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2t rattle sound and surging

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I bought a new 2013 KTM 300xc in April and it is driving me nuts. It's my first 2t since I was a kid and I am 44 now. I came off of a crf450r. I had such trouble getting it jetted right. I finally broke down and put a Lectron metering rod carb on it. This solved most of my problems and I love it now.

The only problems I have now is this rattling sound when I am just cruising along a smooth trail or road just trying to maintain the same speed. When it gets to the "no load" point, it starts this rattle. It sounds like there is a marble in the cylinder or someone hitting the head with a hammer. I immediately add fuel or let off and it stops. THIS IS THE ONLY TIME IT MAKES THIS NOISE. I have gone richer and leaner with no success. It gets worse going leaner and I can't go much richer.

Also, when I let off the throttle, it surges and fires erratically.

It has done both of these things since new. The only thing I have done is had Jeff Slavens do the head mod and added the map switch. No difference.

Any ideas?

2013 KTM 300XC

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Sounds like a lean condition, I know you've experimented but what you describe is just that. Have you tried a leak down test to make sure there are not any air leaks, you can also try the old carb cleaner trick where you spray it around the boot, base gasket, etc while the bike is running and see if it makes a difference in the idle when you spray any of the possible leaky areas.

 

Edit: I meant pressure test not leak down. :facepalm:  

Edited by Squid_Racer

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Sounds like a lean condition, I know you've experimented but what you describe is just that. Have you tried a leak down test to make sure there are not any air leaks, you can also try the old carb cleaner trick where you spray it around the boot, base gasket, etc while the bike is running and see if it makes a difference in the idle when you spray any of the possible leaky areas.

Edit: I meant pressure test not leak down. :facepalm:

Thanks for the help. I'll make adjustments based on your advice. I'll go richer. I just found out I was adjusting the metering rod wrong. I thought I was raising the rod but I was lowering it. It's a two step process with this carb and I got the steps backwards.

It's brand new so I don't think it's a leaking problem. I'm going to take the carb off and clean it up real good. I got some junk in my tank. Thought I got it cleaned up good but I noticed some junk floating in the carb bowl today. It has a clear bowl on it.

Thanks again for the reply. I'll let you know how it goes.

2013 KTM 300XC

Sent from my iPad using Thumper Talk mobile app

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Thanks for the help. I'll make adjustments based on your advice. I'll go richer. I just found out I was adjusting the metering rod wrong. I thought I was raising the rod but I was lowering it. It's a two step process with this carb and I got the steps backwards.

It's brand new so I don't think it's a leaking problem. I'm going to take the carb off and clean it up real good. I got some junk in my tank. Thought I got it cleaned up good but I noticed some junk floating in the carb bowl today. It has a clear bowl on it.

Thanks again for the reply. I'll let you know how it goes.

2013 KTM 300XC

Sent from my iPad using Thumper Talk mobile app

Good luck, and remember forgetting to tighten down the carb boot or anything else can cause a lean condition, I know usually I create a lot of my own peruviana by messing with things.

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it is a lean condition as said, and the surging you describe leads to that for me. Lean on the needle I would say...a head mod can also cause you to need more octane or you get pings from lean condition..I know you probly got a no race gas head mod, but it is probly a part of the problem here, making it a slight bit more prone to the pinging you hear.

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Do you ever adjust the air screw when it surges?if your jetting is close it will help , there is alot of good info on here for jetting . It is a lean condition as the previous posters said. I ride 250sx alot , as temp and humidity change, the little screwdriver comes out and i tweak . Its such a habit i keep a small screwdriver in the bar pad of my smokers.

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it is a lean condition as said, and the surging you describe leads to that for me. Lean on the needle I would say...a head mod can also cause you to need more octane or you get pings from lean condition..I know you probly got a no race gas head mod, but it is probly a part of the problem here, making it a slight bit more prone to the pinging you hear.

Regarding the head mod, I would think Jeff Slavens knows what he is talking about. The head mod he did was supposed to make it run better on pump gas. Can't imagine he would do a mod that causes other problems. He said the mod would not require rejetting.

That being said, it wouldn't be the first time things didn't go as I planned. I'm sure on e I get the carb cleaned up and the float from sticking I'll be able to get it dialed in right. Like I said, I got some bad gas or something and there is a lot of junk floating around in the bowl causing float issues. The float issues are a recent thing. That combined with improperly adjusting the metering rod are hindering my tuning for sure.

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Do you ever adjust the air screw when it surges?if your jetting is close it will help , there is alot of good info on here for jetting . It is a lean condition as the previous posters said. I ride 250sx alot , as temp and humidity change, the little screwdriver comes out and i tweak . Its such a habit i keep a small screwdriver in the bar pad of my smokers.

No air screw to adjust on the Lectron. Just the metering rod and then the power jet for WOT. These carbs are great. I just didn't read the directions close enough. I was adjusting the metering rod basically backwards. I thought I was raising the needle but I was actually lowering it. That is what was throwing me off so much. Now I have a dirty carb to clean up. Once that is done, with the help you all are giving me and knowing how to adjust the metering rod correctly I think I'll be able to get it perfect.

Thanks guys!

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I had the same issue on the 200 lean and surging and a very loud knocking noise.

 

Total bone head installation.  The carb was coming out of the boot on the engine side,  Swapped the boot around, yes there is a difference and problem solved.  I may go 1/4 turn richer on the rod and lean out the air screw (idle).  The idle does act similar to the air screw.  

 

Glad I caught that before a catastrophe.  The guys at Lectron have been great.   

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Total bone head installation. The carb was coming out of the boot on the engine side, Swapped the boot around, yes there is a difference and problem solved.

What do you mean swapped the boot around? I didn't detach mine from the engine. Did you have yours off or something?

Also, did you modify the air box side? I did and I have no issues with fit. It's perfect.

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The carb was binding and coming out of the boot(?) on the the engine side between the carb and reed block. No mattter how tight I made the clamp the carb would come pop out of it.  I removed the rubber boot and sure enough one side is loneger than the other.  I turned it 180 degrees and solved the binding problem.  I have a 2008 so there is not easy way to modify the boot.  The guys at Lectron have been great to deal with. 

 

I am going to turn the rod 1/4 richer and raise (lean) the idle screw to see if I can get a little more low end. 

Edited by tt81621

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I haven't had to call Lectron yet about this but the ordering process was great customer service. I'm sure once I get the junk cleaned out of the carb I'll be able to dial it in. I seem to be the only one having problems. Most caused by me not reading the tuning directions thoroughly enough. Lol. Even with the problems I am having it's still better than the stock carb. Can't wait to get it right!

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The guys at Lectron did say you can and should adjust the idle screw moving the slide up and down for optimal performance.  Aside from obviousl lack of wrenching skills, I can't wait to get it dialed in. 

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Long shot here.  I had an older 200 EXC that made sound like you describe, only at very low throttle.  Mechanics all said it was my header pipe rattling against something.  I did a top end job just because it was due, and I found that a piston ring was stuck.  Bike seemed to be running OK,  Put new piston and noise never came back.

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Ive lived a sheltered life . Ive never seen a lectron carb in person. I do and always have loved the keihin PWK . easy to tune and trouble free. Ive heard the lectron is a step above the PWK, id like to try one out. On my 250sx smokers, the PWKs are stellar, i cant imagine any better.

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Well, I got everything cleaned out good. Put it back together and found the float was set too high. Called Lectron and they told me where to set it. Great customer service. They offered to set it up to spec again for free. Just had to pay shipping. After talking to them, I decided to set the float level myself. Did that and it ran good. Took it for a ride, keeping in mind the advice here as a lean condition so I kept moving the needle up a 1/4 turn at a time until it ran like I had hoped it would. Runs almost as smooth as my old 4t. Might need another 1/4 turn richer but even if this is as good as it gets, it runs far better than it ever did with the stock carb. I couldn't be happier.

Thanks everyone for the help. I couldn't have figured this out without you.

2013 KTM 300XC

Sent from my iPad using Thumper Talk mobile app

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Long shot here.  I had an older 200 EXC that made sound like you describe, only at very low throttle.  Mechanics all said it was my header pipe rattling against something.  I did a top end job just because it was due, and I found that a piston ring was stuck.  Bike seemed to be running OK,  Put new piston and noise never came back.

I put the pwk back on for a ride and the noise immediately went away.  I too am hopeful I solved the lean condition with the CORRECT installation. I need to get this dialed in before the Colorado 500 in 2 weeks,  

 

akaacz please give a ride report after going richer

 

Thanks.  .  

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I had the bike out for a few hours the other day without making any changes. It ran the best it ever has. Still minor surging when coasting off throttle but it is occasional. I think I'll leave the needle where it's at for a bit. It's "four stroking" a bit now so I think it's actually a little rich but I'm ok with that. Better a little rich than lean. Might have to lean the metering rod a 1/4 turn.

I had been running the green spring with the adjuster almost all the way out but it's running so good it's a little too torqey now right off the throttle. Too much like my old 450. I put the yellow spring in but haven't had the bike out yet. That should mellow it out to my liking. I plan on going with a Gnarly pipe when I replace the stock unit. I'll probably have to put the red spring in then. I hear those pipes really boost the bottom and mid, which is where I live.

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Figured out why it was surging and making that rattling sound. Jeff Slavens suggested I run race fuel. Bought some VP C12 and it runs perfectly. I honestly couldn't ask for a better running bike. It runs so smooth and four stroke like now. I was running the green spring but I put the yellow spring back in because it was a little too torquey. Perfect!

I'm running straight C12 for now. After that I'm going to try some 100LL Aviation fuel. My local airport has it for $6/gl. Much better than $17/gl for C12. Hopefully it will run just as well on that.

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