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Author Topic: 75 Z340 serious bog issue  (Read 480 times)

RMK800

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75 Z340 serious bog issue
« on: May 19, 2017, 11:12:02 PM »
I bought this sled that supposedly was raced a number of years ago by the owners and it starts very easy without choke. Running rich and smoking heavy. Cannot even drive the sled. PTO side is noticeably cooler pipe and head temp. Suspected richer on this side than the PTO side. Checked to verify the following were doing their jobs.
Fuel needles...holding air tight at 10 psi now. PTO side originally was leaking at the gaskets but new gaskets and Ultimate gray sealer resolved this.
Enricher plugs were replaced and sufficient slack to assure seal off (verified with Vernier to assure this)
Fuel pumps opened and visually checked and tested. No leaking to the crankcase via pulser lines. All valves perfect and diaphrams not torn or deformed. Ran sled with each pump pulser line off to assure 1 pump can supply fuel to carbs. No issues. Tank clunk check on one was stuck so fixed that.
All internal jets and needles are stock part numbers except high speed jets are 380 instead of factory 400. Should be ok right???
I have had to replace these mid range jets and needles on a 91 EXT special a few years ago as they were actually worn out and the jet ID was larger than new. Same symptoms of running rich. So I dropped the jet needle to the 5 position to see what would happen and the engine did lean out some so it would respond to throttle at least to about half throttle now and then bog out after that. I will replace the needles and jets and see what happens. The thing that is a question about this is that how can a sled with low miles (260 on the gage) assuming the speedo always was working, have worn out jets. Has anyone else had this experience that can comment on this?
78 el Tigre 5000
75 el Tigre 440
75 340 Z
74 el Tigre 295
74 TX 440
79 TX 340

Vintagesleds.com

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    Jeff99

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    Re: 75 Z340 serious bog issue
    « Reply #1 on: May 20, 2017, 06:46:02 AM »
    Does it have spark/good spark on pto side?

    76z

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    Re: 75 Z340 serious bog issue
    « Reply #2 on: May 20, 2017, 07:05:36 PM »
    What was the outside air temp when you were testing this sled. The z free airs like it cold out. Never did get my Z440 running correctly in the warm weather, but get it less than 20 degrees and it would come to life.

    RMK800

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    Re: 75 Z340 serious bog issue
    « Reply #3 on: May 24, 2017, 04:57:58 AM »
    Spark looks good on all 4 plugs. Not missing and spark seems bright (not weak). Air temps are in 50 to 60 F. I have never seen a sled at these temps slobber so much oil, and smoke this much. Skitter fogger quality. No power to move itself. Just bogs. I would at least expect the sled to be able to move. Compression is 150 both sides (factory spec). Will see what happens with new jets and needles.
    78 el Tigre 5000
    75 el Tigre 440
    75 340 Z
    74 el Tigre 295
    74 TX 440
    79 TX 340

    76z

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    Re: 75 Z340 serious bog issue
    « Reply #4 on: May 24, 2017, 12:55:51 PM »
    I tried.

    RMK800

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    Re: 75 Z340 serious bog issue
    « Reply #5 on: May 28, 2017, 04:00:30 AM »
    OK the bog she gone.  :D The Mid range jets were the issue. Installed new jets and needles and walla. No more heavy smoke and good response considering the temps of 20 C (68 F). I have included pics of the jets. The needles were fine when you compared the old to the new. Using a micrometer you can compare the old and new at the same time to see if the old jets are worn. Not detectable but installed new ones anyway. By installing the needles in the old and new jets (removed from the carb) you can see the wear. Also the wear is concentrated at 3 obvious locations and the ID of the old jets is visibly larger. I wonder how many bog issues people are encountering and never consider to change the mid range jets. It seems that the needles are wearing on the jets at least that is my theory as I cannot prove it. 
    « Last Edit: May 28, 2017, 04:02:43 AM by RMK800 »
    78 el Tigre 5000
    75 el Tigre 440
    75 340 Z
    74 el Tigre 295
    74 TX 440
    79 TX 340

    ilikesleds

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    Re: 75 Z340 serious bog issue
    « Reply #6 on: May 28, 2017, 12:19:30 PM »
    Any discernible bends or other deformities on the needles that may have caused the wear in the jet?  Interesting find.  Makes me want to take my carbs apart.
    1973 El Tigre 440 (sold - What was I thinking?)
    1974 Harley 398
    197? Sno-Runner
    1975 Suzuki Fury 440
    1975 El Tigre 440
    1976 El Tigre 5000
    1980 El Tigre 6000
    1981 El Tigre 6000
    1995 ZR580

    73 RATX

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    Re: 75 Z340 serious bog issue
    « Reply #7 on: May 28, 2017, 12:38:06 PM »
    My dad had a Honda Big Red three wheeler that he had since new.  After he had it a number of years it started fouling spark plugs.  Had the same bad part as you.  The engine vibration must wear the needle jet out after many hours of run time.

    RMK800

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    Re: 75 Z340 serious bog issue
    « Reply #8 on: May 28, 2017, 08:02:11 PM »
    Any discernible bends or other deformities on the needles that may have caused the wear in the jet?  Interesting find.  Makes me want to take my carbs apart.
    No bends in the needles. I would say they are perfect compared to the new ones. I have seen this issue in past sleds that was far worse with more noticeable wear. The needles have to be moving around and wearing on the jets. A lot of vibration going on with the carbs mounted to the engine.
    78 el Tigre 5000
    75 el Tigre 440
    75 340 Z
    74 el Tigre 295
    74 TX 440
    79 TX 340