79' CM400t RPM Jump after warming.
Results 1 to 3 of 3
  1. #1
    Junior Member greven909's Avatar
    Join Date
    Jun 2018

    79' CM400t RPM Jump after warming.

    Hey all, my 79' cm400t has a new issue this spring. It starts up and idles nicely(1200rpm), after 4-5 minutes it will begin to make some growl/rumble sounds like its going to backfire, then rpm jump to 4k and sit there.

    I've checked for vacuum leaks and haven't found anything. I will be doing a leakdown test this afternoon and see if I learn anything. I am running pods with 95 mains and 125 secondary. Any thoughts?

  2. #2
    Member ckemps's Avatar
    Join Date
    Jun 2018
    im having the same problem only for my right cylinder. although, once it starts, the right side won't rev immediately and then starts to backfire.
    Did you figure out what your problem was?

  3. #3
    Senior Member Chippe's Avatar
    Join Date
    Apr 2017
    Stockholm Sweden
    I have the same engine and carbs (VB21/31) With UNI pods I couldn't get stable RPM without stacks. https://www.hondatwins.net/forums/63...tml#post189348
    I made mine out of a pvc pipe.

    How many turns out on the idle mixture screw are you?
    Last edited by Chippe; 07-27-2019 at 04:14 AM.
    Honda CM400 1979

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

Similar Threads

  1. CB200 Runs Rough After Warming Up
    By bigjako in forum Fuel Supply and Carburation
    Replies: 4
    Last Post: 03-12-2014, 12:28 PM
  2. Possible for timing to jump???
    By winterwolf in forum Engine Discussion
    Replies: 40
    Last Post: 07-10-2012, 01:46 PM
  3. cb350 revs to 5000rpm and sticks there after warming up
    By Crankybilly in forum Fuel Supply and Carburation
    Replies: 19
    Last Post: 02-03-2011, 05:22 PM
  4. cb450 good idle, then revs jump when put into first.
    By ianwejchert in forum Miscellaneous Discussion
    Replies: 7
    Last Post: 10-18-2010, 09:53 PM
  5. Global Warming??
    By tbpmusic in forum Off Topic
    Replies: 12
    Last Post: 01-14-2010, 06:00 AM