Kitfox Aircraft Stick and Rudder Stein Air Grove Aircraft TCW Technologies Dynon Avionics AeroLED MGL Avionics Leading Edge Airfoils Desser EarthX Batteries Garmin G3X Touch
Page 1 of 2 12 LastLast
Results 1 to 10 of 12

Thread: Carb and gearbox issues.

  1. #1
    Administrator DesertFox4's Avatar
    Join Date
    Aug 2008
    Location
    Arizona
    Posts
    3,562

    Default Carb and gearbox issues.

    Well folks, it's been quite awhile since I last flew my model 4.
    Last day of Feb. 2014 to be exact.
    Today, after all these months, it runs like new again.

    It all started...............way back in Feb. when, on my last flight, the carbs started over-boarding fuel out the overflow tubes on my 912ULS with 875 hours on the meter. Happy it did not catch fire in flight.

    I figured I had a carb acting up so I rebuilt both carbs with kits purchased from our newest forum sponsor, Leading Edge Air Foils. I cleaned as best I could the carbs and installed the "big" rebuild kits that include new needles and diaphragms along with all o-rings and gaskets. You guys know the drill.
    The old diaphragms looked like new by the way but what the hey.

    After reinstalling the carbs it still ran like crap and flooded both carbs spilling fuel out the same little hoses. Now what?

    I considered the age of all my hoses and my motor mount rubber shocks and decided to remove the engine and refresh all hoses and motor mount rubber shocks. Maybe the motor mount is letting it shake too much causing the carbs to flood. Off with the engine. Motor mount rubber shocks ordered from Kitfox Aircraft along with new bushings. New hoses ordered from L.E.A.F. along with more carb parts. Getting to be a large project now. Getting hot by this time in the hangar so I diverted attention away from fixing the model 4 to start building on the Model 7 SS.

    About Oct. I refocused on the model 4. Engine back on. New hoses all bright and shiny. Started it up, gas still flooding out of carbs. No improvement what so ever. Likely not the motor mounts at all but nice to have them all new again.

    Pulled carbs off again. Shipped off to a dear friend who offered to take a look at them and sonically clean both carbs for me and who also installed new o-rings and gaskets just to make sure I didn't miss something in the rebuild that I did earlier. Much appreciated as they came back to me looking brand new and ship shape.

    Installed both carbs and fired up the Rotax. Still shaking the same and flooding out before me and Murle Williams could even get close to syncing the carbs. John McBean explained over the phone how to get a really good mechanical sync done before next start up. I did that. Still ran the same, crappy. Murle did a compression test on all cylinders just in case a valve was stuck or worse. All cylinders checked out like new.

    I called Steve Beatty at AirScrew Performance in Glendale,AZ. Our local Rotax guru and discussed the situation. Should have done this back in March. He saved my bacon back in 2007 when my Rotax developed a gearbox problem and would absolutely not run. In fact it broke my prop. it started so hard one time. He shimmed up the gearbox back then and it solved that problem. Can he do it again this time?

    I told Steve I suspected the gearbox was out of "spec" again but he was less enthusiastic about that then he was back in 2007. He thought it might be a contributing factor but not the biggest factor. He said he thought it was still a carb problem. I decided to try something I was reluctant to try back in 2007 but figured I had nothing to lose. I took the prop off it and started the engine. It ran very smooth and no fuel flooding. Got to be the gearbox. Hurray. Problem solved. Took the gearbox off and took it to Steve. 3 hours later he called and said it was ready to pick up. Can't beat service like that. He found .014 thousands of shims needed is all. Yikes!!! Not near what the 2007 rebuild took. Maybe it's enough to make it work. Steve was still skeptical but hopeful. I installed the gearbox and fired the engine. It ran, not well as both carbs needed to be synced yet but no gas flooding out of the carbs.
    After a few minutes of run time it became quite apparent that something was still off. My egt's were way too low on the right bank of cylinders. I had to hold choke on to keep it running.
    Murle said it was likely that the pilot jet had a blockage on the right carb so we removed it and he took it back to his shop overnight and discovered a bit of varnish blocking the pilot jet.

    Today we reinstalled the right carb, started up the engine and it ran so well I yahoo'ed out loud. Finally it runs like it did 10 months ago. Murle did a slight pneumatic sync as the carbs were almost perfect using John McBeans mechanical sync sequence. I can't wait to get my 3rd class medical scheduled now and get back to flying again.

    A huge thank you to Murle Williams, John McBean, Steve Beatty, Phil Laker for all the assistance getting it fixed. It's great to have such talented folks to call on locally and by phone.
    Also a big thanks to Phil Laker(Desertfox1), Dan Billingsley (Dan B) and E.T. Holm (Desertfox6) for taking me up to "get some air under my butt" as they say while my Kitfox was down. It sure helps the attitude.

    Hope to be posting more flying videos soon also.


    DesertFox4
    Admin.
    7 Super Sport
    912 ULS Tri-gear


  2. #2
    Senior Member Dave S's Avatar
    Join Date
    Oct 2008
    Location
    St Paul, MN
    Posts
    1,833

    Default Re: Carb and gearbox issues.

    DF4,

    This is huge.....you do need to get back to flying! Congratulations on perservering and being kind enough to share your experience with solving your mechanical deals.

    I have to comment on the mechanical sync you described.......I have been reluctant to admit in public that I have never done a pneumatic sync on our 912ULS lest I get reprimanded because "that's not the way Rotax says to do it"......that's right....never done a pneumatic sync....never seen the need for it.

    My experience has been that the engine runs very smoothly with a carefully orchestrated mechanical sync.......which means do it precisely, do it in the right order, recheck your work; and, listen carefully to the engine as the final adjustments are made with the engine running...the engine tells you when it is happy if you listen to it....just my humble opinion.

    Take care & get that bird in the air!

    Sincerely,

    Dave S
    KF 7 Trigear
    912ULS Warp Drive

  3. #3
    KFfan's Avatar
    Join Date
    Oct 2014
    Location
    NE Indiana
    Posts
    142

    Default Re: Carb and gearbox issues.

    It takes a village to raise a child.
    It takes only a community of smart people to repair a Kitfox.
    Lou
    KitFox II
    582

  4. #4
    Administrator DesertFox4's Avatar
    Join Date
    Aug 2008
    Location
    Arizona
    Posts
    3,562

    Default Re: Carb and gearbox issues.

    Thanks Dave & Lou.

    Dave- most times a good mechanical sync will get you very close to perfect. I bought my first Kitfox from a guy in Oklahoma that could mechanically sync the carbs so close it was almost impossible to improve on the settings with a carbmate. Like you he did his by sound only. Works for some folks.
    Murle Williams uses a manifold pressure gauge from a twin engine aircraft. Murle just adjusts the carb cables until both needles on the manifold gauge read the same. Very simple but effective.


    DesertFox4
    Admin.
    7 Super Sport
    912 ULS Tri-gear


  5. #5
    Super Moderator Av8r3400's Avatar
    Join Date
    Jan 2009
    Location
    Merrill, WI
    Posts
    3,044

    Default Re: Carb and gearbox issues.

    Such a familiar story…
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  6. #6
    Senior Member DanB's Avatar
    Join Date
    Jun 2008
    Location
    Mesa, AZ
    Posts
    542

    Default Re: Carb and gearbox issues.

    Congratulations Steve! It's been a long time coming and will be great to have my wingman back. Too many bogies to fight off solo
    Dan B
    Mesa, AZ

  7. #7
    Senior Member
    Join Date
    Dec 2008
    Location
    Garland, Texas
    Posts
    1,476

    Default Re: Carb and gearbox issues.

    It's not all that hard to sync the. I have a Triumph TR6 with a Tripple Carb set up, now that is a challenge. Congrats on getting here airworthy again. I know by now you were suffering severe withdrawal symptoms. I'm already waiting for your next flight video. Have fun & fly safe.
    Paul Zimmermann
    LSRM-A
    Garland, Texas

  8. #8

    Join Date
    Aug 2014
    Location
    Quesnel B.C.
    Posts
    121

    Default Re: Carb and gearbox issues.

    Congrats DF4,
    That was quite the procedure of maladies to solve. Got to love those moments when all that can go wrong will go wrong. Looking forward to seeing your adventures posted here.
    Kurt A

    Kitfox II,
    Rotax 912,
    1100 gross
    Fixer Upper Project

  9. #9
    Senior Member
    Join Date
    Jul 2011
    Location
    milwaukee wi
    Posts
    490

    Default Re: Carb and gearbox issues.

    What is John McB's procedure for the mechanical carb sync? Where can I find it?

  10. #10
    Super Moderator Av8r3400's Avatar
    Join Date
    Jan 2009
    Location
    Merrill, WI
    Posts
    3,044

    Default Re: Carb and gearbox issues.

    Rotax/LEAF procedure for initial idle mechanical sync:

    1. loosen or disconnect throttle cables
    2. back off idle screws untill throttle plates close leaving a gap between the screw and arm
    3. using a feeler .015" gage (business card) tighten screws untill resistance is felt between the screw and the throttle arm
    4. turn in screw 1-1/2 turns
    5. connect/tighten throttle cables at this position


    This procedure sets a very good initial setting for idle.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

Posting Permissions

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