JoeAirPort

My Feedback: (41)

MY ZDZ 50 NG starting having problems flaming out in the air. Then I had troubles tuning it. It needed to be richened after running fine for a year. Then I had troubles starting it and keeping it running. It would just quit for no reason. I took the carb apart and could find no debris or problems. My fuel metering arm is looking a little wierd. For the first few degrees of motion it doesn't move the fuel pin at all. Is this normal? You'd think when the diaphragm moves the arm, the fuel metering pin should move up. The diaphragm and arm have to move quite a bit before the pin pulls up. Could this be the problem? Or am I chasing a ghost here? I do have replacement spring for the metering arm.

If you look at the last picture with it at rest you can see really clearly a gap between the arm and the pin top that it pulls up on. Then look at the picture where I am pushing on the arm and simulating increasing the throttle. The point I'm pushing on it, it's just starting to pull on the pin. Doesn't seem right.

I wonder if this is the pop off pressure adjustment that I've seen people do here. Not sure if this is my problem. I just want to get this engine running well and I'm not sure what it will take.

tande

My Feedback: (48)

This is normal-As soon as the fuel metering arm moves at ALL, the fuel/pressure from the pump will push the inlet/needle off the seat-Nothing "Precision" about that connection-

skip1320

Dont change the spring unless you know its an exact replacment part/#,i would just get correct repair kit ,clean and try again,if it has a great deal of running time on carb check throttle shaft play or wear at throttle plate,good luck.

DMcQuinn

My Feedback: (13)

have you checked the other side of the carb - there is a micro-mesh screen that gets clogged up with lint coming in with the fuel. this will cause the lean running condition you described.

GreaTOne_65

From the looks of your pictures, it looks as though the arm is below the base of the carb. I was told and have always set the arm level with the base of the carb. If it is below the base, might be the reason for the lean runs??

Good luck,

Dale

Truckracer

My Feedback: (19)

Your pictures look normal to me. A bit of free play between the arm and the needle is normal. My guess is that your pump diaphram has problems (warped pump flappers) or you have an air leak in the fuel line somewhere. Of course, check to see that the pulse hole between crankcase and the pump chamber is open and not restricted. I know from reading your past posts that you are aware of the screen so won't go there. These are the most common causes of lean running when an engine just starts to run lean when it has run fine in the past. Of course, there is always the possibility of a case leak that would also cause lean running. Loose cylinder retaining bolts or a bad base gasket being the most common problems for case leaks.

darrolair

Sometimes we over look the obvious. The fuel supply: clunk, fuel lines, fuel tank, or possibly the fuel line to the clunk!!!
Darrolair

Rcpilot

My Feedback: (78)

The pics look fine to me. Check the screen under the welch plugs. You should probably just buy a carb kit and rebuild it. If you got 2 or 3 yrs of use out of it I wouldn't complain.

The welch plugs will pop out by punching them with an awl and prying them out. Clean the screens and replace them. When you put the wlech plugs back in, tap with a wooden dowel rod and a small hammer. Use a little bit of clear finger nail polish to hold them in place. It dries like glue. All you need is a little drop and swirl it around the lip of the plug with a toothpick. Don't get sloppy with it. They fit tight anyway. The fingernail polish is just a little extra protection. Tap it in and wipe off any excess finger nail polish.

Replacer the pump diaphragm and the metering diaphragm. Replace the gaskets. Replace the main jet in your pics too.

JoeAirPort

My Feedback: (41)

I did not look under the welch plugs but will do thanks. I do have a new gasket kit that I can use. Maybe the diaphragm is worn out. I don't like that they don't supply a direct replacement for the the pump gasket. Just some clear blue thing that doesn't look promising (looks like a leaker). That was disappointing.

I did check the screen on the pump side.

Thanks

Truckracer

My Feedback: (19)

I would try just the diaphram before removing the welch plugs. It is very rare to have a problem under those plugs unless you let fuel dry in there and turn to a varnish like goo. There is no need to replace things and repair problems that don't exist. Just replacing the diaphram will work and resolve your problems in 99% of the cases. Those blue mylar diaphrams work just fine as do the fiber reinforced ones (they look like fiberglass cloth). You will have to readjust the needles though if you replace one of the black rubber diaphrams ... needles will have to be turned out some.... richer.

JoeAirPort

My Feedback: (41)

Thanks, since I didn't find anything unusual I'll probably try the new diaphragm....maybe the mylar pump gasket too while I have it open. I didn't get one of those fiber reinforced ones. I did replace the spring but I'm not sure I want to leave the new one in there. It is a Walbro replacement but I wouldn't want it any stiffer since I'm afraid it might make the throttle response suffer (increase pop off pressure too high).

pe reivers

Joe,
the moment when the lever lifts the needle, the fulcrum arm should be flush with the ridge in the carb body. Best way to test it is with a flat object, so jou cannot push down the fulcrum lever too far.
Bend up the lever, until the fuel just (ONLY JUST) starts to be admitted when you push it level with the surrounding body. Attaching a fuel line filled with gas and hung from the ceiling is a great way to check when fuel starts to flow.
I do it with a pressure gauge and depth micrometer. When done well. results should be the same.

Zeeb

My Feedback: (41)

Joe,

Here's a thought for you as I just recently experienced a similar issue with my ZDZ-50NG which had been running flawlessly for some time.

Basically what happened is that the mid-range throttle response pretty much went away and it got hard to start.

I chased all sorts of things starting with the fuel supply, possible air leaks, even overhauled the carb since it had been running for some time and figured it wouldn't hurt. I didn't find any issues with the fuel system or the carb.

Then I went after the electical system....

I chased a every component in the system including a fiber optic kill switch and it all looked good as I couldn't find any problems with high resistance or intermittant problems. Then using a loaded volt check meter I checked the whole system as well as individual components and still couldn't find a problem.

Then I remembered Dick Hanson telling me to try tightening the sparkplug gap to .018 instead of .022. So I tried that and got some improvement, but it still wasn't what it had been and I was suspecting the ignition module. So I called RCS and described the problem and what I'd done to Mike and the first words out of his mouth were "it sounds like a power supply to the module issue" and he suggested just running a battery to the module with nothing in between. I went and borrowed a module from Dick and took all the stuff outside for tests. Plugged a battery directly into the module and voila, problem solved!

I never did try the other module as it obviously was not the problem, and I talked with the engineer at Electro Dynamics about trouble shooting the kill switch. He gave me some other ideas which I tried, but the thing just didn't want to play like it was supposed to and putting a 1.5 amp load on the system showed no problem with the switch, but it wouldn't run the engine right.

I put a new kill switch in it and the thing runs great, even picked up the 100 or so RPM it had lost since I've been flying it. I suspect that had more to do with a new sparkplug and overhauled carb than it did with electrical power as the top end RPM had not really changed with this problem, just the mid-range throttle response and hard starting.

So, I'd suggest you narrow the plug gap and try a different battery directly to the module and see if you have any change.

You'll have to let us know what the final solution is as I chased this problem on mine for a couple of weeks by the time I got the extra parts I needed to trouble shoot everything. Maybe the answer will help us all diagnose problems in the future.

Now I'm sure there are some who will say that a kill switch is just something else to go wrong; that is true and they are entitled to their opinion. However I don't intend to quit using them on my gassers, so those who might suggest I should not use them are wasting their breath....

JoeAirPort

My Feedback: (41)

Veryl good stuff, thanks for the tips. I'll try all of it.

I might even re-check the timing since I have a timing wheel I made up last week. ZDZ only publishes their timing in mm from the sensor to pickup at TDC. I'll have to find out what it is in degrees.

GBR2

My Feedback: (1)

Zeeb

Interesting about the switch. Was it a standard switch or one of the Ultra Switches? Sounds like frame vibration might have had something to do with now allowing the switch contacts to stay closed properly.

JoeAirPort

My Feedback: (41)

Just spoke with Mike Dooley at RC Showcase. He did ask if I had any fuel restrictions. After I told him none he seemed to be think it was more electrical. He says to try gapping the plug at .016". Also said to try a newer/different battery with more capacity. He bought into bypassing the ignition power switch. That would be easy to try.

Zeeb

My Feedback: (41)

Not sure which switch you're talking about?

The ignition switch is an MPI HD unit with a charge port and that did not show any problems although I did get another one to use in trouble shooting just in case.

The fiber optic kill switch which turned out to be the problem is from Electro Dynamics and is solid state.

JoeAirPort

My Feedback: (41)

Yeah I was a little confused about that too. So it was the fiber optic engine kill not the ignition on/off power switch. I was ready to bypass my on/off switch...which is not a bad idea anyway.

Zeeb

My Feedback: (41)

Yeah it was the fiber optic kill switch which caused my problem.

The battery straight to the ignition module just bypasses everything including on/off switches and/or extensions or whatever and if it runs then, you know that either the installed battery is bogus or there's a problem in the wiring/switch components.

While my initial battery replacement was an entirely different unit, I also tried it with the installed VPX size A123 and run directly to the module, it worked too. Mike was suspicious of the A123 as I guess he's not used them...

My module is one of the 4.8 to 9 volt input jobs which had been fine on an unregulated Li-Ion for quite awhile before I converted everything to A123's, so I was not really inclined to believe that pack had gone bad, but I checked it just in case....[8D]

Killer_Matt

My Feedback: (11)

Clean the carb screen, I had a similar problem and that fixed it. When I opened up the carb the screen looked to have a slight orange tint to it but didn't look dirty or clogged. After cleaning it with gas and a fine brush it looked more like a metal screen and the problem was gone.

JoeAirPort

My Feedback: (41)

I did clean the screen thanks. I haven't had time to go back and work on this engine. Hopefully soon.

hardtop351

hi all from the land down under......

just read this thread and would like to suggest some things to check.

the fuel filter inside your carb.....remove it totally. these little buggers clog VERY easily and as we all filter our fuel before it gets to the plane's fuel tank. this filter is fitted to these carbs as the factory don't know on what piece of powered equipment it will be fitted to.

secondly....the pump arm referred to in your photos DOES have a factory setting. and to this end there is a template available from walbro for this purpose.

i would also suggest getting a rebuild kit for this carb as the pump valves do fail after a time.

hope this helps
cheers

DMcQuinn

My Feedback: (13)

Joe AP - please do remember to advise us all whatever it turns out to be.

JoeAirPort

My Feedback: (41)

Ok, I got it to run better. Here is what I did:

1) Installed new ignition battery. It was still holding charge fine but had a cut in the insulation of one of the wires from vibration. The wire was not really cut though. But I replaced it anyway. Mike Dooley said putting a bigger battery might help. So I increased it from 1100 to 1400 mah Nimh ( they were both low impedance 5 cell).
2) Took apart carb, cleaned out screen, blew out jets and orfices, and installed a new diaphragm. Inspected and took apart metering arm.
3) Re-plumbed entire fuel system including inside of tank.

So the conclusion is that it runs very well now. The confusing part is that the WT201 low needles were both 1.5/1.5 and the low is now over 2 turns, the high just under 1.5. It seems like somehting happened that the low needle needs to be so much richer. It's very hard to make it rich in the low RPM's. It runs well but maybe I still have a pop off pressure issue that I've masked with an overly rich low needle? It was doing this before I started to work on it too. That was the original problem (engine would die). Now it seems to run fine but part of the original problem seems to still remain.

Anyway, it runs well. There just remains a puzzle of why the the needles changed so much. I know changing the disphragm did some of it but over a half of a turn?

altavillan

My Feedback: (1)

The demise of the rubber pump diaphram as an option in a carb repair kit, is due to the alcohol content of todays fuel. Problems of retuning will occour when replacing the pump with the stiffer diaphrams. What I have done is install a nipple for an external pulse line that is centered over the pump for maximum effect. And block off the standard pulse porting. This will improve a carbs performance with any type of pump diaphram material. Especialy from idle to mid range.