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Thread: Air Cooled 4 Stroke Decompression Valve - Anyone?

  1. #11
    KTMTalk Member DILLYPOOP's Avatar
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    Default Re: Air Cooled 4 Stroke Decompression Valve - Anyone?

    Quote Originally Posted by orange rider View Post
    In the old days all thumpers had decompression levers they had to in order to get the piston on the right compression stroke otherwise it`s just luck getting the motor started. I have plenty of old thumpers, Velocette scramblers, BSA GoldStars, Norton Manx, Norton International, 1957 Monark 500, 1961 HVA 500 ect. and they all have decompression levers, all work via the cam.
    I think that'd definitely be the more ideal way to go - through the cam. Unfortunately it's not worth retrofitting that somehow. I'm not sure why Kitaco doesn't come out with a head that has some sort of decompression valve for this bike. They do for other makes/models and I'm sure they've known about this for the past 15 years of problems..

    Not many people have the need to add a decomp valve on a xr/crf100.
    '18 Husky TX300
    '17 Sherco 250st Factory

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  3. #12
    KTMTalk Member bearorso's Avatar
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    Default Re: Air Cooled 4 Stroke Decompression Valve - Anyone?

    Quote Originally Posted by DILLYPOOP View Post
    I’ve seen the decomps that piggyback the spark plugs. kind of a neat idea but I haven’t been able to find much on how they really work. Most posts I saw about them were more of “look at this neat decompression valve.”

    Eric said he could easily get it to fit. There’s a oil line from the head to the head cover that may be in the way but I sent that and the plug/cap with the head. Supposedly there’s 3 thread lengths. He said he could get it to fit. I believe he’s doing the “port” type since that’s what he does for every other head.
    Here's the ones I wrote about - Wimmer was the brand. You'd have to have the room for it, but if you had a head / bike that had the room for such a thing, it would be a easy thing to fit for an owner. It's a different 'take' on using the 'pop off' decomp.


    Attachment 40241Attachment 40242

    You can see the 'transfer port' on the plug. A longer, or projected plug, would probably be needed.

    But, the decomp in the head, as I said, is an easy job.

    I'd probably make a Stainless Adapter on such a small head / small Plug pocket among the fins, as the 10 x 1 Pop off type, with it probably being right by the plug, might be a bit close, or in a thin section on the head. Do a Stainless adapter with the female 10 x 1mm thread (and the aforementioned pocket for the decomp valve head) that the decomp would mount to, with a male section using 6 x 1mm thread, with, at the most a 2mm port through it. No welding needed.
    Last edited by bearorso; 09-10-2020 at 12:06 AM.
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    KTMTalk Member DILLYPOOP's Avatar
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    Default Re: Air Cooled 4 Stroke Decompression Valve - Anyone?

    Just got the head back in the mail today. No luck...

    He didn't want to chance it. He said it was too tight for him to be comfortable. I reached out the Millar Race Engineering and they might be able to make it work. And another guy at "KX Guru Racing." Hopefully one of these work out.
    '18 Husky TX300
    '17 Sherco 250st Factory

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    KTMTalk Member orange rider's Avatar
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    Default Re: Air Cooled 4 Stroke Decompression Valve - Anyone?

    Quote Originally Posted by DILLYPOOP View Post
    Just got the head back in the mail today. No luck...

    He didn't want to chance it. He said it was too tight for him to be comfortable. I reached out the Millar Race Engineering and they might be able to make it work. And another guy at "KX Guru Racing." Hopefully one of these work out.
    I would not feel comfortable either. You have to respect him for not doing it, some guys would do it knowing they should not.

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