New Rider with a problem
Page 1 of 2 1 2 LastLast
Results 1 to 10 of 15
Like Tree4Likes

Thread: New Rider with a problem

  1. #1
    Member fender_fella's Avatar
    Join Date
    Dec 2016
    Posts
    43

    New Rider with a problem

    What a way to introduce myself! I'm a brand new rider and I have a 1980 Honda CM400A. I've had it about 2 weeks and it ran great at first but now it won't even idle, there's no acceleration and as I put along in 1st gear, all of a sudden it will backfire and rev up to super high RPM's , to where I have to just kill the engine or it may blow up.

    So Hello everybody, and what the heck is going on with my bike LOL!?

  2. #2
    Senior Member phil71's Avatar
    Join Date
    Aug 2013
    Location
    Brooklyn, new york
    Posts
    1,120
    Welcome ! for one reason or another, one cylinder isn't firing all the time. It could be a dirty carb, or some other fuel supply issue. Next time it starts running crappy, remove the spark plug wire while running. Then the other. One will likely have no effect, the other stalls the bike. Once you've identified the ineffective cylinder, remove the spark plug, and report here with the color , or even a picture if you can.
    It's also pretty cheap to just try a new spark plug. If that solves the problem, it wont solve it for long. But at least you'll be moving towards finding the actual issue.
    bilbikek411 likes this.

  3. #3
    Member fender_fella's Avatar
    Join Date
    Dec 2016
    Posts
    43
    Thank you Phil71! That doesn't sound too major. I'll run it and test it tomorrow and report back. I have a feeling I know which one it will be. I took the right spark plug wire off to see what plugs were there. I replaced it but then this started happening. I've already ordered new spark plugs and spark plug wrenches too.

  4. Remove Advertisements
    HondaTwins.net
    Advertisements
     

  5. #4
    Super Moderator J-T's Avatar
    Join Date
    Jun 2009
    Location
    Lennox, South Dakota
    Posts
    7,356
    Problem: The SOHC bikes have to have both spark plug wires connected for either to fire. Disconnecting either should kill the engine.

    Your runaway rpm sounds like a fuel supply or vacuum problem.
    JT
    81 CM400T Under re-construction
    82 GL500

  6. #5
    Senior Member phil71's Avatar
    Join Date
    Aug 2013
    Location
    Brooklyn, new york
    Posts
    1,120
    can't you dummy plug it, let an extra spark plug rest to ground?

  7. #6
    Super Moderator J-T's Avatar
    Join Date
    Jun 2009
    Location
    Lennox, South Dakota
    Posts
    7,356
    Yes, that would be a way to identify an ignition problem.
    JT
    81 CM400T Under re-construction
    82 GL500

  8. #7
    Member fender_fella's Avatar
    Join Date
    Dec 2016
    Posts
    43
    Thank you both. I am still waiting for my spark plug wrenches to be delivered so I guess I can't remove a plug right now. Fingers crossed that new spark plugs will help.
    By the way - since this IS my introduction to the forum, I'm in Texas and I'm really eager to get some rides under my belt.

    Thanks again.

  9. #8
    Senior Member dtsmjr8dan's Avatar
    Join Date
    Oct 2011
    Location
    Windsor, Ontario, Canada
    Posts
    8,226
    Welcome to the forum. Great to see another 400 series here. Here's some good reading for you...Basic Checklist for that New to You old Bike
    Do you have a proper Factory Service Manual? You need an 18mm deep socket for the spark plugs.
    1979 CM400T (rider),
    1981 CM400T (in surgery receiving transplant)
    1982 CM450 (parts bike)
    1982 CB450 (parts bike)
    Past rides: Vincents, Triumph, BSA's, Suzuki's, Twingle, Corgy, others.
    Remember, today is the tomorrow we worried about yesterday.
    My chest fell, but, fortunately, my belt caught it.
    I don't know everything, nor, have I met the one who does.

    T-shirt sales supporting 66Sprint's LSR Build http://www.hondatwins.net/forums/22-...d-attempt.html

  10. #9
    Member fender_fella's Avatar
    Join Date
    Dec 2016
    Posts
    43
    Thank you dtsmjr8dan. That's a great resource, it may take me some time to get through that. I found a service manual online but the idea of taking apart carbs is pretty daunting to me and not sure how much I can do with it. I am starting with spark plug information, gaps, etc and going from there. Thanks for the 18mm tip, I looked for that information. I have ordered the Denso 4099 plugs and should be here any day.

    I love my 400A though. My motorcycle teacher would be upset that I don't have to use a clutch LOL. I bought it because it reminded me of an old Trail 90 my dad used to have. Riding that thing was a breeze. I can tell you we never did a lick of maintenance on that thing and it kept going and going. If I only knew then what I know now. It would still be running.

  11. #10
    Senior Member dtsmjr8dan's Avatar
    Join Date
    Oct 2011
    Location
    Windsor, Ontario, Canada
    Posts
    8,226
    Get NGK D8EA plugs.
    ancientdad likes this.
    1979 CM400T (rider),
    1981 CM400T (in surgery receiving transplant)
    1982 CM450 (parts bike)
    1982 CB450 (parts bike)
    Past rides: Vincents, Triumph, BSA's, Suzuki's, Twingle, Corgy, others.
    Remember, today is the tomorrow we worried about yesterday.
    My chest fell, but, fortunately, my belt caught it.
    I don't know everything, nor, have I met the one who does.

    T-shirt sales supporting 66Sprint's LSR Build http://www.hondatwins.net/forums/22-...d-attempt.html

Page 1 of 2 1 2 LastLast

Sponsored Links

Posting Permissions

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