sputtering when holding throttle position (kx500

[Eppidemic]

I have a question that I think pertains to all 2 stroke bikes although mine is a kx500.
the bike runs pretty good I think.  Lots of power when turning the throttle. But When I hold the throttle position it surges and sputters pretty bad.  It makes long straight aways and cruising forest roads pretty annoying.
Also the bike doesn't like to idle.  I can set the idle screw way in and it will idle, but then it will surge like a mofo while off the gas coasting.  
I am using one setting leaner than stock on all jets and needle position.  Any help would be great.  I've been really struggling with the pilot jet as of late from a 58 (stock) all the way down to a 48.  I"m at a 55 now which is what most people are running in my bike with it warmer.  

I know 2t are high performance engines.  but should I be able to hold a throttle position while cruising without it sputtering/spitting/surging and jerking all over?  It's usually 1/8 or less throttle in any gear cruising when it happens.  The bike is a pure trail bike.  My spark plug is always black when I bring the bike into my house.  I haven't tried to cut the bike off after a 3rd gear pull.  If the bike is jetted properly, will you get the nice tan color after a 1/4 mile of 25mph riding into my house.  Or will it always be black when going that slow?
 

Thanks guys.

[kxrob]

google spankys jetting guide and work on the pilot and air screw circuit

55 seems very rich in the summer weather for a big bore

my kx250 was standard 52 and im down to a 42 and correct air screw setting and it idles until the tank runs dry

mix oil choose plays a big part as well in keeping the plug clean

is there spooge running down your silencer ?

does the bike smoke excessively once it is warmed up ? 

 

[FORMA MOTO]

Carbs wear out. When the emulsion tube gets ovaled, you will have strange jetting issues.

Replace it, if replacable.

[Eppidemic]

Problem is the bike was idling fine not too long ago before I rebuild the carb and did some other modifications to the bike.

The bike doesn't smoke excessively but I think the needle and Main Jets are where they need to be because I have good power. Not sure if the rich pilot would show too much smoke that I've noticed while riding around.

Another thing I was kind of flabbergasted by. It seems like no matter which pilot I've put in, the bike seem to run best about two screws out and it would choke down with the air screw all the way in. Maybe I need to just go down in Pilot sizes until I can screw the air screw all the way in and not have the bike bog down

I have pilot sizes all the way down to 48 and I'm tempted to just throw it in to see if there's any difference.

This is what the plug looks like


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[Eppidemic]

I don't know why it the top looks Brown, maybe because of the flash, because it's pretty much black. Not a ton of carbon blue buildup but a little, and it's always kind of wet and black

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[FORMA MOTO]

It's impossible to read a plug with pump gas. Too many additives.

 

[Eppidemic]

So do all Two Strokes sputter at 1/8 throttle while cruising? I give it about a quarter throttle and the exhaust tone is nice and it starts picking up quick. But around an 8th or even 1/16 throttle, it acts erratic. I either have to deal with it which is annoying. Or I have to go on a quarter throttle then coast and go off. on and off.

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[FORMA MOTO]

2 hours ago, Eppidemic said:

So do all Two Strokes sputter at 1/8 throttle while cruising? I give it about a quarter throttle and the exhaust tone is nice and it starts picking up quick. But around an 8th or even 1/16 throttle, it acts erratic. I either have to deal with it which is annoying. Or I have to go on a quarter throttle then coast and go off. on and off.

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Again, you need to address all the worn parts first, before changing any jetting. Emulsion tube, slide, choke plunger, air screw oring. etc.

Your description is a rich condition at the transfer from the pilot to the needle.  Try dropping your needle all the way down, to see if it helps that specific problem.

[Eppidemic]

I have gone through the carburetor pretty thoroughly. The slide looks good, the emotion tube looks good. I replace the needle valve and everything that comes with a carb rebuild kit. I also split the carb and half so I can make sure the jet tubes were clear as well and had to find a gasket online to put them back together.. I didn't see an air screw o-ring on my model and a replacement didn't come with the kit which also came with the new Air screw and spring. But no o ring. Keinen pwk 39 Just a spring in there...

I watch the video on YouTube of what a bike sounds like when it's too lean. On the pilot jet. And I've never gotten the motor to cut out like in that video. Assuming the carburetor is in good shape. Is there anything wrong with continuing to go leaner until I get the bike to cut out like in the video? It's just idling for the most part so I don't see the whole lot of chance in hurting the motor. I'll ride the bike the way it is right now. Get it good and hot. Park it and quickly changing the leanest pilot screw I have and see if it'll hold an idle or cut out because it's too lean and then move up from there rather than starting rich and going lean. If I'm careful do you think this would be an okay way to diagnose my idle and sputtering condition?

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[kxrob]

6 hours ago, Eppidemic said:

. Maybe I need to just go down in Pilot sizes until I can screw the air screw all the way in and not have the bike bog down




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correct size pilot should see your air screw between one and 2 turns out , not all the way in

if you search for that guide i suggested above you will understand what i mean

you should be able to jet the bike so you can coast on light throttle

THE KRAN , is right about making sure carb is not warn out

that plug don't look good at all 

[Eppidemic]

So just to see what would happen if I put a 48 pilot in instead of the 58 which is stock and the 55 which I had in yesterday. I put a 48 pilot in and there was almost no difference in the bike. Around one-and-a-half to two screws out on the air fuel jet and it runs about the same with almost any pilot I put in it. The only difference this time was mostly that the bike surged a lot more often which means I think it might have been getting a little less fuel. Does anybody have any idea what might be going on? I can turn the idle up and have it run okay. But one of the problems with that is the bike starts surging all the time which made it difficult in the tight trails. I'm trying to get the bike to idle good and not surge constantly. I'm at a loss I'm about to damn near just buy a new carburetor.

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[kxrob]

what needle is in bike and what clip position from top ?

what temp and elevation you at ?

[Eppidemic]

I'm running a 165 which is one leaner than stock on the main and the stock needle jet second clip from the top which is one clip leaner than stock. I've been on KX Riders com and people there are assured the stock needle is good for all but major engine mods which I don't have. It's been between 85 and 95 at essentially sea level the last few days. There's a jetting chart that everybody uses on the Forum site and although I might not get every ounce of power out of the bike most people say running the settings on that chart will give you decent results and you can work from there.

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[Eppidemic]

Oops. The screenshot is coming through and very shity quality for some reason. But this chart says I should be running stock across the board except a 165 instead of a 168 on the main jet. I'm guessing there's something wrong with the carburetor. It's just weird because the bike is a 2004 butt wasn't even ridden enough to go through the stock rear sprocket. The guy I bought it from never rode the bike and bought it brand new. I bought it off of my boss who bought it off of him and he never rode the thing because he couldn't start it he is just a small guy and it was too much power. He installed a accuproducts decompression valve and so the bike starts with ease now, but my boss sold it to me anyways cuz it was just too much bike for him.
Long story somewhat short, the parts in the carburetor don't show anywhere really and a lot of them I replaced anyways. There's only one last thing I thought it might be and that is when I split the carb and half I guess from a video I saw on YouTube, when you put the top section that holds the needle and top of the carb components together with the lower section of the carburetor it's possible to tighten the little torque screws in a manner that allows it to leak air. I was thinking the carburetor might have been really gummed up from sitting so I tore apart part of it that isn't usually done with the rebuild. I had to buy the gasket special and buy a Torx bolt to get it apart. In the video on YouTube of guy showed how when you blow through the top portion with the float Bowl full of gas bubbles can be very prevalent. He retighten the top more evenly or something and it's supposedly fix the problem.

I'm just rambling now, and this is probably too long for people to pay attention. I'm just at a loss and it's irritated cuz I haven't been able to ride much.

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[GlennRay]

57 minutes ago, Eppidemic said:

I'm running a 165 which is one leaner than stock on the main and the stock needle jet second clip from the top which is one clip leaner than stock. I've been on KX Riders com and people there are assured the stock needle is good for all but major engine mods which I don't have. It's been between 85 and 95 at essentially sea level the last few days. There's a jetting chart that everybody uses on the Forum site and although I might not get every ounce of power out of the bike most people say running the settings on that chart will give you decent results and you can work from there.

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Is it possible that you are trying to ride your bike at a speed that is too slow for your first gear ratio?  You might want to go up a couple of teeth on the rear sprocket or down one on the front sprocket.  Bucking and surging can be caused by "lugging" the engine by trying to ride it slower than the gear ratio will support.

Edited August 2, 2017 by GlennRay

[Eppidemic]

I'm actually running one less tooth on the front already. I'm going to go even larger on the back as well because I want to trail ride it.
Anything is possible I guess. Like I said. It's got great power From 1/8 throttle two full throttle. It just doesn't idle well or at all unless the screw is very far in and then as I mentioned the bike surges like crazy. I can unscrew the idle and the surgeon goes away but then the bike dies all the time if I don't keep it going with my throttle. That's not always easy on the trails.

I'm going to try a couple things tomorrow. I'm going to go back to completely stock jetting except for the leaner main jet that is recommended for hire Temps. I'm also going to split the part the carburetor like I did awhile back to clean it and check and make sure the gaskets seated evenly. I'll update what happens tomorrow.

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[kxrob]

3 hours ago, Eppidemic said:

 It's got great power From 1/8 throttle two full throttle. It just doesn't idle well or at all unless the screw is very far in and then as I mentioned the bike surges like crazy. I can unscrew the idle and the surge on goes away but then the bike dies all the time if I don't keep it going with my throttle. 
 

surging is a lean issue 

are you certain that you don't have an air leak on the flywheel side

how are you setting your air screw ?

[Eppidemic]

I don't think it has an air leak but you can't really figure that out by thinking. It didn't have one in the winter before I started screwing around with the carburetor when things warmed up. The bike ran perfect and then I rebuilt the carburetor and screwed with some jetting and now the thing runs horrible but the temperatures also increase 50 degrees. It could have got an air leak and I think I'm going to test that next. I'm going to put the stock pilot jet in and adjust the air-fuel mixture right words supposed to be and see how the thing runs. Probably take it to my local shop so they can do a leak test cuz I don't have the stuff to do it. How to set the air screw I'm starting at about one and a half turns out. It's usually running a little rough there. I'm screwing in the idle till the bike holds in idle and then screwing out the air screw and stopping when it gets to the its highest RPMs

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[Eppidemic]

Correction. My frustration got the better part of me. The bike doesn't run horrible. I just have to pick between a bike that idles or a bike that surges. Seemingly no matter what pilot should I have in it

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[Eppidemic]

The bike could have an early, but would the bike seem to run perfect from one a throttle to Full Throttle with an air leak? If an air leak only screws with the idol and when they throttle I suppose it's possible that's what's going on

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