Re: Thoughts on a homemade regulator

roddie Mon Nov 17, 2014 6:23 pm

ian1954 wrote:Why not emulate the NVA but without the needle and use a drilled hole to restrict the flow. Number drills can be had quite cheaply.

That's basically the idea Ian.. except I propose a simple short tube/coupler in the fuel line.. that has a greatly reduced inside diameter. A #60 drill (.040" dia.) isn't small enough for what I want to try. If possible... I'd like to arrive at a line-pressure that gives the needle more of an adjustment range.. as it would have on only a suction feed.. without fuel "spurting wildly" through the spray-bar hole, as soon as the needle is cracked open.

ian1954 Mon Nov 17, 2014 7:01 pm

#80 drill is .0135". Number drill sets here are quite cheap. Higher numbers 81 to 107 (0.0019") get very expensive.

http://www.tracytools.com/hss-drill-sets/number-drill-set-hss-61-80

I just thought it easier to start with a small hole for testing and then enlarge it rather than trying to swage metal tubing.

roddie Mon Nov 17, 2014 9:07 pm

ian1954 wrote:#80 drill is .0135". Number drill sets here are quite cheap. Higher numbers 81 to 107 (0.0019") get very expensive.

http://www.tracytools.com/hss-drill-sets/number-drill-set-hss-61-80

I just thought it easier to start with a small hole for testing and then enlarge it rather than trying to swage metal tubing.

Yea.. I don't have any experience with Phil's method of swaging... so that would be a new learning curve for me... I also don't can't see it being done.. without obtaining micro-tubing. A "crude" test could be performed by crimping down a short piece of 1/16" soft alloy tubing (.025" I.D.) on a short piece of .015" music-wire inserted... and see if the engine will run with that restriction. I suspect it will. The question is; "How much fuel can a bladder squirt through a tiny hole?" This will undoubtedly change with temperature because of the oil's in the fuel. Let's say you were able to jet down to an .010 orifice at 68 degrees F. You may need to increase to .015" in colder weather? Making up 3 or 4 test-jets for your fuel line wouldn't be hard. Install down-line near the engine where it's out of the way. Run a filter upstream between the bladder.

faif2d Tue Nov 18, 2014 7:40 pm

You will do better using some capalatory refrigeration tubing. It has a small ID and you need about 6-8" in length. We used to coil it up and put inside the backplate on a Norvel when they came out. Worked on a tee dee as well but the fine thread needle was available for them. To make a small hole in a brass or copper tube take a piece of CL wire (one of the strands) smoke it with a candle, put inside the tubing and fill the end with solder. The soot on the wire will allow you to pull out the strand if you are careful leaving a very small hole.

fit90 Thu Nov 20, 2014 7:09 am

Have you considered regulating the pressure using a pressure relief device? It could be very simple, small and light like a pressure relief valve. It could be used alone or in conjunction with something else.

pkrankow Thu Nov 20, 2014 9:22 am

faif2d wrote:You will do better using some capalatory refrigeration tubing. It has a small ID and you need about 6-8" in length. We used to coil it up and put inside the backplate on a Norvel when they came out. Worked on a tee dee as well but the fine thread needle was available for them. To make a small hole in a brass or copper tube take a piece of CL wire (one of the strands) smoke it with a candle, put inside the tubing and fill the end with solder. The soot on the wire will allow you to pull out the strand if you are careful leaving a very small hole.

Capillary tube! That stuff is pretty easy to order, but not exactly cheap, if only because it comes on a roll that is pretty large for our needs.

Phil

roddie Thu Nov 20, 2014 10:41 am

fit90 wrote:Have you considered regulating the pressure using a pressure relief device? It could be very simple, small and light like a pressure relief valve. It could be used alone or in conjunction with something else.

I don't think that an air-pressure relief device is the answer, because there would be an unsteady flow.. and possible surging of the fuel in the feed line. The idea is to reduce the fuel-pressure at the needle/seat.. The engine shouldn't require the full pressure of a bladder-feed to run. Think of a carburetor on a hotrod.. A "mechanical" fuel-pump supplies fuel pressure which is regulated by engine rpm.. because it is driven off a rotating cam. When an electric fuel pump is used instead.. the line-pressure is constant.. and high. A fuel regulator must be used.. or else the pressure at the carburetor(s) is dangerously high.. and can cause flooding.

The great thing about a fuel-bladder.. is that it feeds fuel without the need for air-pressure.. and will provide constant fuel-pressure in any position until it's empty... unlike a hard-tank on air (case/muffler) pressure.. and where it's possible/probable for air to be introduced into the fuel pick-up as the tank empties. The problem is.. the only thing regulating a bladder's pressure, is the internal diameter/size of the feed-line. Even the smallest common size fuel line is capable of delivering a lot of fuel under pressure. Fill a small primer-bulb or syringe with fuel.. attach a small size piece of fuel line.. and proceed to force the fuel out through it. It empties rather quickly. This is essentially what a fuel-bladder is doing.. and the only thing to slow down the flow, is the needle-valve assy... making for very sensitive adjustment and usually the need for a fine-thread needle.

This experiment will reveal whether a simple "restrictor" in the feed-line would allow for less sensitive adjustment when using the stock needle that was designed for the engine.. and still provide enough fuel to run at wide open throttle without leaning-out. One way of knowing if the restriction is too much; is if air bubbles become present in the feed-line while running. This would indicate that the engine is not getting enough fuel to run, and "suction" from the venturi ensues.

Sponsored content