180 fuel flow issues

[Sturgill]

I have two Cessna 180s. A 1960 and a 1969. We bought the 1960 about nine months ago and it had been stored for 12 years in a hanger with the tanks full of 100 Ll. I was able to put a replacement magneto on it and fly it home the day I bought it. It’s very clean and we really love it. I hate to admit it, but it flies better than my pponk 180 In terms of performance.

We now have about 50 hours onit, and are having a lingering problem that we can’t solve. Occasionally, the engine loses power upon acceleration for takeoff. The first few times this happened the problem was very severe. To the point where we did not takeoff and left the airplane at the outstation while we troubleshot the problem.

This is a stock airframe with 65 gallon bladders. Along the way we have determined that the bladders are in very good condition and clean. They were put in in 1996 and 2006. The finger strainers are clear. I had the filler assemblies off and did find that the bladders were not clipped to all points on the top of the wing interiors and we corrected that.
The gascolator is clean. The carburetor intake filter is clean. The fuel hose between the gascolator and the carburetor is new and is clear. We get over 30 gallons an hour of static flow out of the flex hose measured into a canister.
Normal takeoff on this engine is around 22 gallons per hour and under normal circumstances that’s what we get.

We are not having the severe problem that we once did and it does not happen every time. But tonight on takeoff, there was a momentary lapse, and when I glanced down, I saw only 14 gallons per hour on the fuel flow, but it quickly picked back up to 22. I am running out of ideas.

When this originally occurred as a problem, we found that the static flow was way low. We solved it by blowing backwards through the system to the tanks. I felt like we probably dislodged some restriction, and I figured it was in the tanks, blocking the finger strainers. That got the static flow back up to normal. At the time we drained all the tanks by pumping them out through the filler ports, and filtered all the fuel so we knew we had clean going back in. And this was after flying about 20 hours without issues. With the recent issues, I did open up the tanks and found the bladders to be extremely clean, so that’s not the issue.

I have never had one of these fuel valves apart. Is there anything inside there that could be moving and creating a blockage? That is the only thing between the tanks themselves and the carburetor that we have not had apart.

To summarize, this only occurs on initial acceleration on takeoff. Once the engine gets up to speed, it stays up to speed. Any ideas appreciated!

 

[BC12D-4-85]

I don't know why, just my nature to suspect carbs for this. Like a sticking fuel inlet valve-float combo, a bowl vent issue, a FOD in the float bowl, or something that temp restricts flow, Flow requiring fuel both into the carb and out the main fuel nozzle. The reduced fuel flow means there's still some, but not the 22 you expect to see. Not A&P just suspicious when things don't work like they should.

Edit: Another restriction might be carb ice. Lower air flow = lower fuel flow.

See the attached manual for the MA-4-5 and look at Troubleshooting: Rough engine lean, for example.

Gary

 

[skywagon8a]

It sounds like you did everything except to flush out the carburetor. Pull the drain plug on the carb and let some fuel flow through. Try to catch what comes out in a filter/paint strainer to see if there are any particles or water droplets. Specs of dirt and water can sit in a small sump in the bottom of the bowl...never leaving. Occasionally portions of these contaminants get sucked into the engine giving symptoms as you describe. Flushing is the only way to eliminate totally.

 

[Sturgill]

We did flush the carburetor and also removed and inspected the inlet screen. All clean.

I did swap it with another carburetor for a time. We didn’t experience any issues. But, I didn’t feel confident that the carb was the root problem because of the irregular nature of the issue. Remember, we had a definite flow restriction somewhere upstream that has never been resolved with certainty.

 

[skywagon8a]

To summarize, this only occurs on initial acceleration on takeoff. Once the engine gets up to speed, it stays up to speed. Any ideas appreciated!

Another thought. A carb has different passages for flowing the fuel depending on the throttle position. Fuel flows through one set of passages during the idle phase (up to around 1200 rpm) and through the main jet above that rpm. It sounds as though idle and full power flows properly. It's the transition between idle and full power where the issue lies. This includes small openings near the venturi and the accelerator pump. A restriction in those openings or their passages and/or a leaky/weak accelerator pump could contribute to your issues.

Had this engine been using auto gas prior to it's storage? Perhaps auto gas gummed up small passages inside the carb?

 

[Sturgill]

I do not believe auto gas was used. I was fortunate that the previous owner stored it with 100LL.

 

[Gordon Misch]

Perhaps a loose section of hose lining between tanks and gascolator? Could potentially partly close off some times and not others?

 

[cubdriver2]

Water in carb bowl?

 

[BC12D-4-85]

Don't discount the carb ice buildup potential during taxi. Heat on to the runway then off for takeoff. Try that and see if it happens again.

Gary

 

[skywagon8a]

After sitting for 12 years the accelerator pump leather could have taken a set and not be pumping fuel when the throttle is opened. Disconnect the pushrod from the throttle arm and move the throttle by hand. Is there a resistance? Does fuel get pumped?

There is a ball check on the inlet side of the accelerator pump. If that is not seated properly the fuel will pump backwards. There is another ball check on the outlet side, which creates suction so the pump draws in fuel when the throttle is closed.

If there is any question to the above....I would take the carb apart to check it out. Not a difficult thing to do.

 

[arborite]

in your original post, you mentioned you saw a momentary fuel flow of 14 gph then it returned to 22. what gauge are you using to read this? is it the stock gauge, or is it a flow meter like a Shadin that measures actual flow?

 

[skywagon8a]

in your original post, you mentioned you saw a momentary fuel flow of 14 gph then it returned to 22. what gauge are you using to read this? is it the stock gauge, or is it a flow meter like a Shadin that measures actual flow?

In addition to this, there is a small delay in the flow reading on fuel flow meters after the fuel flows. So the time when the flow is shown may differ from what you think the throttle setting may be.

 

[Sturgill]

It’s a red cube EI flowmeter. Between the gascolator and the carb.

We are going to swap carbs tomorrow. At this point I think it has to be either the carb or something in the fuel valve.

 

[skywagon8a]

It’s a red cube EI flowmeter. Between the gascolator and the carb.

That's the one with which I've noticed the slight delay.

 

[arborite]

I wonder if the float is sticking. contamination/crud in the carb probably most likely scenario. does it go away if you bring in the power very slowly? there’s a lot of things changing from idling to WOT as referenced earlier.

 

[Sturgill]

We swapped to a new carburetor today. It did fine afterwards. It’s beean intermittent issue all along, so I guess we will see how it does over time.

Thanks for all the input.

 

[BC12D-4-85]

Did the old carb shoot gas to the ceiling when the accelerator pump was activated via quick open throttle?

Gary

 

[Cbass]

I had a similar fuel flow issue and decrease of power on take off with a pponk engine. We went through the entire fuel system and narrowed it down to the carburetor. Even though it only had 25hrs on it I had it gone through and the jetting adjusted. When it came back the problems were solved.

 

[Sturgill]

Ok. We changed the carb yesterday. Just flew it. 1st takeoff was fine. 2nd and 3rd, it did it again. Flow drops off to about 14gph for 1-2 seconds and then catches up and runs fine.
So it is not the carburetor.

The clue here is that it always happens under acceleration. Static run ups are fine every time.

At this point I have either changed or inspected everything in between the tank and the carburetor except the valve, which costs $3,500 and is a bear to swap.

Any more ideas? Good thing I have 3 airplanes!

 

[skywagon8a]

I don't know which fuel selector valve you have. The one I had could have the O rings replaced without removing it from the plane. It's a simple device....definitely not worth $3500. Your issue doesn't sound like a fuel valve.

 

[BC12D-4-85]

If you try single tank selection (Left then Right) does it make any difference? I recall a fuel line drain between the valve and fliter (?). Might be inside an inspection cover on the belly. Might make sure it's flowing ok with nothing in a line low spot like debris or water.

Static runs are tail low. Takeoff more level. Does it bog early when tail low or wait until the tail comes up?

Gary

 

[skywagon8a]

If you try single tank selection (Left then Right) does it make any difference? I recall a fuel line drain between the valve and fliter (?). Might be inside an inspection cover on the belly. Might make sure it's flowing ok with nothing in a line low spot like debris or water.

Static runs are tail low. Takeoff more level. Does it bog early when tail low or wait until the tail comes up?

Gary

That fuel drain was an AD note installation.

 

[ZK Kiwi]

"It’s a red cube EI flowmeter. Between the gascolator and the carb."

With a carb you should have the Gold transducer

It’s a red cube EI flowmeter. Between the gascolator and the carb.

 

[BC12D-4-85]

See page 3 for transducer required: https://iflyei.com/wp-content/uploads/FP-5L-D-Sub-II-Rev-I.pdf

Gary

It’s a red cube EI flowmeter. Between the gascolator and the carb.

We are going to swap carbs tomorrow. At this point I think it has to be either the carb or something in the fuel valve.

 

[Sturgill]

It is the gold FT-90. I used the “red cube” name incorrectly. I have installed about 10 of the EI fuel flow systems and have never before had issues.

 

[arborite]

Don’t know about the 180, but the 182 seemed to change the fuel vent line layout every few years to deal with fuel imbalance, siphoning, maybe other issues. Wonder if the tanks aren’t venting properly during the takeoff run for some reason. try different fuel levels and tank selection. If you have vented caps, make sure they are open.

have you tried a tail low takeoff without changing the attitude of the plane?

trying to think of easy (free) things to try. you’ve already spent a lot….

 

[BC12D-4-85]

I think this is what Sturgill says. If run up in 3-point static mode it powers up to redline and will maintain rpm/MP for the typical time it takes to get otherwise airborne. If the C-180 is allowed to takeoff via transition from 3-point, at some stage of takeoff and fuselage attitude the engine may falter. If observed when it falters, the fuel flow gizmo says ~14 gph briefly, then recovers to 22. From then on in any flight mode, attitude, or power setting it performs as expected.

If that's the case, when during the takeoff does it typically falter...fuselage attitude, run time, still on ground or once airborne? Just curious if this is what's happening?

Gary

 

[Sturgill]

It falters when the airplane accelerates from a stopped position. Within a second or two of brake release or full application of power.

 

[Supercubrancher]

Sky geek has fuel valve rebuild kits for around $50. More labor involved than $50, however if it sat for 15 years there could easily be gunk in the valve. The one I put in my build has a pipe plug in the bottom of the valve to drain the low spot in the valve. When I took the valve apart it was clear full of gunk and wouldn’t operate properly. After cleaning and new rings it works great. I am no A and P but it sound like the only thing you haven’t looked at

 

[BC12D-4-85]

It falters when the airplane accelerates from a stopped position. Within a second or two of brake release or full application of power.

Thanks. Does it ever falter when doing successive static runups? From #19: "The clue here is that it always happens under acceleration. Static run ups are fine every time".

Hard to believe there's any significant difference in available fuel supply between static and acceleration with the same fuel on board. That assumes adequate/not minimal fuel at the tank outlets (I assume there's just one per tank?) during both conditions. That also assumes the selector is on both tanks (or is it off and on only like early C-185's?). And that assumes the fuel vent system is unobstructed internally (no moving blockage for example). Does the vent employ a check valve or is it just plain tubing?

If acceleration repositions the low fuel level aft in the tank which drops available head pressure, or the tank vent is temporarily obstructed, then reduced available inlet flow at a contaminated valve could make flow to the carb lower.

Gary