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  1. #1

    Default 73 Shovelhead no starting and power after new wiring + carburetor

    Hello,

    I will tell you the complete story. I have a 1973 shovelhead and it have a Mikuni carburetor. Had a fire once, so didn't trust the carburetor (although it ran great) and tried since 2 weeks a S&S super B. After some tuning the performance was great compared to the Mikuni, but starting was a problem.

    Meanwhile I have new wiring installed via this image:
    Click image for larger version. 

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    The S&S still gave starting problems so I switched back to the Mikuni. And now I still have problems, with installed the Mikuni again, it was 1 kick and the engine want to run.. But without power and it fell out after a few seconds. I have a video:
    https://www.youtube.com/watch?v=xw2wHJpQqzA
    As seen in the video I first tried to start using brake cleaner.

    I switched back to the old wiring, and the problems remains.
    I have also a video how it run before the problems, this is with the Mikuni and old wiring:
    https://www.youtube.com/watch?v=dGeSJ5lQmLM

    Tried another plugs (plugs are black) but no difference.

    Has anyone an idea what I should check?
    Last edited by HarmBMW; 01-22-2020 at 2:14 PM.

  2. #2
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    Were the carbs you are using rebuilt? Did you check float level? adequate fuel supply from tank? Could be the pilot jet clogged not letting fuel through for starting. Got some kind of a choke for cold starts? did you check for any intake leaks? clean air filter? That wiring diagram shows points ignition...points set right? condensers good? 12v to coil(s)? all grounds good - clean, tight. coils tested? plug wires checked? plug caps? swapped plugs? got compression? valves set properly? got a manual?

  3. #3

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    Carbs were rebuilt. I installed the S&S Super B again and now the power is back and had it running for a few minutes. So there's some progress.. There is still flames coming out the carburetor and exhausts.

    I'm little bit afraid of starting the Harley, because the carburetor was on fire 2 times.. What could cause the flames/backfire from the carburetor and exhaust? I think intake leak, but manifold has new O rings and clamps.

    Further.. Float level is okay, engine gets gas. Use enrichener/choke for starting. Points is set right.

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    Sounds to me like the ignition timing is off.

    If this bike were in my shop, I would adjust the valves and do a compression test first. If compression was decent, and balanced for the two cylinders, I would set the timing properly.

    If the motor did not run and idle at that point, I would run a jumper lead from battery positive to the hot side of the coil, to eliminate the entire wiring system, and see if the motor ran and idled properly. If so, the problem would have to be in the wiring for the ignition circuit (wires, switches, breakers).

    Jim

  5. #5

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    Quote Originally Posted by JBinNC View Post
    Sounds to me like the ignition timing is off.

    If this bike were in my shop, I would adjust the valves and do a compression test first. If compression was decent, and balanced for the two cylinders, I would set the timing properly.

    If the motor did not run and idle at that point, I would run a jumper lead from battery positive to the hot side of the coil, to eliminate the entire wiring system, and see if the motor ran and idled properly. If so, the problem would have to be in the wiring for the ignition circuit (wires, switches, breakers).

    Jim
    Very sound advice, it is where i would start also if it was in my shop.

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    Guessin' you've seen this thread for timing;

    Thread: 76 Shovelhead timing question
    http://www.chopcult.com/forum/showthread.php?t=52986

  7. #7

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    Thanks for the information. Just had a quick view on the points, which were .018”. will do a full test including timing when got some time. Bought a compression tester. So you’ll hear from me soon.

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    Quote Originally Posted by HarmBMW View Post

    What could cause the flames/backfire from the carburetor...
    Stupid noobie question - Isn't there a mechanical advance system in there, and if it were worn or stuck.. Couldn't that cause flame out the carb?

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    Trinortchopz mentions checking for intake leaks. You mentioned new gaskets and seals but did you check for leak by spraying brake clean or something around the manifold while engine running? Or are you just assuming it's tight?

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    Quote Originally Posted by TriNortchopz View Post
    Were the carbs you are using rebuilt? Did you check float level? adequate fuel supply from tank? Could be the pilot jet clogged not letting fuel through for starting. Got some kind of a choke for cold starts? did you check for any intake leaks? clean air filter? That wiring diagram shows points ignition...points set right? condensers good? 12v to coil(s)? all grounds good - clean, tight. coils tested? plug wires checked? plug caps? swapped plugs? got compression? valves set properly? got a manual?
    That pretty much covers it all...............

    If you did and checked all of the above it should be running like a charm............

    If it's still running crappy go back and read what Tri said again and again............

  11. #11

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    Past weekend I have checked the points again and set the timing. First kick and he starts, no backfire out of the exhaust or carburetor. So that would be great.. I never did an adjustment on a ignition, it was the first time, also this video helped me https://www.youtube.com/watch?v=tGR2skLM4e8.

    I did the adjustment with the TDC mark at the location as seen in the attached photo. Is that correct? (Sorry, can't get photo rotated).
    Click image for larger version. 

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    If you do the static timing that way, that's only half the job. The book says second step is to set advanced timing with a timing light. So you are halfway there.

    You can also set advanced timing with a static method. Whatever you choose, it's the ADVANCED TIMING that is important to get right.

    Jim

  13. #13

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    I did the points and the backing plate of the points. Via http://www.vtwinmfg.com/Instructions/16/16-0161.pdf but without an ACU-TIMER. So this means I'm done?

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    The point or use of the AccuTimer is to hold the advance unit in its full advance position so that the advance timing can be set. You can do the same thing by turning the point cam to its full advance stop and adjusting the timing plate until the points just break when the advance unit hits its stop. I use some small 90 degree lock ring pliers for this purpose as they are thin enough to get in past the condenser and grab the point cam. You can also remove the condenser for a little more room.

    The point is, the advance timing setting is the one you want to get right.

    Jim

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    Static timing gets you into the park, dynamic timing puts you on home base ...

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