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Thread: 97 KTM 360 idle surge

  1. #1

    Default 97 KTM 360 idle surge

    I recently had my crankshaft serviced (new conn rod kit) and I replaced the crank seals and bearings, new top-end as well.

    I've noticed a surge in the idle once the bike gets warmed up and i'm riding it. It eventually settles down, but I usually have to upshift and 'manually' drop the rpms with the clutch.

    It did this before the rebuild as well.

    I'm suspecting an air leak, probably from the left side crank seal (even though it's new). I'm probably going to apply some gasket sealant and see if that helps.

    I haven't done a leak down test but I'm confident the carb, reeds and intake don't have any leaks. There are no oil/coolant leaks from any of the case gaskets, cylinder, power valve or head.

    Any other suggestions of what could be causing this?

    This is the only issue i'm having, the bike is running awesome throughout the powerband and the plug is a nice brown color, so i think my jetting is correct.

    Thanks.

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  3. #2

    Default Re: 97 KTM 360 idle surge

    How did it run before the tear down? Id check the intake really well. Also check air screw adjust o ring

  4. #3

    Default Re: 97 KTM 360 idle surge

    Quote Originally Posted by Jimmy boy View Post
    How did it run before the tear down? Id check the intake really well. Also check air screw adjust o ring
    Thanks for the reply. The intake looks good, no tears in the boot, filter is relatively new, and the carb clamps are tight.

    I think you might be onto something with the air screw. On the parts diagram there is no o-ring... just the screw and spring.

    I did replace the air screw with a finger adjustable one from Slaven's Racing... that might be it. It always felt a little looser fitting than the oem keihin one.

    I'm going to put the oem air screw back in and see if i still get the idle surge... if that's it, i might use some thread tape if i decide to go back to the Slaven's one.

    The bike had this surge issue before the teardown. I can't remember if it did it before i swapped airscrews. Thanks for pointing me in a direction i didn't think of.

  5. #4

    Default Re: 97 KTM 360 idle surge

    Hi FairWeather,

    If your bike has the PW Keihin carb, the old style choke circuit is known to go bad on them. You may also want to consider changing the jet block o-ring. Another possibility is the ignition system (stator ect). Its possible your bike had the troublesome SEM ignition ?

    Let us know how it plays out for the next guy.

    Thx, -Basi

  6. #5

    Default Re: 97 KTM 360 idle surge

    Quote Originally Posted by Basi View Post
    Hi FairWeather,

    If your bike has the PW Keihin carb, the old style choke circuit is known to go bad on them. You may also want to consider changing the jet block o-ring. Another possibility is the ignition system (stator ect). Its possible your bike had the troublesome SEM ignition ?

    Let us know how it plays out for the next guy.

    Thx, -Basi

    Hi Basi, Thanks for your reply.

    This 360EXC has the kokusan 2k-2 ignition with PWK 38 carb. It has an aftermarket baja designs lighting kit, excel supermoto kit and FMF Gnarly pipe... everything else is stock.

    The carb is new, i got it from JT Jetting a year or so ago. It did not come with the air screw o-ring and washer.
    I think the old carb came with those parts, so I'm in the process of replacing/adding them.

    I'm pretty confident that's where the air leak and idle surge is coming from, feels like I've checked/replaced everything else.

    I'm running a fairly new Ricky Stator and the output voltage is good... i have a backup OEM kokusan 2k-2 as well.

    I will do a follow up post so other 360 owners with this problem can get an idea where to start looking.

    This ktm has been a long-term (expen$ive) project... the bike was pretty tired when I got it 8yrs ago, and needed a lot. I'm close to the end finally, and the bike is currently better than ever.
    The performance of these old, rare bikes is incredible, so I wanted to rejuvenate this one... I've gone thru a lot of hurdles (mostly due to my own inexperience and looking in the wrong places to solve problems).

    Cheers.

  7. #6

    Default Re: 97 KTM 360 idle surge

    I have added the O ring to carbs that came without just to be safe. Teflon tape sounds like another way of sealing but I would use it as a string on the outermost threads to it cannot get inside the passage.
    Victor

  8. #7

    Default Re: 97 KTM 360 idle surge

    check pilot jet is clear?
    Steve
    Ariel MCC
    09 300 EXC-E
    89 125 EXC

  9. #8

    Default Re: 97 KTM 360 idle surge

    Update*

    Rebuild- I did check the pilot jet and there was some build-up in there... i cleared it. The bike still had a bit of idle surge but clearing that jet helped.

    I dug through this forum, and people had similar symptoms on their 380s. I'm convinced there is no air leak, the symptoms (I think) are coming from low octane gas. These bike are designed for 93-95 octane, I live in California and the premium pump gas here is 91 Octane.

    I ran some higher octane race gas and the idle surge went away completely.

    Anyways, thanks for everyone's input and suggestions.

    PS- I have decided to run the air screw with the o-ring and washer regardless.

  10. #9

    Default Re: 97 KTM 360 idle surge

    I miss my old 360, such a fun bike to ride. Glad you got if figured out.

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