Page 2 of 2 FirstFirst 12
Results 6 to 10 of 10
  1. #6
    ...they call me the rocket man... ndwedwe's Avatar
    Join Date
    Apr 2012
    Location
    Mid Wales, UK
    Posts
    334



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

    did you look at your plugs when it was cutting out?
    your CDI was designed to run unleaded so you might not have enough advance up top on leaded but that is something else, it ran fine before
    the new coils might not be giving a brilliant spark up top added to richer jetting, also it was very hot so on that day going richer would have made the situation a little worse
    dunno, im just putting the little i know out there
    1993 TZ250
    1999 TZ250

  2. #7
    ...i smell a trophy... erock768's Avatar
    Join Date
    Apr 2008
    Location
    Cave Creek, AZ
    Posts
    241
    Ndwedwe: All valid points. I'm going with the coils not having sufficient spark strength and combined with the rich jetting it was compounded. Even the manufacturer admitted that although he thought they would work satisfactorily on the TZ he hadn't actually used them on a modern machine. The bike was back to normal after fitting the OE coils. I did also replace the voltage regulator as I was afraid that it might have been damaged when I had a battery fail. When my battery failed it overworked the stator, which fried it. Hence, why I had it rewound. I replaced the voltage regulator as I have heard of battery failures overworking the regulator and damaging it. More precautionary than anything. I replaced the voltage regulator after I fitted the OE coils and determined that that was the fix.
    Eric Moore Racing LLC

  3. #8
    ...i smell a trophy... erock768's Avatar
    Join Date
    Apr 2008
    Location
    Cave Creek, AZ
    Posts
    241
    Also, with regard to the 4DP-40 (97') CDI box being unleaded: I have run it on AVGAS with no issues for years. I run it at the recommended 1.7 mm BTDC on most tracks and advance it up to 1.9- 2.0 on tighter tracks. Always checking the burn back on the electrode.

    Regarding ignition boxes. I want to share this info that was forwarded to me by Ed Sorbo:

    As you know 1996 was the last year for leaded gas. The ignition that year was 4DP-85501-30. At Daytona that year Roland Sands was flying with kit parts that the rest of us had never heard of, that he got through Kristian Kass who ran on his team after bringing the parts from the GPs (you help me and I ll help you). The ignition they were using was 4DP-85501-A0 (presumably A for Avgas but nobody knows). The static setting on a 93 or 95 ignition was 1.5mm BTDC. For 1996 on the -30 ignition it was 1.9mm BTDC but there was a Yamaha technical note saying that it would work better at 1.9 on the top cylinder and 2.05 on the bottom.

    When I measured the ignitions I found that the A0 ignition was identical with the -40 ignition from 1997 (first unleaded) at 10000 and 12000 rpm with no load. There could have been some sort of timing control that I could not measure based on the rate of change of rpm but I don t think there was. The -40 was more advanced at 4000 6000 8000 rpm but this would have no effect during racing normally.

    Therefore if you have a 1999 TZ or earlier a -40 ignition should work very well with leaded gas set to 1.9/2.05 as long as you have a trapped cylinder head volume in the regime of about 8.3 cc particularly at high speed tracks. The -30 ignition might be better for acceleration at stop start tracks, or you could just add up to 0.2mm advance at the expense of loss of over-rev.

    When they changed from 50.7 stroke to 54.5 stroke in 2000 the ignition changed again and also the kit selectors became available which made everything more complicated.

    The amazing thing is that I swear a well put together TZ from those days would still be competitive today maybe one of Rich s old bikes for example. Of course development pretty much stopped after 2000 with only a few detail changes.

    As ignition setups are pretty much the easiest way of destroying two stroke engines all information is provided with the warning caveat emptor which translates as: if you blow it up, you went too far .
    END

    Pretty interesting.

    Also, be sure to check out Ed's wealth of tribal knowledge here:
    http://www.le-suspension.com/tz-250-tuning-secrets/
    Eric Moore Racing LLC

  4. #9
    ...they call me the rocket man... ndwedwe's Avatar
    Join Date
    Apr 2012
    Location
    Mid Wales, UK
    Posts
    334
    yes, i have that printed in my TZ file
    there are guys in UK running 5KE's on avgas with std ignitions, i was only putting it all out there, all 4 things (cdi, coils, jetting and temps) or 3 or 2 or just 1 could have been the cause. when combined they can lean one way
    i'm glad it's sorted though
    1993 TZ250
    1999 TZ250

  5. #10
    ...battling for points... vince24x's Avatar
    Join Date
    Dec 2002
    Location
    orange county, ca
    Posts
    1,986



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

    yo eric,

    the "A" in that ecu part number definitely does NOT relate to avgas. and, while not clear how ed got the timing numbers they dont sound right to me (i.e. more advance for ULP??). further, timing aside, i think the bigger 'downside' to using the ULP box when running leaded isnt so much the timing curve as the powerjet settings...which will definitely dump too much fuel at pk torque to try and avoid det. as well, while you can adjust the static timing to make any particular point on the curve work well, it will absolutely compromise something somewhere else. ALL of the stock curves leave too much advance up top if you get the bottom right, or vice-versa. this is per the experience of marc s, who dyno'd all the AMA bikes back when he was running around w/ the guys ca. 2000. i tend to believe him based on what he showed me.

    that said, as you note, one of the really nice things about 100LL is the super-wide tuning range...so the bike will work on it no prob. its just not 'optimized' is all (but then, is it ever?? ).

    glad you look to be on the path to sorting out the issues. loook fwd to continued good news following your next track outing.

    vince
    CVMA, WERA, WSMC Ex #224
    http://www.mobiusracing.com

Page 2 of 2 FirstFirst 12

Similar Threads

  1. 4DP/4TW engine mounting plates and ignition rotor wanted
    By tzstangl in forum Yamaha TZ GP Motorcycle Parts
    Replies: 0
    Last Post: 01-28-2019, 05:46 PM
  2. Yamaha TZ 250 3YL 4DP 4TW 5KE ignition coils
    By Cristian in forum Yamaha TZ GP Motorcycle Parts
    Replies: 0
    Last Post: 09-19-2018, 07:03 AM
  3. Yamaha TZ 5ke , 4tw , 4dp , Ignition coils
    By Cristian in forum Yamaha TZ GP Motorcycle Parts
    Replies: 0
    Last Post: 08-24-2017, 07:44 AM
  4. gear issue
    By nycstripes in forum TZ Engine Tech
    Replies: 15
    Last Post: 08-16-2007, 04:26 PM
  5. Wanted: Ignition coils (from 4DP.4TW or 5KE)
    By RG/TZ 500 in forum Yamaha TZ GP Motorcycle Parts
    Replies: 0
    Last Post: 11-19-2006, 03:38 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


<% COPYRIGHT %>