1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Newly Rebuilt Motor Wont Start. 10 common faults?

Discussion in 'Norton Commando Motorcycles (Classic)' started by DonOR, Apr 22, 2019.

  1. baz

    baz VIP MEMBER

    May 26, 2010
    Have you recently fitted the mikuni? If so don't forget the throttle must be shut for the enrichening circuit to work
    concours likes this.
  2. DonOR


    Jul 24, 2009
    Many thanks for the great input.

    I put in a new set of plugs. no go

    Then added a small amount of petrol thru the plug holes, refit plugs, no go.

    so I improvised a leak detector, and, with intake and exhaust valves closed ran 40 psi air into each cylinder.

    the only slight loss of air I could detect is thru the timing side of the camshaft. is that normal?
  3. 1up3down


    Jan 12, 2011
    ok so new plugs was not the solution, how old and when recently charged battery?

    try kicking it with the fuel cap open, possible you have a blocked vent hole

    if all above don't get it going then you might have fuel delivery problem getting
    to the Mikuni, to verify that turn the gas lines on and remove or loosen the very bottom drain bolt of the Mikuni bowl, does gas flow out?
  4. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    Step 1) Pull both plugs. If you are working alone, make a clip lead by attaching an alligator clip at each end of a 2 ft. piece of wire. Attach one alligator clip to the plug electrode, the other to a bare metal surface. Kick the engine over. You should see a spark, usually one per kick. Repeat on other plug. This test proves you are "getting spark" ..... it proves the coils, EI, primary wiring, high tension wiring, battery, and EI trigger are working as expected. It does not prove the plugs are firing under a compressive load, but with new plugs, the plugs would have to be a rare case of new-but-defective if they were not firing.

    Step 2) Check that spark occurs at the proper time. With both plugs removed, crank the engine slowly, either using the kick starter by hand, not foot, or with a long bar and socket applied to the cam nut, oil pump nut, or clutch nut. Look into the LEFT plug hole until you see the left intake valve come into view. If you are using the long bar, be sure the crankshaft of the engine is rotating in the normal run direction. Continue rotating the engine until the intake valve fully opens, and then recedes from view. At this point the engine is near BDC. Continue to slowly rotate the engine, and with a long screwdriver or rod, feel for the engine to reach TDC. This is the proper reference point to set up your timing.

    I am not familiar with the procedure to set up your EI, but follow "the book", and you should get the spark on "time".

    Step 3) Check fuel supply and carburetor.
    If you are getting spark, on time, and the engine fails to start, the problem can be either no or insufficient fuel supply, or TOO MUCH fuel supply, that is, an excessively rich mixture.

    Quick check for no fuel .... do this test with both plugs clean and dry, or after heating as Fast Eddie suggests. Spray a 1 sec burst of starting fluid (ether) into throat of carb (both throats if dual carbs) as others have suggested. If engine starts and runs for 2 - 3 seconds, the test suggests you are not getting fuel into the carb, or into the spray tube of the carb.

    Check for excessively rich mixture .... Kick engine over several times and pull the plugs. If the plugs seem excessively wet, it suggest the mixture may be over rich .... remember excessively rich mixture WILL NOT BURN. Check the pilot circuit of the carb, for proper pilot jet size, and pilot mixture adjust. Try leaning out the pilot mixture.

    Last edited: May 19, 2019
  5. acotrel


    Jun 30, 2012
    If you get a bang out of the exhaust, you might have the plug leads crossed, if they do not fire together. If you have too much fuel, you can drown the plugs. But if that is happening , you probably have a jetting problem. If you have fuel and a moderate amount of fuel in the cylinder, you should at least get a pop when you kick it over. If it fires, but does not keep running, you usually have a jetting problem. Don't try to push start the bike - if it doesn't fire-up with the kick-start, you would be wasting your effort. As I said previously, sometimes spark plugs drop dead if they have not been used for a long time, then some fuel hits them.
    If you've got fuel, compression and a spark, the motor should at least cough once, even if the ignition timing is not precisely right. Try fitting new plugs, you probably need them anyway6.
  6. batrider


    Aug 9, 2008
    First, throw that can of starting fluid away. This will just wash the oil off your cylinder walls.
  7. SteveBorland


    Nov 15, 2010
    I had a similar problem once after the first rebuild of my Norton. No joy at all, rather embarrassing since several of my friends were watching. Eventually realised that I had connected the battery as negative earth...
    Once things had been restored the way God wants Nortons to be, first kick resulted in a satisfying level of noise.

    Keep at it, it's (almost) always something really silly :)
  8. Tornado

    Tornado VIP MEMBER

    Dec 5, 2017
    The Wassell EI is basically a copy of the Boyer as far as setup goes. It has a better made stator being epoxy encapsulated. Btw I have seen a static EI test rig showing how you can trigger firing by simply waving a good magnet next to the pick up. Could be a handy quick check when your leg is worn out.

    Something not mentioned. How is the ignition switch? Many reports of poor contacts there. Coil condition? Kill switch?
  9. o0norton0o

    o0norton0o VIP MEMBER

    Apr 27, 2015
    Almost every person who has answered you is telling you in one way or another to use a simple test to see which way to go in your search. (either fuel or spark)

    Get rid of the ether. Instead get a squirt bottle with an integrated straw. Put some fuel in it, remove the air filter, lift the throttle body with the throttle, give a squirt of fuel. Kick it over with the throttle half way up. If it didn't go "POP" in any way, then most likely your problem is spark... not fuel. (so you are back to checking electrical connections and your ignition system)

    IF the bike did go "POP" when you kicked it, or kick back then you are getting a spark, but probably poorly timed.

    IF the bike started, and ran for a few seconds before dieing, then you're fuel delivery is the likely suspect.

    When you're lost for an answer, you use a simple test to narrow down the possible causes. I use the squirt bottle test on all kinds of engines. If the engine fires up with a squirt, I know I'll be messing with carburation, if it doesn't fire, it's ignition... Simple way to cut the possibilities in half quickly
    baz and dynodave like this.
  10. acotrel


    Jun 30, 2012
    If the problem is fuelled spark plugs, squirting fuel down the carbs will only make it worse. So by doing that, you only remove half the possibilities. He only time my 850 has refused to even fire, it was due to the carbon on the plugs conducting electricity. Both plugs were completely useless. I simply fitted replacements and the bike fired-up immediately.
  11. texasSlick

    texasSlick VIP MEMBER

    Jan 2, 2013
    Do the simple plug electrode ground test! In one go it eliminates every electrical possibility except weak plugs and improper timing.

    If it doesn’t pop on pump fuel, but does on starting fluid, that almost guarantees weak plugs, or possibly a weak coil. Ether is a handy diagnostic tool in a can. Just don’t over do it.

    I am not buying the argument that a 1 sec shot of ether will wash down the cyl walls any more than a similar amount of raw gas. Ether in small quantities flashes into a vapor... vapors cannot wash oil on the cylinder walls.

    Last edited: May 20, 2019
  12. Steves


    Oct 16, 2016
    Maybe have a fire extinguisher to hand.
    o0norton0o likes this.

Share This Page