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80" Evo, 4500 RPM Dead Spot

Discussion in 'CV Performance' started by DravenGSX, Apr 8, 2014.

  1. DravenGSX

    DravenGSX Member

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    I need some guidance to make sure I'm on the right path here. The bike is a '98 Dyna with stock 80" motor has the stock keihin CV carb. Since I bought it, the bike hits a wall at 4500 RPM, then by 4700 RPM it's pulling hard again. I replaced the drag pipes with a 2 into 1, replaced the jets (had 45/170) with 46/180, shimmed the stock needle, drilled out the emissions plug and have the screw at 3 turns. I also chopped up a stock airbox and put in a K&N (HD-1390) filter.

    I expected the pipes to fix the problem, but there has been no change. Had a friend ride behind me the other night and gave it a blast and he mentioned that there was an orange glow when I hit 4500 RPM (exhaust note changes, it's sort of violent). The current thought is that the main is coming on too late (right around that time). The question is, how do I fix it? As I understand it, changing the needle may help? Would a lighter slide spring also help? Basically, I need the slide to move up faster, right?

    As far as I know, the slide hasn't been drilled, though the previous owner was in the carb as the slow jet was replaced, however the idle mixture plug was still there.
  2. joshbob

    joshbob Well-Known Member

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    Not knowing what the previous owner may have done to the carb, I'd tear it off and rebuild it with one of the CV Performance kits sold by Ken. And check that the slide hasn't been drilled. Should be no more than 7/64".
  3. hotroadking

    hotroadking Super Moderator Staff Member

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    shim the needle if it's not adjustable, if it's adjustable move the clip down one (lifts needle earlier) see if it helps, adjust one circuit at a time to see if you get any changed meaning move the needle jet up and down from the starting point to see if any changes help with the needle only.
  4. DravenGSX

    DravenGSX Member

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    Sounds like I'm on the right track with the needle. I have shimmed it once already though and while I did notice quite a difference in the midrange, I still have the same problem at 4500 RPM. That is why I started looking into replacing it altogether.

    I have already replaced half of the parts in the kit, so I don't think I need the entire kit.
  5. kenfuzed

    kenfuzed Administrator Staff Member

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    If you are still having this issue I would look into the ignition. It could be an aftermarket ignition with incorrect settings, but part of what you described earlier doesn't sound completely carburetor related.

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