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  #1  
Old 11-29-2017, 09:19 PM
Tram Tram is offline
 
Join Date: Sep 2007
Location: Florence, AL
Posts: 594
Default Help me troubleshoot rough running..

Ok, bear with me, this may be a long post..

2 flights ago, during a cold start (on a chilly day) the plane fired right up and then quickly **** back down. This is abnormal for our 6. Normally always fires right up. Anyway, fired it right back up, started fine, searched for idle for a bit but stayed running.. Good runup, no issues. Went flying.

Today, the same deal. Fired up, shut back down, fired back up and zero issues. Good runup, went flying. No issues.

Fly for about 30 minutes. Land. Plane sits for about 45 minutes, crawl back in, fire it up (starts fine), decently short taxi out, normal run up and depart.

While climbing out, above ~2250 rpm the engine starts running rougher than I like, pull the power back to around 2100rpm and all is fine. Turn downwind and land.

Taxi in and do a quick runup. Oil temps climb a littler higher than normal, about 240*ish, and the plane runs s rough at 2200 rpm and above.

Taxi in, pull the cowl, look it over. Everything looks normal, but there was a funny smell. Semi-electrical. Semi-heater on for the first time in winter. Semi-burnt electric motor type smell. Not a normal smell.

Let it rest, call our mech and he suggests mixture setting as the first place to start looking. Mixture was slightly off. We set it for about a 50rpm rise when killed from idle.

Do a couple quick run ups to about 2250rpm static and then idle shut offs messing with the mixture.

Taxi’d back out for a runup just to see how it’s acting. Run up is good until a few seonds into high power and it begins running rough again. Rpms drop to 2000-2100ish. Back to the hangar. Smell is kinda there, but nothing like the first time.

Call A&P and he suggests maybe it’s fouled plugs and to attempt to burn it off.

Taxi out, attempt to burn off plugs with high power/leaning on the ground and am unable to get steady enough running to really accomplish anything. EGT’s got to around 1250. No improvement.

Pull the power back and just for grins, I checked the mags. Nothing. No drop on either mag. Ah ha! I think. Found it.

Taxi back to the hangar and before shutting down, power back to ~1800rpm and check mags. Got about a 75rpm drop on both. Decent check.

I’m stumped.

Unmetered Air? Bad Venturi or float in the carb? Mags toasted?

Engine details:

Recent (<100 hours) rebuild O-320.
Bendix mags.
Running non-ethanol mogas.

Last edited by Tram : 11-30-2017 at 08:48 AM.
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  #2  
Old 11-30-2017, 06:10 AM
Maxrate Maxrate is offline
 
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I see your running mogas. I had a Cessna 150 years ago that would start sticking exhaust valves and loosing power. May check compression. I heard marvel mystery oil does wonders in the gas and oil as a good lube/fix
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  #3  
Old 11-30-2017, 06:47 AM
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Jesse Jesse is offline
 
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I would definitely look at axhaust valves as well as the venture in the carb.
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Old 11-30-2017, 07:49 AM
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bret bret is online now
 
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Sounds like low fuel flow? 250 on oil temp? my red line take action is 230. are all EGTs equal when it starts to run rough?
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Old 11-30-2017, 08:51 AM
Tram Tram is offline
 
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Quote:
Originally Posted by Maxrate View Post
I see your running mogas. I had a Cessna 150 years ago that would start sticking exhaust valves and loosing power. May check compression. I heard marvel mystery oil does wonders in the gas and oil as a good lube/fix
Compression check is going to be the first thing this weekend.


Quote:
Originally Posted by Jesse View Post
I would definitely look at axhaust valves as well as the venture in the carb.
Thanks.

Quote:
Originally Posted by bret View Post
Sounds like low fuel flow? 250 on oil temp? my red line take action is 230. are all EGTs equal when it starts to run rough?
Our EGTís are at best, sketchy. Which should soon change with a Sky View install, but right now, they all seemed to be the same.

Also, Iím glad you caught the 250. I fat fingered that. Tempts got to just shy of 240, which is still warm for our bird.
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  #6  
Old 11-30-2017, 09:23 AM
greghughespdx greghughespdx is offline
 
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Plugs (one the bench) and wires (on a multimeter) checked?
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  #7  
Old 11-30-2017, 10:45 AM
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Raymo Raymo is offline
 
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My -7A did the same when starting in cold PA weather last week. Started, quit, started, quit. I had to leave the boost pump on to get it to stay running the 3rd time. Once warmed up, all was fine and the flight back to GA was uneventful.

Another cold day in the south and it did about the same thing. I used the boost pump again to keep it running upon start and let the oil warm to 100, as usual, before take-off.

Your other symptoms sound like you are not getting enough fuel for the denser winter air. Also, consider changing to a multi-viscosity oil for easier cold starts.
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Old 11-30-2017, 11:59 AM
gasman gasman is offline
 
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A bad key switch might be part of your problems.
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  #9  
Old 11-30-2017, 12:09 PM
Tram Tram is offline
 
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Quote:
Originally Posted by gasman View Post
A bad key switch might be part of your problems.
How would a key switch play into rough running?
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  #10  
Old 11-30-2017, 03:32 PM
sf3543 sf3543 is offline
 
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Winter blend MOGAS on a warm day, or with a hot engine bay, can cause the symptoms you are seeing. (Or could be a fuel line getting hot from the exhaust pipe, or whatever, causing the gas to vaporize.)
If that is the problem, mixing about 15% to 20% 100LL with the MOGAS should fix it, once the gas in the lines and carb is used up.
I saw this problem once and fixed it by moving the fuel line away from the exhaust and shielding it.
YMMV
Good luck
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