Some more POP dribble, I found this compilation of posts I made from the EC Birt forum. I just took the good parts and left out the waffle. Each 'paragraph' is the essence from each of the threads -
We like it closer to 9 lbs pop, usually no lower and when we go to high altitude we raise it 2 to 4 lbs.
At your altitude you should be higher on pop than if you were at sea level because of the air density differences. On gas a .085 arm height and about 12 to 13 pop should do it.
It should work now, .065 arm height gets the needle open sooner than .075 as the demand diaphram has less distance to move to open the needle and creates more fuel volume in the wet side. If it bogs bring that low side needle out till it quits bogging and pulls hard. After you get it fattened on the low side you may have to lean the top some to get it lean enough to fly on top.
Is this a gas carb? Gas pop-off should be at least 10 lbs maybe a little more. If it was low it would make it rich. Go with 11 lbs pop with a .075 arm height if gas and 8 to 9 pop if alky with a .065 arm height. Then you can tune with the needles to lean it out. Jon
It likes fairly high pop-off , because of the small venturi. Try around 14lbs, if it acts lean, and wants the needles to be way out then drop a couple of pounds.
the lower the pop-off is set the richer the fuel curve is at the bottom.
the pressure of the spring controls pop-off. So ,if you go from a low pressure pop to a higher one, spring pressure must increase. Cooler air is more dense, so pop-off should be lower in the winter, and raised some for higher temps.
We run right at 11 lbs pop-off for our Leapords here in the States, and this is for tracks from sea level to 1500 or so. Higher altitude would require slightly higher pop-off.
it's all about the spring . You can cut a coil off on some springs and still have a full flat coil on the end, if not you should go to a softer or shorter spring to lower. To raise pop, you should either change to a stiffer or longer spring or if your Tec allows we have some .010 shims that go under the spring to raise at about 1/2 lb at a time.
We have a complete assortment of springs that we carry, but there's a lot of them you wouldn't use if you run just gas or just alky. We can pick you a spring that will hit close to what you want then either shim up or cut down to get it right where you want it.
18 lb pop-off is pretty typical for the UK, because of conditions and the way the carbs are built for UK tec. Higher pop-off would take some more fuel away and would only be productive if you were too rich at 18 lbs. As far as arm height , I prefer .085, which is leaner than .075 and will make a big difference in fuel flow. You just have to try some different settings, to see what will work best for you. Go with .085 arm 16lb pop-off, tune it about 1 3/4 low and 1/2 high or whatever on high to get engine heat where you want it. If you find your needle settings want to be way less than this, then raise the pop-off a pound or two.
you need a .085 arm height and about 10 to 12 pop-off pressure, that will get you where you can tune it with the needles. If you were at high altitude you would want it higher. We measure arm height from the carb base down to the top of the arm, and thats with no gasket
You just have to optimize the tune on each individual carb, the main difference will be the 166 having a smaller venturi will have a stronger fuel signal than the 334 which will make the 334 even more touchy about having the correct pop-off. And when you are in the right range of pop-off then you can tune it out with the High and Low neddles. If carbs are on the same motor then 166 needs higher pop than the 334. The 166 12 to 14 at sea level going up as high as 18 for real bad air or altitude. The 334 needs about 10 on a small motor and then go up from there with heat and or altitude.
