Zenith Aircraft Builders and Flyers
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Throttle issues....bing carb
Hello...i am running a 3300A with a bing carb. lately i have been having issues. If i pull the throttle cable back till it stops it stalls the engine...if i adjust the cable to full throttle it starts missing during climb out like it has too much fuel and i have begun having issues with carb ice. at least it acts like carb ice when i pull on the carb heat it runs rough and then straightens out....my worst issue is the engine stall...anyone have similar issues and fixes?
Replies to This Discussion
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Permalink Reply by John Austin on
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When I had a Bing carb on my 3300, it usually would run just a little rough at full throttle. If the throttle was pulled ever so slightly, it would smooth out. Apparently this is pretty common and one theory is that the position of the throttle plate at full throttle induces some turbulence in the mixture resulting in uneven distribution. Don't know if that's true but it sounds good! Ha! I eventually just got in the habit of full throttle on take-off and then immediately pulling back slightly - worked for me. I now have an AeroInjector TBI carb so no longer have that issue.
As far as pulling to idle stalling the engine, even if your idle speed is correctly set (800 rpm), the idle stop on the Bing is not that sturdy and it will actually flex if you pull the throttle too hard and allow the idle to get too low and the engine will stop. This is aggravated by the throttle extension arm supplied with the FWF kit as it gives additional leverage on the throttle arm. On a couple of my initial test flights, of course the adrenaline was pumping and I think I was ham-handed on the throttle and had the engine quit on short final when I pulled the throttle back. After a couple of dead-stick landings, I learned very quickly to have a light hand on the throttle and to gently pull it to idle.
Otherwise, you might need to re-jet or tune the Bing. If you don't have it already, here's an excellent article by Pete Krotje (who ran Jabiru USA) : Tuning the Bing Carburetor on Jabiru Aircraft Engines.
John
N750A
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Permalink Reply by George Snedeker on
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thanks John...i'm glad i'm not the only one it happened to...i also had a dead stick landing...not fun if your approach isn't good and you need a go around...i'll try going easier on the throttle and see if that helps...did you use carb heat alot when you reduced rpms?
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I'm in East Tennessee which has a moderate climate and I'm pretty much a "fair weather flyer" and tend to fly only in good weather. So, I never have flown much in conditions that would make icing likely and as a consequence, rarely, if ever, used the carb heat. Also, AFAIK, I never experienced any carb icing. I now use an AeroInjector throttle-body carb which supposedly is immune to icing. It doesn't hurt that it draws intake air from under the cowl, so it's sort of pre-heated, anyway! :>)
John
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the throttle body option is appealing....i may try a rebuild kit and see if new jets help with the issue...thanks again John
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the throttle body option is appealing
The AeroInjector brings a whole new set of issues/troubleshooting and I would only recommend it if you want to do some experimentation. I primarily switched to it because I like to experiment and was intrigued by its simplicity and lightness, and most importantly, I gained a mixture control which allows much more precise engine management. However, it works best as a gravity-fed carb (I deleted the Jab's mechanical fuel pump) and so it was a natural for my 750. In a low wing such as the 601, it would require a header tank to run it gravity-fed, which I assume would require fuel pumps to keep the header full. It can be run directly off a fuel pump, but that then requires a pressure regulator. So, it goes from a very simple gravity set-up in a high wing to a very complex (and fuel pump dependent) set-up in a low wing.
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yea might be too much of an issue for a low wing
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Ironically, it is very popular in the low-wing Sonex, but in that plane, the single fuel tank is mounted high in the fuselage behind the firewall and under the glare shield, so that allows gravity-feed since the carb is relatively lower.
John
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yea ...i can't envision trying to add a header tank to the 601..the firewall is already cluttered and not much room...it would have to be a very small tank and the fuel selector is above the tanks so ...issues
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Just remembered that one additional thing Pete recommended for the flexible idle-stop problem was (with the idle speed set and the throttle arm against the stop) to put a brass collar with a set-screw on the throttle wire as it exited the sheath. This acts as a secondary stop to keep the cable from pulling against the idle-stop and flexing it.
I never installed it because I never had any problem once I learned to keep a light touch on the throttle! Probably would be a good idea, however, especially if more than one person flew the plane - some people are rougher on the controls than others! ;>)
John
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i did get some brass collars and i think i will try that method
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Permalink Reply by Don Burkholder on
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Hi. My cable had a couple of (two 45 degree) bends in it to do the same as the brass collar stop. Either way it's a simple matter of adjusting the cable sheath clamp with brass collar installed and firmly against end of sheath to allow the throttle arm to rest against idle speed screw. This is better with two people, one pulling the throttle firmly against the collar. I liked the two bends because if I firmly pulled it to idle my 2200 would idle at 400 rpm as a test, then if I let the throttle go the engine would return to 8-900 rpm. At 400 rpm you could not feel the engine running, very smooth. If it did not, something is wrong! Just make sure you have full throttle as the throttle knob contacts the dashboard and you are done.
As far as acting rich at full throttle there are a few adjustments to cure that if indeed you are rich with fuel. Did you ever check what kind of fuel pressure your pump is putting out? Should be 1-1/2 to no more than 3 PSI according to Bing. Changing fuel pressure also changes fuel level ever so slightly. My 2200 was 4.5 PSI and to cure this I simply cut a piece of thick paper gasket to effectively shim the mechanical pump so there is less pre-load on the internal pump spring. If you are over pressured this is worth a try as most regulators are JUNK and not to be trusted to shut fuel off completely. See if you can recreate the problem on the ground first then modify. You did not mention what your EGT's were when flying in the rich condition, when pulled back slightly and in cruise condition. All of the modifications I had done to the Bing resulted in hitting the EGT "numbers" according to the tune up info from Pete given earlier for the 2200. Hand cleaning or reaming the sense port that leads to the atomizer and jet, enlarging the atomizer holes, setting proper fuel level, jet and metering rod adjustments resulted in smooth running and even temperatures in my 2200.
You can do the same and test on the ground, then fly, check your EGT numbers. Do the EGT's rise when pulling back from full throttle? All the cylinders? Just a few? Which ones? Can you duplicate on the ground?
Hope this helps...
Don B
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thanks don...i didn't realize those carbs were so sensitive...when i flew it before it would never shut off at low rpm and never stumble at high rpm which leads me to believe something changed
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