jetting questions...

[KX'er]

I am trying to get the 310 jetted correctly and have ran into a few problems. Since I don't have convenient access to a riding area to just learn by trial and error, I was hoping a some of you could give me a little more insight so I can kind of get a good Idea before I go riding again. Here is what is happening:

1. Bike will not idle on its own. I have to crack the throttle when starting it, hot or cold. It used to start with the throttle totally closed on the first or second kick. To get it to idle I have to blip the throttle every couple of seconds to keep it running. Also, while doing this it will immediately die when I wick open the throttle if the revs are really low. Does this sound like a too rich condition or too lean? Even if I manipulate the air screw until it sounds crisp, it still will not idle or start without using the throttle.

2. When under a light load, at about 1/4 to 3/8 throttle the bike will make a loud crakling sound, and not really run smooth. This is a sign of being too rich on the needle, right? But when I'm cruising along in 4th gear and roll on the throttle, it makes a telltale boooowaaaa sound (lean). Another thing, when I was riding in the sand this weekend, mostly 1/4 to 3/4 throttle, the bike got hot and started spitting coolant out of the overflow. I don't get it, the crakling sound tells me it's rich, but the booowaaaa sound and the overheating tell me its lean....

3. I think the main jet is ok, although I have not been able to do a plug chop since I lack an area where I can go wide open in 5th for 15-20 seconds. It sounds good and pulls hard when wide open. I think the main jet may be a little rich, but I don't mind. I would rather have it on the rich side then too lean.

I think I have the main about right, but am having trouble with the needle and the pilot jet. Also, after riding all day, the plug was black and wet. When an engine is bored and ported, is it common jet leaner or richer to compensate? My guess would be richer due to the engine pulling in more air, but obviously I don't really know. I realize trying to jet an engine over a bbs is impossible, but maybe some one can give me some pointers. :)

For you guys that are running kx310's (preferably 2000 models) how much did you have to alter your jetting from stock. Oh yeah, here are the details of the bike:

2000 kx250
310 big bore kit from eric, ported for mo' better everywhere
PC Platinum pipe
stock reeds, silencer, and air filter.

 

[marcusgunby]

Sounds like you are definatly lean (not rich-you can get a lean poping)try richening the needle clip and the idle is adjusted with the screw on the carb that lifts the slide.

 

[KX'er]

I tried adjusting the idle screw, didn't make a difference. I don't really care about it idling, but I want to be able to set it to idle so I can adjust the air screw correctly. After it is set, I would turn the idle screw down so it will only idle on its own for a couple of seconds.

By the way, when a bike pings (pre-detonation) does it sound the same as a car pinging?

 

[bigred455]

I don't have the 310 kit,but i did try the 265 kit,.It Sounds lean on the pilot,especially if you are just idling, or in your case low rpm's and you crack it, it SHOULD PICK RIGHT UP.Also if you have problems starting it in a few kicks that also sounds like too lean of a pilot or air screw is too far out,but the airscrew is not your case by your explanation.The middle sounds rich to me,Is it sputtering or making like a ta ta ta ta ta ta sound LOL.When you are cruising along in fourth gear like you said and you roll it on where is your throttle positioned at before you roll it on? Does it pick back up after the bogging sound? one more thing I noticed you are using oem reeds,I was smoking them in 2 hrs check them out.Especially,the bottom right one.The reeds could be your problem down low,and that is why it is bogging,and hard to start. If that is your problem down low,get boyesen super stock reeds. EXCELLENT. keep us posted.

 

[Senior KX Rider]

My 310 is not a 2000 but I'll give my input also. I run one size larger than stock on the pilot, stock on the needle(before the 310 I ran it one notch leaner) and one size larger than stock on the main. Sounds like you are a little lean. My bike doesn't idle real well but when you grab a handfull of throttle there is no hesitation at all. It pulls hard all the way to WFO. I have never had my bike run hot and I have run it in sand in 100 degree temps. 455 has a good point about the reeds. I run Boyeson Carbon Fiber Reeds on mine.

 

[KX'er]

When I put the stock reeds back in, I checked them out very closely since I read about all of the problems some people were having. They looked fine, so I put them back in. Do you guys rev the snot out of your bikes, or did I just get lucky and get a decent set of reeds?

The bike isn't hard to start, It only requires me to open the throttle a little to get it lit. It will not start with the throttle closed.

Bigred- It kinda makes a ta ta ta sound every once in awhile, then runs smooth again if I hold it steady at about half throttle. Also, when cruising in fourth I am about at 1/4 throttle then I go wide open. after the bog (booowaaa sound) it hauls..

Anyway, I am going to try one jet richer on the pilot, 1 clip richer on the needle, and leave the main where it is at for now (1 richer than stock). The reason I am going to go richer on the needle is because I would rather try richer and see if it gets worse then try leaner and possibly damage the engine. I am going riding tomorrow so I'll let you all know what happens.

Could I overheat it just from being way lean on the pilot? Also, how hot do your radiators get? Mine are pretty much untouchable now.

Thanks for the help!

 

[bigred455]

If you are at 1/4 throttle in 4th gear like you said and it boggs when you open the throttle,it sounds like the needle or neeedle clip position,Your main sounds good because it is picking back up after the bogg .That is a very good idea what you said go 1 clip rich on the needle,if you aren't sure.That is what i like to do, even if i can't detect a jetting problem i go rich until i notice the sputtering or breaking up then i go back to where it cleans up.Hey do the pilot first,then do the needle.I would also check if you have a head gasket leak ,being you are spitting coolant.Yes i am pretty hard on the revs,but the reeds should not break in 2 hrs.It wasn't a bad set either i wen't through 4 or 5 set's.I think that bottom right reed is getting to much velocity,They wen't to a new stuffer in 00 it has a divider in it,the 99 just had 1 opening.The super stock's are holding,7 hr's on the reeds now.Let us know how you made out.1 more thing you have the right head gasket for that right,( over sized)

 

[Fred T]

One at a time

Originally posted by KX'er

Anyway, I am going to try one jet richer on the pilot, 1 clip richer on the needle, and leave the main where it is at for now (1 richer than stock). The reason I am going to go richer on the needle is because I would rather try richer and see if it gets worse then try leaner and possibly damage the engine. I am going riding tomorrow so I'll let you all know what happens.

Could I overheat it just from being way lean on the pilot? Also, how hot do your radiators get? Mine are pretty much untouchable now.

Thanks for the help!

Make one change at a time so you know whats working and whats not, I suggest you try the larger pilot jet first and then adjust the air screw for best throttle response. It should start with choke on and no throttle. Next try a larger main jet if the first suggestion worked. (Better to be rich at WOT than lean) If it feels lean in the midrange then raise the needle or you may need a different taper needle. Have you thought of trying James Deans jetting spread sheet? You can make jetting configurations on your PC.
I got it and it's pretty cool, lets you try different needles with out touching the carb!

 

[KX'er]

I rode the bike last night with these settings:
pilot: 55 (52 stock)
needle: 4th clip (3rd clip)
main: 162 (stock 160)

It did feel much better on the needle, it didn't bog as nearly as bad. There is still a little bog though. The pilot seemed way rich, as the bike smoked alot and felt really rich down low. I would have to wind it out occasionally to let it clean out. Not much spooge though. The bike still will not idle, and it still dies when I have it reved really low and then crack the throttle. It doesn't do it as bad as before though. My air screw makes no difference.

How hot should my radiators be getting and still be safe? Is there any other signs of overheating besides spitting coolant out of the overflow? BTW, I do have the right head gasket installed and I don't think it is leaking. The coolant level hasn't dropped.

Oh yeah, one more thing. When I go wide open, the bike flat out hauls... Way faster than when it was a 250. I had to ride my friends 125 for a little while yesterday and I was surprised at how much easier it was to ride. I didn't feel like I was strapped to a missile when I opened it up though. I like a bike that scares me sometimes:p

 

[Senior KX Rider]

Originally posted by KX'er
feel like I was strapped to a missile when I opened it up though.

That sounds like its running like it should be but should run strong right off the bottom.

 

[biglou]

This is probably as much a question as it is an answer, so bear with me!
I thought that if your idle adjust or air screw had no effect on the idle, then it is jetted too lean on the bottom. Is this correct?