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Thread: She runs!

  1. #1
    Join Date
    23.11.2018
    Location
    Gibsons, BC, Canada
    Ducati models
    81 MHR
    Posts
    15

    Default She runs!

    Hi folks: 81 MHR update: last Saturday I completed the important stuff, put gas in the tank and she fired up on the fourth or fifth kick; a little lumpy and I could not get her to calm down below 2000rpm so I still have some carb tweaking to do. I've started her up a few more times but didn't get much better with tick over so I just ordered vacuum gauges. Meanwhile, the first coat of green paint is drying on my fairing. Getting closer....



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  3. #2
    Join Date
    19.12.2005
    Location
    Forfar, Angus
    Ducati models
    Supersport 939, 907ie
    Other bikes
    Pantah 500SL, Scrambler Classic
    Posts
    8,708
    Good stuff. That bike is looking really good.

    You are having more success than I've been having.
    I'm currently re-commissioning an MHR900 that hasn't been run for 7 or 8 years. The valve clearances have been checked, they're not spot on but not a mile out. New plugs. The float bowls removed and the jets checked to be clear. The idle mixture screws are at an initial position of 3 turns out.
    From cold I can get the thing to start and it will rev on the throttle no bother. I've been trying to keep it running for couple of minutes holding it on the throttle but then it spits and pops and cuts out, just like it ran out of fuel. There is a gallon of fresh fuel in the tank and the taps are turned to reserve.
    Normally I would keep it running for 2 or 3 minutes then screw up the throttle stops for a fast idle, adjust the idle mixture screws for maximum idle speed, back off the throttle stops to bring the idle speed down to around 1200 rpm, tweak the idle mixture screws again then finally set the idle speed but I can't keep this bike running long enough to do anything.

    I can usually sort most problems out but this one is proving rather difficult so I'm hoping that some of you bevel owners might have some ideas.

    Old enough to know better, young enough not to care

  4. #3
    Join Date
    01.04.2008
    Location
    Dundee & middle of the N. Sea
    Ducati models
    Troy Bayliss 1098 & 900SL
    Other bikes
    Suzuki GS1000S
    Posts
    4,278
    That's a bonnie bike
    Scott C

  5. #4
    Join Date
    23.11.2018
    Location
    Gibsons, BC, Canada
    Ducati models
    81 MHR
    Posts
    15
    Hi Derek: I've been reading a lot! As my bike had been off the road for so long, I stripped and rebuilt the carbs; just cleaning, new O rings and washers. I very carefully examined all the parts for wear, particularly the needles; all looked really good. I also shimmed the heads as everything was tight. This was a lot of fun. I cleaned the pistons and heads, repaired some wiring, put LEDs in my console lamps, rebuilt the brake calipers and master cylinders, put new oil in the forks and a bunch of other little things.

    It started up on the 4th or 5th kick; I started with the mixtures screws out 2 turns each and with the throttle stops just touching the slides. I held the throttle open at around 2000-2500rpm to warm the engine and then started screwing in the throttle stops equally on each carb until the bike was idling at 2100rpm by itself. One cylinder sounded OK the other was lumpy. I tried to correct things by small adjustments of the mixture screws but failed to get the bike happy at a lower idle speed.

    The next day, I swapped the slides over (following more reading) so that the throttle stop screws had virgin slide slopes to work with. With everything as the day before, I tried again but still couldn't find a happy spot. Two more attempts later, I ordered vacuum gauges; waiting for them to arrive.

    I've since got hold of a chapter of a book on Ducati carb tuning tips; tells me that the big 40mm Dellortos should be set to idle at 1400 to 1500rpm as lower speeds will result in plug fouling from running too rich. Send me your email address and I'll forward the document to you.

    I'm running on original Bosch ignition equipment; my little trigger wires all seemed fine and circuit testing indicated there were no breaks; it's definitely firing on two cylinders but lumpy. My old 860GT with 32mm Dellortos was easy to set up compared to this one.

    8 years is a long time for your carbs not to have been cleaned; the ports and jets are tiny. I'd strongly suggest buying rebuild kits and completely stripping them, clean everything and rebuild. It's an easy and very quick job. The slowest part is leaving the brass bits in carb cleaner for a few hours. If you need any help with this just ask.
    Last edited by 81mhr900ss; 26.04.2019 at 05:27 PM.

  6. #5
    Join Date
    19.12.2005
    Location
    Forfar, Angus
    Ducati models
    Supersport 939, 907ie
    Other bikes
    Pantah 500SL, Scrambler Classic
    Posts
    8,708
    Thanks for your offer but I think I'm fairly familiar up Dellorto carbs, having owned 2 bevels previously, recently having rebuilt a 500 Pantah (PHF36 carbs) and having worked on quite a few bevel Ducatis in the last 40 odd years.
    I can get the bike to run on 2 cylinders but can't get it to keep running. I'm fairly certain that the problem lies with the in-tank filters fitted to the fuel taps. The engine is using fuel quicker than the the taps are flowing it. I will be checking them out today and could kick myself for not checking them before putting fuel in the tank. It would have been much easier.

    Old enough to know better, young enough not to care

  7. #6
    Join Date
    14.06.2014
    Location
    Essex
    Ducati models
    900S2
    Posts
    142
    Hi Derek,

    It does sound like blocked taps. I had my 900 stop on me one day, just like I'd run out of fuel. I eventually traced the problem to blocked filters on the taps inside the tank, blocked by a mass of paint flakes.

    81mhr900ss,

    If you set your idle at 1500 RPM it will ruin the gearchange. I find that if mine idles at anything over 1000 RPM, the gearchange gets progressively notchier, as the revs are not dropping enough to allow the dogs to slide in and out easily. I have never fouled a plug due to slow tick over.

  8. #7
    Join Date
    19.12.2005
    Location
    Forfar, Angus
    Ducati models
    Supersport 939, 907ie
    Other bikes
    Pantah 500SL, Scrambler Classic
    Posts
    8,708
    Problem solved. There just wasn't enough fuel in the tank!
    I set about draining the tank to check the taps and drained both sides until no more would come out and got maybe about a litre or two. I had thought there was about a gallon it (I didn't put it in myself). But when I unscrewed the taps from the tank, particularly the one for the rear cylinder about another litre or so came out. The taps were perfectly clear. So it seems that the tank needs a good head above the bottom of the tank to get a good flow of petrol.
    I put it back together and this time made sure it had plenty of fuel, started it and it kept running fine. I now have the idle screws set at just over 2 turns out and the idle set for 1200 rpm, although according to you guys I might be best to increase that a little.

    Old enough to know better, young enough not to care

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  10. #8
    Join Date
    23.11.2018
    Location
    Gibsons, BC, Canada
    Ducati models
    81 MHR
    Posts
    15
    Good news Derek: I just got back from work-related travels and discovered my new SynchPro vacuum gauges in my mail box so tomorrow I try again. On another forum, it has been suggested that my issue is more likely to be electrical so harder to trouble shoot. I'll try setting up the carbs with my new toy first and if this doesn't work, it's going to be swapping electrical components around to work out what's going on. I have a spare Bosch unit; I may start there. I checked the pick-ups, coils and resistors when they were off the bike and then tested everything when it was back together and was getting two strong sparks.

    I also had another Ducati long ago; a 74 860GT. It taught me how to change valve guides, lap valves, set-up a conventional, non-Desmo head, replace and shim camshaft bevel gears and take a whole motor apart and put it together again to replace the gear box. All great fun, especially when broke, with no money and working in Dad's little shed. The MHR was put away clean 29 years ago. It had a leaky tank and an electrical gremlin; one of the Bosch Inducers got hot and failed. All I did this time, 29 years later, was head shimming as all the clearances were too tight, repaired the dash lights using LEDs, fixed a few loom spots, rebuilt the brake calipers, master cylinders and the carbs, lots of cleaning, some painting, added the new rear Ohlins skocks, the Keihan exhaust, new tires and today's fix, a new fuse box. Still all great fun. I think I'm going to have to find a project bike now as I have this big hole in my living room.

  11. #9
    Join Date
    23.11.2018
    Location
    Gibsons, BC, Canada
    Ducati models
    81 MHR
    Posts
    15
    Registered and insured at last; only 2.5 months late:




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