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Older 912UL (1997) with no air box and 138 hours total time on a Zenith CH701.

I knew the aircraft had carb problems when I purchased it so I overhauled both Bing 64 CV carbs. Needle jet is changed to 2.74 (it was running lean with a 2.76 even at position #4) and needle position at position #1. They appear to be functioning correctly (I synced mechanically and pneumatically) and I idle smoothly at 1800 RPM and it runs smoothly through the RPM range up to 5500. Idle air mixture screw is set at 1 1/4 turns (1 1/2 was too rich, I fly out of a 2100’ elevation strip). There is no dribbling from the carb overflow vent and the float levels are set level. I’ve got the prop (warp drive 68”) set for 5500 on take off.

The #2 EGT (cyl. 3) runs high. It has run high since I purchased the aircraft. The probes are 68mm from the port (not 100 as the book says) and I checked to make sure the probes are grounded well (they are). I still get more than 100 degree split between right and left. The plugs look good (medium brown) with the #3 cylinder possibly a little whiter.

Usually the EGT is below the red line on takeoff and climb, but shortly after level off I can see temps over 1650 on the #2.

A differential compression check shows the weakest cylinder at 77 over 80 with the leakage around the rings (it was warmed up).

Any input on the EGT would be appreciated. Oh, and I did do an intake leak check by spraying starter fluid around the intake while it was running. No apparent leak.

Next issue. The last two times I have flow the aircraft the engine wouldn’t shut down completely. I could go to idle, shut one switch off a few seconds and then turn the key off (yes, it is a key switch) and it would kick over for 45 sec, to a minute. Once I even had to shut the fuel off to shut it down.

I check the ground at the switch, cleaned the grounding wires to the intake manifold and gapped the plugs at .26.

The second time is when I lowered the idle to 1800 from 2000 and it still does it. It does have a mag drop of approx. 400 on each side and when I do a mag switch grounding check taxiing out it appears to ground OK. Its the shutdown when it is hot.

Being an older engine it has both ignition modules on top of the engine (yes it has the ground wire service bulletin complied with and it is grounding well).

Sorry this post is so long. I’ve been dinking with this for 4 months now. I’ve picked up a lot of good information from this forum but I’m about at the end of my know how here. Any suggestion would be appreciated.
  • Re: HIGH EGT & WON'T SHUT DOWN

    by » 12 years ago


    Hi Bob,

    When you say you overhauled them does that mean you rebuilt them and replaced all the parts that are in a rebuild kit?
    First the jetting is wrong. The main jet should be either a 155 or a 158, the idle jet is a 35, the needle should be a 2.72 and both carb needle clips in the #3 slot. Start with the mixture screw at 1.5 turns. I'm at a 2400' elevation and it works fine for all the engines on my field and usually for a 912 at most any field. While your back in the carbs make sure the float level is correct and since the floats have some years on them make sure they float in the fuel correctly and equal.
    Then I would plug the EGT hole and put the probe at 100mm for an accurate reading. Your position now is too close and has a hot reading.

    Re-jetting may take care of your shut down issues. So until this is done I wouldn't worry about the other shut down issue. The compression test is okay.

    Rotaxcarbjettingchart.pdf (You do not have access to download this file.)

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: HIGH EGT & WON'T SHUT DOWN

    by » 12 years ago


    Thanks Roger. The idle jet is at 35 the main is at 160 (which is how I got it, but it came from Florida). I'm confident the float level is right but I will order the new main jets (I made the same calculation from the Bing manual but indications were it was running rich). One of the floats is new, I also have new float arms, one new float needle and everything in the rebuild kit. I'm guessing I did everything pretty close to right as the Rotax DVD's came out about 3 days after I was through and I didn't see any real issues when I viewed them.

    What do you suggest plugging the EGT holes with? I'll get that done while I am waiting for new parts to come in (I live in the boonies in Texas).

    I'll let you know how it turns out.

  • Re: HIGH EGT & WON'T SHUT DOWN

    by » 12 years ago


    Hi Bob,

    For plugging the EGT probe holes it depends on the type of EGT mount you have. If you have the type with the worm drive screw clamp then I usually just take them out and put a spot weld on top of the hole. It's quite easy. If you have the screw in type then you can cap that hole and just drill and use the worm drive style clamp EGT.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: HIGH EGT & WON'T SHUT DOWN

    by » 12 years ago


    I have the worm drive clamp type and I'll see if I can get someone at the air patch to weld it up for me so I don't have to pull the exhaust system and take it home.

    I'll let you know how the re-jetting and relocation of the probes works out.

    Thanks for the input.

  • Re: HIGH EGT & WON'T SHUT DOWN

    by » 12 years ago


    I got the new jets in and installed. 158 on the mains 2.72 on the needle and reset to position #3 with the idle air screw at 1 1/2 turns. After syncing the carbs everything looked good and I flew it for 1.1 today. I was pleased with the way the engine ran and the EGT temps were even down (I haven't reset the probes to the proper distance yet). At 5450 RPM I was getting a #1 EGT of 1591 and #2 of 1583. The oil temp was 208 and CHT 192 with coolant (Evans) 191. The mag drop was greatly improved at 50 per side.

    The only issue was that it really didn't want to shut down. It kicked over several times when I tried to shut it down and I turned the key back on, ran it up to 3000, then back to idle (1800) and turned the key off again. The second time it shut down, but a little reluctantly. I may not be letting it cool long enough before shutdown.

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