749s- Bogging Down,misfiring,single Cylinder Firing

Discussion in 'Technical Help' started by Skye Hook, Jun 23, 2024.

  1. Hello All.
    I have another thread on my 'ebay Mistake' project that I am doing up bit by bit, done around 600 miles since I have had her and no problems, until now. dundunduuunnn!

    Some brief history may help. The bike has 8000 miles but was stored outside foir ten years at least, sun damage, rust, a little tatty as you would expect.
    almost no paperwork but belts and oil filters etc done prior to buying it, with notes to say the tank was full of rust.
    It was cleaned according to the invoice, spark plugs looked OK, injectors were freezing, cleaned and flushed. fuel pump assembly rotten.
    new fuel pump fitted
    new fuel filter fitted.

    started Ok today anbd a big pop on acceleration, switching in between one and two cylinders, lurching when both kick in.
    under speed it smooths out but opening right up bogs down onto one again.
    wont handle slow around town at all of course and stalls at stops.
    fuel smell, no overheating.

    So thinking maybe some shite still in the tank (they fitted Flow liner/bio rust whatever that is)?
    injectors going bad again?

    will start to pull the fairings off and hum and hah a bit but any advice or sequence of tests would be appreciated. feels like a block intermittent as it runs lovely when on both cylinders. IMG_1138.JPG
     
  2. On my 999 it started as sometimes cutting out on tick over, to increasingly cutting out at the lights. Then running on one at low speed (having to rev to get firing on both again) to only firing on one. The front coil had failed. Replaced it and it was perfect again.
     
    • Like Like x 1
  3. Your description sounds like intermittent fuel supply or intermittent spark. As you say you can smell fuel, as in unburnt petrol I’d look at a possible spark issue.
     
    • Like Like x 2
  4. ..could be so many things after standing so long but in light of work you've already done then (as said) front/horizontal cylinder coil pack could be the culprit, both might need looking at but front usually plays up first because of water etc ingress during travel.
     
    • Like Like x 2
  5. nice one Chris, will look at that,will try and locate the coils. IMG_1196.JPG just found this split in the tank breather too
     
  6. Finding it impossible to get coils. BERU have stopped making them and even their aftermarket version.Scoured the internet.Anyone have any or know a man who knows a man?
     
  7. Do not forget the dreaded injector/coil/pump relay. It is a 3 quid part that causes all sorts of problems.
    EBay is good for sourcing coils (consider other marques who use the same ones).
     
    • Like Like x 2
  8. I got mine from Ducati Coventry a couple of years ago.
    38010143A Ignition Coil £155.58 - obviously Ducati prices.
    Worth trying them if you haven't. They supplied me with a new subframe about £200 less than anyone else.
     
    #8 Wasted Time Lord, Jun 24, 2024
    Last edited: Jun 24, 2024
    • Like Like x 1
  9. Yes. Still available from the dealers.
     
    • Like Like x 1
  10. OK. Both plugs still sparking fine, so coils are good.
    took the tank off and despite the service notes saying it had been treated for rust it was FULL of shite, literally a sluice of rust swirling around, first fuel taken off was opaque coloiur with rust particles, not see through.
    cleaned the tank out best i can.
    noticed that the cap was popped off the top of this Also the wire was disconnected from Pic 3
    and that the wire was disconnected from pic 2
    pic 1 shows that part loose as the retaining rings were swilling around in the tank (pictures at the side of the part)
    so whatever that spring caop part is,it was bobbing around with the top half off.
    large O ring was damaged and glued back at a break, got a new one coming and a new fuel filter just in case IMG_1202.JPG

    also to note water on the rear cyclinder coil, wet on the plug. IMG_1199.JPG

    IMG_1198.JPG
     
    • Like Like x 2
  11. that 'spring part' i think is called a Thermistor, does anyone know what those thin retaining discs are called? I managed to push one back over the two pins that the thermistor sits on but could do with a second one to secure it properly
     
  12. it's a fuel pressure regulator Skyhook, they are simple and reliable generally, although i've never tested one for accuracy/consistency myself. I wouldn't rule out the coils immediately as could be intermittent. If you find that one cylinder is breaking down/not firing with regularity then you can swap coils to maybe confirm this, although both second-hand coils misbehaving cannot be ruled out 100%!

    It's safer to replace the submerged fuel hoses while you are working on the tank contents, as splits and bulges to the pipes are common particularly after time, and will cause fuel pressure loss and inconsistency which can result in rough running/might only just about idle and will have an inability to get engine to rev to higher rpm.
     
    #12 Chris, Jun 26, 2024
    Last edited: Jun 26, 2024
    • Like Like x 1
  13. As Chris says. That's my point about how it started just sometimes stalling on tick over, then at the lights (which I could have put better, being from the start of a ride when maybe it wasn't warmed up to miles into a ride when it obviously was), progressing to cutting out intermittently at town speeds, at which point I could still hypothesize that the plugs were fouling and running at high speed could clear them up. When I ultimately tested the coils the forward one read complete earth, but it can't have done so earlier when it still ran on both most of the time.
     

  14. thanks again Chris, no problem at smooth mid rev range, maybe a bit of popping but 6000rpm or so is good, but throttling off it gets bogged again.Anyways, I have a sopare coil coming in the post, tank o ring,plugs and fuel filter. will change everything I can and see how that is. the water on the body of the rear cylinder coil baffles me, I gave it a 10 mile run running rough, so maybe thgere was a whole plug hole full of water.
     
  15. excuse the ignorance, but how do you read the coils and what is complete earth?I have a multimeter but no skill set there at all.
     
  16. Push-on washers
     
  17. This is from the manual. Ironically I finally threw away the old coil a couple of weeks ago so don't have one to look at right now (I don't keep the bikes here).
    By complete earth I mean no resistance.
    When I measured mine the good one didn't read the given figure - perhaps because my meter is so old, perhaps because the battery was old, or perhaps in the decades since I'd used it I forgot some detail, but the bad one was so different it was obvious. Meanwhile the original coil was superceded - whatever, anyway once the obvious bad one was replaced, the ignition performed perfectly thereafter.
    Anyway set the multimeter to the milliOhm position and you should see what to connect to (as I recall it's two male spade connectors).
    It's a bugger getting to the horizontal pot (with the wheel in).


    The coil used on this model is called
    "cigar-shaped coil".
    This coil looks like a spark plug cap
    and, besides serving as a spark plug
    it converts the low voltage coming
    from the control unit into high voltage
    for spark plugs.
    To check this component, proceed
    follows:
    Measure the resistance between the
    two PINS (1-15).
    The resistance should be 650
    mΩ±50. If the value is outside the
    specified limits, change the coil.
     
    • Like Like x 1

  18. DONE. after pulling the tank and fuel systemm to bits i now at least have a cleanish tank. REAR COIL was the issue, replaced and running better than before, shitty fuel gone, all is well with the World.
    THANK YOU all for your wisdom and help, I am sure it will not be the last time.
    actually I remember going through something very similar on my 748 a few years back and Chris ended up helping out with a new ECU which fixed it proper job.
    Just another wee question, where to get the male fittings for quick release fuel connectors? female part is no prob, is it OK to switch out the existing L shaped pipes from the tank base?
     
    • Like Like x 1
  19. The people selling the exact timing belts are advertising connectors on their website
     
Do Not Sell My Personal Information