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Radical Fuel consumption increase??

OVEREASYGUY

SPONSOR
New Gloucester, Maine
Pa18 0-320 160 hp carburetor is model 10-3678-32, fuel capacity 46 gallons.

before my $26k engine overhaul I could fly almost 6 hours before landing.
my fuel consumption is crazy now. The carburetor was rebuilt by aerotec at the time they rebuilt the carburetor. No visible leaks. Fuel tanks have vents facing forward & they are open & I see no reason fuel would be coming out of them during flight.
At a flyin I taxied by my friend Harvey Calden & he said it smelled like it was running super rich he could smell the unburned gas.

When in flight the mixture does work however even when leaned out it’s still burning crazy amounts of fuel.

My cub is certified. Is there a range of main jet sizes that are allowed? Might I reduce main jet in hopes of ending up with better fuel/air mixture. The carburetor is pathetically simple I really don’t want to spend $900 having it overhauled & find that’s not the problem! Any help would be greatly appreciated.
also primer was replaced with new one so no issues there.
cliff dow in maine
54ME
Dow.us
 
you would SEE a really rich burn as black exhaust smoke..... well I mean the guy you taxied by would see it...

what to spark plugs look like?

what does inside of exhaust pipe look like?

sunk float?
 
The fuel atomization and discharge nozzle incorporates the main jet - the main jet varies in hole size by carb application and is typically stamped with a number corresponding to size. In addition to a wrong float level another potential source of fuel is the accelerator pump check valve. It normally only opens under accelerator pump pressure during throttle opening, but if it leaks under venturi suction it can add more fuel than wanted. It's externally adjustable for resistance to flow. Primers new and old might leak. Cap off the inlet to the primer and see if there's any change. Or....crack the primer open when running. It should go rich and drop some rpm plus have a stumble from a too rich mixture. If not maybe it's already leaking under partial throttle. Not an A&P here but as an owner I've dealt with leaking discharge valves and primers.

And as Mike notes do your exhaust and plugs look sooty?

Gary
 
HEY CLIFF!!!

Are you seeing high fuel flow numbers or is the fuel just disappearing?

With the engine not running, push the mixture in and see if the carb starts leaking.
 
Left my house the other day with 3/4 in right tank 17 gallons hour later it ran dry. Landed with other tank & fueled up.
just out of annual mechanic found no issues.
carb has a rich/lean adjustment on it I’m assuming that for idle mixture? It was out about 3/4 of a turn does that sound about right?
hoping to do some more testing Wednesday.
 
If you lean it in flight to the point of roughness then enrichen slightly, does it still consume excessive gas?
 
What's your fuel consumption per hour? Used to be about 6 eh?

I guess fuel cap gaskets aren't leaking? Any stains on the tank covers or wing or tail behind them? Make sure the gaskets seal well and the caps tight.

Unburned fuel smell (= heavy sweet exhaust odor): Mags timed and both functioning? Leaning in flight any help?

How soon does your oil turn black? Excess fuel will wash the cylinder walls and end up in the sump with black carbon. Does the oil smell of fuel dilution?

Mixture screw: Should give 25-50 rpm rise at idle cutoff.

Gary
 
How do you know that tank was 3/4? Was the plane parked level? Did you use a calibrated stick? Fill both tanks again, fly for 1 hour switch tanks, fill up the tank. How many gallons did it take? Now start asking questions.
 
What are you burning an hour? What prop? Sensenich for break in? My Sensenich will burn 8.5 gph where my Borer burns 7 gph.
 
What does the engine shop say? Did they run it on a test stand. Have had the carb shop rejet when i had one running to rich. Maybe you were to lean before.
 
We could use some hard numbers. What is the RPM DROP when you pull carb heat at 1800 RPM and 2400? If you have a 4 cylinder EGT/CHT how many degrees does the EGT change before you get first cylinder to go lean of peak? What is exact fuel burn at 2400 RPM? Fill both tanks to top. Fly 1/2 hour on right then 1/2 hr on left NO BOTH!! Refill tanks and get good fuel use numbers for each tank. Do you get a rise in rpm if you pull mixture out slowly to stop the engine? If someone smelled unburned gas as you taxi by I would expect a fuel leak not a carb issue. Check the fuel bowl and make sure it is not loose very common problem you should see some fuel stains on side of carb or fuel slosh if you shake the wings. Did anyone play with the fuel tanks/lines when the engine was rebuilt? Pull the wing root /tank covers and double check everything, shake wings with full tanks look for leaks. Leave fuel on and remove disconnect primer line from engine see if it is leaking (new primer can have issues). We need a bit harder numbers if you are really burning 17 gal at 2400 RPM you should have a pretty big rpm drop or engine should quit unless you are flying at -30.
DENNY
 
Cliff

Just put on the John Deer carb, simple and cheap, nothing to them. From your FB post about carbs and airplanes that they are over priced. :lol:
 
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