O-360 won't idle.

Discussion in 'Firewall Forward / Props / Fuel system' started by bifft, Feb 19, 2017.

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  1. Feb 19, 2017 #1

    bifft

    bifft

    bifft

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    Working on my RV today, finally got the cowling fixed. Wanted to try a taxi test. The engine (Lycoming O-360 with Rotec TBI) starts really easy, but won't run under about 1500 rpm.

    I've only run it once before, and that was running way to rich due to my wiring the primer switch backwards. Got that fixed. So, second time running this engine on this plane.

    Start it up, if the throttle is far enough forward to have 1500-2000 RPM it starts up. Do need to stand on the brakes. Did an ignition test, both the mag and P-mag seem to be working correctly. Seems to respond normally to mixture. Throttle back, about 1500 rpm it starts running rough. Further back (1200-1500) and it just quits completely. Full throttle seems to work fine.

    I'm not really an engine guy, any ideas for things to check? I could get video of it running if it would help.

    Do plan on calling Rotec Monday, I have the day off, but it isn't a holiday in Australia.
     
  2. Feb 19, 2017 #2

    Jan Carlsson

    Jan Carlsson

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    Is it sounding like the rpm is correct? is the rev counter correct?
     
  3. Feb 19, 2017 #3

    Rockiedog2

    Rockiedog2

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    Does the fuel pressure stay up at the lower rpm?
     
  4. Feb 19, 2017 #4

    kent Ashton

    kent Ashton

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    One idea: try to figure out if it's running rich or lean. Don't be reluctant to lean on the ground and if just beginning to lean makes it worse, the TBI is probably running too lean. Of course, it it starts to run better as you lean, you're too rich at idle for some reason. Normally, the RPM will rise slightly as you come off full rich and then RPM will drop off as leaning continues.
     
  5. Feb 19, 2017 #5

    wsimpso1

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    Sounds like the mixture is going dead lean as you reduce power. Could be as simple as a fuel pump or an intake manifold leak...

    Got an EGT? How about a manifold pressure gauge? Fuel pressure gauge? Lots of info from them. Read up on reading plugs. Clean your plugs. Under each condition you will want to adjust mixture to peak EGT and see how the gauges responds to moving the mixture away from that point.

    Run the engine at 1750, find peak EGT, see how instruments responds to richer and leaner. Write them down. Shut down and check a plug. Its condition is important. Clean and reinstall.

    Then run the engine at 1750, find peak EGT with the mixture, then reduce throttle to get into the rough range. Write down readings. What does MP and EGT do during this? Try richer and leaner mixtures and note how the engine runs for each of them, set it back to peak EGT and let it run a couple minutes under that condition, shut down and pull that plug again. What do the plug readings and instruments tell you? Tell us about them.

    Be observant to rpm changes, roughness changes, EGT increases and decreases, MP increases and decreases, etc. They all provide clues.

    Come talk to us when you know more...

    Billski
     
  6. Feb 19, 2017 #6

    Winginit

    Winginit

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    Two quick and easy suggestions. First, there is a slide stop adjuster. It may be that the adjuster is allowing the throttle slide to close too far. I would note or mark where its at now, and then adjust it to a position that is open enough to keep the engine running at whatever speed that takes. Get some help to sit in the airplane and hold the brakes and make restarts. Once you have found the slowest speed it will run, then turn the idle mixture adjustment screw. Before adjusting the idle adjustment screw, gently turn it in until it seats. Don't force it. Make a note of how many turns it took to seat it. Thats your reference so you can return to the original setting if needed later. Anyway, once you have the engine running as slow as possible, adjust the screw in a little,maybe a 1/4 turn and see what the rpm does. Does the engine die. If it dies, adjust it back out 1/4 (+ 1/4) turn and run the engine again. If no change, try another 1/4 turn, etc. When the adjustments begin to have an effect on the engines smoothness (Ha Ha, its a 4 cyl), and you have gotten to where further adjustment of the idle mixture makes things worse, backup 1/4 to 1/2 turn on the idle mixture screw to get the best condition. THEN, adjust the throttle slide stop a little to close the throttle a little and try leaning/enriching the idle mixture again. As the throttle slide is adjusted to a smaller opening, vacuum should increase and the existing mixture setting you have may be slightly rich, so lean it 1/8 to 1/4 turn at a time. Also, try hooking a vacuum guage to the intake so you can see if you have good vacuum and no leaks while doing the adjustments.

    Thats a systematic approach to getting it going if its a fuel/idle problem. Remember, if your ignition is not returning to its base setting (not advanced), that could cause the engine to stop when idling. I'd check the fuel system first.
     
  7. Feb 19, 2017 #7

    TFF

    TFF

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    Rotecs can have too much fuel pressure and freerangequark on his biplane had the gascolator leak air but not fuel and he had lots of run problems until he found it.
     
  8. Feb 21, 2017 #8

    bifft

    bifft

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    Thanks for the help. Went out today to look at it again, was more careful in what I observed. Runs good from 1800-2200, gets progressively worse outside (above or below) that range. Don't have a manifold pressure gauge, do have EGT, CHT. Engine ran best, and highest EGT with mixture full rich. Any other setting was lower RPM, lower EGT and rougher running. So, maybe running too lean?

    Did get spark plug pictures. As they are easier to get to, took out the lower auto plugs connected to the P-Mag.

    IMG_2961.jpg

    See lots of metal bits. Maybe lead? Would that mean too rich?

    In either case, found the mixture line was rubbing on the cowl. Want to fix that before running it more. Need to rebuild the bracket, at least that is something I know how to do, and can do at home instead of having to go to the airport.
     
  9. Feb 21, 2017 #9

    TFF

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    What is the EGT and CHT? What timing are you running on the P mag? 100LL? If that is metal on the plugs, it might be lean and eating the pistons. On the ground unless it fouls plugs or high altitude it needs to be full rich. Usually EGT is lower than peak EGT full rich. You might be on the lean of peak side sitting on the ground. Either that or the p mag is going advanced too much. Just throwing out possibilities.
     
  10. Feb 21, 2017 #10

    delta

    delta

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    It looks like it's running lean to me. If there's ample fuel flow to the injector I'd suspect the injector itself has a problem with contamination, diaphram leaking, or improper jetting. I'd ask rotec what the proper way to test and adjust would be. Make sure your filters are still clear.
    Mixture line?
     
  11. Feb 21, 2017 #11

    kent Ashton

    kent Ashton

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    Lead is not a good indicator. It is scavenged at higher RPM when the plugs get hot and you're not getting them hot enough to remove the lead. I am not sure it's lead anyway.

    You don't appear to be running rich; in that case the plugs would be black and carbon fouled. My guess is that you are running lean at "full rich" or some other problem. I saw lots of discussion of rotec problems by googling "rotec tbi problems". First one I read sounded like your problem
    http://www.vansairforce.com/community/showthread.php?t=114648
     
  12. Feb 21, 2017 #12

    Mcmark

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    There is a idle mixture adjustment on the TBI. In the installation instructions there is a note on its adjustment. It's a 5mm alan/socket head with a lock nut. Depending on the install it's probably behind the throttle linkage on the flat face. If it's new and has not been adjusted, you will need to richen it. Mine was very lean to start. Doesn't require a lot of adjustment for a big change.
    Their website should have the install instructions, if not shoot them an email. They were good to work with when I did mine.
    Good Luck,
    Mark
     
  13. Feb 21, 2017 #13

    wsimpso1

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    Running lean. At somewhere close to stoich, your EGT should peak, and be lower either richer or leaner. If max temp is at full rich setting, it is running lean there. Then as you lower throttle, it goes cooler? Then it is definitely running really lean at reduced speed.

    If you can bump the idle mixture towards rich, you should see a lot of improvement at low throttle, but it sounds like your are lean everywhere.

    If you can bump the low speed mixture towards and lean and it will run slower, mixture might be most of it. If the EGT goes up, but you can not get the engine speed down, you likely have a manifold leak... Air is getting to the engine without it going through the TBI.

    Since it looks like big errors in mixture, go back to the instructional material for the TBI for setting it up...

    Billski
     
  14. Feb 22, 2017 #14

    proppastie

    proppastie

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    lean...richen then idle stop back if idle not right more adjust of mixture. Normal Lycoming carb should be I think 650 rpm not familiar with Rotec. Plug should be Tan, coffee with cream, often idle is richer ( darker color) for cooling. If you had a glass plug you could see a nice blue flame, orange too rich,
     
  15. Feb 22, 2017 #15

    bifft

    bifft

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    Thanks, I think I adjusted the idle screw leaner when I was having the original problem (fixed by the primer switch), so that probably caused this one. The field elevation is 4500 MSL, so I shouldn't every be really using the full rich position. I'll try to get this bracket done and then have something to try next weekend.

    Its great having people I can ask these things of.

    Regarding the CHT/EGT numbers, analog gauges so I don't have exact numbers. CHT around 350, EGT around 1300. Tried to take video of it running, but my camera mount is blocked by my shoulder, so need to remake that as well. Tried putting it on the canopy rail, but it fell off once the engine was running.

    Don't know what it was on the plugs. Dark colored and a bit hard, but could break it in my fingers.
     
  16. Feb 22, 2017 #16

    proppastie

    proppastie

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    dark grey is lead, black is oil/fuel, new engine rings not seated, oil., old engine old rings old guides,oil. also induction leak will show white/black at the same time,white at the tip black around somewhat like what yours looks like. could be an induction leak. What happens is you rich it up at idle to make up for the induction leak and then when at higher power it is lean, which is why it shows both black and white. Also you said you had a primer problem so black could be left over from that.
     
  17. Feb 26, 2017 #17

    bifft

    bifft

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    So, spent most of today at the airport. It was indeed much too lean. Took quite a while, as you need to dismount the throttle bracket to get at the lean screw. Hopping in and out of the cockpit all day, then 10 minutes per change. Also drained my battery flat with so many restarts. Eventually just ran jumper cables from my truck.

    Still not satisfied, it runs good from 500-2000 RPM, but not good at full power. Will keep messing with it.

    Thanks so much for the help.
     
  18. Feb 26, 2017 #18

    Vision_2012

    Vision_2012

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    Try professional repair station: D&G, 1505 N Front St., Niles, Michigan 49120-3933, run by Russ, phone (269) 684-4440. He completely overhauls the carburetor and includes many details that other shops charge extra for. His price on an MA3 is $600. He has a good turn around time.
     
  19. Feb 27, 2017 #19

    proppastie

    proppastie

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    The standard carb (MA3 ?) would be my choice
     
  20. Feb 27, 2017 #20

    bifft

    bifft

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    I do have the original MA3 carb that came with the engine. However, in addition to being about 10 lbs heavier than the Rotec, it won't let me use that expensive inverted oil system I've already installed. Am keeping that as the fall back option.
     
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