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#1
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O-320 way rich after Major + 160HP conversion + Powerflow
The O-320 in our C-172 was professionally recently professionally overhauled
(at 2300 hours and 32 years). This included an STC to 160 HP, new millennium cylinders, new crank (a story, there..), new cam, new carb, a repitched prop, and a powerflow exhaust. We're past break-in now, and the plane flies great, climbs awesome. The recurring problem is that the carb is set way too rich. After a few visits to the A&P (each time involving a lot of carb twiddling), it is getting better each time. It is rich enough that I find that carb heat in the pattern induced pretty good roughness and often backfiring. In fact, I find that I need to keep it leaned even on the ground or in the pattern (our field is only 200' elevation). On the ground, the idle is at 650 with the mixture in, put pull it out about an inch or 2 and it gets a lot smoother and a little bit faster. The mechanic feels that it will take us a few iterations to get it set up right, since there is so much new stuff here. He feels that the exhaust may be a big part of this. One other clue, the EGT now reads a lot lower than it used too. They are apparently going to re-calibrate the thermocouple so it will at least register on the gage. Anyone have any experience like this? Thanks, dave |
#2
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Dave Gribble wrote:
The O-320 in our C-172 was professionally recently professionally overhauled (at 2300 hours and 32 years). This included an STC to 160 HP, new millennium cylinders, new crank (a story, there..), new cam, new carb, a repitched prop, and a powerflow exhaust. We're past break-in now, and the plane flies great, climbs awesome. The recurring problem is that the carb is set way too rich. After a few visits to the A&P (each time involving a lot of carb twiddling), it is getting better each time. It is rich enough that I find that carb heat in the pattern induced pretty good roughness and often backfiring. You're right, that's not good. In fact, I find that I need to keep it leaned even on the ground or in the pattern (our field is only 200' elevation). Leaning on the ground is just normal good operating practice. On the ground, the idle is at 650 with the mixture in, put pull it out about an inch or 2 and it gets a lot smoother and a little bit faster. That sounds like normal operation. Full-rich should be richer than an optimum mixture. If full-rich gave you an ideal mixture, you wouldn't be able to enrichen past that to give you the extra cooling you need during climb operation. The mechanic feels that it will take us a few iterations to get it set up right, since there is so much new stuff here. He feels that the exhaust may be a big part of this. One other clue, the EGT now reads a lot lower than it used too. They are apparently going to re-calibrate the thermocouple so it will at least register on the gage. Anyone have any experience like this? Remove SHIRT to reply directly. Dave |
#3
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-----That sounds like normal operation. Full-rich should be richer than an optimum -----mixture. If full-rich gave you an ideal mixture, you wouldn't be able to -----enrichen past that to give you the extra cooling you need during climb operation. Correct me if I'm wrong, but I think the "idle mixture" does not have anything to do with high power settings. All the "ports" open up with full throttle and gives it more fuel than needed to keep it cool. John Prince "Dave Butler" wrote in message ... Dave Gribble wrote: The O-320 in our C-172 was professionally recently professionally overhauled (at 2300 hours and 32 years). This included an STC to 160 HP, new millennium cylinders, new crank (a story, there..), new cam, new carb, a repitched prop, and a powerflow exhaust. We're past break-in now, and the plane flies great, climbs awesome. The recurring problem is that the carb is set way too rich. After a few visits to the A&P (each time involving a lot of carb twiddling), it is getting better each time. It is rich enough that I find that carb heat in the pattern induced pretty good roughness and often backfiring. You're right, that's not good. In fact, I find that I need to keep it leaned even on the ground or in the pattern (our field is only 200' elevation). Leaning on the ground is just normal good operating practice. On the ground, the idle is at 650 with the mixture in, put pull it out about an inch or 2 and it gets a lot smoother and a little bit faster. That sounds like normal operation. Full-rich should be richer than an optimum mixture. If full-rich gave you an ideal mixture, you wouldn't be able to enrichen past that to give you the extra cooling you need during climb operation. The mechanic feels that it will take us a few iterations to get it set up right, since there is so much new stuff here. He feels that the exhaust may be a big part of this. One other clue, the EGT now reads a lot lower than it used too. They are apparently going to re-calibrate the thermocouple so it will at least register on the gage. Anyone have any experience like this? Remove SHIRT to reply directly. Dave |
#4
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John P wrote:
-----That sounds like normal operation. Full-rich should be richer than an optimum -----mixture. If full-rich gave you an ideal mixture, you wouldn't be able to -----enrichen past that to give you the extra cooling you need during climb operation. Correct me if I'm wrong, but I think the "idle mixture" does not have anything to do with high power settings. All the "ports" open up with full throttle and gives it more fuel than needed to keep it cool. John Prince Don't know, but that sounds plausible. Thanks for the correction. The same mixture knob controls the mixture at both idle and full power, though. Dave Remove SHIRT to reply directly. |
#5
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On Wed, 31 Mar 2004 23:28:37 -0500, "Dave Gribble"
wrote: Anyone have any experience like this? No experience with the O320, but with the Lycoming O360's, the procedure to set proper mixture should be doable on the ground. 1. Start engine and warm up until CHT's and oil temps are normal. 2. Mag check -- if normal, proceed. 3. Set throttle set screw so idle is per airframe mfg recommendation. 4. Slowly move mixture control towards idle cut-off and observe rpm. An increase of more than 50 RPM indicates the mixture is too rich. (An immediate decrease, if not preceded by a momentary increase, indicates the mixture is too lean). 5. When performing step 4, don't let the engine cut out. 6. Adjust the mixture control in the proper direction; run up to 2000 RPM to "clear" the engine, and repeat the above as necessary. If the mixture change has changed the idling RPM, that should be re-adjusted as needed. 7. If the setting does not remain stable, check the idle linkage for looseness. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) |
#6
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Deakin's had an AvWeb column sometime in the last three months on
setting the proper ground mixture. Dave Gribble wrote: The O-320 in our C-172 was professionally recently professionally overhauled (at 2300 hours and 32 years). This included an STC to 160 HP, new millennium cylinders, new crank (a story, there..), new cam, new carb, a repitched prop, and a powerflow exhaust. We're past break-in now, and the plane flies great, climbs awesome. The recurring problem is that the carb is set way too rich. After a few visits to the A&P (each time involving a lot of carb twiddling), it is getting better each time. It is rich enough that I find that carb heat in the pattern induced pretty good roughness and often backfiring. In fact, I find that I need to keep it leaned even on the ground or in the pattern (our field is only 200' elevation). On the ground, the idle is at 650 with the mixture in, put pull it out about an inch or 2 and it gets a lot smoother and a little bit faster. The mechanic feels that it will take us a few iterations to get it set up right, since there is so much new stuff here. He feels that the exhaust may be a big part of this. One other clue, the EGT now reads a lot lower than it used too. They are apparently going to re-calibrate the thermocouple so it will at least register on the gage. Anyone have any experience like this? Thanks, dave |
#7
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Dave Butler wrote:
: Don't know, but that sounds plausible. Thanks for the correction. The same : mixture knob controls the mixture at both idle and full power, though. Yes, but think of the mixture knob as an "absolute" metering adjustment, not a "relative" adjustment. In other words, setting the mixture doesn't set the air/fuel ratio... basically just the maximum amount of fuel that can flow. So, to lean on the ground with the mixture you have to pretty much pull it all the way out. As Deakin says, if you lean on the ground, doing anything shy of almost cutting it off does no good, and possibly harm if you forget to enrichen rull before takeoff. -Cory -- ************************************************** *********************** * The prime directive of Linux: * * - learn what you don't know, * * - teach what you do. * * (Just my 20 USm$) * ************************************************** *********************** |
#8
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#9
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Dave Gribble wrote: This included an STC to 160 HP, new millennium cylinders, new crank (a story, there..), new cam, new carb, a repitched prop, and a powerflow exhaust. I installed tuned headers on a van once. It ran rich after that, due to the reduced back pressure. I had to rejet the carb to fix it. That leads me to suspect your new exhaust, but you've put a new carb on there too. Can you put the old one back on for a flight? George Patterson Treason is ne'er successful, Sir; what then be the reason? Why, if treason be successful, Sir, then none dare call it treason. |
#10
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This is the exact procedure we've used to set the mixture. The idle is 650
rpm and the increase when you move to cut-off is only about 25 rpm. The problem is that it still seems too rich, especially in the pattern with carb heat on. "Ron Rosenfeld" wrote in message ... On Wed, 31 Mar 2004 23:28:37 -0500, "Dave Gribble" wrote: Anyone have any experience like this? No experience with the O320, but with the Lycoming O360's, the procedure to set proper mixture should be doable on the ground. 1. Start engine and warm up until CHT's and oil temps are normal. 2. Mag check -- if normal, proceed. 3. Set throttle set screw so idle is per airframe mfg recommendation. 4. Slowly move mixture control towards idle cut-off and observe rpm. An increase of more than 50 RPM indicates the mixture is too rich. (An immediate decrease, if not preceded by a momentary increase, indicates the mixture is too lean). 5. When performing step 4, don't let the engine cut out. 6. Adjust the mixture control in the proper direction; run up to 2000 RPM to "clear" the engine, and repeat the above as necessary. If the mixture change has changed the idling RPM, that should be re-adjusted as needed. 7. If the setting does not remain stable, check the idle linkage for looseness. Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA) |
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