? for those with crane xr700 ignitions - cutting out | FerrariChat
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? for those with crane xr700 ignitions - cutting out

Discussion in '308/328' started by ilconservatore, Jun 18, 2010.

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  1. ilconservatore

    ilconservatore F1 Veteran

    May 18, 2009
    8,369
    Cincinnati Ohio
    #1 ilconservatore, Jun 18, 2010
    I've been troubleshooting a 308 gt4 that a friend just bought. Its original except for Bassani exhaust and crane xr700 ignition conversion. It has a habit of randomly cutting out - feels like the ignition to one bank just shuts off for a second or so, followed by loud popping through the exhaust as it comes back on and ignites collected fuel.

    It was fine for literally the first few hours he owned it, then started cutting out now and then, and got worse. The popping is loud enough to scare folks on the street!

    I've been through everything - checked source voltage, conections, plug wires, plugs and plug gap, ballast resistors, timing, setup of the triggers, swapped left for right, etc.

    The only thing that cured it temporarily was closing up the plug gap to .035". Then I swapped to a new set of BRP7ES that I had on hand, and it came back with a vengeance. Replaced the old BP8ES and its better. I also re-did the entire wiring harness and temporarily moved the ignition boxes to outside the car to reduce temperature.

    With ballasts hooked up, they get just over 8v, same as the MSD coils (which is what's recommended in the instructions) Yet they get really hot to the touch, even when not in the engine bay.

    Am I missing something? I've checked coils and plugs with a timing strobe and get a stutter here and there at idle from both banks, which leads me to think both modules are either weak, or overheating. I hate to just buy two new units without identifying the root cause.
     
  2. thecarreaper

    thecarreaper F1 World Champ
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    Sep 30, 2003
    17,958
    Savannah
    #2 thecarreaper, Jun 18, 2010
    Last edited: Jun 18, 2010
    i did a thread on this when Jfrazar and i added Crane ignitions to a few points / carb cars. i seem to remember the pickups need to be 135 degrees apart in one dizzy, as the master. maybe one of the optical pickups is dirty, or out of adjustment / damaged. check that and power / ground wires and coil wires.

    verify you have consistent amps and voltage from the alternator and fuse blocks ( through the rev range of the engine) to that circuit. you may be loosing a voltage regulator / diode block, or have a fuse box issue.


    ps Crane and MSD recommended to me to run a .055-.060 plug gap, and we ran BP6ES plugs in all of my 5 308s, and 3-4 local freinds 308s also. a BP5 heat range can be used, but they are "very hot", and usually cover up miss adjusted carbs or leaking throttle shafts issues.
     
  3. ilconservatore

    ilconservatore F1 Veteran

    May 18, 2009
    8,369
    Cincinnati Ohio
    #3 ilconservatore, Jun 18, 2010
    Thanks!

    I checked the pickups and their alignment, but you lost me on "135 degrees apart" - do you mean with respect to the firing order?

    The units will not get any hotter or cooler out of the car - they seem to be at the same temp as the rest of the underhood and msd coils, etc. How hot do yours get?

    Your plug gap is interesting - I actually went down to .030 and it runs fantastic tonight. Smoother and better power than ever. At .40 it missed, at 35 it was hit and miss, no pun intended.

    Plugs look lean and judging by the ground strap are maybe already a little hot? I may try the 7's with the tighter gap.

    Number one plug always seems a little wet though, no matter what I do (scoped it and it always fires, even replaced the wire just in case, swapped plug extenders, etc)

    Not sure if its cured yet but for tonight its much better...If nothing more it was a nice excuse for a drive.
     
  4. ilconservatore

    ilconservatore F1 Veteran

    May 18, 2009
    8,369
    Cincinnati Ohio
    #4 ilconservatore, Jun 18, 2010
    Do you think a hotter plug would be better if its already burning clean?
     
  5. Ferraripilot

    Ferraripilot F1 World Champ
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    May 10, 2006
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    #5 Ferraripilot, Jun 18, 2010
    The Crane XR700 needs a stock gap on the plugs. So .020 to no more then .030. The XR9000 is the Crane's higher performance version with a little inductive discharge mechanism inside and those can run gaps of .040+.

    When I ran Xr700s alone I ran BP7ES with .025 gaps. BP6ES and BP5ES runs too hot at the upper end and caused trace detonation for me with best ignition timing setup. If a person does not really open up the car on a regular basis, I would say 5s or 6s are fine, but for someone who puts fire under it regularly I say use 7s. I went through this on the dyno and tuned it right there so I know what works. I am now having my XR700s fire two high output boxes which makes running 7s much easier (idle was a bit rough with them).

    To properly check your plug heat range, run the engine hard at WOT in a tall gear and shut the engine down asap. Pull a plug and check the plug ground strap. A plug with optimal heat range will have color from the tip to the apex and no further. Mixture can be determined by the soot ring deep inside at the base of the insulator. Check this after a WOT run as well. It should be a little over 1mm thick. Eyeball it as best as you are able.

    Make sure you are running correct total ignition timing and idle timing. I found carb 308s to run best at about 38.5 degrees at 6k. There are only marks on the flywheel for 34 so you are going to have to measure out what is correct. Per the manual it mentions 34 degrees at 5000 which is correct, but the manual does not mention that the dist keeps advancing a couple more degrees past that on up to 6000 or so. It shows this on the distributor advance graph, but there is no mention of it anywhere I have found.


    good luck!
     
  6. thecarreaper

    thecarreaper F1 World Champ
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    Sep 30, 2003
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    #6 thecarreaper, Jun 19, 2010
    we placed both pick ups in one dizzy, 135 degrees apart, and used the other dizzy as a slave only.

    LV had a great reply to your other questions.

    i never noticed our boxes getting hot.
     
  7. ilconservatore

    ilconservatore F1 Veteran

    May 18, 2009
    8,369
    Cincinnati Ohio
    #7 ilconservatore, Jun 22, 2010
    Definitely, thanks lv and reaper.

    After closing up plug gap to a tight .030 over the weekend it is running very nicely with the BP8ES plugs. I may try the brp7's again next time I'm under the hood.

    It does idle a little rough, and there is an annoying click or pop back through one carb on light acceleration in the upper gears. It has low miles and sat for awhile so I'm expecting the carbs need a going over as well. I've tried to balance them as close as possible with a synchrometer but I think there's more work to be done.

    Would the bassani exhaust lean it out noticeably - enough to need rejetting?

    This is the first 308 I've played with...so far I really like it!
     
  8. ilconservatore

    ilconservatore F1 Veteran

    May 18, 2009
    8,369
    Cincinnati Ohio
    #8 ilconservatore, Jun 22, 2010
    Also moved the boxes up and out of the way in the engine bay as much as possible, and as far away from the HT leads as I could get them
     
  9. Ferraripilot

    Ferraripilot F1 World Champ
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    #9 Ferraripilot, Jun 22, 2010
    Richen up the idle mixture on the carb that is spitting back on light acceleration. If there is stock jetting in the carbs, I can tell you right now they are way too lean in the main power band. 55 idles are fine, but the mains should be around 140 with a 200 air corrector as a good starting place. For me, that was still too lien. Others it has been just about right. There is easily 15bhp hiding in correct jetting if you are still stock.

    The exhaust should not change things much.
     
  10. ilconservatore

    ilconservatore F1 Veteran

    May 18, 2009
    8,369
    Cincinnati Ohio
    #10 ilconservatore, Jun 22, 2010
    is the idle mixture the large hex screw at the base or the small screw with the locknut further up on the body? I didn't get much response from the lowers, but found it responsive to adjusting the upper screws out a turn and a half or so.

    With the lower screws I was only able to turn them in and get a stumble at idle, then backed out 1/2 to 1 turn until idle came back up.
     
  11. Ferraripilot

    Ferraripilot F1 World Champ
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    #11 Ferraripilot, Jun 22, 2010

    idle mix screws are at the base of the carbs. the screws with the locknuts up the body are the air balance screws, and those need to be adjusted first along with the linkage arms so that ALL the carbs are sucking the same amount of air. I typically adjust the idle screws via listening to the idle once all the linkages and air adjustments are made and screwing the idle screw in until that cylinder stops firing, and then I back the screw out a little over 1/2 a turn and it is usually just right. You can hear what sounds best around that 1/2 turn area though.
     
  12. ilconservatore

    ilconservatore F1 Veteran

    May 18, 2009
    8,369
    Cincinnati Ohio
    #12 ilconservatore, Jun 22, 2010
    cool, thanks. Sounds like I wasn't too far off. I've sync'd DCOEs before but the way the linkage and adjustments are setup on these threw me for a bit of a curve. They seem to respond differently than what I'd expect, if that makes any sense.
     

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