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needle valve screw don't stay put! Empty needle valve screw don't stay put!

Post  reptile Fri Jul 12, 2013 12:18 pm

Hi Guy's I have one of the grey back plates with the aluminum carb on it in my cox car and these brass needle vales never hold my tuning position they keep moving?
I already shortened it a lot so it was not to long and heavy but that did not work also!

Any tricks to make the needle screws stop moving from the motor vibrations?


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Post  JPvelo Fri Jul 12, 2013 12:31 pm

Slide a short piece of fuel tubing over the needle so that it covers the exposed part of the spray bar and about 1/2 of the needle. The tubing must be a snug fit. It will prevent the needle from moving and also seal out air leaks.

Jim
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Post  RknRusty Fri Jul 12, 2013 1:15 pm

Like this:

Click for full size
needle valve screw don't stay put! Tach_r10

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Post  reptile Fri Jul 12, 2013 1:24 pm

Ok so let me see take out the valve and the spring off put a section of fuel line over the needle about a 1/2 inch ?
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Post  ian1954 Fri Jul 12, 2013 1:30 pm

I have a lot of trouble with needle valve assemblies have the needle threaded so that it screws inside the assembly. Not only are they prone to loosening but they often leak air and don't seal properly. Although "springs"  - coiled or flat (as on the TD for example) - help and prevent loosening. These are no match for the needles that match the internal diameter of the feed tube exactly and the thread is external on the tube. The needle has a threaded shroud that can then be held tight with a "spring" or has a tight and slotted.

On most Cox engines I revert to Jim's suggestion - as in the first picture - and remove the spring.

needle valve screw don't stay put! Nva10

I took this suggestion from this site. Most British engines don't uses external threads on the needle but pointed wire with a shroud.

I took these to try and explain the shroud better. As you can see, I am getting ready to smoke it in the first picture. Now where's my lighter?


needle valve screw don't stay put! Nva110
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Post  reptile Fri Jul 12, 2013 1:50 pm

thanks guy's I did it and it looks like it should work...thanks for the TIP!! Very Happy 
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Post  reptile Tue Aug 06, 2013 8:56 pm

This looked like it worked but when fuel got on the needle valve it got down in the hose around it and then it lubed it and made it turn much easy than the spring set up?

any other method?
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Post  pkrankow Tue Aug 06, 2013 9:35 pm

Has the mouse race method of using a #4 washer and fuel line to replace the spring been tried?

Phil
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Post  dckrsn Tue Aug 06, 2013 9:39 pm

reptile wrote:This looked like it worked but when fuel got on the needle valve it got down in the hose around it and then it lubed it and made it turn much easy than the spring set up?
any other method?
Running a car, I'm sure youre experiencing more vibration than most of us do.
Take a closer look at Rusty's photo. There's a washer(prob #4) sitting on top of the
needle tubing. With the washer, the tubing compresses as you screw the needle in.
Thats where the resistance comes in. Without, the needle shaft just slips into the tube.
If you need some #4 flat washers PM me. Freebies, got a lot.
Bob
edit: Wrote while you were posting Phil.
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Post  reptile Wed Aug 07, 2013 8:06 am

Huh... hunmmm I did not see that washer I have to see if I have any 4mm washers and give it a try.

thanks guy's
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Post  reptile Wed Aug 07, 2013 9:23 am

Dang it tried it!
it won't work with the carb on ! there is no room they have 2 thin plastic lumped up sections so the washer won't work .
this is what I am using

So what I did try is i put a section of fuel line on the needle valve and it then hits against that small line of plastic going down the carb pipe in the back and causes friction so maybe this will work.

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Post  RknRusty Wed Aug 07, 2013 10:38 am

reptile wrote:Huh... hunmmm I did not see that washer I have to see if I have any 4mm washers and give it a try.

thanks guy's
A #4 washer is larger than 4mm. It fits an SAE #4 screw, like a 4-40. English measurements. Any washer that won't allow the tube to slide up the needle will work. I have used one on that type of backplate too. You just have to find a washer that fits, and possibly file a flat on one edge. I don't recall exactly how I did it, however it was not too difficult. Channel your engineering genes.

EDIT: I remember, the needle shaft narrows inside of that housing. Slide a washer up to the the point that it won't go over the wide part and jam the tube on under it. The washer and tube will be hidden from view with that backplate.

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Post  reptile Wed Aug 07, 2013 12:10 pm

RknRusty wrote:
reptile wrote:Huh... hunmmm I did not see that washer I have to see if I have any 4mm washers and give it a try.

thanks guy's
A #4 washer is larger than 4mm. It fits an SAE #4 screw, like a 4-40. English measurements. Any washer that won't allow the tube to slide up the needle will work. I have used one on that type of backplate too. You just have to find a washer that fits, and possibly file a flat on one edge. I don't recall exactly how I did it, however it was not too difficult. Channel your engineering genes.

EDIT: I remember, the needle shaft narrows inside of that housing. Slide a washer up to the the point that it won't go over the wide part and jam the tube on under it. The washer and tube will be hidden from view with that backplate.

Hi I don't think it works because see that plastic line down the back pipe the silicone hose you use already rubs it so when you screw the needle valve down it bunches up in there and hits the plastic sections causing it to get stuck in the already tight spot and makes it not work as a spring anymore.
I will try again with a flat spot on the washer and see if that helps.
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Post  RknRusty Wed Aug 07, 2013 2:02 pm

I'm going out to the shop in a few minutes. I'll take a look and see what i can figure out.

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Post  sdjjadk Sat Aug 10, 2013 11:56 pm

One other thing that works for keeping spring loaded needle valves in place is to stretch the spring out a little just to give the needle valve more spring tension.

Shawn
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Post  dinsdale Sun Aug 11, 2013 3:27 am

sdjjadk wrote:One other thing that works for keeping spring loaded needle valves in place is to stretch the spring out a little just to give the needle valve more spring tension.

Shawn
Yea, I was going to suggest 2 springs - more tension again.
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Post  reptile Sun Aug 11, 2013 7:52 am

dinsdale wrote:
sdjjadk wrote:One other thing that works for keeping spring loaded needle valves in place is to stretch the spring out a little just to give the needle valve more spring tension.

Shawn
Yea, I was going to suggest 2 springs - more tension again.
2 springs I never thought of that I will have to give that a go!


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Post  Ken Cook Sun Aug 11, 2013 7:55 am

Doesn't that spraybar have a plastic friction seal over it where the needle goes into the spraybar? Replacing the existing or installing a new one would certainly help the problem. It should have one and they do wear out . They also get quite slippery after due time and no longer hold the needle properly. Ken
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Post  reptile Sun Aug 11, 2013 8:05 am

Ken Cook wrote:             Doesn't that spraybar have a plastic friction seal over it where the needle goes into the spraybar? Replacing the existing or installing a new one would certainly help the problem. It should have one and they do wear out . They also get quite slippery after due time and no longer hold the needle properly. Ken
even on new ones it happens but it may be worth picking up a few of them you know who sells them?

THANKS

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Post  Ken Cook Sun Aug 11, 2013 8:56 am

One thing to keep in mind, these can be a real pain in the rear to get off. Don't force it with a screwdriver and slip rendering the screwdriver through your hand. Work a little of it at a time and it will come free. Some fall off while others are glued to the spraybar. When you reinsert the needle, the plastic is going to be very difficult to screw into so don't cross thread the needle. Just take your time and get it started correctly and all should be good. I've found vibration with that long needle to be very problematic. Seeing yours is R/C I have no idea how that is on the needle. In my situation, I might just be hitting that certain resonance causing it to go haywire. Ken
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Post  reptile Sun Aug 11, 2013 9:04 am

Ken Cook wrote:              One thing to keep in mind, these can be a real pain in the rear to get off. Don't force it with a screwdriver and slip rendering the screwdriver through your hand. Work a little of it at a time and it will come free. Some fall off while others are glued to the spraybar. When you reinsert the needle, the plastic is going to be very difficult to screw into so don't cross thread the needle. Just take your time and get it started correctly and all should be good. I've found vibration with that long needle to be very problematic. Seeing yours is R/C I have no idea how that is on the needle. In my situation, I might just be hitting that certain resonance causing it to go haywire. Ken
yes with the carb and long brass needle it blows! what I did was put a section of silicone hose up on the needle shank way above the threads what this does....  makes the silicone hose on the shank hit up against the back plastic section running down the pipe that the carb sits on.. it holds the needle tighter.

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Post  RknRusty Sun Aug 11, 2013 9:19 am

RknRusty wrote:I'm going out to the shop in a few minutes. I'll take a look and see what I can figure out.
Sorry I never replied. Any engine I had like that is now only pieces in a drawer, so I didn't have anything to show you. I was lucky that someone gave me a bunch of those little black friction tubes at the base of the needle. They help some.

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Post  SuperDave Sun Aug 11, 2013 10:30 am

In such cases I've found the running a properly balanced prop lessens the vibration therefore lessen NV "looseness".

It certainly worked that way on my "Lil' Swamp Buggy" powered by the same engine and carb combo shown in the pictures.

SD
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Post  reptile Sun Aug 11, 2013 11:50 am

here is what I did with this set up to help.

put a section so it hits up the back of the carb pipe when you screw in and out the needle valve... I used dubro medium size fuel line.
needle valve screw don't stay put! 049copy_zps5f3a3461
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Post  RknRusty Sun Aug 11, 2013 1:42 pm

That should do the trick.

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