CB900 Cafe Racer project - Page 48

CB900 Cafe Racer project

This is a discussion on CB900 Cafe Racer project within the Project Builds forums, part of the Caferacer.net Forums category; Originally Posted by tjurek51 I'm getting a little frustrated. After correcting the vacuum Port issue with the carb piston, I started it back up, warmed ...

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Thread: CB900 Cafe Racer project

  1. #471
    Senior Member steveo's Avatar
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    Oct 2013
    Colchester, England
    Quote Originally Posted by tjurek51 View Post
    I'm getting a little frustrated. After correcting the vacuum Port issue with the carb piston, I started it back up, warmed it up, resyncd the carbs and now it won't really come close to mid or WOT RPMs. Idles great, but as soon as I open the throttle, it dies. Didn't do this as i syncd the carb, but as soon as I put the vacuum screws back in place, I get the described condition. Could it be the secondary pump?

    Might be an idea to check the vacuum take-off screws are sealing properly.
    "It's better to keep your mouth shut and appear stupid than to open it and remove all doubt"

  2. #472
    jcw is offline
    Senior Member jcw's Avatar
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    Jul 2015
    chicago burbs
    Are the slides moving?
    If there is a question then just take a look?
    leave the airbox off, twist the throttle, see if the slides lift. Get a faceful of fuel.

  3. #473
    Senior Member tjurek51's Avatar
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    Sep 2015
    btw, did the float check using the glass sight approach. very handy. all 4 level registered right under the top ridge of the bowl. looked correct to me. thanks for the advice on that one.
    TrialsRider likes this.

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  5. #474
    Senior Member tjurek51's Avatar
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    Sep 2015
    There was a whole boat load of insights provided regarding this carb issue. for some reason, they're no longer part of this thread. However, just to update everyone, the issue (it turns out) was the exhaust wrap. seems it cools down the outflow enough to starve the engine in the low to mid-range. the fix, it turns out, was easy. stepped the primary jet up from .68 to .95, and turn the idle screw out from 2 1/2 turns to 3 1/2 turns. Revving out to 10K now, with no issues. timing, compression, seals all test out great. looking forward to actually getting this on the road next season.

    The previous pictures are about as close to the finished project as I'm going to get. just need to install the handle bar mounted mirrors and this project will be done (well, sort of... ). Thanks to everyone who contributed to this thread.

    Stay tuned for my next thread, to start this spring. Decided this morning my next project will be that CB750 SS. Given what I learned during the 900 project, this project should be a bit more straight forward. Thinking... high compression pistons/rings/shafts, Keihin CR carbs, pods, under the seat electricals and some frame mods to handle the added stress load of the modified engine. should be fun!

  6. #475
    Senior Member Geeto67's Avatar
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    Oct 2005
    Columbus, Ohio
    Quote Originally Posted by tjurek51 View Post
    My issue is I can't get the bike to work right. it idles nicely. mid range starts to sputter at 4K RPM and I've only gotten it to 6K+ RPM a few times. when under load, I can get it to about 35 mph. I've back the pilot off at 1/4 increments until I was 3 turns from seat. it helped a little, but not nearly where it should be. i'm at a loss. any advice is appreciated.
    Check the electrical, esp coils, pulse controllers, and timing. On my old 750F, I ended up replacing pulse controllers, coils, stator, reg/rect, and the battery. Each time the symptoms felt like carb issues, until the component fully failed and then the bike wouldn't start. I remember riding a 900F on the Long Island expressway that had that same issue you described but it was the Reg/Rect failing when it got hot (worked when cold though). when it finally failed I had to push that pile a mile to the next exit, and then through a neighborhood in Brooklyn to a friends shop.

    Start with the timing and see if it is advancing properly, and work your way through the whole system.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

  7. #476
    Senior Member irk_miller's Avatar
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    Nov 2018
    Augusta, GA
    I'm guessing posts are disappearing again. I've never seen this before on any other forum. Once I commented, the last two posts became visible.
    Last edited by irk_miller; 11-26-2018 at 12:07 PM.

  8. #477
    Senior Member tjurek51's Avatar
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    Sep 2015
    Calling this project officially done. From this...
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    to this...
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  9. #478
    Member upperb's Avatar
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    Feb 2012
    Cabot, PA

    Very nice. Is the number 51 in your moniker and on your bike a tribute to Dick Butkus, former linebacker for the Chicago Bears? When we raced short track in the early 80's, one of my friends chose 51 as his competitor number for this reason.

  10. #479
    Senior Member TrialsRider's Avatar
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    Jan 2011
    Ontario, Canada
    lol no 51 is my rider number it's a tribute to me

  11. #480
    Senior Member tjurek51's Avatar
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    Sep 2015
    Thinking my shop name will be Motor51.

    the black and gold are my college basketball team colors and number 51 is (appropriately) my traveling game jersey number.
    Last edited by tjurek51; 08-20-2019 at 08:13 PM.

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