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  1. #1
    ...On the Grid... gbowie's Avatar
    Join Date
    Jan 2006
    East London, South Africa

    a d v e r t i s e m e n t

    Has any one had any experience of using bored out carbs on a TZ.
    I have recently acquired a '91 3YL with 4DP barrels and CDI and on investigation found that a previous owner has bored the carbs to 39mm.
    The bike pulls well, but tops out between 11-11.5k, I have checked the power jets (found one with a broken wire and repaired this) and they get 12v at high revs in neutral .
    I have done a check on the settings and find as follows :-
    Power jets..80
    Pilot jets..20
    Nozzels... R 3 ?? (Unlisted in the parts manual)
    Needle clip.. one richer than middle.
    air screws.. 1 turn out
    Squish.. around 0.8mm .
    Timing.. 1.59mm BTDC.
    I am running at sea level using 102 octane leaded petrol and Motol 800 (motocross) at 30:1.
    Has anyone any suggestions as to what difference the extra 1mm bore dia would make to jetting and why it won't rev to ( I'm told 12500-13000).
    Also it won't idle, but I suppose that comes with buggering around with the carbs.
    Any ideas.

    Attached Thumbnails Attached Thumbnails IMG_1381.jpg  

  2. #2
    ...quite the collection, eh?... Dale Whelan's Avatar
    Join Date
    Aug 2001
    Mesa, Arizona
    try replacing the plug caps
    Dale Whelan
    Racing Grampa

  3. #3 fingers hurt...
    Join Date
    Sep 2005
    Melbourne, Australia
    Weird jetting. I'd put the needle back where it should be then
    go to R6 nozzles to save it from seizing on the over-run.

    Do a plug chop.

    I'd have thought 360 mains & 60 power jets would be more likely unless you are running oxygenated fuel, but do the plug-chops.

    The dead power jet solenoid will also reduce over-rev by making it rich above 11,500-12,000, but it wouldn't be so bad if you were closer with the mains.

    And they're not meant to idle.


  4. #4
    ...On the Grid... gbowie's Avatar
    Join Date
    Jan 2006
    East London, South Africa
    Thanks for the info guys, Unable to test the bike until the next race 16/17 June...Dale, on checking the plug caps I found the bike fitted with shortened Bougicord supressor cables and caps off a car, have fitted copper cables with new NGK supressor caps.. Can't find unsupressed caps ??
    grahamb, have ordered R6 nozzles Ex Japan ...3 weeks and will try the suggested jetting at our next race.
    Will keep you posted.

  5. #5 I go again... T678's Avatar
    Join Date
    Jul 2005
    san francisco, CA

    a d v e r t i s e m e n t

    Geoff, welcome aboard!

    I've never known tz's to idle. Is it possible or does it matter? Anyone on this?
    My slide is a 4.5 and factory on (my 93tz, leaded) is of course 3.5
    Should I change it back if I live in california?
    AFM # 678

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