440ex jettin help

[spicer669]

hey i just recently did a 440 build on my ex its got stage 2 hotcam 12.5:1 wisco piston full kibble white valve train standar size i havent put many heat cycles on it because it dosnt seem to run quite right i put a 160 main jet in it for staring off an it seem to idel fine an take a quick rev but wont hold a solid rpm i left the stock pilot jet in it im thinkin that could be the problem but not sure what i should bump it up to if it is im also runnin a stock air box with the lid an a uni filter any help would be greatly apperciated

[Thumpin440ex]

50 pilot, 2.5 on the needle, step up to a 185-190 main.. Give it a shot there

John

[spicer669]

what do u mean by 2.5 on the needel?

[spicer669]

oh an im running a 50/50 mix of 93 pump gas an av gas that i think is around 100 octane

[kt1148]

Check this thread, the first chart has a 440 bore listed on it...http://www.exriders.com/vbb/showthread.php?s=&threadid=445695&highlight=jetting+placement...I would use a 42 pilot, a 50 pilot would be for a 450 carb.

[JOHNDOE83]

I use a 220 main jet in mine.

[spicer669]

thanks ill check out that link

[jessieherrera]

Hello,
Carb jetting:
First, always run the carb dry when you are finished riding by shutting off the gas at the petcock and let it idle until it stops running. This is the best practice for any small or industrial engine. You may have a Mikuni. Even if you don't many carbs are similar in design and parts. Mikuni carbs are very easy to work with. Make sure that you have no vacuum leaks whatsoever.
Usually, the bigger the carb, the smaller the jets.
With today's gas it is almost impossible to read a spark plug. It used to be that if they were a soft white to a medium tan the mixture was correct. Today, you may want to try this to get the right mixture.
Adjusting your carb/mixture/jetting:
1. The idle air screw always starts at 1 1/2 turns from closed. Let the engine warm up and open or close an 1/8 of a turn at a time. Give it about 5 seconds to settle. Continue until the engine reaches its highest RPM/speed. This is called your best lean idle.
2. The cutaway on the slide regulates your mixture just off idle. The different cutaways enrich or lean the mixture.
3. The slow speed jet regulates the mixture until the needle in the slide takes over. This is initially about 850-1000RPM. Increase the jet size one at a time where you get the highest RPM at that slide or throttle position, not RPM as this will change with jet size. You should feel more power at that throttle position. Your needle on your slide should not be active or at the taper.
4. The needle in the slide regulates the mixture to wide open throttle. The needle has a taper to it which regulates the fuel amount from the main jet. It also has a few notches that will raise or lower the needle. Raising position enriches. You will feel more power at that throttle position.
5. The main jet regulates the mixture at "wide open" throttle. Read below to adjust.
I have found that the best way to jet your engine is by what's called "seat of the pants performance".
Adjust the jet size by enriching the jet until you get the highest RPM/speed at that specific RPM/throttle position. An example would be the slow speed jet at let’s say, 850-1000 RPM though this will change with the richer jet so actually it's better to go by slide position.
The high speed jet you do by accelerating through the gears until you reach top end. Keep increasing the size one size at a time until you get the maximum speed and feel of power. Once that is reached go down one jet size.
With different pipes and types of driving as well as types of intakes jetting will change. Altitude is also a factor. An example of intakes would be velocity stacks or air cleaner inside configurations. Different lengths of these passages affect you RPM and acceleration. High performance demand will always require richer mixtures as moderate driving will perform better at leaner mixtures.
Good luck.:)