03 kfx400 questons ??

[jonboy]

No problem. Its not tough at all. Can be arbitrary at times but once you understand how your carb works, like which jet controls what function, you'll know directly where to start.

[emlejeen]

Hello,

I just recently purchased an '03 KFX400 and have been making minor mods to optimize performance. I have a K&N with a precharger and a White Brothers exhaust. After purchasing, it ran fine, but then I wanted to change the jetting or at least check it to verify that larger jets were installed to account for the air and exhaust mods. When I disassembled the carb, I noticed the main jet was smaller than stock so I change it to be stock (thinking this would give me a little boost). The second time I rode it ran like crap. It would cut out on me and it finally just died and stopped starting. I removed the spark plug and found that it was completely black, which I assume is too rich. I also realized that the choke had been stuck in the open position due to corrosion where is connects to the carb. I am currently cleaning out my carb and fixing the issue I have with the choke.

Assuming the choke was on all the time, would this first account for the smaller jetting? And second, once I get everything back together, should I stay with the stock jetting or should I be able to increase that as well?

Please let me know if more information is needed.

[jonboy]

Yeah, Sounds like some dope didnt wanna fool with repairing the choke. Its amazing how some people repair things. Lol. Get a push/pull choke off ebay for it and eleviate some of your issues that occur with the cable setup. Yeah with those mods, the main will need to be larger. Depending on your elevation but , with the mods you stated you should have around a 160 main. Is the lid off the airbox?

[emlejeen]

After removing the choke from the carb we were able to free it up. I am putting my carb back together today and I think the choke will be working fine.

The lid to the air box is currently open and I think the largest jet I have is a 150.

Any other suggestions to get a boost would be cool.

Emily

[jonboy]

You should be able to buy individual jets at your local bike shop. just tell them the size you need.

[TeHar1585]

I must admit I am a little new to the KFX's myself, but from my experience with snowmobile carbs it seems a little high. I believe the stock main jet is 130 in the KFX 400. Would a K&N intake and aftermarket exhaust really need a 160 main jet? Is this just to be on the safe side for her, to ensure she doesn't blow it up going to lean? What kind of hp gain's are the intake and exhaust giving her? Thanks.

[jonboy]

The z400 motor is very suseptable to slight mods. You'd be surprised how much just opening up the airbox would do. Just changing the factory intake tube with the 400ex is worth approximately 2-2.5hp on a dyno run.