Finished upgrades on a 05 220 - jetting problems?

[kaptiankent]

Hi guys, I posted on here awhile ago about getting some upgrades for my 2005 KDX 220.

I have installed everything now.
-Wiseco piston
-Boysen Rad Valve
-FMF desert pipe
-FMF Q silencer

I have been riding on my bike a few times since doing everything, there is a big difference in power from the bottom to the top. I haven't noticed any loss on the bottom end power and I guess there is more on the top. But I usually ride in the lower rpm range anyway.

I still have the stock jetting.
main: 145
pilot: 42

The main is good because the bike really rips good at the top end, plug colour is a good tan.
Now on the low end which I assume is the pilot jet it seems to miss and sputter sometimes at about 1/4 throttle. I have adjusted the air screw and it makes it better but it still misses and sputters in that range. it runs best with the airscrew at 1.5 turns out.
I have also tried raising and lowering the needle one clip and it just makes it worse.

What could it be?
Thanks in advance

 

[rus23]

Bigger Main jet. if your needle change didn't make a difference the amount of fuel getting thru the carb didn't change. The main jet seems pretty small, and who said a tan plug is good, I want mine brown, bordering on black. go up in the main till it sputters on top and then back it up a size. then start worrying about the low end.

 

[kaptiankent]

Bigger Main jet. if your needle change didn't make a difference the amount of fuel getting thru the carb didn't change. The main jet seems pretty small, and who said a tan plug is good, I want mine brown, bordering on black. go up in the main till it sputters on top and then back it up a size. then start worrying about the low end.

So you think that going one size richer on the main may clear up the 1/4 throttle miss/sputter.?

I will try the jet change later this week.


If anybody else has any pointer or thoughts let me know.
Thanks

 

[rus23]

I think the main mau be limiting fuel flow at lower throttle openings. I have been told by very experienced two stroke racers to get the main jet about right before playing with anything else, the way you described it sounds like its lean on top. These engines run the best and make the most power just before they seize from getting too hot due to lack of fuel. I roadrace an aircooled rd 400 and a water cooled yamaha rz 350 and the radiators really make the jetting easier, the rz is a lot more forgiving. THat being said, my racing involves long straights that require full throttle 6th gear runs for 8-15 seconds, I've seized the air cooled rd at the end of front straights twice now due to improper jettiing. I have a permanent bump on my left shoulder thanks to one of them. The trail riding I do rarely involves full throttle straights, just a quick blip thru the gears and turn, so the jetting is not nearly as crucial to engine life. Get the main right and then move on, up in size(may need a 155, I have a 160 in my KDX 220)till it runs poorly and then back down one or so.

But, thats just me, I am so used to swapping jets I do it without thinking.

 

[G. Gearloose]

Bigger Main jet. if your needle change didn't make a difference the amount of fuel getting thru the carb didn't change. The main jet seems pretty small, and who said a tan plug is good, I want mine brown, bordering on black. go up in the main till it sputters on top and then back it up a size. then start worrying about the low end.

Changing the main will never clear up the 1/4 throttle position, this aint no chain saw.

egad that is soggy advise, literally.

and a 155 main in an unbored 33 mm carb = spooge and fouled plugs

You must like to waste gas and have less power.
My plug is white with a 2.5 mm soot ring
White means heat and heat equals power.
Plugs are meant to self-clean and need heat to do it.

Grey is the bad color.

 

[whenfoxforks-ruled]

Is it backwards week and nobody told me? Standard procedure, and the design of the overlapping circuits, you start on bottom. http://www.dirtrider.net/forums3/showthread.php?t=159938, also a must read, http://www.dirtrider.net/forums3/showthread.php?t=92818. The technical forum always has the least people in it. Who is scared to learn?

 

[longerdeeper]

I am running a 165 main 42 pilot and needle clip 2nd from the top on my KDX220, Vforce 3 reeds FMF fatty rev pipe, runs great. get a copy of spankys jetting guide
http://www.mxnewsfeed.com/phpbb2/viewtopic.php?t=21

 

[rus23]

As I stated, several times, I roadrace two strokes, the main gets done first, then you fine tune the rest.

 

[whenfoxforks-ruled]

Hey, at least I kept it in the house!

 

[kaptiankent]

Well I was out for a ride yesterday and on the way home I ringed it out down the road and killed the engine. I coasted into my driveway and pulled the plug.

It was dark but had a gray color to it. I think I will need a bigger main.

It seems to run better when its warm out. So that would indicate its a little lean.

 

[whenfoxforks-ruled]

rUS23, Do you have anything to back up your vast expereance in jetting 2 stroke DIRT BIKES? Read the links! Learn how to read a plug, with a plug viewer?

 

[kaptiankent]

Hi Guys, I finally got a 148 main jet and stuck it in. Went for a ride today. It seemed to definitely run better. The temp was about 27C during the ride.

I did check the plug after a wide open straight. I looked down in the bottom and it was black. The insulator and tip was a brownish gray colour.

It seemed to run better throughout the rpm range. almost no miss/sputter in the lowend.

I was a little concerned about the plug having a gray colour on it but according to the jetting guide the insulator and tip mean nothing.

What do you guys think?

 

[whenfoxforks-ruled]

If it is a fresh plug, you can use it for reference as to being lean or rich on a given circuit. The only way you can view the plug for the main is to cut the threads off, or get a quality plug viewer. You can tell from riding it, get it to pull hard off bottom, all the way up. Make drastic changes so you can tell what lean is, when it gets erratic revs. Once you come down from blubbering rich, it will still be rich for a couple jet sizes. Experiment with the pilot, then the needle clip, then main.

 

[kaptiankent]

Well it seems to run better now. I will still play with the jetting a bit just to see what difference it makes.

Thanks for your help sofar.