Black Widow Run time

The engine should be running more than 30 seconds. Is it out of fuel? Is it overheating? Have you had the engine apart? Is the fuel pickup still intact and tightly fit onto the backplate nipple? Is this Black Widow a plastic backplate Widow or a diecast backplate? It's not uncommon for the screws to leak . You would see the fuel running out. Without taking it apart , carefully screw the needle valve down until it seats, pressurize the fuel tank via the filler nipple and cap the other one off. The syringe shouldn't be able to force ANY air into the tank. It will fill the tank and have resistance. If the syringe is leaking down, you have a issue. Tank to backplate leak, tank to crankcase leak, needle valve leak, o-ring to backplate leak, one or more screws leaking etc.

Thanks for your feedback, your suggestions are really appreciated. Yes, fuel supply seems to be the problem. I stop it when it runs backwards and restart forwards to make sure the head is cooled. I have dismantled it, cleaned all parts (ultrasonically), reassembled with a new backing plate, carefully as the old one had a small crack. Will check the orientation of the pick up tube, and arrange the motor as if it had centrifugal force for the pick up (ie sideways). The motor ran for 30 seconds when in upright position, then stopped. I then started it again to run for another 30 seconds (using a stop watch) and it stopped, so I figured it was not out of fuel the first time, but I will check your recommendations. Will use a gauged syringe for next fill. Tank is aluminium (red annodised). Will see if I can get a gasket and new o ring, maybe a new pick up tube as well...Setting the needle to 3.5 turns open and then leaning off to achieve high speed, not enough run time to get the tacho on it. Was not able to upload a *.jpg picture of either plane or motor, can someone advise? (I have a lot more cox motors to get running after this one and a few unassembled control line planes.)

It's pretty obvious your engine is fuel starved. One thing I do which can easily be overlooked for those not familiar where to look is the needle valve assembly. Remove the fuel pickup tube and insert a wire into the hole with the needle removed. You should be able to look down the spraybar and see the wire. Insure no blockage or crud is on the end of the wire or pin you poked through. On the backplate itself at the bottom of the spraybar where the air intake on the backplate is located is a small hole where the point of the needle seats. Very carefully insert a small but stiff enough wire back through that hole. The wire or pin can also be inserted through the spraybar the opposite direction. Insure that this entire area is free of blockage. You should be able to look through the spraybar with the needle removed and see light through that hole in the bottom holding it up to a light source. Regardless of pickup location, your engine should be running more than 30 seconds. Your needle valve is opened up enough I'm assuming? Start with about 3.5 turns out which would insure a rich start and lean it from this point.

Diagnosing via the internet is a challenge for both parties. It's frustrating for you because it doesn't work and it can be just the same for us on the other end trying to figure out what is the problem. We can only offer up tips and suggestions due to experiencing similar issues. I have somewhat of a checklist, mostly from memory but a lot of it sounds like a broken record constantly repeating. You need to start at the above where I just mentioned in regards to the needle valve. You also need to look at the reed and also venturi gasket. REGARDLESS OF NEW, these items DON' T ALWAYS WORK and must be checked. If the reed is leaking, the engine will not work properly. I use the suck and blow test. If you don't have a large syringe you need one. A 2 oz. will work but a 5 oz. is better and insure that it is a Luer lock syringe which you can acquire small tips for. These are inexpensive and they will tell you more in one push of the plunger in 5 seconds than any post on the forum can convey.

         Hook a piece of small fuel tubing to the syringe and attach the other end to the tank assembly with the reed valve in it. THIS WILL ONLY WORK FOR THE CIRCLIP STYLE BEES. You shouldn't be able to withdraw the plunger AT ALL. Not a little , you should only be able to push it down. If you can withdraw it, the reed is not working and this will 100% cause a problem. Take the reed out, flip it over and try again, this may require another reed. If this is still being problematic, place a drop of oil on the reed and try it once again. It must seal, if it's not the reed, it's the seat of the reed on the tank and it can be compromised. I prefer Mylar reeds for two reasons, one they tend to seal for me better . Their lifespan is shorter because they distort and get sucked down the hole which is the downside. The other positive is that they CHIRP when the engine is flipped over. I can tell that a reed isn't stuck by the audible noise they make when flipping over.  This is the heart of a reed valve engine and it needs to be closely observed prior to engine assembly.


Once your insured that all is good and the engine is ready to be assembled do this as well. Prior to assembly, I use a bottoming tap to clean out the holes of the crankcase to insure that the screws are all tightening and not bottoming out on crud allowing the parts to draw together properly. Assembly and then you need to close down your needle and pressurize your tank as I mentioned in my earlier post. Once again NO air should be leaking. If you hear hissing air leaking, you need to determine where it's coming from. If it's leaking out the air intake, the venturi o-ring is not sealing. This can be the root of a lot of problems and this can be for several reasons.

A couple of observations.  You say that the engine is a Black Widow, but you mention that the tank is anodised red.  The red tank is normally not vented for stunt use and is used on the Texaco.  (It should have no top & bottom vent pipes). The Texaco (which also has a black crankcase like a Black Widow) has a vent nipple either side of the needle valve on the backplate, wheras the Black Widow backplate has no vent nipples.  If you were to use a Texaco tank with a Black Widow backplate, the tank cannot vent and would build up a vacuum, starving it of fuel.  You mention that the backplate has also been replaced.  (Texaco backplate is originally grey, not black.)  

Great theory on my part, except that you wouldn't be able to get fuel into the tank which would now have no vent/filler nipples.
If you have vents and can get fuel in, my theory is irrelevant,    but I enjoyed the thought process.  

Rod, the red tank was made with a up and down nipple stunt configuration for the QRC engine.

but I enjoyed the thought process. lol! wrote:

For pictures check this out >>> https://www.coxengineforum.com/t9504-how-to-post-an-image-in-a-topic-updated-3-10-2016?highlight=how+to+post+images