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Yenn

Bing carbie

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I recently stripped my Bing carbie in the Corbie, with a Jab 2200 engine. It had been running OK, but using excessive fuel. Both checkable from the duel per hour and the plugs being sooty.

I found nothing amiss except that the float level was a bit high.

Re setting the float level is a horrendous job, I have done it several times and it goes from not enough fuel, that is about 8mm in the bowl to too much, which is less than 12mm from the top of the bowl in the blink of an eye. I have measured the height of the tang which contacts the needle valve and less that 0.05mm goes from too rich to too lean.

Has anyone else experienced this?

The engine will not run at all well, when lean and bogs down when rich, tending to pick up a bit as it starts to empty the bowl, but it will never get anywhere near full power.

I blew everything out then I pulled the carbie down and it was as clean as a whistle. I could see through the main jet, so didn't clean it. I later removed the main jet just to check it and then found a loose jet rolling around on the floor. Obviously the needle jet that the needle valve runs in, so it went back in above the main jet carrier.

I have never liked working on carbies, although I have done it many times, but I am really wondering what I have done wrong. It is definitely a carbie problem, not mags or general engine condition.

Anyone got any bright ideas?

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Hi Yenn - I speculate:

 

  • Sounds to me that you have a worn main jet/needle.
  • Float chamber fuel level is important but such a small variation in level, that you quote, should not make so much difference in air fuel mixture, unless you have been inadvertently trying to compensate for worn jetting.
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Get  Bing workshop manual or download pages.

You need to know what part of the carby is responsible for what phase - idle, increasing power, WOT

Then you know what to focus on and it makes thing much easier.

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I've got a motorcycle that wears out main jets by flogging the chrome off the needle in one spot. I'm on my third set now. They are cheap and easy to replace.

 

the symptoms I see is a marginally increased consumption but it runs like a goat at mid throttle and runs super rough at carpark speeds

Edited by mnewbery
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4 minutes ago, mnewbery said:

I've got a motorcycle that wears out main jets by flogging the chrome off the needle in one spot. I'm on my third set now. They are cheap and easy to replace.

 

the symptoms I see is a marginally increased consumption but it runs like a goat at mid throttle and runs super rough at carpark speeds

What carbies?

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No idea other than its a CV carburettor. Probably Mikuni. The float tang isn't adjustable

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27 minutes ago, mnewbery said:

No idea other than its a CV carburettor. Probably Mikuni. The float tang isn't adjustable

Did a lot of work with Mikuni concentric but no experience on CV, sorry.

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It works fine, until it doesn't. Then I fix it and it works fine again. There is no "problem" :cheers:

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1 hour ago, Yenn said:

I recently stripped my Bing carbie in the Corbie, with a Jab 2200 engine. It had been running OK, but using excessive fuel. Both checkable from the duel per hour and the plugs being sooty.

I found nothing amiss except that the float level was a bit high.

Re setting the float level is a horrendous job, I have done it several times and it goes from not enough fuel, that is about 8mm in the bowl to too much, which is less than 12mm from the top of the bowl in the blink of an eye. I have measured the height of the tang which contacts the needle valve and less that 0.05mm goes from too rich to too lean.

Has anyone else experienced this?

The engine will not run at all well, when lean and bogs down when rich, tending to pick up a bit as it starts to empty the bowl, but it will never get anywhere near full power.

I blew everything out then I pulled the carbie down and it was as clean as a whistle. I could see through the main jet, so didn't clean it. I later removed the main jet just to check it and then found a loose jet rolling around on the floor. Obviously the needle jet that the needle valve runs in, so it went back in above the main jet carrier.

I have never liked working on carbies, although I have done it many times, but I am really wondering what I have done wrong. It is definitely a carbie problem, not mags or general engine condition.

Anyone got any bright ideas?

Hi Yenn  If you talking about setting the carb float brackets (will be part of the process your doing with the tab); the trick is to buy the tool for setting and measuring this gap with feeler gauges.  Bert flood sells them about $30 and gets them set perfect every time.  It tool screws on where the main jet goes.  When finished you take it off and screw in the main jet.  Disregard if not what your doing.  Cheers Mike

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I doubt that jet or needle wear could cause the problem. It happened suddenly, not gradually.

I tried to download the  Rotax  heavy maintenance and it twice locked up my computer. I have the Jabiru manual which has a Bing section, but not really good. I will look up the CPS manual, that may have something in it. Only have to find it amongst my filing debris.

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Idle runs reasonably well, but will have to be reset, when I get tis problem fixed.

I am wondering if I have lost the diffuser which is above the needle jet. I will have to take a trip to the airstrip and check .

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2 hours ago, Yenn said:

I doubt that jet or needle wear could cause the problem. It happened suddenly, not gradually.

I tried to download the  Rotax  heavy maintenance and it twice locked up my computer. I have the Jabiru manual which has a Bing section, but not really good. I will look up the CPS manual, that may have something in it. Only have to find it amongst my filing debris.

Fair comment my suggestion was based on the often very precise/finicaty relationship between float chamber fuel level and fuel metering. Some carbis are intolerant of jetting variation/wear, shut off valve wear, float level variation - usually running rich but the opposite can happen as well.

 

Sorry about the lock up - it works fine fp my PC and the PDF prints out well

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Jabiru carb version has different float system to Rotax, AFAIK

is the float valve rubber tip in good condition? 

also the spring inside the valve working properly?

 

I replaced my valve some years ago because the carb would leak a little while parked

It still does (possibly needs a new seat) but I turn the fuel off at the end of the day per the manual

 

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Vent tube is good.

I had another good look at the carbie and all seems well. Ran it again and still crook. I tried running with fuel turned off and it didn't run any better as the bowl must have emptied. I tried running it where it was rough and applying the start part of the carbie. That made no difference. I still have one other thing to try, which is a real wild card, but it has been way too hot here to let me get up any enthusiasm for playing mechanic.

I went for a flight in the RV instead.

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Where the vent tube ends up is what matters. It can /does affect mixture, quite a bit. The choke function only works on idle to just above idle. Nev.

  • Agree 1

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A few things to check on a Bing...

vent tube location is important 

is the stackup between the main jet and needle jet in the right order? It’s possible to put bits in upside down. 

Is the diaphragm spring correctly seated and not bent up?

is the diaphragm and slide in the correct location? You will notice a little alignment lug on the diaphragm that sits in a little rectangular socket. 

Does the needle and slide move smoothly in the bore?

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Have you checked that the float is floating properly? This is one of the checks for the Rotax engines as some floats can get fuel in them and the don't float at the correct height.

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