Jetting for Dum....I mean jetting explained..
#11
06-21-2010, 02:41 AM
Off topic, but. The cam in this motor is more of an efficient street bike grind and doesn't really scavenge well, at 1mm lift (where measurable flow starts) it has almost no overlap. Why intake and exhaust mods will only get you so far, then you just have a loud pipe and an airbox that honks.
#14
06-21-2010, 04:17 AM
Join Date: Aug 2008
Location: Vancouver Island, British Columbia
Posts: 1,389
Redpillar, did you remove the backfire screen from the exhaust or the air box. I looked at mine and the air box screen is put in with phillips head screws, not like the '06 which has bolts and I figured I would just wait and remove it later. I read somewhere that someone removed the whole air box to get their '09 screen out. I don't want to bugger the head of the screws trying to get them out. Any advise?
#16
12-02-2010, 03:58 AM
Tagging for later use
Just wanted to tag this thread for future use. My carb needs some serious tuning with the 351 kit that I just installed and this thread has some good links that explain how to think in these terms. Thanks guys for the info.
With same jets I had after rejetting initially, my bike is crap at idle and spews black smoke when I crank on the throttle. Plan to go to a 132 main and 40 pilot. I'm leaving the needle as is since I am not really sure where to go with that. I would like the needle to be in the best position for fairly even riding with the occassional high speed aceleration to pass big rigs on the interstate, but I don't want it jumping off the line at every intersection. If anyone has any further suggestions than I am all ears.
With same jets I had after rejetting initially, my bike is crap at idle and spews black smoke when I crank on the throttle. Plan to go to a 132 main and 40 pilot. I'm leaving the needle as is since I am not really sure where to go with that. I would like the needle to be in the best position for fairly even riding with the occassional high speed aceleration to pass big rigs on the interstate, but I don't want it jumping off the line at every intersection. If anyone has any further suggestions than I am all ears.
Last edited by dacoontz; 12-02-2010 at 04:02 AM.
#17
12-02-2010, 04:13 AM
Join Date: Apr 2009
Location: Fort Collins, CO
Posts: 117
Popping on decel is a classic symptom of a leaking header gasket... you might try tightening the header bolts and see if it goes away.
#18
12-02-2010, 05:49 AM
Fire in the box?
Great thread. Makes my head spin just a little...or more. Wouldn't it be fun to have dyno just hanging around for testing this all out?? Could be a good way to spend those snowy weekends (10" fresh on the ground today 
) with a couple bikes and a brew or two?
On removing the backfire screen...this one was on my list until a couple weeks ago when a local working on his bike had the fluke misfire into the airbox. Bike on fire
. He was able to put the flamer out, but only after grabbing tools (luckily in the garage), pulling seat, and blasting with the fire extinguisher. He too had removed the screen and lid. I'm guessing if either were in place it may not have flamed. Any of you KLX'rs had a backfire like this? My screen is staying -- i don't see how it can impede that much air or cause freaky turbulence, especially after installing a higher flow filter and opening up the box.
) with a couple bikes and a brew or two?On removing the backfire screen...this one was on my list until a couple weeks ago when a local working on his bike had the fluke misfire into the airbox. Bike on fire
. He was able to put the flamer out, but only after grabbing tools (luckily in the garage), pulling seat, and blasting with the fire extinguisher. He too had removed the screen and lid. I'm guessing if either were in place it may not have flamed. Any of you KLX'rs had a backfire like this? My screen is staying -- i don't see how it can impede that much air or cause freaky turbulence, especially after installing a higher flow filter and opening up the box.
#19
12-02-2010, 12:57 PM
Just my opinion.
Back fire on decel has NOTHING to do with performance and should not be considered with jetting the bike. Its a natural thing when changing exhaust.
All the exhaust and intake need to be sealed properly to help get decrease backfire on decel. These need to be done before tuning a carb anyhow.
For us lowly folks with no Air fuel meters or dyno hit or miss is the best way. Reading the spark plug, exhaust color and feel of the bike are the best indicators we have.
Stick your finger in the exhaust. If it comes out black, you are too rich.
Idle needs to be adjusted for lean best idle. That means turn the screw in and out till the warmed engine runs the fastest or has the highest vacuum. Then it needs to go just a little leaner to help compensate for engine temperature changes and to keep from dumping too much fuel when you crack the throttle. Another way to do it is set the idle and put an unlit propane torch in the intake. The engine should speed up A LITTLE then slow down. This tells you its just a little lean.
If the engine idles faster as it warms up, its a little too rich.
If its idling and you cover the intake with your hand and the engine speeds up its too lean.
With cars we used to set for fastest idle then lean it out and look for a 50 rpm drop. This could be 1/16 - 1/4 turn of the mixture screws.
Every bike is different, so we can not all set things the same.
David
Rimbender, thanks for the valve graphs.
Back fire on decel has NOTHING to do with performance and should not be considered with jetting the bike. Its a natural thing when changing exhaust.
All the exhaust and intake need to be sealed properly to help get decrease backfire on decel. These need to be done before tuning a carb anyhow.
For us lowly folks with no Air fuel meters or dyno hit or miss is the best way. Reading the spark plug, exhaust color and feel of the bike are the best indicators we have.
Stick your finger in the exhaust. If it comes out black, you are too rich.
Idle needs to be adjusted for lean best idle. That means turn the screw in and out till the warmed engine runs the fastest or has the highest vacuum. Then it needs to go just a little leaner to help compensate for engine temperature changes and to keep from dumping too much fuel when you crack the throttle. Another way to do it is set the idle and put an unlit propane torch in the intake. The engine should speed up A LITTLE then slow down. This tells you its just a little lean.
If the engine idles faster as it warms up, its a little too rich.
If its idling and you cover the intake with your hand and the engine speeds up its too lean.
With cars we used to set for fastest idle then lean it out and look for a 50 rpm drop. This could be 1/16 - 1/4 turn of the mixture screws.
Every bike is different, so we can not all set things the same.
David
Rimbender, thanks for the valve graphs.
Last edited by David R; 12-02-2010 at 12:59 PM.
#20
12-02-2010, 01:43 PM
When you install one of my big bore kits (B&B Cycle Restoration) I send a fresh air blockoff plate with the kits. If you seal & install it correct this will stop the deceleration popping in the exhaust. When using the stock carb you need to increase the pilot jet one size larger & two sizes larger on the main jet. these numbers are above the jetting that you were using before installing the 351 kit.