Thread: carb pop off pressure chart
11-25-2008, 08:38 PM #1
carb pop off pressure chart
This will give you idea how different combos work.
11-25-2008, 09:10 PM #2
Mikuni has added a new N&S to their line 1.8, I don't have data yet, but will be getting some soon.
11-25-2008, 10:38 PM #3
How to Check CArb Pop-off Popoff Pop Off
You can fill the fuel inlet hole IN THE MAIN BODY OF THE CARB with WD-40 then insert the end of the pop off gage into or over the hole and pump the gage slowly till the needle pops off it should pop.
A good needle and seat will "Pop-Off" at the desired setting, drop 1/2 to 1 pound and hold. A very slow leakage from this hold pressure won't affect the performance of your carburetor but a complete drop from the desired setting to ZERO of the gauge will cause very poor carburetor performance and must be cured.
Never check your "Pop-Off" Pressure with the carburetor dry.
You can also fill the line of your pressure tester with WD 40 then when you pump this in to test the "Pop-Off" Pressure, the needle will be wet and closer to the condition it will be when running."
Pop-off pressure testing:
1) Before testing we must make sure that the carburetor is "wet" inside. If it was overhauled, before testing, it needs to have fuel or WD-40 inside. Otherwise the pressure value will not be accurate.
2) Connect fuel hose to the fuel inlet of the carburetor.
3) Start pumping until desired Psi of pressure ise achieved.
4) Stop pumping. If the pressure holds, the needle valve closes tight. It the pressure drops the needle valve and seat needs to be replaced.
5) Increase pressure until a sudden drop is noticed. This means that the needle valve opened. The value at which it opened is the pop-off pressure.
1) Too high pop-off pressure leads to fuel starvation, hot engine, overheating and even seizing, if the engine is run at full power for long periods of time.A good indicator of this will be of course a high temperature reading on the CHT, EGT or a very "clean" white-gray spark plug insulator. This is NOT an indicator that the oil used in the mixture is good and burns clean! It shows that there is TOO much AIR in the mixture and not enough FUEL. The combustion is done in excess of oxygen. Such a combustion generates excessive heat.
2) A too low pop-off pressure will cause a too rich mixture which is not really dangerous for the engine on the short run but will decrease its performance and cause too much carbon buildup. On the long run, the excessive carbon deposits may fragment, get caught in between the piston and the cylinder wall and cause scoring. If not detected in time, this deposits will sooner or later "load the spark plug" cause a short and an engine out.
• engine flooding
• difficult warm engine starts
• rough mid range RPM
• lowered maximum RPM of the engine.
Also, When checking popoff also keep this in mind
Measuring Fulcrum Arm Height
11-25-2008, 10:41 PM #4
11-26-2008, 01:19 PM #5
I dont know if anyone has posted this yet but there is a new spring chart showing that the 115gram gold spring has been replaced with a platinum color 115gram spring. Please note when you buy new ones.
Haven't actually seen them so dont really know the true color yet.
11-26-2008, 11:19 PM #6
11-27-2008, 07:43 AM #7
It has to due with being ROSH compliant. No more Cad plating.
11-27-2008, 08:29 AM #8
aH !..yup..Rosh....cadmium and lead-free
11-27-2008, 10:48 AM #9
I have some, they have been coming in the new kits from Mikuni. It's basicly another color of silver. I will see if I can get a pic of all three that shows the differences.
I would call it bright silver.
02-19-2009, 07:47 PM #10
- Join Date
- Jun 2008
- Hillsborough, North Carolina
Pop Off pressure test question...
I've just rebuilt carb on 99'xl1200ltd and I've got a question about the two different pressures that the n/s seem to be lifting at. Let me describe, I'll try to be brief but thorough....
I am testing for about 42-43 psi pop-off with a 95g spring and 1.5 N/S. (I don't think the hi/lo jets matter do they? or the #turns i've set the t-handles to?)
I've connected hoses to the inlet/outlet ports on the pump body and blocked off all but one inlet which is connected to my test gauge which is then connected to isolation valves and then through a regulator from my pressure supply. (I'm actually using nitrogen instead of compressed air-this shouln't matter should it?)
I'm spraying wd-40 all over the n/s (& manually depressing the arm so as to get wd40 under it too) and jets side of the carb and am also spraying it in the inlet hose before I start charging the inlet to perform the test. What I'm finding is when it initially lifts (about 50psi) only for a quick spurt and then holds pressure fine. Then as I continue the test, it must be pushing the wd-40 out of the inlet hose and it starts lifting right at about 43psi. Its just that first initial lifting that is around 50 psi, the next 3-4 times it lifts @ 43psi before all the wd40 sprays out of everything and that's extent of my test. I've taken about 3/4 of a turn off the 95g spring to get it to lift at these pressures so far, It started at around 65psi before I cut it down.
Is this okay? Do I go by the very first time it lifts with the liquid in the inlet hose (50psi) or the readings that follow and its lifting at the 43psi? Or do I continue cutting the spring until I get the initial lifting down to 43psi?
Thanks for reading all of this and keeping me straight guys!
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