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Bing carb help (long...)


FastEddieB

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I spent Saturday at the hangar. My intent was to replace the fuel lines and to properly secure the ends of my fire sleeve with the clamps and the clamping tool I had bought, and some 600º clear silicone I had gotten from Wick’s aircraft.

 

The install went pretty smoothly (I thought), though the cheap tool I got from Wicks was a PITA. In any case, once done, I hit the boost pump to check for leaks, but did not see any fuel pressure. I had done the hoses one at a time, so there was no way I misconnected any. I tried to start the plane, but after one half-hearted attempt at starting, nothing - like it wasn’t getting any fuel.

 

To track the problem down, I started at the engine driven fuel pump. As soon as I released the screw clamp on the “out” hose, pressure was released. I removed the hose and could not blow through it. Long story short, though I thought the clamps had been installed so as to barely compress the fire sleeve, apparently I had over-tightened them to the point they had pinched off the fuel line. Not knowing if the other clamps might similarly be restricting fuel flow, I removed them all and just used safety wire to lightly secure the ends of the fire sleeve for now.

 

I turned on the boost pump, and now had pressure on the gauge - voila!

 

But...

 

...when I started the plane, it ran very roughly. From idle on up to close to 3,000 rpm, something was clearly not right - above that it felt OK.

 

I thought that maybe some debris from the new fuel line or some wayward bit of silicone had made it into the carbs, so I pulled the float bowls. I found what may be part of the problem:

 

5652801029_0d6172ae88.jpg

 

When I did my last annual, I was having trouble getting the float bowl gaskets to stay in place and I put a tiny bit of “gasket maker” silicone around the lip of the float bowl to hold it in place. BAD IDEA!!! Apparently either the fuel or the ethanol worked on it and really puffed it out. I had had a previously unexplained rough engine incident on the way to FL about a month ago, and now I suspect it may have been a bit of this silicone being ingested. I now know the proper way to get the gaskets to stay in place is with a very thin coat of grease, which works.

 

In any case, I thoroughly cleaned off any residue - and, if anything, the other float bowl actually looked worse. Reassembling everything, the engine is still rough below about 3,000 rpm. I checked and there seems to be good fuel flow to each carb.

 

My working theories:

 

Theory 1: Somehow some silicone, or something, made it into the main jet. There may have been some bits of silicone floating on the fuel in the fuel bowl, and when the float bowl ran dry, it got sucked up and is lodged in the main jet. My plan is today to go back out the the hangar and to pull the main jets to check for blockage.

 

Theory 2: Somehow some silicone or foreign material in the new fuel line made it to the little needle and seat that controls flow into the float bowl. I was alone Saturday, but Karen’s back home and I can check this theory by having her gently hold up the brass float arm to make sure the flow stops when the float bowl fills.

 

I’m certainly open to a Theory 3 or 4 or any advice that might get me back to square one with these carbs. In any case, its a good learning experience.

 

By way of background, I’ve had 2 BMW motorcycles which have nearly identical Bing carbs, and I’ve done a couple major overhauls on these - so I kinda know my way around the inner workings of a Bing carb.

 

5653342458_b5aa6a46b1.jpg

 

BTW, you can see I installed inline fuel filters on the BMW. Might these, in metal, be a good idea on a Rotax?

 

Thanks in advance - I feel like a bit of a doofus, but “That which does not destroy us makes us smarter” (to paraphrase Nietzsche).

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Hi Eddie,

 

When using those other clamps put them as near the end of the hose as possible where the fuel hose is supported by the fitting and won't let it collapse. You can over tighten these types of clamps, but they don't have to be super tight just nice and snug. I see you have the cork carb bowl gaskets. I never use those as they seem to leak more often. Call CPS and get some good fiber gaskets. Never use any silicone of any type around our fuel system It does not dissolve in fuel and most people always apply too much so it squishes out and floats in globs in the fuel until it hits a tight spot like the carb jets. You should only use a little white grease on our "O" rings or a light coat on a fuel gasket. White grease when hot or in fuel will then go back into an oil and dissolve in the fuel and burn through the engine and never clog anything. From looking at that carb bowl I would pull both carbs and strip the jets out. Use some spray carb cleaner and flush every orifice out in the carb and the jets. You can just put one fuel filter back upstream some where and don't need one for each carb. One will flow more than enough fuel.

 

For the CT guys:

If you ever pull the fuel bulkhead plate and use the Hylomar to seal the gasket make sure you let it get tacky before reassembling and never ever use too much or it will squish out and clog the fuel filter, gascolator and carb jets. Never put fuel in immediately in the tank. If you can let it set for the day or at least a few hours your far better off.

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Roger,

 

Thanks.

 

I'm going to try to do as much cleaning as possible with the carbs in place - seems like I have good access.

 

It seems I could pull the main jets from below and the diaphragm from above and get a good look at the fuel's path. The tiny jets in the bowls themselves (part of the starting circuit, IIRC) were clear.

 

I will order the correct gaskets. The "rubber" ones I ordered on eBay seem a tad too thick - I possibly could force them into place, but it doesn't seem prudent.

 

The safety wire on the fire sleeve should be OK for now. Next summer I may fly out there and hire you to do the 5-year rubber replacement and we can tidy up the fire sleeve then if I don't mess with it before.

 

Any recommendations on an aircraft-quality 1/4" inline fuel filter?

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Roger is dead on. The tell tale sign of a clogged idle jet is a rough running engine below 2800 RPM. (rotax that is). It sounds like this is true with your engine as well. After a certain RMP (2800 or so ) the idle jet is bypassed.

 

The straw from any automotive carb cleaner fits perfectly in the idle jet and will squirt thru the other end as well as 4 holes on the body of the jet. It only takes a piece of debris the size of a grain of salt to clog the idle jet.

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That silicone seal on carbs is the devil's work. I made the same mistake on my Datsun B210 about 30 years ago. Car ran fine 50 miles out to a destination. Wouldn't go faster than 20 mph while blowing vast quantities of smoke coming home. I think I had to pull and clean it twice before I got all of it out. Since then, all I've ever used is a thin coating of grease, like Roger says.

 

Be careful flying after you think you have it fixed. Still might be crud floating around that could bite you.

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I got out to the hangar yesterday. First I pulled the right float bowl (would be the left on a tractor installation), since that was the one that looked goopiest Saturday. With a mirror and flashlight I looked up into the main jet and the idle jet and I immediately saw a bit of crud on the idle jet - exactly as forecast. Pulled that jet and...

 

5655330885_bf4971eb69_z.jpg

 

Cleaned it up (that Gumout straw does fit perfectly!) and went ahead and pulled the main jet as well - it looked clear. With the jets out and a mirror and flashlight I could verify the passages above the jets were clear. Closely inspected the float bowl and floats for any wayward silicone and reassembled. Went ahead and did the left side and both jets were pristine.

 

Reassembled that carb and did the runup and EUREKA! - back to normal!

 

Observations and feedback:

 

1) I want to emphasize that I used a TINY bit of gasket-maker, lightly applied with a Q-tip, and being careful to compress the gasket a bit and wipe off any silcone that oozed out. I just didn't allow for how fuel and/or ethanol would affect it - it really puffed out and became jelly-like. I had thought it would firm up and become a gasket, as advertised.

 

2) As far as a more thorough cleaning - it couldn't hurt, but I don't see how any goop could get past those really tiny holes in the idle jets, and any getting past the main jet and past the needle would have been sucked into and burned by the engine, right? I can't think of any other placed "downstream" of the float bowl where more goop could be lurking.

 

3) Since the goop was introduced at the float bowl, I can't visualize any way it could have flowed "backwards" past the needle and seat to affect anything "upstream" like the fuel pressure sending unit. Plus that drop in indicated fuel pressure had been gradually going on for a long time prior to the last annual.

 

4) My working assumption is that my rough engine on the way to Florida (rough enough that I declared an emergency and had chosen a field before the engine gradually smoothed out again) was caused by a partial blocking of the main jet, which cleared itself.

 

5) Though I don't think it turned out to be the issue here, its probably a good idea to inspect newly purchased fuel line for potential blockages - it seems feasible that insects or other crawly things could be making a home there. Maybe even manufacturing "flash" or other imperfections. Maybe a routine blowing out with an air hose prior to installation?

 

6) I may have mentioned this before, but there's a poster that shows a biplane in a tree and says something about how flying is, by its nature, unforgiving. Glad this little blunder turned out to be just a learning experience and not far worse!

 

Thanks again!

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Hi Eddie,

 

If for any reason the carbs don't balance, the idle gets rough, the engine runs rough at hiher rpms or the fuel pressure sender starts to read really low then a thorough cleaning by stripping them down will be needed. There could possibly be little blobs floating around until they hit a small enough orifice.

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Thanks!

 

I'm about to order the fuel bowl gaskets from Pacific.

 

Would this filter be a good one to put inline?

 

7351L.jpg

 

$14.95 from Pacific.

 

 

I used those filters (one to each carb.) for some 350 hours on a 912ULS in a Zenair 601XL. They were fine except after landing on and taking off from a very rough sod airstrip one time. The screw-on end on one of the filters had loosened up and the filter sucked air resulting in erratic fuel pressure readings (no obvious engine roughness though). I subsequently secured both ends of each filter to the respective glass tubes with vinyl tape and had no further issues.

 

PRW

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As an update, I received the new float bowl gaskets and they look a lot better than the 4+ year old, many-used cork jobbies:

 

5708604114_3fc18abb34_z.jpg

 

You can see that in spite of my best intentions, a tiny bit of silicone was still clinging to the old gaskets.

 

I've now thoroughly cleaned and inspected both carbs, from the bottom and from the top, removing the slides and inspecting the needles and diaphragms. Everything looks spic 'n' span. I was going to test-fly today, but on inspection I found my first broken exhaust spring:

 

5708037319_8fe7bafeab_z.jpg

 

The safety wire held it in place, esp. important in a pusher configuration. I got it out and was ready to install a new one when I remembered my safety wire was at home.

 

5708037761_38258fb7b4.jpg

 

So now I have something to do tomorrow!

 

Looking at the corrosion, I plan on hitting them all with Corrosion-X - it can't hurt.

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I used those filters (one to each carb.) for some 350 hours on a 912ULS in a Zenair 601XL. They were fine except after landing on and taking off from a very rough sod airstrip one time. The screw-on end on one of the filters had loosened up and the filter sucked air resulting in erratic fuel pressure readings (no obvious engine roughness though). I subsequently secured both ends of each filter to the respective glass tubes with vinyl tape and had no further issues.

 

PRW

 

When you say "the screw-on end", do you mean the brass fittings? Or do the ends attached to the glass unscrew?

 

With your caution in mind, I tried this while in the hangar yesterday:

 

5739917080_9161f3ed68_z.jpg

 

I don't see how the fittings could unscrew once secured to the fuel line, but it seems like the safety wire couldn't hurt to hold the whole thing together.

 

My thought is to install it between the fuel pump and the splitter/manifold that sends it to each carb and the pressure sender.

 

Thoughts?

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Hi Eddie,

 

The ends on the fuel filter do unscrew so you can drop a new element in it. Your safety wire should be fine. I used to use that exact one many years ago and I know they are very common in the experimental world. i have never seen or heard of one coming apart. Do you have an electric boost pump? If you do put it after that, but before the Rotax pump.

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Hi Eddie,

 

Do you have an electric boost pump?

 

Yep!

 

If you do put it after that, but before the Rotax pump.

 

Not arguing, but what's the logic there?

 

With a high-mounted engine, my Sky Arrow is totally dependent on fuel pumps to feed fuel up to the engine. As seen in the photo below, it would be just as simple to place it before or after the engine-driven fuel pump. My reasoning to put it after was that if it ever got partially blocked, more pressure would be available with BOTH pumps providing pressure to it.

 

But I'm always open to suggestions - that's why I'm here!

 

5740924055_141500b29f_z.jpg

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Hi Ed,

 

There is nothing wrong with your idea and yes if you ever get a clogged filter then both pumps can help push past the debris. I just don't really know of anyone mounting a fuel filter there, plus my second concern is the temps under the cowl cooking the fuel and maybe causing some vapor. It will be a fairly large area that is exposed to the heat under the cowl. That was my only reasoning for not putting it there was all the heat. I would never expect your filter to ever become that clogged. No real world evidence not to put it there, just trying to think ahead a little.

 

 

p.s

Shame on you. You haven't put those band clamps on your fire sleeve yet. unsure.gifbiggrin.gif

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p.s

Shame on you. You haven't put those band clamps on your fire sleeve yet.

 

Actually, that was a "file photo" taken back when I was having fuel pressure sender issues.

 

After the band clamp fiasco, I just went with safety wire for now:

 

web.jpg?ver=13060145390001

 

Not the most elegant solution, but combined with that 600º silicone, it should serve its purpose for now. The blob of red RTV is to cover the cut end of the safety wire.

 

BTW, flew 3 hours yesterday without a hiccup. Only issue is the slightly elevated idle, which I still need to investigate.

 

What sort of instrument do you use for carb balancing? I have an old MotionPro carb stick, but I think it may need mercury, which I'm not sure where to get.

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Hi Eddie,

 

Ditch the carb stick. It's a PITA. You can use either a set of nice liquid filled gauges mounted on a little fiber board or use a Syncromate or Carb Mate. If you set up a set of gauges put a needle adjustment valve in line to dampen the carb pressure impulses. This will make the needles nice and steady and keep them from pulsating all over. I find the gauge to be much faster and easier to use. They tell me which carb I want to adjust and in which direction to make the adjustment. The other two work well for accuracy, but take a little longer because it won't tell you which carb or which way to move an adjustment. I'm not 100% sure if that type of accuracy is really needed.

That decision I'll leave up to you. The perfect idea would be a hybrid between the two systems. Use the Carb Mate and then cut the lines about 3" below the instrument and put the gauges in line. Then you have the best of both worlds.

Carbs need to be balanced every 100 hours and or the annual.

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Hi Eddie,

 

Ditch the carb stick. It's a PITA.

 

Agreed. Its out of mercury (possibly spilled or evaporated over the years, neither one a good thing). It did serve me well balancing Bings on my Airheads over the years, but I'll probably spring for one of the electronic ones you mentioned.

 

BTW, my local O'Reilly's has a "Mr. Gasket" fuel filter for under $10. It appears identical to the one I got from CPS, though without the brass fittings. Now that I have the brass fittings, it may be a convenient and slightly cheaper alternative:

 

41AWAR2EBRL._SL500_AA300_.jpg

 

Another possible source, lot of others online:

 

http://www.amazon.com/Mr-Gasket-9706-Universal-Clearview/dp/B00068OR8M

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Hi Eddie,

 

It is the same. Use some good solid fittings. If you aren't very experienced you may find balancing carbs with gauges verses an electronic one is much easier. If you don't use the gauges then I would pick the Carbmate over the Syncromate. The gauges are faster and easier and I'm not convinced that the accuracy of the electronic ones are really needed because just shortly after you hook the system back up and run for a while they will be ever so slightly off anyway.

If you use a barbed fitting on the end of any balance setup make sure you sand down the barbs to a flat smooth finish. If you insert a barbed end into a rubber hose it will start to flake on the inside of that hose. A smooth end won't give you any problems.

post-3-0-59097300-1306349883_thumb.jpg

912 carb sync.pdf

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post-3-0-67492900-1306349981_thumb.jpg

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