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McPilot

Active Member
I did some searching on this topic but wanted to get a fresh take on it. I have a Superior O-360 with standard compression pistons in my -7A. I have dual P Mags. It has been a while since I have flown a non fuel injected engine.

I am a bit picky as to engine operation parameters. I realize that the rule of thumb is to lean to roughness and then enrich to smooth. My question is at 75% power, what is your usual fuel flow? I am running at ~10GPH and getting carbon on my spark plugs. (BR8ES)

I had a Grumman Tiger with an O-360 and don't quite remember what the fuel flow was...

You guys with IO-360s are obviously in a different arena on this so I would like to hear from the carbureted guys only....
 
At full power with 180hp you should be burning about 16-17gph. At 75% power and the same richness you should be about 12gph. Leaning to 10gph seems about right. Your real efficiency should come around 60-65% power.

Are you fixed pitch or constant speed? What are you using to determine 75% power? Combination of Manifold Pressure and RPM?
 
Jesse said:
At full power with 180hp you should be burning about 16-17gph. At 75% power and the same richness you should be about 12gph. Leaning to 10gph seems about right. Your real efficiency should come around 60-65% power.

Are you fixed pitch or constant speed? What are you using to determine 75% power? Combination of Manifold Pressure and RPM?
Click to expand...

Hi Jesse. At full power I am getting 18gph. I have a constant speed prop and am using mp and rpm. My Dynon EMS D10 is confirming 75%. 24" and 2400 rpm or there about.
 
18gpg at takeoff with 180HP seems too rich. Maybe that's where your carbon is coming from. What are your EGT's at takeoff and what do they peak at?
 
IMG_0302_zps146k2m2d.jpg


Here is a screenshot.. It looks like the FF EGT at take off is ~1310 density altitude was ~2400
 
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McPilot said:
I did some searching on this topic but wanted to get a fresh take on it. I have a Superior O-360 with standard compression pistons in my -7A. I have dual P Mags. It has been a while since I have flown a non fuel injected engine.

I am a bit picky as to engine operation parameters. I realize that the rule of thumb is to lean to roughness and then enrich to smooth. My question is at 75% power, what is your usual fuel flow? I am running at ~10GPH and getting carbon on my spark plugs. (BR8ES)

I had a Grumman Tiger with an O-360 and don't quite remember what the fuel flow was...

You guys with IO-360s are obviously in a different arena on this so I would like to hear from the carbureted guys only....
Click to expand...

I think you are more likely to get carbon fouling on the plugs due to oil burning rather than rich fuel mixture. Your mixture doesn't seem rich enough to produce carbon deposits. I believe overly rich mixtures are prone to leaving lead deposits, not carbon deposits. You can run pretty rich without getting carbon deposits. How much oil do you burn / replace? Also, take a peek at your cylinder tops through the plugs holes. Oil-based carbon deposits will often leave a very rough surface and the deposits will be thick.

Larr
 
The spark plugs are dry. It has been over 10 hours since oil change and have not added any. It is at 6 quarts. started at 7
 
Tiger POH

McPilot said:
.....

I am a bit picky as to engine operation parameters. I realize that the rule of thumb is to lean to roughness and then enrich to smooth. .....

I had a Grumman Tiger with an O-360 and don't quite remember what the fuel flow was...

........
Click to expand...

The Tiger POH recommends the same leaning procedure that you mention above and gives 10.8 gall/hr as the 75% fuel flow number.
 
.45 lbs per hp per hr is a good number for a well leaned engine at 75% power, which would be just above 10gph for a 180 hp engine.

Any chance the plugs are too cold a range?

If you have a c/s prop, have you gone up to ~8k ft & done a run at full throttle & 2700 rpm, with it leaned? That will come very close to 75% power to give you a baseline. Even with a f/p cruise prop, you should be able to come pretty close to those numbers if it's pitched right.

Charlie
 
NGK plug numbers run so the bigger the number, the colder the plug. If you want to try a hotter plug, the BR7ES would make sense. At $2 each this would be a cheap experiment.

I have a lot of hours on dual pMags with BR8ES plugs and offer that if you constantly run way ROP like you state, this may explain why the plugs look to have some carbon build up. I ran my engine LOP for 90% of the time and the plugs always look good - but I had a back fitted AirFlow Performance fuel injection system bolted onto my O-360-A1A from Van's. I never even took the carburetor out of the box when the engine arrived - I just sold it.

So - if you ever get to the point of rebuilding/replacing the carburetor recommend you consider back fitting the AirFlow Performance system as an alternative.

Carl
 
I have an O360 FP Sterba. At sea level I'm seeing 14.5-15 GPH on takeoff. 8000' 2450rpm and 20mp I'm seeing 8.5-9gph. I lean to rough and turn in till smooth.
 
I had an O-360-A4M before, now I have an IO-360-A4A in my RV-9A. I ran Slick mags for the first 300 hours or so and at 2550 rpm, fixed pitch prop. I was burning right at 10 gallons per hour. I installed one P-Mag on the right using auto plugs and the fuel burn dropped to 9 gal/hr, same rpm. 200 hours later, I installed a P-mag on the left and the fuel flow dropped to 8.5 gal/hr same rpm with 155 KTAS on the Dynon. I R & R'ed the -A4M with the -A4A at 1330 hrs. Same prop and same rpm the KTAS is 152 and fuel flow is still 8.5 gal/hr. Just one data point, YRMV. Dan
 
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ECi O-360 with the standard 8.5:1 pistons with a FP prop (Catto) and dual P-mags.

On take off my max fuel burn is 12.1 GPH (28.4" and 2136 RPM at 51.1 Kts).

In cruise, I can run easily run between 50 and 100* LOP. When doing so I wait until I'm above 6500' DA and then pull back until I'm at 65% power, as displayed on the Dynon. Then I lean until the Skyview tells me I'm 50* LOP, or more. This typically gives me between 150 and 155 knots true and between 6.9 and 7.2 GPH. Density altitude has a lot to do with how smooth it runs and how LOP I can run.
 
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