"Engine Problems" Solved !

[Dan Michaels]

Re: "Engine Problems" Solved !

Just run it up on a set of blocks 4" or so. Drain the fuel through the gascalator. Take it back off the block and see how much if any fuel comes out. You could also run it up on just one block (One wheel) and see if that makes a difference. That would simulate going around the corner fast and taking off.

Dan

[Robert Lees]

Re: "Engine Problems" Solved !

I tend to agree with Daryl, in that I am not convinced it's an unporting issue. But 30 seconds of googling found this (behaviour of fluid under linear acceleration).

If one assumed the tank as a cube (and I know it is not), it suggests that 1g of forward acceleration would unport the opening with Bill's 6 gallons (1/2 full). Max acceleration (0-45mph in say 3 seconds) is 0.67g.

My calculations are not accurate enough for real-time scenarios, so we need a fluid dynamicist to do the calcs for the correct-shaped tank.

But it invites the question: why does this not happen all the time on all the Taylorcraft in the world, especially with less that 6 gallons?

I would assume that if the float was going to bind up it would bind up when I ran it up to check the mags ?

Have you considered the axial movement of the float? In your skidding turn, if the endfloat (excuse the pun) of the float permits it to bind up (perhaps on the lockwire) then this is the time it will happen (quite why this does not manifest itself in a sideslip, I know not).

I have never to my knowledge come across a problem like yours that was not a sticking float.

[N96337]

Re: "Engine Problems" Solved !

I'm going to have agree with Jason and the others...I've layed in bed, thinking about this most of the night...along with sitting here until way past my bedtime, looking at it and scratching my head...and there isn't much hair left there.
I've had to sit there with the fuel valve off and wait for it to quit too...takes a while to drain that line and gascolator. In fact, I usually start mine with the valve shut if I can't find anything to tie down to or chock it with...and it seems to have plenty of time for me to get clear of the prop and walk to the door to turn the fuel back on. Also, there are lots of Tcrafts on bushwheels and 8.50's, and I don't remember anyone mentioning this before. Maybe Robert is on to something with the float or needle hanging up when not sitting still?? That would be more apt to follow suite with what is happening. I've got to say Jason has a good point in wanting to see the fuel line and layout... This is definately a puzzler!
John

[flyguy]

Re: "Engine Problems" Solved !

The more I think about it, the more it keeps coming back to the carb not delivering fuel when there is weak head pressure from the tank.
Question: do you shut your engine down by cutting off the fuel or with the ignition switch? Might be a clue there.

One additional thought: I have seen specs indicating that some other carbs require more head pressure to operate reliably. Perhaps knowing why that is so for those carbs would give a clue as to what is going on with yours.

Just grasping as straws for you here.
Darryl

[VictorBravo]

Re: "Engine Problems" Solved !

Thanks for all the head scratching guys. I cannot imagine the float sticking with a side load on the ground and not doing it during a sideslip (well, forward slip). I do some fairly wild slips on landing like most all of us. Never had an issue.

My fuel system is fairly normal as I see it.

The line from the shutoff valve goes through the firewall in the center, turns 90 degrees towards the pilot's side, then 90 degrees down to the gascolator, which is mounted on the very bottom of the firewall near the lower left engine mount tube. (The gascolator is NOT mounted on the welded tab partway up on the engine mount tube... which would put it closer to the !($*^%#$ exhaust.)

The -6 firesleeved Teflon/stainless hose from the gascolator goes upward and forward, with a slight curve for flexing, to the carburetor. The gascolator is below the carburetor in the 3 point position, and slightly below it in level flight attitude.

I do not believe this is related to the ignition system at all, I've never had any issues in flight. The mag check shows an even drop of 60-75 each.

Keep the ideas coming folks, I appreciate it.

[Robert Bradbury]

Re: "Engine Problems" Solved !

Thanks for all the head scratching guys. I cannot imagine the float sticking with a side load on the ground and not doing it during a sideslip (well, forward slip). I do some fairly wild slips on landing like most all of us. Never had an issue.

My fuel system is fairly normal as I see it.

The line from the shutoff valve goes through the firewall in the center, turns 90 degrees towards the pilot's side, then 90 degrees down to the gascolator, which is mounted on the very bottom of the firewall near the lower left engine mount tube. (The gascolator is NOT mounted on the welded tab partway up on the engine mount tube... which would put it closer to the !($*^%#$ exhaust.)

The -6 firesleeved Teflon/stainless hose from the gascolator goes upward and forward, with a slight curve for flexing, to the carburetor. The gascolator is below the carburetor in the 3 point position, and slightly below it in level flight attitude.

I do not believe this is related to the ignition system at all, I've never had any issues in flight. The mag check shows an even drop of 60-75 each.

Keep the ideas coming folks, I appreciate it.

I had a friend with a Baby Great Lakes having the same issues. He was using car gas and the needle was swelling . He changed to Teflon and never had an issue again. I'd borrow a carb to see if that solves the problem and then move on to the ignition. Be Careful though, that is spooky stuff .

I fly often even at three gallons or less and I've never had a sputter from my C90 continental which probably has 25% more fuel demand.

[Howard Wilson]

Re: "Engine Problems" Solved !

Partial vapor lock after long taxi? Standard cooling baffles?

[Robert Lees]

Re: "Engine Problems" Solved !

I've been scratching my head too. I do rolling take-offs all the time (including swinging in the yaw axis up to 180 deg tail-up and tail-down before the mains line-up) and I've never had this problem on two A-65 planes plus one C-85 model that I've done these manoeuvers on. At low fuel levels too.

Bill, can you see into the tank to make sure there are no obstructions to the fuel tank finger strainer? The mesh should extend all the way to the base of the tank, making all fuel usable. Has it ever been repaired in that area (check for welded plates on the underside of the tank)? Can you use the borescope (strut fitting inspection) to look real close inside the tank?

[quote=VB]The line from the shutoff valve goes through the firewall in the center, turns 90 degrees towards the pilot's side, then 90 degrees down to the gascolator, which is mounted on the very bottom of the firewall near the lower left engine mount tube. (The gascolator is NOT mounted on the welded tab partway up on the engine mount tube[quote]

I can't see this being the problem (the head of pressure should be the same as any other gascolator at the lowest point); I can't see it being a fuel flow to the carb problem at all, unless there is a loose fitting which is allowing air into the fuel, so preventing the full head of pressure.

If all these areas are satisfied, and I'm sure they are, the next step is the carb, IMHO.

In that there is still a problem, would it be wise to consider the cheapest option first?

It might be difficult to borrow a loaner carb for the duration of testing it in flight, waiting for those exact same set of circumstances (especially as winter draws in, and flight opportunities diminish).

I would be tempted to buy a carb overhaul gasket kit from such places as Aircraft Spruce (40 bucks or so) and open the carb up, under the supervision of your IA of course, just to satisfy yourself that:
a) the needle is not neoprene
b) there is no debris in the float chamber, potentially blocking the jet or interfering with the needle/seat interface [the bowl drain is not the lowest part of the bowl, as I'm sure you know]
c) the needle seats properly and doesn't twist as it goes up-and-down on its spindle
d) the float is full-and-free, and the seat wire-lock (or any gasket sealant [heaven forbid] does not interfere with float travel.
e) the carb/spider interface is leak-free

Download the "stromberg.pdf" from Harry Fenton's site for explanation of most things Stromberg.

Sorry to be so long-winded, and sorry if I'm going over old territory.

Rob

[Len Petterson]

Re: "Engine Problems" Solved !

Old sloshing compond in the tank or something similar what can move and plugg the tankoutlet under the right circomstanses.
I would check for it!
Len

[VictorBravo]

Re: "Engine Problems" Solved !

Sorry to be so long-winded, and sorry if I'm going over old territory.

Rob

Well it's not like I could say anything about anyone else being long-winded, ever, considering the length and detail of most of my postings I am GLAD to have everyone here thinking about this.

I do have the neoprene carburetor needle. With the exception of one previous episode of this problem over a month ago (after a full tank of reportedly alcohol free car gas), I have used only straight 100LL avgas. There has been at least two hours of straight avgas through it since the car gas. The one flight using car gas went perfectly with no problems at all anyway.

An experienced IA disassembled this carburetor and checked/set the float level, checked the functionality of the float, verified no debris in the bowl, verified the seat was not loose, and reassembled it. It ran perfectly 95% of the time (25 hours) ever since.

If something significant is wrong with this carburetor (bad needle, stuck float) , it should exhibit this problem more than just intermittently.

However, for the sake of safety I will ask my friend if we can take another look at the needle and see whether it has been damaged by the car gas. There's just not that many things here which could cause this.

[Robert Bradbury]

Re: "Engine Problems" Solved !

Well it's not like I could say anything about anyone else being long-winded, ever, considering the length and detail of most of my postings I am GLAD to have everyone here thinking about this.

I do have the neoprene carburetor needle. With the exception of one previous episode of this problem over a month ago (after a full tank of reportedly alcohol free car gas), I have used only straight 100LL avgas. There has been at least two hours of straight avgas through it since the car gas. The one flight using car gas went perfectly with no problems at all anyway.

An experienced IA disassembled this carburetor and checked/set the float level, checked the functionality of the float, verified no debris in the bowl, verified the seat was not loose, and reassembled it. It ran perfectly 95% of the time (25 hours) ever since.

If something significant is wrong with this carburetor (bad needle, stuck float) , it should exhibit this problem more than just intermittently.

However, for the sake of safety I will ask my friend if we can take another look at the needle and see whether it has been damaged by the car gas. There's just not that many things here which could cause this.

Have you done a fuel flow test ? Debris in the tank as someone mentioned could be a real problem. I had a similar problem with a Volksplane that I had. It would run for a bit and cut out. Turns out the old red AV gas had evaporated leaving behind a lod of solid crud which fouled the screen .

Other considerations: Water in the gas, Ice cyrstals from water if cold, vapour lock in the line if high heat locale or where a fuel line passes the exhaust, oh,and I just though about carb ice if the conditions are cherry.

[Mark Julicher]

Re: "Engine Problems" Solved !

We once had an Aeronca Chief in the local area that kept changing owners. One fellow would buy it and fly it six months and then suddenly sell it - cheap.
This happened several times until a good friend of mine bought it and was out flying minding his own business when the engine quit. He dead-stick landed and upon touchdown the engine came back to life.
He thought it might be water in the fuel, but the same thing happened to him again!!
Carburetor was immediately torn down and a neoprene needle was the culprit. I can't vouch for what kind of fuel was being used, but this was 28 years ago. I'm sure mogas was used some of the time but not always.

[NY86]

Re: "Engine Problems" Solved !

..Max acceleration (0-45mph in say 3 seconds) ...

No way! Unless you have after burners or a catapult...

[jgerard]

Re: "Engine Problems" Solved !

There is a lot more to how a carburator works than the needle and float. I would inspect and clean all air passageways including the mixture plate area. The Stromberg meters fuel by the back suction pressure on the float bowl.

[N96337]

Re: "Engine Problems" Solved !

There is a lot more to how a carburator works than the needle and float. I would inspect and clean all air passageways including the mixture plate area. The Stromberg meters fuel by the back suction pressure on the float bowl.

Very true... Bill, have you checked the part number and verified the settings for that engine? Does it just cut out, or just start running rough? There's a really good thread over on Supercub.org aobut a small Continental going to "auto rough" sometimes, and they chased alot of things around, including carb and carb ice, and finally discovered it was valve springs that were out of tolerance for tension...and from the sounds of it, there were a few more that found the same thing.
John