Question about 2001 KTM EXC 300

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I have a 2001 KTM 300 EXC with less than 500 miles. I left it sitting too long with gas in it last year and it gummed up the carburetor. I have thoroughly cleaned it and put it back on. The bike starts right up. It idles fine and the choke work as it is supposed to when cold starting, but bogs and has no power through mid throttle in the low gears then hits really hard at upper rpm range in third gear. I can't seem to get this corrected with the air screw and I do not know how else to adjust this out.

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  • KTM Master
  • 46,420 Answers

Hi, Jameswpage you may need to soak your disassembled carburetor in some "CARB DIP" Yamaha makes the best because it does not attack rubber parts like automotive carb dip and your A/F mixture screw only manages your idle circuit, that being said engine "BOG" is mainly caused by a rich air and lean fuel condition but it can also be caused by a lean air and rich fuel condition this situation rarely occurs and is only caused by the misinformed weekend warrior that owns a toolbox.
The more you open your throttle the more vacuum you are creating in your carburetor venturi and your intake manifold. When you are operating at higher RPM any unmetered air that leaks into your system can become more obvious.
Unmetered air is air that is getting into your system after the fuel has been delivered. If you have unmetered air getting into your system between the butterfly/slide of the carburetor and the cylinder head this will create a lean condition.
All of the rubber components of the fuel system like vacuum hoses and intake manifold that you mount the carburetor to are made of rubber. If none of these components have been changed out they are more than likely highly degraded and probably cracked in places to allow unwanted-unmetered-contaminated air into the combustion chamber. Check all of your vacuum lines and vacuum plugs for carburetor synchronization. The vacuum plugs are in the head just after the rubber intake manifolds. The petcock has a vacuum line as well as part of the emission system.
1. Check the intake manifold for cracks.
2. Ensure the bands used to tighten the manifolds down on the intake are secure and have not bound up the manifold.
3. Make sure air box fittings are not warped and fit completely over the carburetor.
Your airbox is metering air and is the first step in a process of consuming air and fuel. The system requires the resistance of the air filter in order to get the proper vacuum to "SUCK" the fuel out of the float bowl and create the proper venturi effect.
Improper mounting and sealing of the airbox will create a small lean effect. This might seem like no big deal but you are inviting dust and debris in your engine that is doing slow damage by not having proper fitment. Fix it so you know it's not contributing to your issue. Pick the low hanging fruit first.
Do not go and start adjusting anything at this point. It ran fine before. There is something wrong with the assembly or a component. Do not adjust your floats. Get it back to where it was. The moment you start tweaking everything is the moment you lose OEM settings which are a must have for fine tuning and maximum performance.
Fine tuning your carburetor and multi carb syncing come at the very end following the proper procedure established by the Carburetor Gods.
For more information about your issue and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day.
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Posted on May 22, 2017


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I would recommend getting the front tire balanced. Get the front wheel off of the ground and spin it to see how "out of round" it is.I know the tires on these are DOT approved, but they are not a comfortable ride at highway speeds. Head shake is usually caused when the front end gets light. (My Husaberg does it bad at 90mph) You can play a little with the suspension, or even move the forks up a little in the triple clamps, or the enevitable, get a stabilizer.

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Posted on Oct 08, 2009

  • 106 Answers

SOURCE: runs great with choke on but continues to die when

Hey mate,

you definately have a problem with your fuel system, I would say you have had some dirty fuel thru your bike, the first thing i would check would be the fuel filter between your tank and the carby then if still does not run drain your carby bowl... after this if it still does not run you will need your fuel system/carb stripped down and flushed would recommend getting this done by a mechanic as there is alot of small parts involved...

Hope this helps

Posted on Dec 16, 2009

  • 2702 Answers

SOURCE: KTM 520EXC Starts with choke but you cannot take off choke

well you hit it right on the head there,, its the jets in the carb blocked up,,strip down carb and clean out all the jets with carb cleaner and compressed air dont go poking any thing into the jets as you will distroy them that way,,, another way of clearing the jets out that you could try first is,,,take off the air filter and start the engine up on choke in needs be,,rev the motor up high and slam your hand over the carb intake,,removing it just before the motor cuts out do this a good fuw times and it some times??? only some times clears the carb jets out for you

Posted on May 20, 2010

Woods Goat
  • 85 Answers

SOURCE: i have a 91 ktm 300 exc and it bogs down and dies

Your carb needs to be cleaned. More specifically, the pilot jet, but if it's clogged it'd be best to go ahead and clean the whole thing.

Remove the carb from your bike and then remove the bowl from the bottom. You'll then be looking at the jets and float valve. The jet causing your issue is the smallest one. Remove it and carefully spray it out with carb cleaner. Then hold the jet up and see if you can see light through the hole and that it appears clean and round-meaning no obstruction left. Locate the mixture screw on the outside of the carb. It should use a flat screwdriver. First turn the screw in and count the number of turns. Then remove the screw, followed by the spring and ,if applicable, a small o-ring. Spray through the hole and make sure it goes through and comes out somewhere. Replace the screw in the reverse order and set to the original setting you counted in the beginning.(rough estimate is 1.5 turns out. Cleanliness is the key to the carb working. So keep it spotless inside and reinstall. This should take care of your problem.

Posted on Jun 11, 2010

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Hi, Frank_sydow you're getting ready to go riding you pull out the dipstick to check your oil level and are greeted with the unmistakable smell of gasoline. What happens next depends on the following:
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Bikes been sitting for about 2 yrs, no use.

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