Benelli 900 Sei ignition timing and carbs
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Thread: Benelli 900 Sei ignition timing and carbs

  1. #1
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    Benelli 900 Sei ignition timing and carbs

    Hi

    I have a 1983 Sei with only 6000 miles on the clock. It ran OK but the plug leads disintegrated and the choke lever does not stay in the up position when you try to start the bike, so I've decided to do a number of mods to get my Sei on the road for this summer.

    I have replaced the coils, leads and plugs supplied by Selwyn and fitted an excellent Motobatt battery. I'm sure I've connected everything right and there is spark at the plugs but the bike now won't fire at all.

    I noticed there is no smell of fuel on the plugs. It could be that the carbs need overhauling. I could send them to JRS in Swansea but I have been told that a good performance mod is to fit Moto Guzzi V65 carbs with a Kawasaki 1 into 3 throttle cable which would not cost a lot more than a carb overhaul. Would like to know if anybody has experience with this carb set up. It would also mean I could ditch the existing airbox and filter set up. My only worry would be setting the 3 into 1 cables and keeping it in tune.

    I have also purchased Sachse electronic ignition which will hopefully sort out the annoying 'surging' when pootling along at 30mph which I have noticed happens on my other Sei (I presume it will be the same on this one). I haven't fitted it yet but would like to know how to find top dead centre.

    Summer is nearly here nad I'm desperate to get the beast on the road!

    Any advice greatly received!

  2. #2
    Senior Member R Powell's Avatar
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    Richard Powell
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    Hi Shaun,
    I think the carbs are clogged with modern fuel, to get my SEI going after a long lay up i do the following;
    1) take all 3 float bowls off this can be done with the carbs still on the bike.
    2) remove the choke, main and slow running jets being carbs being careful not to mix them up.
    3) blow the jets out with an air line to clear crystalised petrol from them( dont poke anything through the jets as this will damage them)
    4) reassemble the jets and float bowls.
    5) turn fuel on and check for leaks ( try tapping any carbs that flood to free the float this often works)
    6) try starting with full choke this should do the trick.

    Re the saches ignition to find top dead center you will need a dial guage down cylinder no 1. It is important to set this accurately as mine did not tick over well when i did it a less accurate way.
    Good luck might see you at Mallory Park if you can make it.
    Richard

  3. #3
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    Benelli 900 Sei ignition timing and carbs

    Thanks Richard, I'll take a look at the carbs. If it looks too daunting I know Selwyn can overhaul them for me!

    Do you know where I can get a dial gauge from and how much they are? I've never used one before. I'm more used to timing Triumphs and Nortons which are a bit more agricultural!

    Regards
    Shaun

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    Smile Benelli 900 Sei ignition timing and carbs

    Hi Richard

    Result!

    Took the jets out of the carbs (middle carb a bit tricky) and couldn't even see through the holes. Blasted them clean, refitted and as soon as I hit the starter button it burst into life. Quite made me jump! I can feel the MOT getting closer...

    Thanks for the guidance.

    Shaun

  6. #5
    Senior Member R Powell's Avatar
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    Richard Powell
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    Hi Shuan,
    Glad you got the the bike started the best way to keep a Benelli going is to start it frequently. The small jets block easily with modern fuel if you are not going to use it over winter drain the carbs ! .
    I bought my dial gauge and adaptor from EBAY if you are not sure about connecting the ignition it might be best to go to Selwyn.

  7. #6
    ems-benelliman
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    ENRIQUE MARTINEZ
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    Lloking For The Top Death Center

    Hi:
    The easy way to find the TDC of a SEI engine is fitting an centrifuge advance from Honda CB500-550 Four, including the hexagonal nut 23mm to fix it to the crank and to turn the engine over. Benelli copyed the engine from Honda, and even the trick to fit the TDC for cylinders 1-6, to adapt any electronic ignition. Using an original tool (graduated disc etc) is very complicated and expensive. You can use the 750Sei advance unit or form a Benelli Quattro but they rare to find. An aditional pleasure to ride a "classic" bike is to get the option to made by yourself all these adaptations and maintenance in your bike and to able to repair it under "normal" circonstances.
    Regards from Spain
    Enrique Martinez
    Benelli Club of Spain
    [email protected]

  8. #7
    Senior Member tucandugu's Avatar
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    Tdc

    Quote Originally Posted by shaunboat View Post
    I have also purchased Sachse electronic ignition which will hopefully sort out the annoying 'surging' when pootling along at 30mph which I have noticed happens on my other Sei (I presume it will be the same on this one). I haven't fitted it yet but would like to know how to find top dead centre.

    Any advice greatly received!
    Hi, in the attached pics you can see how to find the TDC. Are from my 750 SEI, when installing the Sachse. You must align exactly the first vertical line close to the "T" with the upper mark. Mine works perfect after doing this with the new ignition system.
    Good luck!.
    Carles.



    Benelli TNT 1130 Sport EVO 2008 - Benelli 750 Sei 1977 - Moto Guzzi 65cc 1957 - Vespa Primavera 125 1977

  9. #8
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    Benelli 900 Sei ignition timing and carbs

    Hi Carles

    You sent me details and a couple of pictures a back in May on how to time the Sachse electronic ignition using the 750 centrifuge unit. I have done this exactly as you said but the bike wouldn't start at first. I then changed around the spark plug leads and it now runs. Is it normal to have to change the leads around or have I done something wrong?

    Also the bike runs a little rough with some noticeable vibration. I did fit S&B filters and larger jets to the carbs, plus I raised the needles. Could the vibration be that the carbs need balancing or might it be that the ignition timing is wrong.

    Thanks for your advice, I'm slowly getting nearer to getting the bike on the road!

    Regards
    Shaun

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