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Thread: 453 starts running real rough at 8K RPM: why?

  1. #61
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    Default Re: 453 starts running real rough at 8K RPM: why?

    Quote Originally Posted by pushstart View Post
    Verify the cam and cam timing could be 1 tooth late.
    Way back at https://ktmtalk.com/showthread.php?5...-why&p=5500310 was when I checked the valve timing. The camshaft gear marks were horizontal with the head casting at TDC as they should be, and the chain is good, there are clicks left on the tensioner.

    I don't know if you can do this easily on a RFS motor but verify the ignition timing.
    I don't think you can. From what I've seen, KTM thinks it never needs adjustment. The timing reference the CDI uses is from the pulser coil, which picks up the passage of the flywheel ridge. There is a spec in the manual on the radial gap between the pulser and the ridge, which would affect timing a little probably, but the location of the pulser body is fixed by its mounting screws. Anyway, while the engine is buttoned up, there's nothing marking TDC to shine a light at, and no inspection covers to get at one.

    At least hook up the timing light and rev it up in nuetral to see if the spark craps out.
    I did that at your suggestion IIRC and I'm pretty sure the light was dimming a bit in time with the cutting out. But I couldn't see anything on the scope to correspond to it. Still I'm going to get a loaner pulser and ign coil and swap some parts.

    I don't know what the specs are but 57 degrees btdc seems way too advanced should be more like 34-39 degrees.I don't believe the 57.
    Since there's no way I know to tell for sure, in those oscilloscope traces, I just guessed where TDC might be, and measured rotation before that. So the degrees I posted are probably wrong, unless I guessed right about where TDC occurred on the trace, and I probably didn't. Maybe the relative advance numbers (at 3900 RPM is advanced 27 from idle, and at 7900 it's advanced 47 from idle) makes sense but I'm not even sure about that. The CDI is advancing the timing though, I am sure about that .

    On the other hand what if the rotor key sheared causing the ignition timing to be late.
    That would be bad and I checked that, pulled the flywheel, key and keyway perfect, no problems that I could see.

    I doubt it's bad gas but it reminds me of a story of the 60's when Honda was road racing these 50 and 125 multi cylinder bikes that would rev to 20000 RPMs. They used regular gas which burned faster than premium. Talk about a narrow powerband they needed lots of gears
    Yeah I hope Chevron premium pump gas is good enough. But I happened to have a couple gallons of 100LL avgas and ran that through just to see, and no difference.

    I remember the Honda 350 6 cylinder. We thought it was silly at the time. That was more 70's though. And I don't know if they raced it.
    Last edited by Q-B; 08-02-2020 at 10:30 PM.
    I don't wanna pickle.

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  3. #62
    KTMTalk Member Speedy88's Avatar
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    Default Re: 453 starts running real rough at 8K RPM: why?

    Quote Originally Posted by Q-B View Post

    As a substitute for that I just removed it and ran open pipe for a test. As far as the bad running above 8K goes, it didn't change anything.
    How did your neighbors like that?

    Was this at about 11:15 this morning?

    I think I might have heard you!!
    '68 Bultaco Lobito 100 -Long gone
    '71 Hodaka Super Rat-Gave it away!
    '71 CZ250-Sold after 39 years! Ow
    '76 Maico 250 AW-Gone
    '83 Honda CR250R-Gone
    '86 500MXC Wicked -Gone
    '87 Cow KDX200 Gutless-Gone
    '91 300MXC Goat-Gone
    '97 360SX Pipey .....-Gone
    '00 380EXC Sweet-Gone
    '04 525EXC My 1st 4T. It's like cheating!-Gone
    '05 525EXC Barn find, barely broken in -Gone
    '13 500XC-W Nice bike, like new. Plated!

  4. #63
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    Default Re: 453 starts running real rough at 8K RPM: why?

    LOL I was wrong to say it didn't change anything. It did get louder

    This was up at my friend's place up near Paso Robles. He has a couple acres, nearest neighbor is a little ways. I might have scared some horses.
    I don't wanna pickle.

  5. #64
    Lifetime Team KTMTalk caflash's Avatar
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    Default Re: 453 starts running real rough at 8K RPM: why?

    Needle jets themselves can wear. 02 needles did not normally have a spring holding the needle clip down. Weird stuff but ?
    Rfs DocBob

    Current: rebuild 560 smr motor
    520 to 613.p

    ALL rfs engines available....other than 250s


    2004 613 rfs titled
    2002 520 rfs titled
    2005 483 rfs titled
    1996 620 lc4 titled
    (2)2007 613's in the works

  6. #65
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    Default Re: 453 starts running real rough at 8K RPM: why?

    Its gotta be your coil cap and wire that's why the timing light strobe went dim. Your cam photo is at overlap looks a little crooked but we cannot really tell from this side view. Spin it around on compression tdc and look at the Mark's again ( I bet you already did this)

  7. #66
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    Default Re: 453 starts running real rough at 8K RPM: why?

    The voltage peaks on the pickup are even and consistent . I doubt its that.

  8. #67
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    Default Re: 453 starts running real rough at 8K RPM: why?

    Quote Originally Posted by pushstart View Post
    Your cam photo is at overlap looks a little crooked but we cannot really tell from this side view. Spin it around on compression tdc and look at the Mark's again
    Here's the timing gear at compression TDC. Alignment of marks is not perfect. But if you moved it a tooth either direction, it would be definitely worse.

    Click image for larger version. 

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    I don't wanna pickle.

  9. #68
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    Default Re: 453 starts running real rough at 8K RPM: why?

    Quote Originally Posted by caflash View Post
    Needle jets themselves can wear.
    Way back at post #9 in this thread I checked the needle jet for wear. Visual inspection was good, I didn't see any wear.
    I don't wanna pickle.

  10. #69
    Lifetime Team KTMTalk caflash's Avatar
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    Default Re: 453 starts running real rough at 8K RPM: why?

    Difference between needles themselves is .0004 but you tried way rich and lean already so I doubt that thats it.

    your flywheel, pickup and coil and wire and cap for your testing are here for the pickup
    Rfs DocBob

    Current: rebuild 560 smr motor
    520 to 613.p

    ALL rfs engines available....other than 250s


    2004 613 rfs titled
    2002 520 rfs titled
    2005 483 rfs titled
    1996 620 lc4 titled
    (2)2007 613's in the works

  11. #70
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    Default Re: 453 starts running real rough at 8K RPM: why?

    I would swap to a known good carb, personally.

    2005 EXC 565cc (100x72) Caflash Ultralight/HMC Cam, Stock head, KibbleWhite stock size intake valves, stock exhaust valves, sharpened intake divider, Gen III carb testing now, Innovate AFR gauge.

    39mm Gen III carb. 38 pilot, ocemr 3rd with emulsion tube 2nd without, 140-145 main.

    Prior engine combos are 532cc/806 cam, 532cc stock cam, 565cc/833 cam, 565cc hotcam, 565cc Cut 7 cam, 565cc Thumper Stage 5 cam, Beautifully ported Cut7 head, DJH +1 head, 39mm Gen3 carb, 41mm straight bored carb, 41mm Gen3, 43mm Straight bore carb.

    NOST Suspension and Midvalves, 14/52 gearing. 14mm triple clamps, headstay, Scott's underbar stabilizer and 1" riser. Seat Concepts seat. Narrowed FLEXX bars. Tubliss rear with Pirelli MT16 front and rear.

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