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Vacuum gage reading

Discussion in 'Early CJ5 and CJ6 Tech' started by lynn, Apr 30, 2007.

  1. Apr 30, 2007
    lynn

    lynn Time machine / Early CJ5 HR Rep Staff Member

    Huntingdon PA
    Joined:
    Sep 20, 2002
    Messages:
    3,437
    Well I got the CJ running much better now. Saturday I started it, it ran crappy at first. I warmed it up, then pulled the air cleaner. As I was pondering, I noticed that the choke plate was halfway closed. I checked inside at the knob, it was all the way in... I put a clothespin on the plate to hold it open... and it ran way better!!!
    I must not have set it right after the carb rebuild...

    So I straightened that out yesterday, and it was running mostly alot better. I put the vacuum gage on it at idle. It was bouncing very quickly from 13 to 17. I reved it to 2K, and it steadied. Burnt valve? Sticky lifter?
    I drove it around the block, got a couple backfires out of the exhaust one or twice on acceleration, and a couple times on decel.
    I drove it again, on a bigger loop, where I could really wind it up, hitting about 4K in 2nd a few times, to "blow it out". It seemed to stop the occasional backfiring after that. I ran out of time, I should have put the gage back on and see what it was reading... maybe I blew some carbon off the valves and the vacuum would be steadier... I'll have to check that later this week. I think I'm going to drive it to work a few days later this week... first time since last spring :oops:

    Looks like it will be OK for the Tioga run :)
     
    lynn, Apr 30, 2007
    #1
  2. Apr 30, 2007
    tommy b

    tommy b Member

    Golden, Colorado
    Joined:
    Oct 23, 2005
    Messages:
    341
    Easy test for a burnt valve:

    With the engine idling, Hold a small sheet of paper to the top of the end of the exhaust pipe with your thumb, letting the paper hang down over the end of the pipe like a flapper valve. If you have a burnt valve, every time that cylinder pulls a charge into it on the intake stroke, the paper wil snap against the end of the pipe. This is because with a burnt valve, the vacuum generated by the piston moving downward is transferred through the exhaust pipe (because the exhaust valve is not sealing) and tries to suck the paper back up the pipe. FWIW.

    tommy b
     
    tommy b, Apr 30, 2007
    #2
  3. Apr 30, 2007
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
    Joined:
    Aug 12, 2003
    Messages:
    1,035
    AKCJ, Apr 30, 2007
    #3
  4. Apr 30, 2007
    sparky

    sparky Sandgroper Staff Member Founder

    Perth, WA
    Joined:
    Sep 20, 2002
    Messages:
    9,221
    What an awesome page, thanks for the link!

    My plug gaps must be too close. :oops:

    Never could figure out why I had a tiny flutter, that's probably it, it's 1" at most.
     
    sparky, Apr 30, 2007
    #4
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