needle valve screw don't stay put!

Like this:

Click for full size

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 ?

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.



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?

thanks guy's I did it and it looks like it should work...thanks for the TIP!!  

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?

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

Phil

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.

 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

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.

reptile wrote: 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.

RknRusty wrote:

reptile wrote: 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.

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

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

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.

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!


THANKS

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

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

Never mind I found them.

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

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.

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.

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

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.

That should do the trick.