Did I get the right needle valve?

batjac Sun Dec 08, 2013 1:44 am

For the speed contest I bought a red backplate from Bernie (http://coxengines.ca/cox-.049-backplate-red.html) and this needle valve (http://coxengines.ca/cox-.049-needle-valve-brass-long.html) to build my engine. Trying out the needle valve, it doesn't seem to be a great fit. It seems a loose fit, and with it screwed all the way in, there still seems to be a lot of threads left sticking out of the insert. From all the way out, to fully seated, is 10 turns. I didn't see any other needle valve on the website that looked like it fit. Did I get the right needle valve?

The Unsure Mark

**RknRusty** Sun Dec 08, 2013 4:06 am

Hook a fuel line to it. Close the needle, see if you can blow through it. You should not be able to. Gradually open it and see if you can begin to pass air through it. If so, then it's working. If you can blow through it when it's closed, there may be a burr or cross thread jamming it.
Post a picture.

Rusty

roddie Sun Dec 08, 2013 11:04 am

batjac wrote:For the speed contest I bought a red backplate from Bernie (http://coxengines.ca/cox-.049-backplate-red.html) and this needle valve (http://coxengines.ca/cox-.049-needle-valve-brass-long.html) to build my engine. Trying out the needle valve, it doesn't seem to be a great fit. It seems a loose fit, and with it screwed all the way in, there still seems to be a lot of threads left sticking out of the insert. From all the way out, to fully seated, is 10 turns. I didn't see any other needle valve on the website that looked like it fit. Did I get the right needle valve?

The Unsure Mark

Mark, I haven't checked mine for fit yet... but I just received my order from Bernie last week; which was for the exact same red back-plate and long Brass needle... (along with a new cyl./piston.)

The needle you ordered is the right one... You had the option for the more expensive Aluminum needle... (which is also correct for that back-plate) The only other needle Bernie sells, is for the "tanked" back-plate... which would NOT be the correct needle.

My previous experience using this (brass/horseshoe) needle/back-plate design; is that it's a rather "delicate" fit as compared to the "tanked" versions "positive" feel... when your "threading-in" the needle.

For a reliable "seal"... you can omit the spring that came with it... and instead; cut a short pc. of silicone fuel tubing (slightly longer than the thread-length on the needle) and find a small steel flat-washer; just large enough for the threaded portion to pass through and stop at the shoulder on the needle shaft. Install this washer on the needle, and then insert the needle's taper into the fuel-line pc. before threading into the back-plate's spray-bar seal. (stretch the fuel-line around the black plastic "spray-bar seal) The idea is to have the fuel-line "seal the needle" where it enters the back-plate's spray-bar seal. This prevents air-leaks; which can make for frustrating needle adjustment. (A good mod. for "any" needle-valve...)

Rusty's suggested pressure test is a "must-do" in any case...

(edit) These photos are courtesy of Paul Gibeault

Did I get the right needle valve? 11-24-10

Did I get the right needle valve? 11-24-10

Did I get the right needle valve? 11-24-11

John Goddard Wed Dec 11, 2013 7:08 am

batjac wrote:For the speed contest I bought a red backplate from Bernie (http://coxengines.ca/cox-.049-backplate-red.html) and this needle valve (http://coxengines.ca/cox-.049-needle-valve-brass-long.html) to build my engine. Trying out the needle valve, it doesn't seem to be a great fit. It seems a loose fit, and with it screwed all the way in, there still seems to be a lot of threads left sticking out of the insert. From all the way out, to fully seated, is 10 turns. I didn't see any other needle valve on the website that looked like it fit. Did I get the right needle valve?

The Unsure Mark

That red back plate is The Nuts for balls out speed Mark.
However, in my experience the NV is extremely wayward and adjusts itself
constantly whilst running which can be frustrating to say the least.
The only fix I found worked reliably was to sleeve a piece of fuel tubing
the whole length of the N/V

Very Happy

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Did I get the right needle valve?

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