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07-10-2013, 11:12 AM
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Join Date: Jan 2005
Posts: 3,646
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Very narrow lean range. Need to ground a/c?
In the process of tracking down some high temps, I did a lean test through Mike Busch's Savvy Analysis Program. The lean range for my four cylinders are:
1-205F
2-222F
3-68F
4-62F
Test is conducted at 6000 ft at about 60-65% power, starting from full rich, then leaning until each EGT peaks.
Obviously, #3 and #4 are running really lean even at full rich. What concerns me is that if I'm running this lean at 6000 ft at 65%, how lean am I on takeoff while at lower altitude (1750 MSL) and at high power? Is it likely that #3 and 4 are in that range just rich of peak that should be avoided in order to avoid the risk of detonation? I'm particularly concerned given my #3 CHT can break through 400 in climb.
Savvy suggested checking for induction leaks on 3 and 4, and also commented that this could be the result of poor distribution on my carbed engine but, until I get that figured out, should I not be flying? Was headed to Arlington this week, but maybe not.
Thanks for the help. There are so many things I didn't think about before when flying planes without good instrumentation!
__________________
Steve M.
Ellensburg WA
RV-9 Flying, 0-320, Catto
Donation reminder: Jan. 2021
Last edited by alpinelakespilot2000 : 07-11-2013 at 11:19 PM.
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07-10-2013, 11:27 AM
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Join Date: Dec 2004
Location: Gold Hill, NC25
Posts: 2,400
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You should be able to get a 150F or better EGT spread on all cylinders.
Induction leak is a good place to start. A can of ether is your friend.
Remember induction leaks are easily discernible at low MP. De-cowl, let it idle, spray ether, and find.
I would not fly this plane until I found the problem. You have not determined based on this data what the spread is at TO power and low altitudes. I would not attribute this to carb at all.
Breaking through 400 in a climb should not alarm you.
__________________
Kahuna
6A, S8 ,
Gold Hill, NC25
Last edited by Kahuna : 07-10-2013 at 11:30 AM.
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07-10-2013, 04:05 PM
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Join Date: Oct 2005
Location: Geneva, AL
Posts: 491
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Carb Jet
Steve,
I had the same thing going on when I was flying my 40 hour test period. I read everything I could find and finally did that test. I was POSITIVE I had no intake leaks. I finally drilled the jet out on the carb, which was a painless operation, and it took care of it. It even pretty much evened up the temps to peak.
For reference, mine is an O-320 also.
__________________
Paul Rose
RV-9A 91300
N417PR
SERFI 2013 Awards
Inspection Complete!!! 7/7/12
First Flight 7/22/12
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07-10-2013, 04:46 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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These are the richest MA4-SPA carbs, better than drilling out the jet.
10-5009N
10-5135
10-5217
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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07-10-2013, 05:48 PM
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Join Date: Jan 2005
Posts: 3,646
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Quote:
Originally Posted by Kahuna
You should be able to get a 150F or better EGT spread on all cylinders.
Induction leak is a good place to start. A can of ether is your friend.
Remember induction leaks are easily discernible at low MP. De-cowl, let it idle, spray ether, and find.
I would not fly this plane until I found the problem. You have not determined based on this data what the spread is at TO power and low altitudes. I would not attribute this to carb at all.
Breaking through 400 in a climb should not alarm you.
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Thanks Kahuna. This test is now on my very short list.
__________________
Steve M.
Ellensburg WA
RV-9 Flying, 0-320, Catto
Donation reminder: Jan. 2021
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07-10-2013, 05:51 PM
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Join Date: Jan 2005
Posts: 3,646
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Quote:
Originally Posted by PaulR
Steve,
I had the same thing going on when I was flying my 40 hour test period. I read everything I could find and finally did that test. I was POSITIVE I had no intake leaks. I finally drilled the jet out on the carb, which was a painless operation, and it took care of it. It even pretty much evened up the temps to peak.
For reference, mine is an O-320 also.
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Thanks Paul. Out of curiosity, did drilling up happen to also do anything to your CHTs or oil temp? These are what drove me to explore the gami lean and induction tests in the first place.
__________________
Steve M.
Ellensburg WA
RV-9 Flying, 0-320, Catto
Donation reminder: Jan. 2021
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07-10-2013, 07:11 PM
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Join Date: Feb 2007
Location: Fresno, CA
Posts: 321
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Quote:
Originally Posted by Walt
These are the richest MA4-SPA carbs, better than drilling out the jet.
10-5009N
10-5135
10-5217
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I'm not trying to be flippant, but how are these better than drilling the jet to a larger size?
__________________
Timothy Cone
Sierra Skypark (KE79) Fresno CA
RV-8, XP360, RV200
Flown Sept. 12, 2007
1600 hours on the hobbs and loving it
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07-10-2013, 07:19 PM
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Join Date: Nov 2012
Location: Mosheim Tn
Posts: 30
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I have an0-360,drilledthe main jet and i made a big difference in temps,easy to do also!
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07-10-2013, 07:31 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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Quote:
Originally Posted by tcone1
I'm not trying to be flippant, but how are these better than drilling the jet to a larger size?
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Thoughtful engineers have carefully tailored the idle circuit, the accelerator pump, and main jet for optimum performance. A modified nozzle jet may cause the air/fuel ratio to be overly rich. There is a point of diminishing returns, where high-end fuel flows no longer increase but mid-range fuel/air ratios become too rich.
Sure, your high-end fuel flows begin to look better and so do your CHTs and EGTs. But unfortunately, mid-range fuel flows may become exceedingly rich.This rich condition is especially apparent as you transition between idle and full power and may cause problems on throttle application (like TO or GA).
There is no "approved" method to accomplish this procedure and if you mess it up you'll end up buying a new carb.
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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07-10-2013, 07:37 PM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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Walt is correct. There are several documents out there that detail exactly what he is talking about and the effects it can have written by the folks that designed these things.
That being said, I did drill mine but was careful to sneak up on it and not go too far. A reamer is the best thing to use if you are going to do it....
I found that the typical 10-3878 is too lean for a typical O-360 in an RV7.
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