1996 gsx
Heres some more help.
Accurately tuning a PWC carburetor requires a basic understanding of its functions and adhering to a few basic rules. Most importantly, you can only expect the carb to work as well as your engine does; the performance of your carb cannot make up for a weak or worn out engine. Another point to stress here is that you may not be able to achieve maximum performance from your watercraft simply by changing jets in the carb. A mismatch of engine components and or porting may create a carburetion nightmare. The best advise is to use quality parts and service from reputable dealers. To achieve an accurate calibration with a carb you should adjust the tuneable circuits in the following order:
1. LOW SPEED ADJUSTER -To adjust a smooth idle
2. POP-OFF PRESSURE -Just off idle to 1/4 throttle in conjunction with the low speed jet.
3. LOW SPEED JET -Just off idle to 1/3 throttle.
4. HIGH SPEED JET - 1/3 to 3/4 throttle.
5. HIGH SPEED ADJUSTER -3/4 to wide open throttle.
The reason for adjusting the circuits in this order is because several circuits contribute to the total fuel delivery of the carb. Changing the low speed jet for example, affects wide open throttle fuel delivery to some degree The exceptions to the rule are the low speed adjuster and the regulator portion: the low speed
adjuster has no effect past 1/3 throttle. The regulator portion has no tuning effect past 1/4 throttle, although it continues to control the fuel supply.
IDLE STOP SCREW
The idle stop screw is used to adjust the idle speed (rpm) by opening or closing the throttle valve. Refer to your watercraft owners manual for the correct idle speed. As a rule of thumb, adjust the idle speed to approximately 1100 rpm.
LOW SPEED ADJUSTER
The low speed adjuster is used in conjunction with the idle stop screw to adjust and maintain idle speed and smoothness. Experiment turning the low speed adjuster in and out in small increments until a smooth idle is obtained. As the idle stop screw is turned in our out to raise or lower idle speed the low speed mixture is also affected. For clarification, if the idle stop screw is turned out to lower idle speed, this action increases manifold pressure slightly and richens the low speed mixture so that a mixture adjustment may be required. The low speed adjuster is very sensitive and adjustments should be made in small increments only.
Note: Remember, the low speed adjuster is only for adjusting the idle mixture. If you use the adjuster to help get rid of a low speed hesitation, you will probably find that your engine will load up in no wake zones, or after extended idling.
POP-OFF PRESSURE AND LOW SPEED JET
How do pop-off pressure and the low speed jet work together?
These two circuits overlap, although the low speed jet continues past 1/4 throttle where pop-off pressure has little to no effect. In general, if your pop-off is slightly too high, you can compensate by increasing the size of the low speed jet. The opposite is also true; if the low speed jet is slightly too small, you can compensate with less pop-off pressure. Once you get to the point where you think each is adjusted correctly, it's best to try varying the two to make certain you have the best combination. For example: If you have pop-off pressure of 30 psi and a 67.5 low speed jet, you should also try a pop-off of say 35 psi and a 70 low speed jet. To verify that you have the correct combination there are two things to test:
1. Throttle response should be crisp, with no hesitation.
2. Ride the boat at a constant 1/4 throttle opening for about 1 minute and then quickly open the throttle fully, there should be no hesitation and the engine should not show signs of being loaded up. If it hesitates, it's lean; if it's loaded up, it's rich. The first test is to check pop-off pressure, the second test is checking the correctness of the low speed jet size. Take the time to ride the boat slowly and thoroughly test your jetting changes. After a jet change, it takes the engine a few minutes of use to completely respond to the change.
When does it become necessary to adjust pop-off?
When personal watercraft come from the factory they have fairly high pop-off due to the fact that they also have somewhat restrictive air intake systems that cause the engine to generate very high manifold pressures; the higher the manifold pressures, the higher the pop-off pressure required to properly regulate the fuel delivery to the engine. As you modify or change your watercraft's flame arrestor to a less restrictive type you will most likely start to experience a lean hesitation caused by a decrease in manifold pressure. This change will require an adjustment in pop-off pressure to regain crisp throttle response. Because most
aftermarket flame arrestors are less restrictive than stock, you will need to decrease pop-off to compensate.
The Super BN carbs that come from Mikuni America are already set up for performance applications, and come with pop-off settings lower than the carbs that come as original equipment. Pop-off pressure, (the regulator portion of the Super BN) is a tuneable component of the Super BN and works in conjunction with the low speed jet for good initial throttle response. The components that make up the regulator portion of the Super BN are:
1. Needle Valve, available in 4 sizes, 1.5, 2.0, 2.3 and 2.5 (Note: Some OEM carbs have 1.2)
2. Arm Spring, available in 4 sizes, 115gr., 95gr., 80gr. And 65 gr.
3. Arm
4. Regulator Diaphragm
The arm has a limited range of adjustment; from the arm being level with the adjacent carb surface to being bent upwards no more than .040" (1mm) above that surface. If the arm is bent upwards too much, it can cause the needle valve to be held open when the diaphragm and cover are installed. If the arm is bent down, its movement becomes limited and may not be enough to allow the needle valve to open fully.
ADJUSTING POP-OFF PRESSURE
Pop-off pressure is adjusted by replacing the arm spring with one of a different gram rating. Sometimes, in order to achieve the desired pop-off pressure, it is also necessary to change the needle valve size; keep in mind that it's always best to use the smallest needle valve size to obtain the correct pop-off pressure.
MEASURING POP-OFF PRESSURE
You can measure pop-off pressure with a "pop-off" pump, available from Mikuni through your dealer.
CHECKING POP-OFF WITH A POP-OFF PUMP
1. Attach the pump to the fuel inlet nipple.
2. Cover, or in some way plug the fuel return nipple.
3. Remove the regulator diaphragm to observe the needle valve.
4. During testing, it is important to obtain consistent readings. To accomplish
this, it is necessary to keep the needle valve wet. Use WD-40 or something
similar to wet the needle valve. Note: Don't use gasoline because of the fire
hazard. Protect your eyes from the spray when the needle pops open.
5. Pressurize the carb with the pump until the needle valve pops open, being
careful to note the indicated pressure. Test the valve 3 times to assure an
accurate reading.
An indication that your pop-off needs to be adjusted is a lean hesitation when you open the throttle from idle; in the extreme, the engine may even die. It is much easier to detect a lean pop-off than it is a rich one, so it is wise to adjust your pop-off until you get it too lean and then back up until the lean hesitation disappears.
Note: It is recommended that you do not use too large a needle valve for your
application. Many tuners recommend using 2.3 or 2.5 needle valve in all cases. Actually, we recommend using the smallest needle valve that gives you the correct pop-off pressure for your engine. A 1.5 needle valve can flow the maximum amount of fuel that the Super BN can pump, so the only reason to use a larger needle valve is to obtain the correct needle valve and arm spring combination (pop-off) for your watercraft.
HIGH SPEED JET/THROTTLE POSITION AND JETTING
The high speed jet begins contributing fuel at about 3/8 throttle, overlapping the low speed jet. The high speed jet is the primary tuning component from ½ to 3/4 throttle. As you have probably noticed, tuning circuit operations are denoted in fractions of throttle openings.. the reason for this is simple: Carb jetting does not relate to engine rpm or the boat's speed, it only recognizes how far the throttle has been opened; each circuit of the carb responds in turn. This is why it's very
important, when trying to diagnose a carb problem, that you identify at which throttle opening the problem occurs, in order to adjust the appropriate circuit.
The procedure for testing for the correct high speed jet size is the same as for the low speed, except that you should now hold the throttle at a constant ½ open for one minute, then quickly open the throttle fully to check engine response. If the engine hesitates, the carb is lean. If the engine takes a second or two to clear out and then accelerate, the carb is too rich. In either case, make the appropriate jet change and do the complete test again.
HIGH SPEED ADJUSTER
The high speed adjuster is the last circuit to adjust. It primarily controls fuel delivery from 3/4 throttle to wide open throttle. Turning the screw clockwise reduces fuel flow, counter clockwise increases fuel flow. The maximum fuel flow is achieved at three turns out from closed. To test the high speed adjuster it is recommended that you start with a fresh set of spark plugs to get quicker plug readings. Unless you have an exhaust gas temperature gauge, you will have to rely on plug readings. You will need to be in an area where you can hold the throttle wide open for several minutes (Factory Pipe suggests that you only do this for about 30 seconds, longer times with a lean setting could cause engine damage) then chop the throttle and stop the engine just prior to removing the
plugs to read them. Ideally, you're looking for a nice brown color on the electrode
Another indicator of proper adjustment is a maximum rpm reading on a tachometer. If the carb is lean or rich, it won't pull as high an rpm reading as when it's right on.
PERFORMANCE TIPS
The "Left Turn Syndrome"
You will find in all instances that your watercraft will turn more easily to the right than to the left. The reasons are basically simple. First, engine torque constantly places pressure on the hull to turn right. If your engine's performance is marginal, you can notice a dramatic fall-off in power in a hard turn. This power fall-off can't always be blamed on the engine, being over-propped can also cause the engine to slow enough to fall off its power peak. An engine with a peaky power curve is especially susceptible to a very dramatic power loss in a hard left turn. Most recently, with the increase of Sport and Runabout racing, there has been a marked improvement in hull design with a dramatic increase in "G" forces encountered while turning: over 2.5 G's. In some instances such a hard turn can cause momentary loss of power due to fuel starvation in the carbs. Jetting changes cannot correct this situation, the best solution is to rotate the mounting of the carbs 90 deg, so that their throttle shafts are perpendicular to the crankshaft axis rather that parallel. To date, this solution to the problem has been 100% successful.
Fuel Dripping From The Inner Venturi At Idle
This situation occurs periodically and is easy to cure. What causes this problem is a combination of two things. First, low pop-off pressure (due to installation of a 2.5 needle valve with a light spring pressure) together with an engine that has substantial vibration at idle. The engine vibration causes the needle valve to leak, which causes the engine to run even rougher. You can view this occurrence by carefully looking into the throat of the carb at idle, you will be able to see fuel dripping from the inner venturi. In this same way you can also check to see that the problem is corrected. The cure for the problem is to increase pop-off pressure until the dripping stops.
Engine Hesitation When Accelerating After a High Speed Deceleration
You may find it desirable to increase the number of anti-siphon valves (part# BN34/107), If you ride very fast and find that you have a noticeable stumble when reopening the throttle after a long, high speed deceleration. This is caused by excess fuel in the carb. The engine revs fairly high while decelerating, but it uses very little fuel. The fuel pump still pulses hard, but there is no demand for the fuel. A small amount of fuel will overfill the fuel chamber, leak through the high speed circuit and get deposited on top of the closed throttle valve. This fuel causes a momentary rich condition when the throttle is reopened. The solution is to use one or two additional anti-siphon valves. Never use more than two extra, and recheck your calibration after installing any extra valves; in some cases extra valves can adversely affect throttle response.
__________________
LEAN CONDITION Air leaks anywhere into the motor case will cause a lean condition. Backfireing may result.
Check to see if the throttle cable has slack in it when it is at rest. The most common problem of a runaway idle is that the last guy did not install the throttle cable with enough slack in it. But that only appluies to one that has had work done to the carbs or to the cables.
Sometimes richening the low speed adjusters will stop this runaway condition, unless the jets or filters inside the carbs are clogged up.
They run away because they are too lean for the amount of fuel being put into the motor. They get too mch air, and not enough fuel.
Air leaks anywhere into the motor will cause a lean condition.
Tight cables cause a lean condition.
Clogged fuel systems and pet**** valves and carbs cause a lean condition.
L.S. Adjusters set too lean cause a lean condition at idle speeds.
Engines that shut off by themselves when riding along are often seizing the pistons from a lean condition, same as if you pulled the lanyard off. When this happens, it is often mistaken for an electrical issue.
WONT START WHEN HOT? A pressure test consists of two tests. One when assembling the carb, by installing the needle valve, the lever and the spring, then soaking the needle with gas or WD40, then pumping up the pressure and watching for bubbles around the needle valve, then more pressure to measure when it pops off.
The second test comes after full assembly. This is the one that gives you an idea if they leak or not. You pump up at least 10 psi and watch the guage to see if it leaks off. It should hod 10 psi for ten minutes.
What is happening if the needle valves are leaking after full assembly, is that the diaphrams that you installed over the lever, is actually holding the levers down enough to allow the otherwise good needle valves to leak. This can be stopped by bending those lever arms down a little bit so the nipples on the diaphram are not resting against the levers that open the needle valves..
Compression or Rotary Problem
If you install a rotary valve 180 degrees off, it will effect the compression readings in both clyinders but they should still pump a decent number and they should still both be even.
When the port is sealed off by the rotary valve when it should be open, you will get less air into the clyinders to compress. Atmospheric pressure is around 14 psi, an open port allows atmospheric pressure to aid in filling the clyinder with air to compress.
So, do not say it won't matter, because it will. But it usually is not the reason a piston shows low compression numbers.
Dual Carbs
Here's detail tricks on the carbs: Remove the cover, diaphram, and check valve block over the jets. Spray carb cleaner into the pilot jet, with the tube connected on the carb cleaner can. Look into the carb throat, and you'll see three microscopic holes and one larger one off to the right that has carb cleaner coming out when you spray. After spraying initially, get someone else to slip their finger over the large hole to increase pressure to the three small holes. You will actually see the streams getting larger as the cleaner cleans out the varnish in the holes. This step is critical, if you want to have crisp throttle response on the bottom end.
Synchronize your carbs! 90% of the time one butterfly opens more than the other, reducing performance, max rpms, throttle response, and fuel efficiency. Use a flashlight, and lay an inspection mirror in the carb throat. Open the throttle wide open, and visually line it up with the atomizer. Then check the other butterfly the same way. Zip-tying the throttle to the grip keeping it wide open makes it easier. Use 2-8mm open-end wrenches to break loose the locknuts on the coupler between the carbs and rotate accordingly to get the butterflies in the same position.
Insure the pop-off is the same or within 1 psi of each other, for fuel flow syncronation thru both the carbs.
For the carbs to work, you have got to have the flame arrestor on. This is what creates resistance, along with the manifold pressure created by the compression of the engine, to get the gas to the motor. So, if you don't have the flame arrestor on, you'll never get fuel to the motor.
QUICK CLEANING DUALS
Get a large can of carb cleaner. I used this to clean the internal filter screens...it can clean one in about 30 seconds.
Here's detail tricks on the carbs: Remove the cover, diaphram, and check valve block over the jets. Spray carb cleaner into the pilot jet, with the tube connected on the carb cleaner can. Look into the carb throat, and you'll see three microscopic holes and one larger one off to the right that has carb cleaner coming out when you spray. After spraying initially, get someone else to slip their finger over the large hole to increase pressure to the three small holes. You will actually see the streams getting larger as the cleaner cleans out the varnish in the holes. This step is critical, if you want to have crisp throttle response on the bottom end.
Spray carb cleaner into the main jet too, but don't look into the carb while doing it unless you want it in your eyes!
Make sure you spray carb cleaner through the hose barbs, in and out. Remove the needles to get good flow through the inlet barbs.
Synchronize your carbs! 90% of the time one butterfly opens more than the other, reducing performance, max rpms, throttle response, and fuel efficiency. Use a flashlight, and lay an inspection mirror in the carb throat. Open the throttle wide open, and visually line it up with the atomizer. Then check the other butterfly the same way. Zip-tying the throttle to the grip keeping it wide open makes it easier. Use 2-8mm open-end wrenches to break loose the locknuts on the coupler between the carbs and rotate accordingly to get the butterflies the same position.
Hope this helps, Bills86e.
Heres some more help.
Accurately tuning a PWC carburetor requires a basic understanding of its functions and adhering to a few basic rules. Most importantly, you can only expect the carb to work as well as your engine does; the performance of your carb cannot make up for a weak or worn out engine. Another point to stress here is that you may not be able to achieve maximum performance from your watercraft simply by changing jets in the carb. A mismatch of engine components and or porting may create a carburetion nightmare. The best advise is to use quality parts and service from reputable dealers. To achieve an accurate calibration with a carb you should adjust the tuneable circuits in the following order:
1. LOW SPEED ADJUSTER -To adjust a smooth idle
2. POP-OFF PRESSURE -Just off idle to 1/4 throttle in conjunction with the low speed jet.
3. LOW SPEED JET -Just off idle to 1/3 throttle.
4. HIGH SPEED JET - 1/3 to 3/4 throttle.
5. HIGH SPEED ADJUSTER -3/4 to wide open throttle.
The reason for adjusting the circuits in this order is because several circuits contribute to the total fuel delivery of the carb. Changing the low speed jet for example, affects wide open throttle fuel delivery to some degree The exceptions to the rule are the low speed adjuster and the regulator portion: the low speed
adjuster has no effect past 1/3 throttle. The regulator portion has no tuning effect past 1/4 throttle, although it continues to control the fuel supply.
IDLE STOP SCREW
The idle stop screw is used to adjust the idle speed (rpm) by opening or closing the throttle valve. Refer to your watercraft owners manual for the correct idle speed. As a rule of thumb, adjust the idle speed to approximately 1100 rpm.
LOW SPEED ADJUSTER
The low speed adjuster is used in conjunction with the idle stop screw to adjust and maintain idle speed and smoothness. Experiment turning the low speed adjuster in and out in small increments until a smooth idle is obtained. As the idle stop screw is turned in our out to raise or lower idle speed the low speed mixture is also affected. For clarification, if the idle stop screw is turned out to lower idle speed, this action increases manifold pressure slightly and richens the low speed mixture so that a mixture adjustment may be required. The low speed adjuster is very sensitive and adjustments should be made in small increments only.
Note: Remember, the low speed adjuster is only for adjusting the idle mixture. If you use the adjuster to help get rid of a low speed hesitation, you will probably find that your engine will load up in no wake zones, or after extended idling.
POP-OFF PRESSURE AND LOW SPEED JET
How do pop-off pressure and the low speed jet work together?
These two circuits overlap, although the low speed jet continues past 1/4 throttle where pop-off pressure has little to no effect. In general, if your pop-off is slightly too high, you can compensate by increasing the size of the low speed jet. The opposite is also true; if the low speed jet is slightly too small, you can compensate with less pop-off pressure. Once you get to the point where you think each is adjusted correctly, it's best to try varying the two to make certain you have the best combination. For example: If you have pop-off pressure of 30 psi and a 67.5 low speed jet, you should also try a pop-off of say 35 psi and a 70 low speed jet. To verify that you have the correct combination there are two things to test:
1. Throttle response should be crisp, with no hesitation.
2. Ride the boat at a constant 1/4 throttle opening for about 1 minute and then quickly open the throttle fully, there should be no hesitation and the engine should not show signs of being loaded up. If it hesitates, it's lean; if it's loaded up, it's rich. The first test is to check pop-off pressure, the second test is checking the correctness of the low speed jet size. Take the time to ride the boat slowly and thoroughly test your jetting changes. After a jet change, it takes the engine a few minutes of use to completely respond to the change.
When does it become necessary to adjust pop-off?
When personal watercraft come from the factory they have fairly high pop-off due to the fact that they also have somewhat restrictive air intake systems that cause the engine to generate very high manifold pressures; the higher the manifold pressures, the higher the pop-off pressure required to properly regulate the fuel delivery to the engine. As you modify or change your watercraft's flame arrestor to a less restrictive type you will most likely start to experience a lean hesitation caused by a decrease in manifold pressure. This change will require an adjustment in pop-off pressure to regain crisp throttle response. Because most
aftermarket flame arrestors are less restrictive than stock, you will need to decrease pop-off to compensate.
The Super BN carbs that come from Mikuni America are already set up for performance applications, and come with pop-off settings lower than the carbs that come as original equipment. Pop-off pressure, (the regulator portion of the Super BN) is a tuneable component of the Super BN and works in conjunction with the low speed jet for good initial throttle response. The components that make up the regulator portion of the Super BN are:
1. Needle Valve, available in 4 sizes, 1.5, 2.0, 2.3 and 2.5 (Note: Some OEM carbs have 1.2)
2. Arm Spring, available in 4 sizes, 115gr., 95gr., 80gr. And 65 gr.
3. Arm
4. Regulator Diaphragm
The arm has a limited range of adjustment; from the arm being level with the adjacent carb surface to being bent upwards no more than .040" (1mm) above that surface. If the arm is bent upwards too much, it can cause the needle valve to be held open when the diaphragm and cover are installed. If the arm is bent down, its movement becomes limited and may not be enough to allow the needle valve to open fully.
ADJUSTING POP-OFF PRESSURE
Pop-off pressure is adjusted by replacing the arm spring with one of a different gram rating. Sometimes, in order to achieve the desired pop-off pressure, it is also necessary to change the needle valve size; keep in mind that it's always best to use the smallest needle valve size to obtain the correct pop-off pressure.
MEASURING POP-OFF PRESSURE
You can measure pop-off pressure with a "pop-off" pump, available from Mikuni through your dealer.
CHECKING POP-OFF WITH A POP-OFF PUMP
1. Attach the pump to the fuel inlet nipple.
2. Cover, or in some way plug the fuel return nipple.
3. Remove the regulator diaphragm to observe the needle valve.
4. During testing, it is important to obtain consistent readings. To accomplish
this, it is necessary to keep the needle valve wet. Use WD-40 or something
similar to wet the needle valve. Note: Don't use gasoline because of the fire
hazard. Protect your eyes from the spray when the needle pops open.
5. Pressurize the carb with the pump until the needle valve pops open, being
careful to note the indicated pressure. Test the valve 3 times to assure an
accurate reading.
An indication that your pop-off needs to be adjusted is a lean hesitation when you open the throttle from idle; in the extreme, the engine may even die. It is much easier to detect a lean pop-off than it is a rich one, so it is wise to adjust your pop-off until you get it too lean and then back up until the lean hesitation disappears.
Note: It is recommended that you do not use too large a needle valve for your
application. Many tuners recommend using 2.3 or 2.5 needle valve in all cases. Actually, we recommend using the smallest needle valve that gives you the correct pop-off pressure for your engine. A 1.5 needle valve can flow the maximum amount of fuel that the Super BN can pump, so the only reason to use a larger needle valve is to obtain the correct needle valve and arm spring combination (pop-off) for your watercraft.
HIGH SPEED JET/THROTTLE POSITION AND JETTING
The high speed jet begins contributing fuel at about 3/8 throttle, overlapping the low speed jet. The high speed jet is the primary tuning component from ½ to 3/4 throttle. As you have probably noticed, tuning circuit operations are denoted in fractions of throttle openings.. the reason for this is simple: Carb jetting does not relate to engine rpm or the boat's speed, it only recognizes how far the throttle has been opened; each circuit of the carb responds in turn. This is why it's very
important, when trying to diagnose a carb problem, that you identify at which throttle opening the problem occurs, in order to adjust the appropriate circuit.
The procedure for testing for the correct high speed jet size is the same as for the low speed, except that you should now hold the throttle at a constant ½ open for one minute, then quickly open the throttle fully to check engine response. If the engine hesitates, the carb is lean. If the engine takes a second or two to clear out and then accelerate, the carb is too rich. In either case, make the appropriate jet change and do the complete test again.
HIGH SPEED ADJUSTER
The high speed adjuster is the last circuit to adjust. It primarily controls fuel delivery from 3/4 throttle to wide open throttle. Turning the screw clockwise reduces fuel flow, counter clockwise increases fuel flow. The maximum fuel flow is achieved at three turns out from closed. To test the high speed adjuster it is recommended that you start with a fresh set of spark plugs to get quicker plug readings. Unless you have an exhaust gas temperature gauge, you will have to rely on plug readings. You will need to be in an area where you can hold the throttle wide open for several minutes (Factory Pipe suggests that you only do this for about 30 seconds, longer times with a lean setting could cause engine damage) then chop the throttle and stop the engine just prior to removing the
plugs to read them. Ideally, you're looking for a nice brown color on the electrode
Another indicator of proper adjustment is a maximum rpm reading on a tachometer. If the carb is lean or rich, it won't pull as high an rpm reading as when it's right on.
PERFORMANCE TIPS
The "Left Turn Syndrome"
You will find in all instances that your watercraft will turn more easily to the right than to the left. The reasons are basically simple. First, engine torque constantly places pressure on the hull to turn right. If your engine's performance is marginal, you can notice a dramatic fall-off in power in a hard turn. This power fall-off can't always be blamed on the engine, being over-propped can also cause the engine to slow enough to fall off its power peak. An engine with a peaky power curve is especially susceptible to a very dramatic power loss in a hard left turn. Most recently, with the increase of Sport and Runabout racing, there has been a marked improvement in hull design with a dramatic increase in "G" forces encountered while turning: over 2.5 G's. In some instances such a hard turn can cause momentary loss of power due to fuel starvation in the carbs. Jetting changes cannot correct this situation, the best solution is to rotate the mounting of the carbs 90 deg, so that their throttle shafts are perpendicular to the crankshaft axis rather that parallel. To date, this solution to the problem has been 100% successful.
Fuel Dripping From The Inner Venturi At Idle
This situation occurs periodically and is easy to cure. What causes this problem is a combination of two things. First, low pop-off pressure (due to installation of a 2.5 needle valve with a light spring pressure) together with an engine that has substantial vibration at idle. The engine vibration causes the needle valve to leak, which causes the engine to run even rougher. You can view this occurrence by carefully looking into the throat of the carb at idle, you will be able to see fuel dripping from the inner venturi. In this same way you can also check to see that the problem is corrected. The cure for the problem is to increase pop-off pressure until the dripping stops.
Engine Hesitation When Accelerating After a High Speed Deceleration
You may find it desirable to increase the number of anti-siphon valves (part# BN34/107), If you ride very fast and find that you have a noticeable stumble when reopening the throttle after a long, high speed deceleration. This is caused by excess fuel in the carb. The engine revs fairly high while decelerating, but it uses very little fuel. The fuel pump still pulses hard, but there is no demand for the fuel. A small amount of fuel will overfill the fuel chamber, leak through the high speed circuit and get deposited on top of the closed throttle valve. This fuel causes a momentary rich condition when the throttle is reopened. The solution is to use one or two additional anti-siphon valves. Never use more than two extra, and recheck your calibration after installing any extra valves; in some cases extra valves can adversely affect throttle response.
__________________
LEAN CONDITION Air leaks anywhere into the motor case will cause a lean condition. Backfireing may result.
Check to see if the throttle cable has slack in it when it is at rest. The most common problem of a runaway idle is that the last guy did not install the throttle cable with enough slack in it. But that only appluies to one that has had work done to the carbs or to the cables.
Sometimes richening the low speed adjusters will stop this runaway condition, unless the jets or filters inside the carbs are clogged up.
They run away because they are too lean for the amount of fuel being put into the motor. They get too mch air, and not enough fuel.
Air leaks anywhere into the motor will cause a lean condition.
Tight cables cause a lean condition.
Clogged fuel systems and pet**** valves and carbs cause a lean condition.
L.S. Adjusters set too lean cause a lean condition at idle speeds.
Engines that shut off by themselves when riding along are often seizing the pistons from a lean condition, same as if you pulled the lanyard off. When this happens, it is often mistaken for an electrical issue.
WONT START WHEN HOT? A pressure test consists of two tests. One when assembling the carb, by installing the needle valve, the lever and the spring, then soaking the needle with gas or WD40, then pumping up the pressure and watching for bubbles around the needle valve, then more pressure to measure when it pops off.
The second test comes after full assembly. This is the one that gives you an idea if they leak or not. You pump up at least 10 psi and watch the guage to see if it leaks off. It should hod 10 psi for ten minutes.
What is happening if the needle valves are leaking after full assembly, is that the diaphrams that you installed over the lever, is actually holding the levers down enough to allow the otherwise good needle valves to leak. This can be stopped by bending those lever arms down a little bit so the nipples on the diaphram are not resting against the levers that open the needle valves..
Compression or Rotary Problem
If you install a rotary valve 180 degrees off, it will effect the compression readings in both clyinders but they should still pump a decent number and they should still both be even.
When the port is sealed off by the rotary valve when it should be open, you will get less air into the clyinders to compress. Atmospheric pressure is around 14 psi, an open port allows atmospheric pressure to aid in filling the clyinder with air to compress.
So, do not say it won't matter, because it will. But it usually is not the reason a piston shows low compression numbers.
Dual Carbs
Here's detail tricks on the carbs: Remove the cover, diaphram, and check valve block over the jets. Spray carb cleaner into the pilot jet, with the tube connected on the carb cleaner can. Look into the carb throat, and you'll see three microscopic holes and one larger one off to the right that has carb cleaner coming out when you spray. After spraying initially, get someone else to slip their finger over the large hole to increase pressure to the three small holes. You will actually see the streams getting larger as the cleaner cleans out the varnish in the holes. This step is critical, if you want to have crisp throttle response on the bottom end.
Synchronize your carbs! 90% of the time one butterfly opens more than the other, reducing performance, max rpms, throttle response, and fuel efficiency. Use a flashlight, and lay an inspection mirror in the carb throat. Open the throttle wide open, and visually line it up with the atomizer. Then check the other butterfly the same way. Zip-tying the throttle to the grip keeping it wide open makes it easier. Use 2-8mm open-end wrenches to break loose the locknuts on the coupler between the carbs and rotate accordingly to get the butterflies in the same position.
Insure the pop-off is the same or within 1 psi of each other, for fuel flow syncronation thru both the carbs.
For the carbs to work, you have got to have the flame arrestor on. This is what creates resistance, along with the manifold pressure created by the compression of the engine, to get the gas to the motor. So, if you don't have the flame arrestor on, you'll never get fuel to the motor.
QUICK CLEANING DUALS
Get a large can of carb cleaner. I used this to clean the internal filter screens...it can clean one in about 30 seconds.
Here's detail tricks on the carbs: Remove the cover, diaphram, and check valve block over the jets. Spray carb cleaner into the pilot jet, with the tube connected on the carb cleaner can. Look into the carb throat, and you'll see three microscopic holes and one larger one off to the right that has carb cleaner coming out when you spray. After spraying initially, get someone else to slip their finger over the large hole to increase pressure to the three small holes. You will actually see the streams getting larger as the cleaner cleans out the varnish in the holes. This step is critical, if you want to have crisp throttle response on the bottom end.
Spray carb cleaner into the main jet too, but don't look into the carb while doing it unless you want it in your eyes!
Make sure you spray carb cleaner through the hose barbs, in and out. Remove the needles to get good flow through the inlet barbs.
Synchronize your carbs! 90% of the time one butterfly opens more than the other, reducing performance, max rpms, throttle response, and fuel efficiency. Use a flashlight, and lay an inspection mirror in the carb throat. Open the throttle wide open, and visually line it up with the atomizer. Then check the other butterfly the same way. Zip-tying the throttle to the grip keeping it wide open makes it easier. Use 2-8mm open-end wrenches to break loose the locknuts on the coupler between the carbs and rotate accordingly to get the butterflies the same position.
Hope this helps, Bills86e.
