Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: Exhaust Leak Causing Misfire?

  1. #1
    Join Date
    Mar 2008
    Location
    Jacksonville, FL
    Posts
    209

    Default Exhaust Leak Causing Misfire?

    I have a 1940 EL, and noticed that the engine would miss (as best I could tell, only one cylinder), and have gone through the points and plugs and tested the coil. All seem to be fine. In checking things out, I noticed that the exhaust pipe from the front head felt a little loose at the exhaust port, and wondered if that could be causing a miss. Can anyone tell me if that could be the culprit? If so, any suggestions on tighter fit? How about using some sort of gasket sealer around the exhaust pipe? I'm a little leary about doing that with it being so close to the chamber. The exhaust pipe seems to fit up into the exhaust port about 3/8", but has a little wiggle.

    Thanks.

  2. #2
    Join Date
    Mar 2008
    Location
    Jacksonville, FL
    Posts
    209

    Default Exhaust Leak Causing Misfire?

    One more thing causing me to think it might be the exhaust ... It only misses in low-to mid-RPM, and usually when I initially apply throttle. Once it revs up, or when idling, there is no issue. Thanks again.

  3. #3
    Join Date
    Feb 2007
    Location
    Hummelstown, PA
    Posts
    901

    Default

    Typically an exhaust leak like that would cause her to bakfire quite badly when you rolled off the throttle hard. Have you checked for an intake leak? I would also test the coil hot and make sure all wires and mounting bolts were tight, low to mid RPM is usually were the good vibrations are.
    Brian

  4. #4
    Join Date
    Mar 2008
    Location
    Jacksonville, FL
    Posts
    209

    Default

    Thanks, Brian ... I'll check the coil again ... and the intake. Appreciate your input.

  5. #5
    Join Date
    Jun 2001
    Location
    Central Illinois, USA
    Posts
    4,314

    Default

    40 Nuck!

    The best way to test for a vacuum leak is with air pressure and soapy water:
    http://virtualindian.org/11techleaktest.htm

    Good luck!

    ...Cotten

  6. #6
    Join Date
    Mar 2008
    Location
    Jacksonville, FL
    Posts
    209

    Default

    Cotten!

    Thanks for the link ... great info and detail.

  7. #7
    Join Date
    Oct 2005
    Posts
    268

    Default intake leak

    nuck,
    i have a 41 u (for sale!) that was doing the same thing you describe , and some other neat stuff to.i built a intake leak testing device ,as describe by cotten in the virtual indian piece and started testing . i had leaks in places i never would have thought to check!after many hours of fixing all the isms the bike runs great now , i have since checked all my other bikes and repaired those as well .making your own tester is well worth the effort ,especially if your bike isnt a trailer queen and gets ridden good luck in chasing down this gremlin , tom
    1946 chief 1948 chief 1948 wl 1950wl 1941ulwith sidecar 47 chief(in the works)65bsa

  8. #8
    Join Date
    Jan 2008
    Posts
    133

    Default

    All of the above info is good. Make sure you have the correct main nozzle, and I would definitely recommend one of Cotten's floats. If you are running a brass float, or one that is fuel-logged, the air hole in the main nozzle won't kick in at the proper time causing a very rich mixture at low speeds. You can pull the bowl, cork the bottom hole, and connect it to the fuel line to get a wet fuel level. It should be 5/8" below the top of the bowl. Having this right makes a HUGE difference.

    Also, make sure you have the correct tophat washer under the low-speed needle spring. The ID size meters the idle and low speed circuits. If it's missing or way off in size, you can adjust for the idle, but the low speed mixture will still be off. There are at least 3 different ones. I think I'm running a .106" ID.

  9. #9
    Join Date
    Feb 2007
    Location
    Hummelstown, PA
    Posts
    901

    Default

    I was unaware of the different tophats. Where would one find a list of wich carbs used wich one?
    Brian

  10. #10

    Default

    The info about the tophat "washer's" id is interesting...

    I had one on my WLA (M-88)....that I thought was just worn out...I mean the ID was huge..

    Got a NOS one and now it runs good..

    Wish I could remember where I put the old one....I seem to remember that it was not oval from wear....I'll try and find it and measure the ID..

    A list of the possible ID's and applications would be nice.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •