Maybe, as it would alter the taper shape further down to partially lean off the setting for midrange.
I will see if I saved the page text in a moment.
My thought's appear in various threads.... here is a synopsis...... Most of it applies to stock motors, running 39mm PWK carb.
Most CR500's I have seen appear to share similar conditions...
1. They wont idle
2. There too rich from off idle to 1/2 throttle
3. Their too lean at 3/4 throttle
4. Their too rich WFO
What to do.... What to do......
The pilot... This controls the fuel ( in concert with the air screw) to set the idle mixture. In math 8+2. 7+3. 6+4, 5+5 all equals 10 right? Well, the pilot and the air screw work the same way to achieve the goal. Most PWK's like a high 30 to low 40 pilot, PJ's seem to prefer a high 40 to mid 50 pilot. Depending on the temp, altitude, humidity, etc..etc. you fine tune the mixture with the air screw to get the mixture right for the current conditions where your riding. When you have the correct pilot, this screw becomes pretty sensitive. 1/4 of a turn should do allot. If it doesn’t, or if you are more than 2 turn out, you probably have the wrong pilot. Also if the engine idles about the same with the choke on or off, you probably have the wrong pilot.
ZipTy makes this killer " Air Screw" that makes adjusting it a breeze when out on the trial.
http://www.ziptyracing.com/products/...px?id=MTA5OQ==
When everything is as it should be, it should start easy (cold) with the choke on, then as its warming up it should start running crappy until you shut the choke off. Then it should run smoothly, and predictably ( No stalling as an example) for the rest of the day. If it starts easy (cold) with the choke off, your way rich. It wont surge during deceleration or run "choppy" at part throttle settings when its set right. It should run fairly "four stroke" like . On my bike with a PWK I run a #40. In the high desert my A/S is about 1.5 turns out to lean things, down at sea level is about .25 turns out to richen it. Start wrenching and congratulations once you reach this point. NOTE: Changing the pilot and airscrew setting will have hardly any effect on other throttle settings, don't goof up your pilot settings chasing other issues!
The needle, your best friend.....
First off, understand the needle does not control the fuel flow at most throttle settings... Its the difference in area between the needle diameter and the fixed hole machined into the carb body that it slides up and down in that controls the fuel flow. I mention this as people assume that what works for one bike will work for another. WRONG!..... If the carb you have has a larger hole than your buddies ( due to age, wear, or different tooling used during its manufacture) your bike will be forever "richer" if you run the same needle he does. Understand this important fact? Mukini's have a screw in "needle jet" and are superior to Keihins in this regard.
I assume you do, so moving on heres the rest of the story. As I stated, most CR500's seem rich down low. This causes lazy-ness, plugged pipes ( I ve seen them weigh it at 25 lbs...) the dreaded "spooge", and poor mileage. The cure? Increase needle diameter. Stock Honda needles ( R1368) are 2.68 mm thick. Something in the low 70's ( 2.72 as an example) really cleans up the mess.
The other parameter of the needle we are interested in is the taper, or how quickly it gets pointy for those board members in Virginia. Under a good load, on a hot day, allot of bikes ping at around 3/4 throttle. Increasing the taper from 1.3 degrees to 1.4 ( or even 1.5 for you duners) richens up the mixture to about 3/4 throttle and helps reduce detonation problems.
So, what’s the "Bob's Magic Needle" number? As you can see, there isn’t one. Its depends heavily on your bike. I good place to start is a 1472 ( DGN) , and start in the 3rd clip from the top.
Main jet. Once you crank that throttle OPEN and get the dang needle out of the way, the main jet comes into play, AND NOT BEFORE! Folks often keep playing with the main jet trying to fix anything from hard starting to fouling plugs. These same folks probably never pin it either and are accomplishing nothing. Main jet sizes from the mid 160's to mid 170's are the norm. If you find you are going beyond these numbers in either direction,something is probably wrong elsewhere.
Other points to ponder....
1. Use a fuel filter.
2. Use quality 2 stroke oil at 32 / 44:1 ( as you lean out the bottom end, you are also reducing the amount of oil entering the engine.
3. ONLY use REAL Keihin parts. They cost more because their worth more. As an example, the main jets are drilled, then flowed, then stamped with the proper number. Aftermarket jets are simply drilled, then stamped, and are very inconsistent.
4. DONT GET FANATICIAL REGARDING JETTING! I have seen guys waste a whole day when they could be riding playing with their carb. Guess what? These carbs are low tech, marginal mixers at best and its rare you ride in identical conditions day to day. YOU WILL NEVER HAVE YOUR CARB SET PERFECT. Live with that statement, and have fun instead of frustration.
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Kinky is using a feather. Perverted is using the whole chicken
Actually it is a replaceable part, sort of. But yes check with torch for ovality.
The carbs come apart and I have seen the posts that contains the jet on eBay. Or you can take it out and get a toolmaker to make a precise replacement bit of brass.
Don't you look at my accountant.
He's the only one I've got.
Yeah its real precise. Anyway grab a torch and check it. Once it's oval you get wet drops so its impossible to jet properly. That said my kdx went a billion times better with the right needle, pilot and main. Got specs from the justkdx website.
Don't you look at my accountant.
He's the only one I've got.
Nah. Just set it so it doesn't overflow and just overflows when on the stand on a slight downhill and its fine. Won't affect things in-between failure mode. Obviously bike has to have had a run through the gears before it will behave. Old gas will affect starting and cold riding considerably, warm riding a little. Plastic tanks lose end gases quickly.
Don't you look at my accountant.
He's the only one I've got.
Pwks are good carbs but can be temperamental for flooding or starving on long uphills if set too low. Won't affect jetting like some old carbs though.
Don't you look at my accountant.
He's the only one I've got.
Went for a ride today and got to really open it up. I was doing runs up and down a open woop area. Full throttle in 4th she was bellowing blue smoke. So way to fat on the main.
Also did the highest idle speed on the air jet trick and it runs fastest at idle at 5 turns out. Again, way out of range.
Current jetting is 40/155. Will drop to 35/145 and see what happens. Its got new Boysen reeds which do say you may need to lean it up.
Bike did feel great under power.
Blue smoke on full throttle doesn't ness mean too rich like black smoke on a 4 stroke. And you are proposing 4 jet sizes smaller. Move with caution try a size smaller and see if it runs better. Same with the pilot, try a 38 first. 5 half turns or 5 full turns? That woul be too far out and airleak territory.
Don't you look at my accountant.
He's the only one I've got.
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