Need help with our 049 Tee Dee II

Mr. Bernie, according to what you say, I understand that the needle does not make a difference in gear when moving it, so:
1) Completely disassemble the spray bar.
2) Clean the entire spray bar, carefully clean the duct where the needle closes, use solvent and a steel wire from a steel brush, that is, very fine, the diameter of a hair.
3) Clean the metering hole of the spray bar.
4) Clean the fuel inlet of the spray bar with steel wire (hair type).
5) Also clean the three metering holes of the venturi.
6) Check that there are no leaks between the crankcase and the crankcase body, by tightening the nut behind the propeller support.
7) Check that there are no air leaks between the spray bar, the venturi and the crankcase body.
Your customer says that the crankcase has no cracks, so you need to make sure.
9) Place a piece of neoprene over the check needle.
Assemble the assembly (engine) and test it.

Thank you for all the input. Our office is closed today because of a public holiday but will take this up tomorrow with the customer.

Just a heads up that this engine is a brand new unit that I personally assembled, and likely the customer's first attempt at running it.

I was initially thinking "needle valve / spraybar" but I tested for flow and seal on every engine during the assembly process. Also, the carb bodies were mostly a bit difficult to install and sometimes had to be heated with a heat gun prior to installation, so it is unlikely that they would not seal properly.

However, there is a reason that this is happening, and together we shall get to the bottom of it

Insert a wire through the spraybar to insure no metal is blocking the hole. I would also do the same for the peripheral jet holes within the venturi. They can be blocked.

Check the back plate for a good seal and no leaks. Try a different carb body and needle.
                                          Mike1484

Ken Cook wrote:           Insert a wire through the spraybar to insure no metal is blocking the hole. I would also do the same for the peripheral jet holes within the venturi. They can be blocked.

I am trying to wrap my mind around the concept of airflow, and am having little success. There could certainly be a manufacturing defect in the needle valve body but would an airflow restriction not decrease the RPM, instead of increasing or maintaining it? I am more of a marketing person that a techie

Mike1484 wrote:Check the back plate for a good seal and no leaks. Try a different carb body and needle.
                                          Mike1484

If there is an air leak through the backplate, would that increase or decrease the RPM?

The carb bodies are our brand-new production ones but it is conceivable that one could leak through the mating surface with the crankcase, or the venturi threads being off. If there is a leak, does this increase of decrease the RPM?

Generally, screwing in the needle valve, increases the RPM to a point where the engine stops running because the mixture is too lean. In the case at hand, the customer is complaining that the engine runs at high RPM even though the needle vale is almost fully unscrewed.

I think that I need to be educated as to unintended airflow (or airflow blockage) as it relates to RPM, as I obviously don't get it. Please keep in mind that, although I acquired all this Cox inventory, that does not make me a technical expert. Still lots to learn  

Just my ten cents...

A leaking backplate or a leaking crankshaft in a worn crankcase would cause the same erratic run, if the engine started at all, because the crankcase suction to inhale fuel-air mixture, then crankcase compression to shoot the charge into the cylinder, would both be impaired.

Dear Bernie, your customer tells you:
The engine runs at high rpm even though he almost or completely unscrews the needle.

It is clear that the needle is not working and there is something inside the housing that is causing the hole to close, (it could be metal residue from machining).
So do the following:
1) remove the needle from the spray bar.
2) insert a surgical needle in order to remove material if there is any.
3) inspect the hole with backlight, it should look like the photo of my engine.
4) put the needle back in and turn the engine on to see if it improves.

Bernie,

I think it may be time to check for crankcase/intake leaks. Consider an engine teardown removing the crank, piston and cylinder. Install the glowplug right on the block. It may take an o-ring to seal the glowplug/block interface. Plug the intake above the spray bar (a finger should do for a quick test). Blow into the crank about and observe if the block leaks out the backplate, around the plastic crankcase body, or the venturi/spraybar area. If the needle is closed, then no air should flow out of the fuel line port.
If nothing else, this rules out suspect leaks.

Can you provide the state your customer is in? Maybe one of us is near him/her?
Guys, any volunteers?

Thanks to everyone for your valuable contributions and I will now respond to the customer; who lives in Bosnia and Herzegowina.

Yeah...I don't think we'll have a forum member anywhere close to the customer. Sigh.

I myself have already had this problem, I had used the wrong gas line tube, the internal diameter of the tube was smaller than the hole in the inlet. Of the spray bar And nothing to help the situation the back plate was not well sealed It was a new engine made from parts that I had assembled from parts that I had ordered from COX international, the rear plate Had a small flaw as if it was difficult to screw in fully  I still have the engine and I haven't touched it since I had just fixed the small leak in the back plate and I hadn't restarted due to lack of time but I think the problem is solved and that with the right size of gas tube the engine should be able to run normally and be able to reduce the rpm with the needle !!!  Now To check for leaks in the crankcase I would start by adding fuel to fill 3\4 of the crankcase Use your finger to block the air inlet of the ventury and using the fuel tube and blowing lightly into the engine the piston must have passed the cylinder intake ports but the spi sub piston induction closed and crankchaft ports window Barely open as it will be about to close at this position If a leak is detected, soapy water can be used to better distinguish the location of the leak. Keep in mind that a small leak at the front of the engine crankcase is more or less normal but should not prevent an engine from being able to run rich and slow. The only possible cause that I can see plausible is multiple leaks or a gas restriction as for me it was the bad tube that amplified the back plate leak problem But for example too much oil could reduce the fuel flow and add a leak to that and you get this kind of symptom too

The customer got the beast running by drilling though the nipple of the carb body, attaching a line and pressurizing the tank.

Don't ask, because I really don't know and can't explain it

Thanks for the heads up. That makes me think the tank wasn't set up right from the start. I really need to get mine on a test jig.

944_Jim wrote:Thanks for the heads up. That makes me think the tank wasn't set up right from the start. I really need to get mine on a test jig.

He is an experienced modeler. He tried 3 different plastic and metal tanks (all vented), situated right behind the firewall, in line with the crankcase.

He also put rubber fuel tubing over the needle valve, as well as checked the needle valve body and venturi for clogs.

Given that pressurizing works, it seems like the engine was not drawing fuel properly because of an air leak somewhere.

The engine is now running, and he is happy

I might have figured out the problem.

Today, whilst assembling those TD engines, I came across a needle valve body that had little or no airflow once the needle valve was screwed in, if even only partially. I generally do a flow test once the engine is assembled, but must have missed that user's one.

It seems that the pinhole that is drilled from the inside of the NVB into the spraybar was not done correctly; either wrong angle and missed the spraybar or simply not deep enough. This would explain why, when the needle valve was backed off on the user's engine, nothing happened as nothing really changed.

Why the user was able to get the engine to work by pressurizing the tank is beyond my comprehension but I'm sure that someone has an explanation for this. Perhaps there was only some debris in the hole and it then coincidentally came out?

I assume the hole either .missed the NV cavity, or, was too small and only pressurization could help meter out the required flow.

balogh wrote:I assume the hole either .missed the NV cavity, or, was too small and only pressurization could help meter out the required flow.

I just checked with a sewing needle and it only goes in about 1mm, and I am guessing that the vendor's drill broke at that one.