KX310 surges at zero throttle position

[Bandit9]

Rich,
I need your opinion on this. My EG KX310 surges at zero throttle position. It does it when warm, at idle, and when I am blasting down a trail and let off to set up a turn. It just keeps surging. I have always been treating it as a lean condition on the slow/pilot circuit. Went from a #8 throttle slide to a #7. Tried up to a 58 pilot jet. Tried 5 different needles in all positions. Unplugged TPS. New reeds. Cleaned all jets and passageways numerous times. Repacked silencer, all holes are free of carbon. Air leak tests, including crank seal behind stator. All to no avail. The bike still surges at the zero throttle position. You have any ideas. Powerjet solenoid???

 

[CRguyStan]

Your idle is set too high.










Couldn't resist :laugh: :laugh: , no clue after what you already mentioned.
Stan

 

[Bandit9]

I wish it was something that easy!!!!

 

[ditchound]

Could it be your carb body and or slide is worn and air is leaking past?

 

[KXtrailrider]

I know it would be hard to do but maybe try to pressure test it with it warm. It sounds like an air leak to me too, but maybe it will only do it when it is warm. KX's sometimes get base gasket leaks under the reed cage, I have been using hi-tack on my base and reed gasket lately with no problems. Good luck in finding it. I made my own pressure tester and us it often. Good luck finding the problem. Ed

 

[Bandit9]

Wouldn't a base gasket leak be picked up doing a starter fluid spray test?

I am in no way implying that this surge problem has anything to do with the 310 kit. I wish I could possibly record it for all of you to see and hear. The bike seems to run fine, compression is still really strong. Really, if the surging just occured at idle, I wouldn't care. But it happens when I let of the throttle to set up a corner. It keeps revving and it pushes me deeper into the corner, which causes me to hit the brakes harder, which causes me to slide more than I want to. I have learned to deal with it, but it needs to be corrected so I can ride without worrying about it all the time. I was hoping Rich would come to the rescue. The Power Jet remains a factor though. I do know that the jet itself is not clogged. It is free of blockage. Maybe the solenoid is malfunctioning. I don't know how I would test it???

 

[KXtrailrider]

Starting fluid is a good test but if it were mine I would pressure test it also. The power jet solenoid lets fuel through when it has no power to it so if you unplug it fuel goes through the jet all the time making your jetting rich. It is off or open most of the time closing at high rpm so you get more overrev by leaning out the top end. You can test the solenoid by putting 12volts to it it should extend and block the passage with no voltage it should open the passage. You can take it out of your carb and test in your hand with 12volts, it will go in and out with 12volts on and off. You can hook up a volt meter to your bike plug in and rev it up and watch for voltage to see when your black box is turning it on and off. Good luck Ed

 

[Martin Cole]

This problem sounds very similar to one I experienced some years ago with a TY80. I could never get it set up to run right brcause of the surging and decided to sell it. The guy who came to buy it said he knew exactly what was wrong as the TY was susceptible to leaking crank seals. He was happy enough to take the bike as it was and fixed it promptly.It may not apply in your case but could be worth investigating.
MC.

 

[Bandit9]

Yeah, the ignition side crank seal passed the starter fluid test. Now I have thought since the beginning that it is an air leak. Sounds just like one huh? I have been suspicious of the right side, but I was told that if there wasn't any white smoke coming out the silencer, then it wasn't leaking. It doesn't have any white smoke at all and the same amount of tranny fluid comes out each time. So I don't think that is it, nor do I know how to go about testing the right side crank seal.

 

[KXtrailrider]

Pressure testing tests both seals and the base gasket and the reed gaskets and the power valve seal. To do it you plug the exahust port the intake manifold and with mine you put 5psi in with a modified sparkplug with a hole in it hooked to a hand pump and gauge. A blood pressure tester works for the pump. Don't go over 5psi. The motor should loose less than a 1/2psi a minute.if it looses it fast it needs to be fixed. To find the leak spray soapy water on seals and gaskets and look for bubbles. You may have to remove the clutch cover and stator. Your problem sounds like a air leak to me also. Ed

 

[Bandit9]

So how did you modify the spark plug? Drilled it out and put a valve on it?

 

[KXtrailrider]

Yes I knocked out all the porcelain out and welded a pipe nipple to it then used a rubber hose to the hand pump with a low pressure gauge in there too. I think Motion Pro sells one but mine is home made. This is the best way to find an air leak that I have found. I hope you find a solid problem that you can just fix and be done with it. We just last week found my friends KTM200's right side crank seal leaking with this tool. The KTM was easy because we didn't have to split the cases to change it but on the KX you have to split the cases to change the seals. Good luck. Ed

 

[Eric Gorr]

Try a bigger slow jet, that should richen the mixture which sounds too lean

 

[Bandit9]

Eric, I have gone from a 45 to a 58pj and it hasn't improve the surging. You would think that I would notice some sort of difference with that big of change???? It surges the same, and at the same throttle position too. I will throw a 60 and a 62 in there to see.....

 

[steve.emma]

just a thought but as you and everyone else seems to think this is a lean surge condition, maybe you could try engaging the choke when you let off the throttle and see if the extra fuel supplied changes the way the bike behaves. if there is no change then it cant be a lean problem.

steve.

 

[ditchound]

Hate to sound like a broken record, but a friend had a KX-500 that did the same thing, it surged after you shut the throttle off and at idle. He chased crankcase leakage for months, then we swapped the carb from a KX-250 and that fixed the problem. We concluded that althought they looked fine the carb body was slighly worn and the slide was also slightly worn and together they would let air leak past and cause the bike to surge! Check this out and at least eliminate it as the possible problem. Let us all know what the problem was when you get it fixed.

 

[bigred455]

Did you check your float level height,also check your petcock filter.

 

[Bandit9]

Bigred,
Float was off a little, this created a great sense of anticipation upon testing. I thought that was it.Didn't solve it. Petcock is clean as a whistle, wasn't anything in it. I had pretty much run out of easy stuff to try before I posted this thread.

I had a guy that raced off road for Team Green for 10 years on 300 and 310kit KX250s ride my bike a few weekends ago. He said his bikes did the same thing and that after trying the richest jetting possible, it still did it. He finally fixed the problem by putting a KX500 carb on it.I believe it was a 40mm. After all of this, I am starting to think that the carb body might be worn in a critical area. I know it isn't the slide, b/c I have tried 3 different slides. I have two buddies, one has a GasGas that has the same carb I think, and another with a new 05 KX250. I will try and talk them in to letting me try their carbs and see if that works. Maybe even this sunday.
Thanks Dirthound.

 

[Bandit9]

Attempted to swap carbs today. Didn't work out, the throttle cables were different. But I made a discovery. My throttle cable was frayed pretty bad in just the right spot where it could possibly be causing the surge at zero throttle position. I have one ordered. This could be it. I am hoping so, b/c it is only $12. I will let ya'll know when I get it in.

 

[ditchound]

That sounds like the problem, glad to here you solved it Bandit9.

 

[Bandit9]

Ha! I called you "dirthound", but clearly you are a "ditchound". Sorry bout that.

I didn't say it solved the problem. Only that it could possibly be the answer. I was lucky and found a cable in stock at a stealer today. Going to install tonight and test tomorrow. I will let ya'll know.

 

[Woodsquest]

My '02 KX250 and a friend's '03 KX500 was doing the exact same thing. In both cases, we found that the air screw, when set to what we thought was correct, (best throttle response from 1/4 throttle at low rpm and speed), we would both experiance this surge. By turning the Air Screw in 1/4 turn from this setting, the surge dissapeared. Seems the air screw was causing a lean condition when the throttle was chopped from an open, high rpm situation; such as setting up for a turn. Try setting your air screw in by 1/4 to 1/2 turn and see if that helps. I'm running a 50 pilot, stock needle on the leanest setting, 155 main and stock slide and power valve. Hope you find it an easy fix!!!

 

[Bandit9]

It still does it. Not nearly as bad, but it still does it. It still surges, but at a lower rpm. I discovered that a friend has a leak tester. I am going to do that and get back with ya'll.

 

[ditchound]

how is that 310 running? Get the surging problem fixed yet?

 

[Bandit9]

After putting a good ride on it Saturday, it still surges. It is the same as before, no different. I thought it was better after the new cable, but evidently I never got the motor up to temperature before Saturday. I am trying to find the time to bring it to a friends house to do a proper leak test.

I will let ya'll know. Any other ideas feel free to post.