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Engine starving for fuel

Not unusual to see a little water and debris in bottom of float bowl.
presence of some crap in the bowl may not indicate that’s the cause of your issues.
Fly it carefully till you confirm you’ve found the problem.
 
Not unusual to see a little water and debris in bottom of float bowl.
presence of some crap in the bowl may not indicate that’s the cause of your issues.
Fly it carefully till you confirm you’ve found the problem.

Oh I will it does get my full attention when it starts to stumble. Not so bad when I’m over pastures but over the timber it sucks. It’s been doing it for awhile and I was running out of things to try and it takes all the fun out of flying worrying if it’s going to quit
 
Make sure you don't have an up and down area in the fuel line routing. I've seen this when the aircraft in question had an extra long flexible line between the gascolator and carb, so had some of the excess length of fuel line tied off to the engine mount to clean up the installation. The line was routed in such a way that it went up, then back down, then up again to the carb. That created an air trap that would intermittently stop the fuel flow and was the cause of multiple engine failures and forced landings. Just rerouting the line to eliminate the air trap was all it took to fix the issue.

-Cub Builder
 
While the cowling is off grab the airbox and twist to see if the carburetor bowl is loose. If the carb halves are loose---fix it. Marvel Scheblers can get weird if the parts are not tight and it seems no two carbs act alike. One might idle 200 RPM faster and refuse to quit at idle cutoff and the next one might lope at cruise. This is my first place to look.
 
So raise the tail to level flight and check the GPM flow at the carb fuel line , then sump then, carb bolt drain plug, do it with the left, right both. Rotate the fuel selector and study the flow. rule out the fuel system. Finger screens? GPM flow should be reasonably the same at all three stations, sump, fuel line , sump bowl. Sticking bowl float? wouldn't fly it till I found the smoking gun. I I would think you should be flowing 17 oz. per minute plus or over 8 plus gallons per hour by gravity.Max GPH for a O 200 ? got have the same in gravity flow rate.
 
So raise the tail to level flight and check the GPM flow at the carb fuel line ,
You want to do a flow test with the plane in the most adverse position. That means tail very low at the very least. Preferably done on a slope with the nose high.
For this particular purpose of flushing the carb, just all wheels on the ground will work.
 
Even better and I agree there Mr. Skywagon8a. Just thinking about establishing a base line for level flight. But you do make a good point.
On a side note, Every super cub I have ever flown including mine will run out of gas at full continued climb tilt.
 
Well I put a rebuilt carb on my cub . Two trips checking water hasn’t quit . That fixed it ( I hope)


Sent from my iPhone using SuperCub.Org
 
Increase the size of the fuel lines by 125%.


Wasn’t the fuel lines. I didn’t have covers on the gooseneck fuel caps and it was letting dust get in the tanks and plugging up the filter. When I would land it would back flush the filter and run ok for awhile. I put cover on the gas caps and a quick drain in front of the filter to sump it. No problems now
 
About 7 days to final inspection on my Experimental Super Cub, with a Titan IO-370, with electronic mags. Checked gravity fuel flow in a 3 point attitude at the inlet of the Aeromotive Silver Hawk, and got 17 gal per hour, from both tanks. Have read where it should be a certain amount above highest consumption, which I suppose would be about 15 or so an hour. Does this sound like the correct flow. Using 3/8 fuel lines. Thanks
 
About 7 days to final inspection on my Experimental Super Cub, with a Titan IO-370, with electronic mags. Checked gravity fuel flow in a 3 point attitude at the inlet of the Aeromotive Silver Hawk, and got 17 gal per hour, from both tanks. Have read where it should be a certain amount above highest consumption, which I suppose would be about 15 or so an hour. Does this sound like the correct flow. Using 3/8 fuel lines. Thanks
Sounds to be too low. Do you have the pressurized fuel cap vents? That will help.

This is the FAA requirement for certified airplanes:
CAR 3
3.434 Fuel flow rate for gravity feed systems. The fuel flow rate for gravity feed systems (main and reserve supply) shall be 1.2pounds per hour for each take-off horsepower or 150 percent of the actual take-off fuel consumption of the engine, whichever is greater.

3.435 Fuel flow rate for pump systems. The fuel flow rate for pump systems (main and reserve supply) shall be 0.9 pound per hour for each take-off horsepower or 125 percent of the actual take-off fuel consumption of the engine, whichever is greater. This flow rate shall be applicable to both the primary engine-driven pump and the emergency pumps and shall be available when the pump is running at the speed at which it would normally be operating during take-off. In the case of hand-operated pumps, this speed shall be considered to be not more than 60 complete cycles (120 single strokes) per minute.
 
Given that the Silver Hawk is an injection servo, and that this airplane probably has 2 fuel pumps, wouldn't the required test be with a single pump running rather than a gravity feed test? If both pumps fail the engine is going to quit no matter how fast the gravity feed.

Just asking.
 
3.435 Fuel flow rate for pump systems. The fuel flow rate for pump systems (main and reserve supply) shall be 0.9 pound per hour for each take-off horsepower or 125 percent of the actual take-off fuel consumption of the engine, whichever is greater. This flow rate shall be applicable to both the primary engine-driven pump and the emergency pumps and shall be available when the pump is running at the speed at which it would normally be operating during take-off. In the case of hand-operated pumps, this speed shall be considered to be not more than 60 complete cycles (120 single strokes) per minute.

Given that the Silver Hawk is an injection servo, and that this airplane probably has 2 fuel pumps, wouldn't the required test be with a single pump running rather than a gravity feed test? If both pumps fail the engine is going to quit no matter how fast the gravity feed.

Just asking.

If his engine is producing 195 hp(?), he should be flowing about 29-30 gph with the aux pump running. 195*0.9=175.5/6=29.25 gph.
 
Interesting topic, and should be in its own thread, not in one about intermittant fuel starvation.
 
It's interesting that the Part 23 fuel flow requirement is slightly less stringent than CAR 3, which is quoted in #48.

Here is 23.955
"(b) Gravity systems. The fuel flow ratefor gravity systems (main and reservesupply) must be 150 percent of thetakeoff fuel consumption of the engine.(c) Pump systems. The fuel flow ratefor each pump system (main and reserve supply) for each reciprocating engine must be 125 percent of the fuelflow required by the engine at the maximum takeoff power approved underthis part."

https://www.govinfo.gov/content/pkg/CFR-2011-title14-vol1/pdf/CFR-2011-title14-vol1-part23.pdf

Edit: FWIW, data from my -12:
[FONT=&quot]Conditions:[/FONT]
[FONT=&quot]Fuel lines are 3/8” aluminum tubing.[/FONT]
[FONT=&quot]Right-hand tank only, because it has the longest run of fuel line and no forward outlet.[/FONT]
[FONT=&quot]Approx 5 gallons of fuel in the tank[/FONT]
[FONT=&quot]Pitch angle is 11 deg up from 3-point attitude, which corresponds to full power, no-flaps climb at 40 MPH.[/FONT]
[FONT=&quot]3-point attitude is 11.5 deg up from level HRL. Therefore, total pitch up angle of the HRL is 22.5 deg for this fuel flow test.[/FONT]
[FONT=&quot]Fuel line disconnected at the carburetor and flowed into a 250 ml graduated cylinder.[/FONT]
[FONT=&quot]Flow start-up for each test is not instantaneous - it takes approx 1 second to fully develop due to inertia of the fuel column in the line. Therefore 0.5 second is subtracted from each flow time.[/FONT]

[FONT=&quot]Data:[/FONT]
[FONT=&quot]Trial #[/FONT]
[FONT=&quot]Volume (ml)[/FONT]
[FONT=&quot]Measured Time (sec)[/FONT]
[FONT=&quot]Adjusted Time (sec)[/FONT]
[FONT=&quot]Adjusted ml/sec[/FONT]
[FONT=&quot]Adjusted gal/hr*[/FONT]
[FONT=&quot]1[/FONT]
[FONT=&quot]218[/FONT]
[FONT=&quot]7.6[/FONT]
[FONT=&quot]7.1[/FONT]
[FONT=&quot]30.7[/FONT]
[FONT=&quot]29.1[/FONT]
[FONT=&quot]2[/FONT]
[FONT=&quot]219[/FONT]
[FONT=&quot]8.9[/FONT]
[FONT=&quot]8.4[/FONT]
[FONT=&quot]26.1[/FONT]
[FONT=&quot]24.8[/FONT]
[FONT=&quot]3[/FONT]
[FONT=&quot]215[/FONT]
[FONT=&quot]9.1[/FONT]
[FONT=&quot]8.6[/FONT]
[FONT=&quot]25.0[/FONT]
[FONT=&quot]23.8[/FONT]
[FONT=&quot]4[/FONT]
[FONT=&quot]210[/FONT]
[FONT=&quot]7.7[/FONT]
[FONT=&quot]7.2[/FONT]
[FONT=&quot]29.2[/FONT]
[FONT=&quot]27.8[/FONT]
[FONT=&quot]Average[/FONT]
[FONT=&quot]26.4[/FONT]
 
Last edited:
Sounds to be too low. Do you have the pressurized fuel cap vents? That will help.

This is the FAA requirement for certified airplanes:
CAR 3
3.434 Fuel flow rate for gravity feed systems. The fuel flow rate for gravity feed systems (main and reserve supply) shall be 1.2pounds per hour for each take-off horsepower or 150 percent of the actual take-off fuel consumption of the engine, whichever is greater.

3.435 Fuel flow rate for pump systems. The fuel flow rate for pump systems (main and reserve supply) shall be 0.9 pound per hour for each take-off horsepower or 125 percent of the actual take-off fuel consumption of the engine, whichever is greater. This flow rate shall be applicable to both the primary engine-driven pump and the emergency pumps and shall be available when the pump is running at the speed at which it would normally be operating during take-off. In the case of hand-operated pumps, this speed shall be considered to be not more than 60 complete cycles (120 single strokes) per minute.

Does look like mine is low, looks like about 22.5 or higher is needed. I do have the Altee caps with forward snorkels. Will disconnect from the fuel selector outlet and see what I get there. Note the engine runs fine with no fuel pump on, but will not turn up full static RPM. IMG_0741.jpg
Thanks for the reply
 

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Note the engine runs fine with no fuel pump on, but will not turn up full static RPM. View attachment 56959
Thanks for the reply
Is that prop a constant speed or ground adjustable? Adjust the low pitch stop to a lower blade angle for more static rpm. If it has a governor, back out the high rpm stop screw for more rpm.
Did you run your aux fuel pump to get your flow rate? That should flow more fuel.
 
Note the engine runs fine with no fuel pump on, but will not turn up full static RPM.

What is the fuel pump configuration on this airplane? I would expect an engine driven mechanical pump and an electric aux pump. What is the fuel pressure with no pump running?
 
It is a ground adjustable Whirlwind prop, set at 15 degrees. Fuel flow was gravity only no pump. The engine does have an electric pump, and mechanical. The mechanical was shipped on the new engine. Aeromotive suggest in trouble shooting that, if you can not increase RPMs over a certain level, it may be oil in the air chamber. Some what typical on an updraft set up for Lycoming type engines.
Thanks for all the help, will see what we find out
 
Did the fuel flow yesterday with the boost pump on, it nearly doubled the flow, about 31 gal an hour. That meets all the requirements mentioned. Still concerned if wot and fuel pump failed. Will keep working on getting the gravity flow up, but for now, the boost pump did the job.
Really appreciate the advise and comments
 
Did the fuel flow yesterday with the boost pump on, it nearly doubled the flow, about 31 gal an hour. That meets all the requirements mentioned. Still concerned if wot and fuel pump failed. Will keep working on getting the gravity flow up, but for now, the boost pump did the job.
Really appreciate the advise and comments
If the fuel pump fails at wot, you just turn on the boost pump. That is what it is for.
Do not be concerned with the gravity flow. You have a "pumped" system and do meet those requirements.

Enjoy your new Cub.

I have the same prop on my IO-360 Cub. It pulls like a work horse. You will be happy.
 
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