ZDZ 40RV Problems

I have a problem where the engine will not run correctly. It will for
example run up to full throttle if you go there slowly, and it runs solid
at that speed. It idles good with no problems, and anywhere in between as
long as you go slowly. I had a problem a week or so ago when it died in
flight and wouldn't run at all, took it apart and cleaned out the crud I
found in it and it seemed to work fine. A week later I go to fly and it
act's up.
If you goose it a couple times it will die and you must then choke it to
get it running again, contrasted to a normal shutdown where it will start
on one flip if warm. When it quits it act's like it's starved of fuel, or
too lean.
For now, I suspected an airleak in the pheonolic gasket between the engine
and carb, so I've taken it apart and used some RTV to seal it back up, I
guess I'll have to wait 24 hours for a cure to see if it helps or not.
There were/are no blockages of any of the ports, I've checked that out,
and the diaphram seems to be pretty flexible and doesn't have any pinholes
that I can see.
Changing the mixture does not help it out a bit, whether it's rich or lean
it acts the same. It's a Bing 48 Carb for what that's worth and I've not
found a source to buy a rebuild kit for it in case I needed one, and RC
Showcase hasn't returned any of my phone calls so far so I don't know if
they can get me a kit or not. The specific model number of my carb
is 48C114A.
So, what else would you guys look at on this? I haven't checked the
popoff pressure since I don't really know what it's supposed to be for
this engine, things like that aren't really listed in most places. A WAG
would say 10 - 12 but who knows for sure?
Reply to
Matthew P. Cummings
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I test run it after the RTV application, no difference. Since I had the cowl off and easy access to the needles while it was running (the ZDZ's carb is way back and safe to adjust if you're careful) I noticed some interesting things. The lowspeed idle would adjust the mixture easily and I could then run it up as high as I could get it and the high speed needle did almost nothing at all. I could run it nearly in with no change, and nearly out with no change.
If I want to insure the high speed passages are clean, what's the best way to do it? I squirted some cleaning fluid into it when I had the carb all apart and watch it come out the holes. Is there a better way?
Reply to
Matthew P. Cummings
What prop are you running??
Reply to
Eddie
make sure your throttle butterfly is not set up backwards. This seems to happen a lot on ZDZ's.
Brad
Reply to
Brad Lorance
I'm using a 20x10 on it.
Reply to
Matthew P. Cummings
The throttle plate cannot get turned wrong on the ZDZ40. I had a similar issue with mine. Disassembled carb and cleaned all the small passages with a very small piece of wire, then carb cleaner then air. Also turn the plate with the atmosphere hole so that it faces the rear of the plane and not forward, as it is from the factory. Could be pressure from the prop blast causing you a problem with the diaphragm. Hope this helps.
Reply to
Eddie
I have seen several people do a mod where they drill a hole in the diaphragm cover and silver solder a small piece of brass tubing in the hole. they then add a piece of fuel tubing which goes to another piece of tubing (curved) which is mounted on a convenient carb screw and points straight into the venturi. The idea is that the carb then senses the atmospheric pressure at the intake rather than a false reading it might otherwise get. I know this is confusing. If anyone knows of a link showing the process, please post it.
Reply to
jeboba
The tubing you are referring to goes back into the fuselage away from the cowling area that can get pressurized and hold the diaphragm in a locked position. The hole needs to see atmosphere pressure so the diaphragm can operate properly. Facing in the venturi would cause a different pressure from atmosphere and would probably cause all kinds of problems.
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Reply to
Eddie
I've seen them the other way more than the way you describe. Someone want to jump in here and explain? I'll look for a link.
Reply to
jeboba
I saw a link to a gizmo just like you described. He was selling those items, just unbolt your plate and put his on. He said they worked real good too.
In any event I might have it running again, will have to fly it and see how it does. For some reason my lowspeed idle needle needs to be turned out 2.5 turns now, it used to be less and was closer to 1.5 turns before.
The highspeed idle will adjust now like it's supposed to. One thing I noticed, my oil covering the bottom of the plane is back, I had though as it was decreasing that the breaking process was getting closer since the black goo was going away each time I flew, but in reality the mixture was getting leaner each time I flew.
I did take the carb apart again and found no blockages in the passages, and I did manage find one source of a rebuild kit at
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and ordered a gasket kit from them.
I could find nobody around here locally that had stuff or could even order stuff for a Bing, few had even heard of them except on bikes.
Reply to
Matthew P. Cummings

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