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hawkins(at)cms.udel.edu
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 Posted: Mon Jul 09, 2007 8:12 am Post subject: Engine Cough? |
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All-
We're having a minor intermittent problem on the left engine of N2760B. They are Lycoming G0-480-DIA's. Geared engine with pressure carburetors.
When reducing power, the engine will cough/sputter as soon as it hit's 21" of manifold pressure. Doesn't quit - just skips and runs a bit rough.
Doesn't happen when increasing power.
All gauge reading in the green - nothing obvious.
About 15 hours on the engines since major overhaul. Did not happen during first 10-12hrs - started during past couple of flights. Won't happen every time - but about 75% of the time. Just a little disconcerting on final!
Any thoughts?
Matt
********************
Matthew Hawkins
Director, Marine Ops
R/V HUGH R. SHARP
302-645-4341
FAX: 302-645-4006
hawkins(at)udel.edu
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steve2(at)sover.net
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| Posted: Mon Jul 09, 2007 8:54 am Post subject: Engine Cough? |
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Induction leak?
Loose induction tube (not seated right), or cracked flange on a tube?
I'll quit speculating.
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steve2(at)sover.net
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| Posted: Mon Jul 09, 2007 3:05 pm Post subject: Engine Cough? |
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Matt,
Wouldn't happen to have a 6 probe EGT aboard? Be interesting to see what it
said when the engine burps.
I've seen now several tubes crack underneath the clamp in the flange. Plus
they are a little tricky to seat. But I don't want to send you on a wild
goose chase.
Rich wasn't a bad suggestion either. Couple months back I posted about
having an injector servo go WAY rich when reducing power. You're running a
pressure carburetor, different from our rig and outside my experience, but a
similar situation seems concievable.
This might be a goofy idea, but have you pulled the plugs yet to see how
they're doing cylinder by cylinder? Right after you had the condition might
be informative.
Ok, now I'll really stop speculating. Honest.
Steve
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gmosh(at)charter.net
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| Posted: Mon Jul 09, 2007 3:39 pm Post subject: Engine Cough? |
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Make sure your (aluminum) fuel lines don't have any pin holes - sometimes
they're nearly impossible to see! They were on my 560.
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yourtcfg(at)aol.com
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| Posted: Tue Jul 10, 2007 9:04 am Post subject: Engine Cough? |
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After checking the other suggestions, It is probably an adjustment to the pressure carb. Try this. While it is acting jacking up, manually lean the carb and see if it clears up. If it does, it is rich, if not, most likely lean. There are two adjustment on the carb. One for idle mix, the other for "off idle" It is probably the off -idle but both will need touched up. If you have a manual for the engine it will cover this procedure, if not let me know and I can walk you through it. One last thing, make certain the carb heat is not on. Sometimes the linkage will allow the carb to pull in hot air and with the temps rising it could just now be showing up. If the engine has had a backfiring incident recently, if could have bent the little carb heat butterfly doors in the carb heat box. I have seen several of these over the years and they too will let hot air into the carbs causing them to stumble . Conversely, an exhaust leak in the cowling can overheat the ambient air in there and trick the carb into thinking it is really hot outside and it will try to compensate by leaning. jb 360-903-6901
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hawkins(at)cms.udel.edu
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| Posted: Fri Jul 13, 2007 7:10 am Post subject: Engine Cough? |
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JB-
Looks like you might have nailed it on this one! We found the carb heat linkage maladjusted - we'll let you know if that solves the problem.
Many thanks!
Matt
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