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  #1  
Old 03-24-2021, 02:20 PM
GHARBEN GHARBEN is offline
 
Join Date: Nov 2019
Location: Gainesville, Georgia
Posts: 33
Default O 320 Hard to Start

N12HR fly's about once a week. I have owned it about 2 years. It has always taken too much twisting to crank. I have disconnected the primer and it appears to be working. After a lot of cranking it suddenly bursts to life. Never a pop or crack! It feels like there is no gas or no spark. When you turn the propeller and as the impulse coupling spins ahead there is a weak spark about every 3rd try. I don't believe the mags have been overhauled in the last 800 hours. Should the boost pump be left on for starting?. I generally turn it off after I build up the fuel pressure. When first doing a condition check, it appeared that the electric pump flooded the carburetor. For that same reason, I do not use the boost pump for take off.
It also appears very ez to flood.
The engine is an O 320.
Any thoughts?
G Harben
N12HR
S/N 1664
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  #2  
Old 03-24-2021, 02:32 PM
KAdriver's Avatar
KAdriver KAdriver is offline
 
Join Date: Dec 2017
Location: Louisiana
Posts: 44
Default

Master on
Mixture full rich
Throttle wide open then boost pump till you hear the pump under pressure and about 2 seconds. Pump off
Throttle 1/4 inch
Crank it.
Mine usually hits on the 3rd revolution.
Cold weather way more prime.

Thatís my method at least.
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RV6
KASD
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  #3  
Old 03-24-2021, 02:39 PM
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Raymo Raymo is online now
 
Join Date: Nov 2014
Location: Richmond Hill, GA (KLHW)
Posts: 2,319
Default

Slick recommends IRAN on their mags every 500 hrs. Consider swapping the impulse mag for an electronic ignition and having the other OH'd. The boost pump should not flood the engine; something else to correct.
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RV-7A - Slider - N495KL - First flt 27 Jan 17
O-360-A4M w/ AFP FM-150 FI, Dual PMags, Vetterman Trombone Exh, SkyTech starter, BandC Alt (PP failed after 226 hrs)
Catto 3 blade NLE, FlightLines Interior, James cowl, plenum & intake, Anti-Splat -14 seat mod and nose gear support
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  #4  
Old 03-24-2021, 04:45 PM
Tracer 10 Tracer 10 is offline
 
Join Date: Mar 2011
Location: Oregon
Posts: 141
Default O-320 Hard Starting.

I agree with these suggestions.
Also if the spark plug gap is excessive (due to normal wear); it will be very hard to start.
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Restored L2-M; flown 7 years & sold.
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  #5  
Old 03-24-2021, 07:40 PM
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avrojockey avrojockey is offline
 
Join Date: Aug 2019
Location: Appleton, WI
Posts: 349
Default

Could be mag, you can remove and check with spark tester. The spark will jump a significant gap (1/4" to as much as 1") on good mag spinning the impulse coupling by hand. Check the impulse mag, as it's the one doing the work during the start. It's definitely worth having the slick mags inspected every 500 hrs, and some recommend cracking them open for visual inspection every year...surprisingly fragile beasts inside

No reason to have the boost pump on during starting...certainly not on a carbureted 320.

Does your primer use the boost bump? What signs indicates its flooding during start?

I suspect only a little priming (if any) is needed in typical Georgia weather for a cold start. Prime requirement is dependent on fuel temp...not ambient temp. They are many times the same, but not when the engine is warm or has been preheated. That's why no prime is required when hot starting.

Remember, to get a combustible mixture you need the correct mix of air (containing the requisite O2) and fuel vapor...vapor is what's needed, not fuel. The vapor quantity is highly dependent on fuel temp. The colder the fuel, the more fuel quantity to achieve the required vapor.

FWIW...I live in WI, it's still snowing occasionally here. I don't have a primer on my aircraft. I preheat any less than 40F-50F. For cold starts I use the accelerator pump 1-2 times (dependent on fuel temp) during cranking, then I use the zero-throttle technique. Hot starts...just crack throttle 1/4" travel and crank. Starts, immediately, every time
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Appleton, WI
RV-9A N904DC
2019-2021 Dues Paid

Last edited by avrojockey : 03-24-2021 at 07:55 PM.
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  #6  
Old 03-24-2021, 07:57 PM
YellowJacket RV9 YellowJacket RV9 is offline
 
Join Date: Oct 2012
Location: Clearwater, FL KCLW
Posts: 1,316
Default

Perhaps unrelated to your starting problem but I would be concerned that your boost pump is flooding your carburetor, you should not have to leave it off during takeoff (probably the most important time to have it ON). In addition to a mag overhaul, you may be in need of a carb rebuild or inspection.

Chris
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RV-9A - Done(ish) 4/5/16! Flying 4/7/16
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  #7  
Old 03-24-2021, 08:00 PM
avrojockey's Avatar
avrojockey avrojockey is offline
 
Join Date: Aug 2019
Location: Appleton, WI
Posts: 349
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Also, the boost pump shouldn't flood a carb...if so, there's something wrong with the carb.

EDIT: Chris beat me to it!
Quote:
Perhaps unrelated to your starting problem but I would be concerned that your boost pump is flooding your carburetor, you should not have to leave it off during takeoff (probably the most important time to have it ON). In addition to a mag overhaul, you may be in need of a carb rebuild or inspection.
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Appleton, WI
RV-9A N904DC
2019-2021 Dues Paid
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  #8  
Old 03-24-2021, 08:04 PM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
Posts: 1,405
Default TLC

Forgive me here for stepping into this....
Sounds to me the engine needs some TLC.
Maybe even have a fellow RV driver assess how abby-normal the engine is. Sometimes we live with things that aren't quite right and not realize they are seriously bad.
If I was you, I would ask a friend to look over your starting trouble.
Maybe even check compression, overhaul the mag and overhaul the carb. I say the carb because the boost pump flooding the engine could be a bad float or seat.

JMHO. Stay safe
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John S

WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Dues paid 2021, worth every penny

RV9A- Status:
Tail 98% done
Wings 98% done
Fuselage Kit 98% done
Finishing Kit 35% canopy done for now
Electrical 85% in work
Firewall Forward 5% in work
Fiberglass 0%, thought i was building in metal?
www.pilotjohnsrv9.blogspot.com
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  #9  
Old 03-24-2021, 09:28 PM
OKAV8r OKAV8r is offline
 
Join Date: Feb 2007
Location: Seattle
Posts: 152
Default Primer nozzles

How long has it been since the primer nozzles were cleaned.
I've seen them so carboned up that no fuel would pass through....
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  #10  
Old 03-24-2021, 10:01 PM
NM Doug NM Doug is offline
 
Join Date: Mar 2012
Location: Saint Paul, MN
Posts: 160
Default

FWIW, we were having terrible starting problems on our O-320, and it turned out it was the out-of-spec high internal resistance on our Champion plugs. With the Tempest new plugs, we start up right away now.

~Doug
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