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900ss Carb Vs Ie Engines

Discussion in 'Supersport (1974-2007)' started by Welshlamb, Jun 13, 2019.

  1. Hi , What exactly are the differences between these two engines mechanically?

    Things I'm aware of are the cams and I can see no external oil feed lines from crankcase to cyl. (how does ie allow for cooling then?) Also I believe internal gear ratios are different (2:1 on carby and 1.84:1 on the ie)) ...resulting in a 15/37 final drive on carby and 14.40 on the ie.

    But are heads and valves the same? what parts are interchangeable. Swinging arm pivot wider acroos cases? I've got a cosmetically tired '93 ss engine (probably with the 'fragile head studs?) and looking at rebuild and tune up (head work and 39mm FCRs) but have also picked up a 16k miles, 2002 ie engine . (engine and donor bike below)

    Donor 900ss ie engine 2.jpg donor ss900.jpg Just wondering whether to rebuild or just swap.

    Your collective wisdom and experience please!
    #1 Welshlamb, Jun 13, 2019
    Last edited: Jun 13, 2019
  2. I have both a tuned Carby and an ie, with a third bike being built, with an ie bottom emd and carby heads!....(long story)

    I have not been into the ie engine, but from what I understand the camshafts are different, providing 2mm or so extra lift so the valves may be different length wise. A lot is the same, charging system, and barrels, with their internal oil ways, being 2 obvious exceptions I can think of. The ie cams are a halfway house between the carb cams and the ST cams I recently got to drop into my carby.

    So to your question. The ie engine revs higher and gives more top end. I find its also a smoother motor. I have K and N, Open airbox, Arrow exhausts and a Power Commander on mine.

    My carby is more modified, with lightened flywheel, total aftermarket ignition, FCR41s, full Sil Motor exhaust system and lightweight wheels, along with a few other mods. Its a great bike and my favourite. So if you are willing to spend plenty money on the carb motor, I would say strip it and modify it as much as you want. I cant stop myself and planning 944 HC pistons, ST2 barrels and cams along with a Hall effect ignition pickup systems, with new faster charging coils to replace my CA Cycleworks ones.

    If you just want a smoother more refined motor, stick the ie one in along with the Ignition system. Its been done before.

    I love the rawness of the carb motor, but also like the ie moter, just not as much.

    Hope this helps
  3. whatever I do it will be a carby engine so if it fits the frame I would likely go with the ie engine. On the other hand I hate to change engines unless I really have to and if (the carby) motor is being rebuilt then it retains the originality externally . Sounds like cases , barrels, gears etc are all ie specific so either need to change the whole motor or just pick whetever parts suit. I may just swap the heads/cam for my rebuilt /tuned engines (need the ST/ie cams and short manifolds to get the benefit from the FCRs) and the put the standard head's ? cams on the ie engine and make that into a Carby MK2?
  4. Are you getting split FCRs? I have banked ones
  5. At the moment I’ve got the banked but I’d like go to split carbs. Problem is finding either a single horizontal / side fraught or a split pair at an affordable price ( new set splits from Allen’s is over £1700)
  6. I believe, dont quote me here, that you can split the banked ones. Yiu will beed extra cables and I am not sure how the fast idle screw would be attached to the second one. I remeber reading something about this before I got my carbs.
  7. Yes but also need cable pulley etc. Main issue is the need for correct inlet stubs to get float chamber angle within specs. There is a specific ‘horizontal/ side fraught) carb for the vertical cylinder, both carbs in the banked set are downdraught
  8. Ah, yes I remember now, its not quite as starightforward as I first thought. Youve looked into this more than I have
  9. Maybe but I still havent found an answer!:confused:
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