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Thread: Sportster electronic ignition

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  1. #1 Sportster electronic ignition 
    frequent forum contributor Club Member
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    Oct 2018
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    38
    Hello,

    I'm slowly learning about my "new to me" Sportster and I'm wondering if anyone else has a "Lumenition in association with GEMS" electronic ignition setup on a BMW 6 cylinder running triple Weber carbs? The distributor seems to be one of those fixed units running off the front of the cam, and there is a small heat sink Lumenition unit next to the coil, and a larger blue module in the passenger footwell, labelled as a Competition Engine Management System, Type C410, Serial No 01168, made in 1996. The unit has a D-type multi-pin connector on its lower surface, with 9 pins. I suspect the blue unit can be connected to a laptop in some way to allow adjustments, but no details came with the car, and I can't find any details on-line, having spent a couple of hours Googling. The car was built by Marlin themselves in 1997, so I suspect this was their way of overcoming the engine management system issues associated with ditching injection and moving to triple Webers. I've emailed Lumenition and GEMS, but thought it also worth trying on here as well in case they no longer provide support. I suspect the timing may be a bit too advanced at the moment - there is popping back through the carbs, a biggish flat spot under acceleration, a high idle and I suspect I can sometimes here pinking under load. The engine is a BMW M30 unit, I suspect from a 635 based off the engine number.
    I've hopefully managed to paste an image of the blue module below.
    Capture.JPG

    That aside, I took my Dad for a run yesterday afternoon and its still an epic ride, even if its not quite spot on yet. We went up to Bentham from Burnley, which gave us view of the Lake District fells, Morecambe Bay and Ingleborough before we headed home.
    Capture2.JPG
    Original builder of SWB Cabrio chassis no. 04-33 reg. no. CRN540Y - had a 2.8L Cologne V6 when I sold it in 2011
    Briefly owned Marlin Berlinetta Q670XBB for about 4 months in 2012
    Did own SWB Marian 1800TC Roadster Q741LPP - modified for trials by Fourtune Engineering
    Now own Marlin Sportster with 3.5L BMW straight six powerplant P764DOD - proof that absolute power corrupts absolutely!
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  2. #2 Re: Sportster electronic ignition 
    frequent forum contributor Club Member
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    38
    A bit of an update.

    GEMS replied that they'd never heard of the unit, but when I rang Lumenition I spoke to someone who seemed very familiar with this particular installation. He reckoned that a great deal of effort went into setting up the system, which also incorporates a throttle position sensor and a crank angle sensor, and it was very unlikely the timing would move unless a component was deteriorating. Lumenition no longer make this, or anything like it, but they can provide software support, but it runs on 1990's verisons of Windows.

    Now I am a mechanical engineer by training and education, and I'm always ready to blame electrics and electronics first, but I decided in this case it was also worth checking fuelling. I am an absoulte beginner on Weber DCOE's, and to be honest have always felt a bit daunted by their complexity, so I bought Des Hamill's book on Weber and Dellorto sidedraft carbs. After spending an hour on Wednesday trying to adjust idle mixture, it was apparent I probably had idle jets that were way too weak. So I pulled all 6 and found I had two different sizes, but both were well on the weak size in terms of recommendations for jet versus cylinder capacity. Further on-line checking tended to confirm that. I then pulled the main jets, air correctors and accelerator pump jets. and found all tended to be well on the weak side of recommendation.

    My car was sold to me as a 3.3litre engine, but checking actual engine numbers makes me suspect its a 3.5litre unit, possibly from a shark nose 635csi. I couldn't find much in the way of jetting recommendations for a 635 engine on triple Webers, but I could find a complete list of jets etc. for a 3.4litre Jaguar straight six - close enough in capacity for a first attempt. So at 22:00 on Wednesday I ordered £80 (including next day delivery) worth of bits on-line from Webcon - jets for idles, mains, accelerator pumps and air correctors. I want to use the car on a drive to Tan Hill Inn tomorrow, but thanks to Webcon's excellent service everything arrived ready for me to fit when I got home from work today. After a quick test drive, the car seems transformed. There is only very slight, very occasional spitting back, and the acceleration flat spot seems to have been greatly reduced if not disappeared completely - I need some open roads to confirm. I haven't had time to bottom idle mixture adjustment or individual carb airflow's yet, but its miles better to drive than it was before today, with all six idle mixture screws just set to 1 1/2 turns from closed.

    I'll report back a bit more after tomorrow's run. I have also ordered a Bentley Publications manual on the BMW E28 5 series , which has the same engine as I suspect I've got, so I will be checking the timing when it arrives, but at the moment I think my original diagnosis of the timing being out was probably wrong.
    Original builder of SWB Cabrio chassis no. 04-33 reg. no. CRN540Y - had a 2.8L Cologne V6 when I sold it in 2011
    Briefly owned Marlin Berlinetta Q670XBB for about 4 months in 2012
    Did own SWB Marian 1800TC Roadster Q741LPP - modified for trials by Fourtune Engineering
    Now own Marlin Sportster with 3.5L BMW straight six powerplant P764DOD - proof that absolute power corrupts absolutely!
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  3. #3 Re: Sportster electronic ignition 
    frequent forum contributor Club Member stevepritch's Avatar
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    Sep 2017
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    Tamworth Staffs.
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    Its really interesting to read the whys and where fores of others. thanks for the story so far.
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  4. #4 Re: Sportster electronic ignition 
    frequent forum contributor Club Member greyV8pete's Avatar
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    Nov 2011
    Location
    Exeter
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    Re the spitting back on acceleration I would try a richer accelerator pump jet. As the rest were on the weak side I would suspect this is too. Worth a try anyway and a quick cheap fix. Pete.
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