74 Z50 Stumped

Discussion in 'Tech Area' started by Beretta, Sep 17, 2020.

  1. Beretta

    Beretta Member

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    K-- Boys- Here's the deal !
    Runs perfect without the Air cleaner Rear Housing and Filter.
    Put the Filter and Rear Housing on and it Misses Mid range on up !
    Too Rich -Right ? Plug looks black !
    Next- New Plug- Exchanged Carb off my other Z that runs perfect !
    Exact same Mid to full throttle seems like the choke is on !- Plug Black
    Next- Hoist up on the Bench- Checked the Points gap-- Perfect .014,
    Next- Checked Valve Gap- Perfect .003
    Any Ideas ?? Before I set this on Fire ?
     
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  3. racerx

    racerx Administrator
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    Seems fairly obvious where the problem is...the airbox assembly. Only a question of whether it's the foam element or rear housing. How's it run with the housing assembled, sans foam?
     
  4. Beretta

    Beretta Member

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    I changed Air boxes and Filters- As soon as I put on the rear Cap with out the filter the same symptom mid-range to WO stumbles.
    As soon as I remove the rear Cap it'll go wide open- No Problems.
     
  5. Clayton

    Clayton Active Member

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    I have the EXACT same problem with my K5 (74) Z50, if I use a “sock” filter it runs great but with the factor air box and filter it bogs down. I hope your find the answers because I have been fighting this issue for months now with no luck. Iv posted about this before and will add my links so you can read the replies I received.
     
  6. Beretta

    Beretta Member

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    I'm going to take a different approach and start with the basics-1st is a compression test- New Gauge set will be here today.
    If that test ok- I'm trying a 3rd Carb from My Grandsons Z50 (72) That worked fine on His Tired Old Engine-His is torn down for a full Restore anyhow.
    New Plug
    Check Points again
    Check Valves again
    I'll check back in later today

    Thanks
     
  7. Beretta

    Beretta Member

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    Rich Stumbling with Air Cleaner on !

    Compression Test---150 lbs---Eng warm Throttle full open------- I'm good with that --- Specs call for 170 lbs- must have been at Sea Lever and No Barometer -- That will make a difference to the numbers- 10 to 15 %
    Put the 3rd- Older Carb on with the Air Filter and Housing - Adjusted to Specs- Perfect-- No Stumble at all through full open Throttle. Took it for a test ride and Wow -- Really Runs Nice.

    Carb # 3 has a 55 main Jet
    I need to look into Carb # 2 and Carb # 1 the Aftermarket Carb to confirm Jet size- Maybe Someone upped the Main Jets= Pulling too much fuel.
     
  8. Beretta

    Beretta Member

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    Rich Stumbling with Air Cleaner on ! Conclusion and Observations.
    Carb #2 the Orig Carb has a 55 Jet but No O-Ring for sealing- Also a Minor Clog- Float level looked ok- I suspect it was permitting Fuel up past the non-existent O-Ring - Therefor too Rich
    Carb# 1 the Aftermarket Carb --Main Jet has No number on it- as best I can measure the Hole -looks to be .060 -using different strands of copper wire to measure.
    Well that's it for now--Until the next unfamiliar challenge arises.
    Learning as I go !
     
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