Thread of Needle Valve

[Iceberg]

Got a couple .049 backs recently that are in good condition BUT they need the needle valve screwed all the way in to run basically ok. I'm used to 2.5 to 3.5 turns out to run properly. I have tried multiple needles and they run similar. They need like another .5 turn in to be perfect.

What is the thread size if I died the thread to go in another .5 turn or so? Or will the needle bottom out at the bottom?


What could be the reason (if the needle is ok) for the excessive fuel pickup? The motor seems to be overfueled but all the normal repairs are done already ie the Venturi gasket, hose under the needle valve to eliminate leaking etc.

Wonder for the thread size please and thoughts?

Thanks
Iceberg

[Marleysky]

looks like Babe Bee backs (metal plate) are 80 TPI

https://www.coxengineforum.com/t1097-049-needle-valve

https://www.coxengineforum.com/t14834-differences-between-needle-valves?highlight=needle+valve

some of the Product Engines came with the "fine Thread"  needle valves with 128 tpi.

might want to check an verify the "tip" of the NV is not broke off or shortened.
https://www.coxengineforum.com/t12552-the-stuck-broken-cox-needle-tip-in-the-back-plate-got-it?highlight=needle+valve

[944_Jim]

Ice,
Are the needle valves pointy tipped, or cut blunt/short? Or maybe someone augered the spray bar hole larger, so you need to close up the needle more to offset the gaping hole. It may be worth trying the suspect needles in an engine you know, just to see if it is the needle, or spray bar. And then trying the known-nomal needles in these suspect backplates.

In the end, as long as the engines run, I don't worry about how many turns this engine needs vs that one. Once running, any adjustment is just that...an adjustment.
I know...this doesn't answer the mystery.

OR, maybe these are Texacoes, which use less fuel and turn slower, so they may need more turns in. I admit I have no first hand knowledge of Texacoes beyond what I mentioned above (gleaned from online reading).

I'm betting the needle seats got hogged-out, either during cleaning with a pin or wire, or some time someone really screwed in the needles and opened the holes.

[balogh]

Excessive, forced closure of the NV or lasting NV vibration may hammer our the spraybar internal near the metering hole and even total closure will not cut the flow of fuel. Typical with aluminum or bronze spraybars, IMHO.

[Iceberg]

Thanks Jim
Yes I understand that the real number of turns is not important when the adjustment is correct. However in this case I feel that another partial turn in would be better. so I would like to cut another turn of thread on a NV to see if that adds the fine tuning I'm looking for. With the additional kind comments made I found the thread size is 4-80 is that correct?

FYI the backs are the new aluminum ones and they seem to be very generous in their fuel supply. Maybe someone has used the brand new backs and has some ideas. But it seems that that when I bottom out the NV it just basically reaches a reasonable mixture however it sounds to me like it needs another partial turn in to peak out properly at about 17k currently low 16 k. Judging from my other tests with older metal backplates on same motor.

Thanks again!
Ice

[944_Jim]

The New backplates...mmm. That makes "abused" less likely. Are the threads of the NV running out before you get to the point of too lean?

I don't remember off-hand which needles were blunt tipped, and which were pointy. My gut feeling is that a pounty-tuoped one may be able to get deeper in the transfer hole. I remember cleaning backplates and seeing the needle tip poking into venturi from above (with respect to needle coming in from the top). But at that point the transfer hole was effectively closed such that only air was travelling through the venturi.

Most of this can be tested while only the backplate is in your hands. Screw in needle, blow in fuel pickup tube/nipple (or use a syringe and alcohol), see if it comes out through either end of the venturi.

I want this understood as much as you do. I had it in my head to buy a few of these new backplates. Please keep us informed as you test/diagnose the issue.

Thanks much!

[Iceberg]

Love the look of the new aluminum backplates.... HOWEVER....

Managed to get a 4-80 Tap and got another turn out of the needle into the NV assembly. I did manage to finely get a setting that allowed the motor to run for a full flight. Did three complete flights with th aluminum backed motor. However it still had mid flight mixture fanning. But the Venturi gasket is good. However the NV is EXTREMELY sensitive. Even 1/16 turn one way or the other was the difference between flood and starve on fuel mixture. Will someone invent fuel injection for these little guys??

Any other needles out there that might be better, longer or different tip configuration to get extra fine metering? The NV seems to be the culprit. Goes from flooding to starving too quickly.

Thanks
Ice

[Ken Cook]

Fuel injection as you state has been in use for over 60+ years. Pen bladders, surgical tubing bladders, pipette bulbs and pacifiers. All of the problems you have posted about will no longer be a problem.

[Iceberg]

Hi Ken
Your experience is wonderful. Is there any shop drawings that would help a basic flyer like me to do this kind of fuel injection? This sounds great!!
Ice

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