Carburetor Questions

[Predator303]

hi guys. i got a couple questions. i know some basics of the carb but on the other hand im not quite sure about some things. right now i run the stock carb and looking at the new spark plug, i run way too rich. i already checked the clip and its on the highest position which should be lean. i was dealing around with the fuel screw for lower idle rpm and think i might made it richer. i have the feeling i waste way too much gas compared to couple weeks ago so i might messed something up.

i don't run an air-filter currently.

here my questions:

- turning in the fuel screw, will make it richer or no?
- how can i adjust the carb almost perfectly by myself and is there any other way for testing if the mixture is perfect other than wasting a couple spark plugs?

thank you

 

[Moto]

What carb, nt or cns?

 

[Predator303]

nt. stock xxxxx

 

[nightcruiser]

I echo the question, "What carb? CNS? NT?"
Carb tuning is a balance between the jet size, air filter dampering and exhaust back-pressure. The air and idle screws only effect how she runs at idle in the very low RPM range, the needle effect the mid throttle range mix, at WOT the jet size is completely responsible for the mix.
What you really need to do to tune your carb properly is get the air filter and exhaust you want to run in place and make sure there are no air leaks, then warm up the motor and ride her WOT and do a plug chop. Let the motor cool then pull the plug and inspect it. The color of the plug along with how the motor was running at WOT will help you decide if she is rich/lean or just right at WOT. From there you adjust the air/fuel mix to correct whatever condition exists. A change in air flow (filter or exhaust) can be made, or more often an adjustment to the main jet size would be done. The float setting can also have a big effect on the mix at WOT, with the CNS carb my first stop after doing the WOT plug chop would probably be to do a float adjustment. (never had an NT so I can't comment)
Once you have the mix proper at WOT then you move on to the mid throttle range, ride and observe, plug chop in the mid throttle range to diagnose condition. Adjust the needle to correct an improper condition.
The idle screw just holds the throttle open a little bit, so after the needle is set adjust the idle screw for your best idle speed and then adjust the air screw to where the idle speed is highest.
There are lots of differences between the CNS and NT carbs, and some easy tests you can do to see what conditions your dealing with, depending on which carb you have??? So let us know exactly what carb you have so you can get some more specific help tuning your carb...
I am not a mechanic, but this has been the basic procedure I have come up with for tuning these carbs and it has worked out well for me. There are some real mechanics here in the forum, so perhaps they might correct anything I have wrong or add something I missed, I read this forum to learn and have learned a LOT.

 

[Predator303]

alright if the crews dont effect the mid throttle mix and the clip of the needle is already in highest (for lean) position, then how can i get it leaner? also something i should mention. i lost a piece in the end of the exhaust in the beginning and i kept it because i like how it sounds but the exhaust got lose couple of times for different reasons and last time when i had the air coming out before the exhaust because there was an opening, the bike ran crazy fast.

 

[nightcruiser]

alright if the crews dont effect the mid throttle mix and the clip of the needle is already in highest (for lean) position, then how can i get it leaner? also something i should mention. i lost a piece in the end of the exhaust in the beginning and i kept it because i like how it sounds but the exhaust got lose couple of times for different reasons and last time when i had the air coming out before the exhaust because there was an opening, the bike ran crazy fast.

You can go to a smaller jet size to make it leaner. If your air filter were to offer less resistance to air flow that should also lean her out. I haven't messed with the exhaust yet so I will let someone else comment on the effect of modifying the exhaust. However, if you like the exhaust the way it is then I would say you should just make sure there aren't any air leaks and move on to jetting.
When I assemble the jug I use red loctite on the studs where they seat in the jug, I use a gasket sealer compound on both sides of the gaskets, then use blue loctite on the threads where the nuts go on. Torque the nuts properly, not overtight, and let it all dry. When you install the carb on the intake push it onto the intake firmly while you are tightening the screw. That should give you a nice air tight system that will last. If you develope air leaks all the tuning you are about to do will go out the window....
With the jet, you can either buy a new smaller jet to lean her out, or you can solder your existing jet closed and then drill it out with a smaller hole using machinist drill bits. A set costs about $5-8 on ebay or amazon or a local store. Sets with a range of #60 to #80 bits are common and cover the appropriate range for jetting these carbs. Look for one that comes with a hand drill handle cause you are not going to actually use these drill bits in a drill, spinning by hand is all you will need.
I'm pretty sure SikeBikeParts.com has a selection of different size jets for the different carbs (make sure you order the right one for YOUR carb). I'm not exactly sure what the stock size jet is for the NT carb, so perhaps an NT carb rider will chime in on that....

 

[Predator303]

i do have a tiny leak between exhaust and head because i am using metal gaskets for motocross bikes since the paper gaskets get blown away after a week.

thank you for the good explanation. i will get into that