lynxgen
Well-Known Member
IDLE SYSTEM
Idle-1/8th throttle:
Piolet screw is set at 2 turns from factory.
Gently bottom it and turn back out 2 turns.
Next run the engine till it hits normal operating temp.
With the engine idling smoothly, adjust the piolet screw OUT (Richer) slowly until the idle either slows or becomes irregular, then turn the screw IN (Leaner) until the engine again slows or begins to idle irregularly.
Count the number of turns between the two positions.
Set the screw mid-way between these too-rich and too-lean positions.
Use the Idle adjuster to re-set the idle speed.
If the engine becomes too hot during the adjustment procedure, the resulting idle mixture will probably be on the lean side of correct.
If you have a large fan, use it while adjusting the mixture. If you do not have one, you may need to take time out for a short ride to cool the engine back to normal temperature.
NOTES:
IF the best idle is achieved with the screw less than one turn out, then your jet is too large and needs to be downsized.
If the engine speed does not slow after 2.5 turns out, then the jet is too small and needs to be upsized.
Jet needle:
Off idle to 1/4 throttle:
the straight diameter portion of the jet needle controls the mixture from just above idle to aproximately 1/4 throttle. If the mixture is too rich or too lean in this throttle range, the needle will need to be exchanged for one with a larger or smaller diameter.
Lean needle:
If the needle is too lean, part throttle acceleration will be flat. There may also be some detonation during part throttle acceleration in the 2500-3000rpm range, (Alhough this may have other causes such as an ignition that advances too quickly).
A lean needle also results in an abnormaly slow warm-up. If any of these conditions exist, install a one size richer needle and compare the performance.
Rich Needle:
While a black, sooty spark plug is a sure sign of richness, others are more subtle. If your engine responds crisply at low throttle openings when cold, chances are the needle is one size smaller, (Richer) than it needs to be. This assumes of course that the idle mixture is correctly tuned.
Poor fuel milage is another sign of an over-rich condition.
Go one size leaner needle.
Jet needle 1/4-3/4 throttle:
The tapered portion of the jet needle rises out of the needle jet at about 1/4 throttle. From that point until the main jet takes over near 3/4 throttle, the jet needle taper is the main control of mixure strength.
Lean:
If the acceleration seems soft or flat and the engine is slow to respond when the throttle is quickly opened from the 1/2 throttle position, the mixture is too lean. Raise the needle one notch and repeat the test.
Rich:
If acceleration is crisp but the engine hesitates or staggers as the throttle is quickley closed from 3/4 to 1/2 throttle, the mixture is too rich. Lower the needle one notch and repeat the test. The needle will be correct when acceleration is crisp at mid-rpm yet the engine does not load up during throttle shut down.
MAIN JET:
Testing - Roll-off method:
This is a good way to get the main jet either correct or within one size of correct. It is based on the fact that as the throttle is closed, the air fuel mixture richens momentarily. This normal enrichening can be used as a diagnostic tool.
The test is started with the engine running at an rpm high enough to ensure that it is "On the cam."
Open the throttle fully and let the engine pull for several seconds. hen quickly close the throttle to about the 7/8ths position.
If the engine seems to gain power, the main jet is too small (Lean).
If the engine hesitates as the throttle is rolled off, the main jet is too large.
when the main jet is correct, the engine will continue to run smoothly and evenly as the throttle is closed.
Note: a main jet that is far too rich or lean may cause the engine to misfire at full throttle.
For those that have that pesky "Warrior" off idle stumble/bog..
pretty much raise the needle till it stumbles (Rich), then test at a notch lower at a time til it leans out to where it doesnt stumble anymore and accelorates good.
This guide/info was gleaned/adapted from Mikuni's website.
http://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf
that is the guide I used. I also used this to re-jet my warrior. helped me make sense of what was what and what was going on.
there are other great jetting guides here on the forum as well, this is just the same thing, but a bit more symptom based, worded differently, and jsut makes simpler sense to me!
Im now running a 150 dynojet, with the needle on the fourth clip from top. Base mixture about 1.75-2 turns out.
This is on 92 warrior, stage one hotcam, supertrapp exhaust, K&N filter.
Further tuning to commence.
Idle-1/8th throttle:
Piolet screw is set at 2 turns from factory.
Gently bottom it and turn back out 2 turns.
Next run the engine till it hits normal operating temp.
With the engine idling smoothly, adjust the piolet screw OUT (Richer) slowly until the idle either slows or becomes irregular, then turn the screw IN (Leaner) until the engine again slows or begins to idle irregularly.
Count the number of turns between the two positions.
Set the screw mid-way between these too-rich and too-lean positions.
Use the Idle adjuster to re-set the idle speed.
If the engine becomes too hot during the adjustment procedure, the resulting idle mixture will probably be on the lean side of correct.
If you have a large fan, use it while adjusting the mixture. If you do not have one, you may need to take time out for a short ride to cool the engine back to normal temperature.
NOTES:
IF the best idle is achieved with the screw less than one turn out, then your jet is too large and needs to be downsized.
If the engine speed does not slow after 2.5 turns out, then the jet is too small and needs to be upsized.
Jet needle:
Off idle to 1/4 throttle:
the straight diameter portion of the jet needle controls the mixture from just above idle to aproximately 1/4 throttle. If the mixture is too rich or too lean in this throttle range, the needle will need to be exchanged for one with a larger or smaller diameter.
Lean needle:
If the needle is too lean, part throttle acceleration will be flat. There may also be some detonation during part throttle acceleration in the 2500-3000rpm range, (Alhough this may have other causes such as an ignition that advances too quickly).
A lean needle also results in an abnormaly slow warm-up. If any of these conditions exist, install a one size richer needle and compare the performance.
Rich Needle:
While a black, sooty spark plug is a sure sign of richness, others are more subtle. If your engine responds crisply at low throttle openings when cold, chances are the needle is one size smaller, (Richer) than it needs to be. This assumes of course that the idle mixture is correctly tuned.
Poor fuel milage is another sign of an over-rich condition.
Go one size leaner needle.
Jet needle 1/4-3/4 throttle:
The tapered portion of the jet needle rises out of the needle jet at about 1/4 throttle. From that point until the main jet takes over near 3/4 throttle, the jet needle taper is the main control of mixure strength.
Lean:
If the acceleration seems soft or flat and the engine is slow to respond when the throttle is quickly opened from the 1/2 throttle position, the mixture is too lean. Raise the needle one notch and repeat the test.
Rich:
If acceleration is crisp but the engine hesitates or staggers as the throttle is quickley closed from 3/4 to 1/2 throttle, the mixture is too rich. Lower the needle one notch and repeat the test. The needle will be correct when acceleration is crisp at mid-rpm yet the engine does not load up during throttle shut down.
MAIN JET:
Testing - Roll-off method:
This is a good way to get the main jet either correct or within one size of correct. It is based on the fact that as the throttle is closed, the air fuel mixture richens momentarily. This normal enrichening can be used as a diagnostic tool.
The test is started with the engine running at an rpm high enough to ensure that it is "On the cam."
Open the throttle fully and let the engine pull for several seconds. hen quickly close the throttle to about the 7/8ths position.
If the engine seems to gain power, the main jet is too small (Lean).
If the engine hesitates as the throttle is rolled off, the main jet is too large.
when the main jet is correct, the engine will continue to run smoothly and evenly as the throttle is closed.
Note: a main jet that is far too rich or lean may cause the engine to misfire at full throttle.
For those that have that pesky "Warrior" off idle stumble/bog..
pretty much raise the needle till it stumbles (Rich), then test at a notch lower at a time til it leans out to where it doesnt stumble anymore and accelorates good.
This guide/info was gleaned/adapted from Mikuni's website.
http://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf
that is the guide I used. I also used this to re-jet my warrior. helped me make sense of what was what and what was going on.
there are other great jetting guides here on the forum as well, this is just the same thing, but a bit more symptom based, worded differently, and jsut makes simpler sense to me!
Im now running a 150 dynojet, with the needle on the fourth clip from top. Base mixture about 1.75-2 turns out.
This is on 92 warrior, stage one hotcam, supertrapp exhaust, K&N filter.
Further tuning to commence.
