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pop-off sp 1997
- Thread starter guillaume french
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AKnarrowback
Well-Known Member
Oh man... Welcome to the forum.
I don't speak French but I'll give this a shot and hopefully you can decipher it.
The only way to check pop off pressure is to use a gauge hooked into the carb on the bench.
If you are rebuilding your carb use only genuine mikuni rebuild kits, do not buy a cheap aftermarket kit. When doing the rebuild re-use the pop off spring that was in your carb when you took it apart, they don't wear out.
The carb charts you are showing do have some errors in them. Sometimes you have to just run the machine to see if your settings are good then go into the carb to adjust any rough running on the low end.
I don't speak French but I'll give this a shot and hopefully you can decipher it.
The only way to check pop off pressure is to use a gauge hooked into the carb on the bench.
If you are rebuilding your carb use only genuine mikuni rebuild kits, do not buy a cheap aftermarket kit. When doing the rebuild re-use the pop off spring that was in your carb when you took it apart, they don't wear out.
The carb charts you are showing do have some errors in them. Sometimes you have to just run the machine to see if your settings are good then go into the carb to adjust any rough running on the low end.
AKnarrowback
Well-Known Member
Pop Off Pressure - The pop off pressure is not an adjustment that exists on the carb, but rather a specification that is a combined function of the needle valve size, and the spring rate of the float arm spring. This specification has a wholesale effect on the fuel metering in the 0 - 40% fuel range. Because the pop off pressure has this far reaching range that overlaps with several other metering ranges, we consider it a fundamental starting point.
The term "pop off pressure" refers to the amount of fuel pressure needed to push the float needle valve away from it's sealing seat. Pop off pressure is checked with a hand pump that is fitted with an in line gage. The pump is connected to the fuel input fitting of the carb. The return line fitting is then sealed off with one finger while the pump pressurizes the float chamber. The pressure reached on the gauge when the needle gives way is called the pop off pressure. "Adjusting" the pop off pressure is discussed below. If you don't have a pop off pressure gauge, you should get one that has a gauge and pump capable of 30 psi. (Most Mikuni distributors carry them) At the beginning, it's only important to check that the needle holds the pressure back with no leaking up to the point where it pops cleanly away from the seat. Perform the pop off test several times to confirm the actual pop off pressure. Initial pop off pressures on the Mikuni and Kiehin carbs (unless otherwise specified) should be no less than 25 psi and no greater than 35 psi.
We will address pop-off adjustment again later in this document, but the pre-existing effect of the pop-off on other ranges must always be kept in the fore. There is no specific "ideal" pop-off pressure for all engines. But when the pop-off is far off of "ideal spec" for a particular engine format, it can cause the other circuits to not come into adjustment or not function properly.
In short, the pop-off pressure should be changed if a collection of low range circuits cannot accommodate the current pop-off specification. The best indicator of this is the setting of the low speed adjustment screw.
Low Speed Screw - Theoretically, "every" pwc engine (no matter how radically modified) should be able to start with the touch of the button (no throttle required) and then maintain a reasonably steady idle. Even engines with enlarged and modified throats should be able to deliver this type of operation.
The low speed screw should be adjusted to the setting that offers the highest "sustainable" idling rpm. This setting is easiest found by viewing a digital tachometer with a warmed up machine running in the water (tied to a trailer is fine). As richer and leaner settings are tried, you will quickly see the trend toward higher idle rpms. In truth, you will see the highest rpm when the low speed screws are slightly too lean. However you will notice on the tachometer that those high rpms will waver up and down, not steady and sustained.
You will eventually find a range of about ¼ turn that offers this good idle (about 1300-1400). Within this adjustment range, find the setting that allows the engine to come down to the same steady idle rpm after you snap the throttle open momentarily. An additional test of the perfect setting is to stop the engine (about 30 seconds), then restart without touching the throttle. In this test the engine should come back to it's normal steady rpm number.
The low speed adjustment screw carries it's greatest impact in the 0 - 20% throttle opening range. It continues to have a lesser impact up to 40% opening. The low speed screw setting is almost wholly responsible for allowing easy starting and steady idling. We say "almost" because the pop-off pressure can affect the setting of the low speed screw that will finally offer the ideal starting and idling that you want.
As an example, an engine with dual 38 carbs may have a pop off pressure of 35 psi, and offer perfect starting and idling with the low speed screws set at 2 ½ turns out. In a perfect world, it's desirable to have the low speed screws end up "in the vicinity of" 1 turn out. The 2 ½ turns of our example is actually an excessively rich compensation for a pop-off pressure that is too high. By reducing the pop off pressure, with a lighter pressure float arm spring, the entire 0 - 40% range is slightly richened. This additional richness will allow for a much leaner (closer to 1 turn out) screw setting that will offer perfect starting and idling. It has been our experience that the pop-off pressure that allows for this "close to 1 turn out setting" will also usually yield the best overall low speed response. If you find your best operation at a setting of less than ½ turn out, the pop-off pressure should be raised slightly. If you find your best operation at a setting above 2 turns out, the pop-off should be lowered slightly.
The term "pop off pressure" refers to the amount of fuel pressure needed to push the float needle valve away from it's sealing seat. Pop off pressure is checked with a hand pump that is fitted with an in line gage. The pump is connected to the fuel input fitting of the carb. The return line fitting is then sealed off with one finger while the pump pressurizes the float chamber. The pressure reached on the gauge when the needle gives way is called the pop off pressure. "Adjusting" the pop off pressure is discussed below. If you don't have a pop off pressure gauge, you should get one that has a gauge and pump capable of 30 psi. (Most Mikuni distributors carry them) At the beginning, it's only important to check that the needle holds the pressure back with no leaking up to the point where it pops cleanly away from the seat. Perform the pop off test several times to confirm the actual pop off pressure. Initial pop off pressures on the Mikuni and Kiehin carbs (unless otherwise specified) should be no less than 25 psi and no greater than 35 psi.
We will address pop-off adjustment again later in this document, but the pre-existing effect of the pop-off on other ranges must always be kept in the fore. There is no specific "ideal" pop-off pressure for all engines. But when the pop-off is far off of "ideal spec" for a particular engine format, it can cause the other circuits to not come into adjustment or not function properly.
In short, the pop-off pressure should be changed if a collection of low range circuits cannot accommodate the current pop-off specification. The best indicator of this is the setting of the low speed adjustment screw.
Low Speed Screw - Theoretically, "every" pwc engine (no matter how radically modified) should be able to start with the touch of the button (no throttle required) and then maintain a reasonably steady idle. Even engines with enlarged and modified throats should be able to deliver this type of operation.
The low speed screw should be adjusted to the setting that offers the highest "sustainable" idling rpm. This setting is easiest found by viewing a digital tachometer with a warmed up machine running in the water (tied to a trailer is fine). As richer and leaner settings are tried, you will quickly see the trend toward higher idle rpms. In truth, you will see the highest rpm when the low speed screws are slightly too lean. However you will notice on the tachometer that those high rpms will waver up and down, not steady and sustained.
You will eventually find a range of about ¼ turn that offers this good idle (about 1300-1400). Within this adjustment range, find the setting that allows the engine to come down to the same steady idle rpm after you snap the throttle open momentarily. An additional test of the perfect setting is to stop the engine (about 30 seconds), then restart without touching the throttle. In this test the engine should come back to it's normal steady rpm number.
The low speed adjustment screw carries it's greatest impact in the 0 - 20% throttle opening range. It continues to have a lesser impact up to 40% opening. The low speed screw setting is almost wholly responsible for allowing easy starting and steady idling. We say "almost" because the pop-off pressure can affect the setting of the low speed screw that will finally offer the ideal starting and idling that you want.
As an example, an engine with dual 38 carbs may have a pop off pressure of 35 psi, and offer perfect starting and idling with the low speed screws set at 2 ½ turns out. In a perfect world, it's desirable to have the low speed screws end up "in the vicinity of" 1 turn out. The 2 ½ turns of our example is actually an excessively rich compensation for a pop-off pressure that is too high. By reducing the pop off pressure, with a lighter pressure float arm spring, the entire 0 - 40% range is slightly richened. This additional richness will allow for a much leaner (closer to 1 turn out) screw setting that will offer perfect starting and idling. It has been our experience that the pop-off pressure that allows for this "close to 1 turn out setting" will also usually yield the best overall low speed response. If you find your best operation at a setting of less than ½ turn out, the pop-off pressure should be raised slightly. If you find your best operation at a setting above 2 turns out, the pop-off should be lowered slightly.
guillaume french
New Member
thank you for your answer my problem and since I have this engine it has never worked well I do not know if the resort is the right one my idle and good no problem until 1/4 then the engine stalls unless I go up the accelerator has more than 1/2 the left I rebuilt my carburetor with a kit mikuni the needle and new when I pull a bit on the choke it accelerates I do not know what to do
guillaume french
New Member
thanks I will try
guillaume french
New Member
problem more or less solved by changing the spring I have almost no more hole at acceleration thank you for taking time for me
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