I finally got my minimax flying with a used 503 in it. I have about 7 hours on it now. I was flying home and about 3 miles out from the airfield, 800 agl when all of a sudden the engine slowed and died. At first all I saw was trees ahead but then saw out of the corner of my eye a field. Very lucky, I was over a big cow farm. Where I fly there isn't much but giant pine trees.
I dove down and made a 180 degree turn and hopped over the fence, then ground looped it hard to avoid hitting the next fence. I was luckily able to ground loop just enough to turn 90 degrees. When I got out the only damage was the tiniest rubbing of the aieleron tip fabric. Just missing a little paint.
I felt fuel starvation was most likely, popped the bowl and sure enough, empty. I think what happened is my knee might have pinched a fuel line in the cockpit. I have that see through fuel lines.
Pumped the primer to fill the bowl and tried to start engine. A few pulls and it started up. The farmer came out (who I happened to know as we buy his milk). He wasnt too worried just said "You probably don't want to leave it here or the cows will rub all over it". LOL
I let it run a few minutes, taxied over to the edge of the field, gave her full throttle, turned between two trees as I lifted off the ground, climbed to 3000 feet over the farm in case I had another problem, and returned to base. No issues at all...
Im going to replace the fuel lines with the thick, hard black rubber ones so they can't get pinched again. But very happy to have no damage. Very blessed day, thank-you God!
Also just ordered a new fuel pump. I hear the diaphrams get soft with age and this ones been sitting a really long time.
If it flies, floats or fornicates.... rent it! Flight Leader
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Well done for dealing with it! I had an EFATO in my 'Max and it was a jammed non-return valve in a brand new Primer Bulb. As the engine ran down (at around 200 feet, I grabbed for the bulb and found it sucked flat) I've since removed it completely. Well worth changing the pump diaphragms regularly as you say. Nice 'Max by the way
Really good to hear how that worked out for you!!!!!!!!!!!! JMHO, But I think I would be looking at rerouting the fuel lines vs. changing them to aa different type . Of course you could do both. But the FIRST ANSWER to (ME) would be to never have that situation happen again. IE: How would you feel if you changed to the thicker line & for some reason they got a little soft & the same thing was able to happen again? As I see it the problem is NOT the type of fuel line but where it is routed. I think some guys even PREFER the see through line so they can see the fuel flow & as well see all those tiny bubbles in it that makes everyone nervous. Just something to think about. TTT
Max, that may have been the issue as well. fuel was sucked all the way back to the primer bulb. Its new but Ive heard they can cause problems. I was thinking of using a couple tees in line to make an alternate path for fuel to flow around the primer bulb incase it jammed up. That probably was the real cause of the issue. How do you get fuel to an empty bowl if you dont have a primer bulb?
Well done for handling a potentially serious problem. So glad a field appeared just when you needed it!
I would replace your fuel line with Tygon (yellow line, but beware, not all yellow stuff is actually Tygon). This will last much longer without hardening or swelling, etc. And it's see-through. I would also fit a Facet electric pump in place of the hand bulb. The 503 makes plenty of electrical power for it, and a small 12v battery is useful for radio, etc. if you don't already have one fitted.
How do you get fuel to an empty bowl if you dont have a primer bulb?
Pull the wire clip from under the float bowl and remove the bowl, taking care to check the anti-foam plastic thingy doesn't depart the carb (mine never has), chuck out the stale partially evaporated muck then fill the float bowl to the top with filtered fuel and re-fit. Dead easy, dead quick. Been doing it for ten years.
No deteriorating primer bulb, a bit less aircraft weight, no sticky valves, no worries.
Filling to the top gives a kind of 'super choke' effect. Wang the prop over a few times with mag off choke on and throttle closed (feel for the slack in the carb cable!) I am very disappointed if my 503 doesn't start first pull after this.
Sometimes I do a very counter-intuitive thing; fill the bowl from the gascolator drain point. That will give you potentially very mucky fuel or fuel that's fine. Anyway, you can look into the bowl and see the muck ( I never see any). You might see water in the fuel so it's not actually a bad idea because you'll get a warning of things not hunky-dory. If it's all water (can look like fuel and smell like fuel), you'll not get off the ground anyway!
Glad you made it down safely without flipping over. Your 180 seems to show your utter confidence in the 503.Would the 25 hour rule have made this experience any different ? The knee cutting off the fuel does not seem plausible.Changing the fuel pump seems like a good idea. The auto electric pumps are cheap and having a second pump full time in parallel seems like a good idea. The fuel filter needs to be plastic/metal mesh and not paper. Also the impulse pipe to the pump be of the rigid type.If you think its the knee then a metal tube joint would look like a good idea in the knee area.Also check the Tank and lines for any intermittant debris. Also testing the installed system with a fuel pressure gauge ONCE would seem appropriate.
Glad you made it down safely without flipping over. Your 180 seems to show your utter confidence in the 503.Would the 25 hour rule have made this experience any different ? The knee cutting off the fuel does not seem plausible.Changing the fuel pump seems like a good idea. The auto electric pumps are cheap and having a second pump full time in parallel seems like a good idea. The fuel filter needs to be plastic/metal mesh and not paper. Also the impulse pipe to the pump be of the rigid type.If you think its the knee then a metal tube joint would look like a good idea in the knee area.Also check the Tank and lines for any intermittant debris. Also testing the installed system with a fuel pressure gauge ONCE would seem appropriate.
I agree, the knee probably was not the issue. Im thinking the fuel pump or the primer bulb, both of which are going to be replaced/ removed.
Why does the fuel filter have to be mesh? I currently have a paper one installed.
Paper filters are forbidden here. Water in the fuel clogs them and the engine stops. Your problem will almost certainly be the new primer bulb, though. Too much of a coincidence to be anything else.
Since we are giving opinions here, here is mine. Get a mesh filter, ditch the primer bulb, and install a oil injection pump. I have over 200 hrs on 2 503,s without a failure. I have done a top end and resealed both engines and noticed very little wear or carbon buildup on pistons and cylinders.
How do you get fuel to an empty bowl if you dont have a primer bulb?
If I may speak from my own experience (20+ years of UL flying). - Primer bulbs aren't needed and are often the cause of trouble. - Instead use a primer pump. ( https://www.aircraftspruce.com.....FCFoe5xoC9YEQAvD_BwE ) Use small diameter tubing plumbed in parallel with the main fuel tubing. The intake manifold must have a small injection port fitting....most newer Rotaxs come with the fitting installed. The primer pump injects fuel directly into the intake manifold; 6-8 pumps provides a good starting charge; the engine will usually start and run with no further pumping required but if the engine starts to stumble you can pump a couple more times. - The best fuel line I've found is the clear, heavy wall tubing that is used between the engine and the pulse fuel pump. This tubing is stiff and can't be collapsed with normal finger pressure. https://www.aircraftspruce.com/catalog/appages/pulseline.php?clickkey=183731 - Mesh fuel filters are fine, but so are paper filters. I've used Fram G-1 filters for years. ( https://www.midlandhardware.co.....RYSwTphoCk-YQAvD_BwE ) Most important is having a large enough filter so that it won't clog with minor debris. I had one filter clog shortly after filling the plane with dirty gasoline (bought at a local airport). I've never seen or experienced water clogging a paper filter. - In the case of my clogged filter it didn't result in an engine out because I used a low pressure sensor in the fuel line. Honeywell sells low pressure switches. The switch required is a 2 psi NC (normally closed) 5000 Series part no. 76061 ( https://www.alliedelec.com/product/honeywell/76061-00000020-01/70111580/ ). Install the switch just before the carb input port. Mount a red warning lamp in the cockpit wired to the the pressure switch. When the fuel pressure at the carb drops below 2 psi the switch closes a circuit and the lamp lights. Several times I would see the lamp just begin to flicker telling me the pressure was dropping. Changing the filter always made things good again. - I never used an electrical fuel pump, just the normal Mikuni pulse pump. Keep the pulse line short (less than a foot is good). Mount the pump above the engine pulse port and be sure the pump has the weep hole.
This pretty much makes the fuel system bullet proof in my experience.
In the UK we're always told to use mesh filters on 2 strokes. This is because of bacterial growth in 2 stroke mix that builds into a transparent slime. This clogs the paper filters, but is less damaging on mesh filters, although it will clog them eventually if not cleaned. The best way to clean them is to push fuel backwards through the filter to get the slime off the other side of the mesh.
Also, from experience I would say to use the largest filter you can fit. That way, you minimise the possiblity of the whole filter surface becoming blocked. In the past I've used very large automotive paper filters, and replaced them every 6 months. The filters are very cheap on Fleabay, about 50p each (70cents), so it makes sense to buy them 10 or 20 at a time, and replace them often.
If I may speak from my own experience (20+ years of UL flying).
- I never used an electrical fuel pump, just the normal Mikuni pulse pump. Keep the pulse line short (less than a foot is good). Mount the pump above the engine pulse port and be sure the pump has the weep hole.
Thanks for the helpful info. I too was told an electrical pump is not really necessary. Is there a reason why the pulse pump has to be mounted above the engine pulse port. I just figured mine happens to be an inch below the pulse port.
If the pulse pump inlet is below the engine pulse port, fuel from crank case vapors can accumulate in the pump and hydraulic lock the diaphragm from pumping. This is the reasoning for the weep hole, to allow accumulated fuel to drain out. You also want the weep hole to be pointing down, or at a down angle laterally. Joe
There are two ways for a pulse pump to fail. One is if a membrane fails, and the other is if the pump fills with oil and prevents the membrane from moving. The weep hole is to vent excess oil from the pump. Mounting the pump above the engine pulse port prevents oil from flowing from the engine to the pump.
If your pump is only an inch below the port it is fine, I'm sure.
RadfordC and Joe.scalet, Thanks for that information. My pulse pump connecting tube is only about 4.5 inches long from engine pulse port to pulse pump, but it slopes down at an angle of about 8 to 10 degrees from motor to pulse pump. I guess I will re-position the pump a little higher when I get a chance.
TTT, The electrical or facet pump does provide an extra layer of protection for sure. Since I did not install an electrical pump in parallel, I just need to be a bit more vigilant on the state/ condition of my pulse pump.
Another little tip I picked from RadforsC's note above is the use of the fuel primer/plunger. I used to prime it about 2 to 3 strokes before hitting the starter button, and it never seemed to have any effect. Yesterday while starting the engine, I jabbed the plunger about 8 times and the motor fired right up on the first crank. So that was another little lesson learnt.
Good idea to raise the pump position realitive to the position of the engine pulse port. Everything I have ever read says the pump should be above the port. I installed my electric pump in series in the fuel line system. It's not the redundancy of a " true " properly designed parallel system BUT it does fill the carb.fuel bowls to their top level and made a noticeable difference in crank time when starting the engine after it had been sitting a few weeks or more. And the series setup is considerably less complicated than a proper parallel system. I guess a (Y) fitting before the pulse pump to bypass it and then (T or Y) back together to continue to carbs. would be the next simplest way to go for a little bit of pulse pump failure security. But the pulse pumps if properly installed.& maintained have proven to be pretty darn reliable. The prime plunger is probably the better way to go for the quickest starts. TTT
One note of caution, not all of the Mikuni pulse pumps came with a drain/bleed hole. The hole is very small. Look and be sure yours has one. There is information on the CPS web site among others. Joe
- In the case of my clogged filter it didn't result in an engine out because I used a low pressure sensor in the fuel line. Honeywell sells low pressure switches. The switch required is a 2 psi NC (normally closed) 5000 Series part no. 76061 ( https://www.alliedelec.com/product/honeywell/76061-00000020-01/70111580/ ). Install the switch just before the carb input port. Mount a red warning lamp in the cockpit wired to the the pressure switch. When the fuel pressure at the carb drops below 2 psi the switch closes a circuit and the lamp lights..
Radfordc: You have a lot of useful tips, and I will adopt your fuel low pressure warning. I have been thinking of installing a pressure gauge, but I really don't need another gauge to monitor. Du you have a photo of your installation? Is the pressure switch mounted to the firewall, or to the engine?
If you want an easy way to monitor all critical parameters install a Grand Rapids Technology (GRT) EFIS. I have an analogue Airspeed and Tachometer for at a glance information (duplicated in the EFIS) plus all the temps, pressures, etc. in the EFIS. You can program all of your limits into the system, both high and low. If any limit is exceeded a Large, bright, red light comes on and the offending limit is displayed. It can also provide a headset tone. I call this the "LAND NOW" alert. The digital instruments are a lot more reliable than the analogue ones for an equivalent total price. This way I don't have to be distracted reading/interpreting numbers. You could probably do this with an Android App and phone but I don't think it would be as rugged or accurate. Just my 2800 bits worth! Joe
If you want an easy way to monitor all critical parameters install a Grand Rapids Technology (GRT) EFIS. I have an analogue Airspeed and Tachometer for at a glance information (duplicated in the EFIS) plus all the temps, pressures, etc. in the EFIS. You can program all of your limits into the system, both high and low. If any limit is exceeded a Large, bright, red light comes on and the offending limit is displayed. It can also provide a headset tone. I call this the "LAND NOW" alert. The digital instruments are a lot more reliable than the analogue ones for an equivalent total price. This way I don't have to be distracted reading/interpreting numbers. You could probably do this with an Android App and phone but I don't think it would be as rugged or accurate. Just my 2800 bits worth! Joe
Sorry no pics. The low pressure switch is located at the engine. Install a "Tee" fitting in the fuel line between the fuel pump and the carb. The pressure switch is connected to the Tee. Run a wire from one terminal of the switch to ground and another wire to one terminal of a lamp in the cockpit. The other lamp terminal goes to the battery positive terminal through a master switch. You need the master switch because the lamp will light as soon as you shut down the fuel pump. See if this diagram makes sense.
The fuel pressure switch looks to be on the same principle as the ordinary car oil pressure switch and warning light system.It is calibrated to a lower level.The real question to ask is what happens when the light comes on.If one is over an area with landing sites and help it sounds alike a good idea, On the other hand if its a remote area with no help ( e.g middle of Taklamakan) then an electric standby fuel pump seems like a good idea even if it is a cheap automotive one.It can at least take you to the next civilization.
Oops, in the diagram I forgot to show the fuel filter. The pressure switch goes between the filter and the carb.
When using the pressure switch you will see the lamp just start to flicker as the fuel pressure at the carb drops close to 2 psi. This is still enough pressure to keep the carb full. Unless something really drastic happens the time between the lamp flickering and a full engine stoppage is many hours.
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