that right?

Ken W
Sonex 959
Camit 3300

[ldmill]

Hi Ken,
I just realized I haven't sent my extra jet's to you yet, will try to get them out tomorrow. Try a cruise setting of 2750-2800rpm. At 2850rpm I'm into the main jet - the needle jet has a very small impact on temps for me. At 2850rpm my fuel burn is somewhere around 6.5gph. At 2790rpm, it's dropped back to around 5gph with average EGT temps around 1315f. At 2850rpm, my EGT temps are down into the 1200's.

Lorin

[kmwoody]

Lorin,

I know the EGTs rise into the lower 1200s when I am in the 2750 range. I was going by the "Tuning your Bing" guide by Jabiru. My Prince must be slightly off pitched because I only run 3050 rpm wide open and at 2850 I run +11 mph over your avg. Static is 2825 rpm. My cruise would probably be more in the 2750 range.
Thanks for the info.
You don't need to send the jets because I am already running leaner jets and the engine is running strong.

Ken

[DCASonex]

Ken,

Running a 282 main jet with a "standard" Jabiru Economy needle, but one that has been ground down a bit in the swelled area as I ran too lean in cruise. That is with no cold air intake and just a K&N filter on carb inlet. Think I have your direct e-mail so will send drawing of that needle profile. However, since your engine flat out quit with smaller main jet, suspect your EGT readings are not true for some reason or other. I have the HACman mixture control on mine and can very easily get the EGTs too hot before engine quits.

David A. CAMit 3300 in Sonex TD

[kmwoody]

David,

I have read in the archives of others jetting. I am trying what I can first before I file needles. I don't like messing with carbs in the first place much less machining parts on them. I think my best bet would be to order a Jabiru needle and see where my temps are with it.
My engine would not stay running when I put in a 2.68 needle jet and a 250 main. I then switched to a 2.72 needle jet and 245 main, what I have in now, and EGTs are still low on main and needle jet.
My EGTs are located as per CAMit instructions at 42mm below 1,3,5 and 35mm below 2,4,6. I might try insulating my cold junction, as it could be too hot located on the firewall.

Ken W

[DCASonex]

Ken,

Did not have CAMit's recommendation for EGT locations when installing mine which are at the old location 100 mm down from ports, should be hotter at your locations closer to ports. With Jabiru "economy" needle, was getting too much spread between WOT and cruise. My "machining" consisted of putting the Jabiru standard economy needle in chuck of an electric drill, and pinching the swelled area between two small knife sharpening stones. Only removed a couple of thousandths of an inch, even a few ten-thousands will make a difference.

However, from your reported results, still would look at possible problems in EGT sensing, but doubt if cold junction at firewall will account for the majority of the differences you are seeing. Those do seem to be undersized jets. One attempt to fly mine with a 2.76 jet, all went red (EGTs too hot) on takeoff It is possible that If you are not seeing black on the plugs or out the exhaust at those EGT's you might be so lean as to be operating lean of peak even at WOT. On opposite extreme, too much fuel can wash oil from cylinder walls resulting in scoring. Proceed with care.

If ordering new needles, I would get two so you will have a standard to compare to, and one to play with. I needed a 2.85 jet with the stock economy needle but am running a 2.82 jet with the modified needle. If I did not have the HACman installed, probably would use a 2.80 jet. If you have an air-box or any other type of intake other than filter directly on the carburetor, or significant differences in cowl or baffling, pressure at your carb may vary your results. (I have the carb's air pressure sensor line directly into the air filter.)

If all looks reasonably close with standard Jabiru economy needle and a 2.85 jet but too much spread between cruise and WOT and do not want to attempt to polish a needle down to size, could mail me one, takes only a minute or so, but no guarantees it will be correct for your installation.

Note on jet sizes, the designation 280 indicates a bore of 2.80 mm, and these can be slightly opened up to a larger size with appropriate drill bit.

David A. CAMit 3300 in Sonex TD

[DCASonex]

Ken,

Re-reading your last post in Bing carb jet sizes., I may have over looked something. Been about 2 years since last played with mine. But although your are finding EGT's too low, the small size of the jets you mention has me thinking you may have your engine running too lean. If that is the case it may be due in part to main (bottom) jet. You mentioned trying 250 and 245 main jets, but if memory is correct, I found I needed at least a 255. A secondary consideration to keep in mind is that the needle and main jets are in series. The main or bottom jet is intended to restrict the flow only when needle is fully retracted at WOT. However, if the needle jet's cross section area minus the cross section area of the tip of the needle does not let enough fuel pass through, increasing the size of the main (bottom) jet becomes irrelevant. This is what happened to me when testing the 2.76 jet. Ground run looked okay, but when revs increased in flight, fuel consumption should have increased as well but was restricted by the needle jet not the main bottom jet and had to back way off to get EGT's back down out of the red to finish trip around the pattern. The two jets being in series, either may be cause of running too lean at WOT, but only needle jet "should" effect operation at other than WOT. The bottom jet was not even used on early models, its addition made tuning simpler by making WOT fuel flow independent of the needle and its jet, but this is true only if needle jet is able to pass enough fuel for WOT.

Would try as large a bottom jet as does not cause obviously over rich operation at WOT, and then adjust needle jet for proper operation. If running lean at WOT, you will know it is the needle jet that is the restriction, and you will need a larger jet. If that corrects the operation at WOT but it then runs too rich at other than WOT, cross section of the needle (not the jet) needs to be larger, but I have not seen that condition with mine and needed to slim down the swelled area of a stock economy needle a bit to get proper fuel flow and EGTs at cruise.

Hope this helps.

It is April 2, but about 15 degrees F and everything is white again, and likely to remain so through rest of the week, so not even thinking of going to the airport for a while to double check what main jet I have in there.

David A. Camit 3300 in Sonex TD

[kmwoody]

Hi David,

Thank you very much for the information, I was searching the weekend and couldn’t find much info on the Bing. I e-mailed CAE, they jet the Bings they send by your location and have there own CAE specific tapered needle. I wanted to flight test with different parameters last weekend but it was very windy here in Iowa.

Everywhere I read, Jabiru articles, SonexBuilders, pointed to 2850 rpm being cruise. At that rpm my EGTs were low, speed and fuel consumption high. So I started thinking around my tunnel vision brain.

I finally tested yesterday by checking where the EGTs were the hottest. On take-off and climb my EGTs were 1183 avg, still low on the main jet, which is a 245. I am probably over-throttling on take-off and dumping too much fuel in, I'll check that next time. In cruise I started throttling back from 2800 and finally after letting the temps settle, 2650 rpm was the high point for the EGTs, which averaged 1240, with #1 being 1320 and #5 1170. I have a 2.72 needle jet.

At that rpm my indicated was 148mph at 2500 msl using 5.5 gph.

My static rpm is 2825 and my rpms at full throttle tops out at 3050.

The highest CHT I have is #5 which averaged 317 with a high of 321 during the flight. All the others were in the normal cruise range.

I was happy with the results of my test yesterday but if you see somewhere that I could improve, please let me know. I have been contemplating a Hackman valve for cruise so I don’t mind the temps being on the low side. I am pleased that I will be able to cruise at 2650-2700 rpm and still get a good cruise speed and climb is at least double what the Aerovee was. The engine will certainly be “happier” at the lower rpms.

Ken W
Sonex 959
CAMit 5.5 hours

[DCASonex]

Ken,

Your latest numbers do not look that far off of the norm, but still surprised by the small main jet you are using. Mine would be running lean with that at WOT and any any needle. What color do you see on your plugs? Your CHTs are not a problem, and will continue to decrease as engine breaks in.

I give it full throttle on takeoff, and just off top of my head, see EGTs in the mid 1,200s and fuel flow of about 8-1/2 to 9 GPH. Leveling out with RPMs increasing while still at full throttle, fuel flow increases to about 10 GPH. My peak EGTs occur in cruise around 2,700 RPM, but that is strictly a function of my needle shape. Fuel flow at 2,850 RPM runs about 6 GPH when leaned to put EGTs about 1,300. Exact numbers vary with load and conditions.

If you have not already done so, would recommend you also join the Jabiru - CAMIt forum.
>>> https://groups.yahoo.com/neo/groups/JabCamit/info <<<

There are a several very knowledgeable folks for this type of engine on that forum, many of them fellow Sonex drivers, who can provide additional information.

David A. CAMit 3300 in Sonex TD

David A.

[kmwoody]

Hi David,

I went flying this morning after I got off work, cool, 34 degrees, but the sun was shining and the air was calm.

I climbed at Vy after takeoff for 1:30. EGTs averaged as you in mid 1200s. Fuel flow is the same as yours on climb out, tops out at 9.5, level, but my RPMs only top out at 3050. Peak EGTs occur at 2650 RPM, averaging mid 1200s. I too think the main jet is small, but I can't get the temps any higher.

CHTs topped out at 310 on #3 in climb, 290 in cruise. Yes #3. I was finally OK with #5 being the warmest at 317 in cruise so I riveted my deflectors in place. I did have a 1/8" vertical deflector on the curve of your design tapered deflector over #3. I left that off to see what the temp would be. #3 went up 20 degrees and #5 came down 30 degrees. I think I will try a flat piece of aluminum extending 1/16" or less from the curve to even the temps out. It amazes me how such small increments make big differences.

E-mailing Brydan at CAE he noted they make their own tapered needle specifically designed for the CAMit engine. Maybe thats the reason I can run with a 245 main.

I am on the new JabCamit forum.

Ken W