Full power fuel starvation

[Keenaviator]

I've heard of the inside of the fuel line being shaved when installing onto a spigot on one of the many fittings. Sounds like you fuel flow is being restricted somewhere. Also ensure there are no kinks in the lines. Laurie

 

 

[JabSP6]

JabSP6Type 2 fuel pump with the 74mm pushrod fitted (type 1 has 72mm)

At least you can cross that one off the list Frank. Was just thinking outside the square what could cause this problem. Let us know what you find please Frank.

Safe flying

 

Andrew

 

 

[Oscar]

I remember having a problem with a mechanical fuel pump on one of my cars, everything seemed to spec, then (finally) I discovered that the spacer between the pump and the engine block was the incorrect thickness - too thick! Have you tried disconnecting the fuel delivery line to the carby and pulling the engine through say 10 revolutions and seeing what the delivered fuel quantity is? That might not be enough to do an accurate conversion to the required delivery rate / revs but if it's definitely on the marginal side it might show up. I've also experienced a fuel line on the suction side that, because it was twisted when installed, actually managed to pretty much close itself off due to the change in radius of the curve from the suction pressure.

 

 

[Jabiru Phil]

Had the same problem on a cabin cruiser some time ago. Frustrated me until I removed the engine cover and noticed the clear fuel line to the carby collapsed when under full load.

 

Still a mystery to me as it was after the pump and supposedly under pressure.

 

I coiled some wire around the hose so it didn't collapse until I replaced the line.

 

Frank, can you test with the cowl off?

 

Phil.

 

 

[frank marriott]

Spacer between engine block and pump would be critical as the difference between type 1 and tyre 2 pumps is a 2mm difference in the pushrod. Can only assume the spacer is correct.

 

Phil - can run without cowls, everything appears normal. The problem being with the original pump it works normally at full power static and have to fly it i.e. Get plus 2900rmp for the problem to arise. The new replacement pump however causes a loss of power at static rpm full throttle????

 

It all points to the pump to my way of thinking. But unlikely with 2 new pumps. I'm thinking might have to test the fuel rate of the mechanical pump/ s to prove one way or the other.

 

I will get new fuel line and connect it as a test as suggested in earlier posts, but I'm not confident of a fix there as the fuel

 

Line would have to have gone faulty during the week of the engine change (possible so I will eliminate that one as well)

 

I guess I'll have to check with Jab on Monday for their ideas.

 

 

[Bob Llewellyn]

Spacer between engine block and pump would be critical as the difference between type 1 and tyre 2 pumps is a 2mm difference in the pushrod. Can only assume the spacer is correct.Phil - can run without cowls, everything appears normal. The problem being with the original pump it works normally at full power static and have to fly it i.e. Get plus 2900rmp for the problem to arise. The new replacement pump however causes a loss of power at static rpm full throttle????

 

It all points to the pump to my way of thinking. But unlikely with 2 new pumps. I'm thinking might have to test the fuel rate of the mechanical pump/ s to prove one way or the other.

 

I will get new fuel line and connect it as a test as suggested in earlier posts, but I'm not confident of a fix there as the fuel

 

Line would have to have gone faulty during the week of the engine change (possible so I will eliminate that one as well)

 

I guess I'll have to check with Jab on Monday for their ideas.

If the hose liner is playing up, the normal bending and inserting of an engine change can trigger it. It would be nice if the solution is this simple...

(thinks out loud) can you grab a second electric pump, or borrow one from something with a larger flow requirement, and plug that on in lieu of the engine? If such a super-sucker delivers an adequate flow rate into a bucket, then there's nothing wrong twith the airframe fuel system, and it could only be the engine pump. (thinks again) how much time have you wasted on this already? V. frustrating!

 

 

[deadstick]

Have you performed the gravity feed check? cant remember what the figure is but with the hose disconnected at the firwall it should flow so many litres an hour. This will and has caused the symptoms that you describe, in the wing fittings there are finger filters, also check the fuel float seat for correct height.

 

 

[frank marriott]

Deadstick

 

Question: If the float level was the problem, would not the problem also occur with the electric pump???

 

Also if an obstruction such as the finger filters was the cause would it not also occur with the electric pump??

 

I'm certainly open to suggestions - just checking if my logic is right.

 

Given the problem did not exist before the new installation my thoughts are something other then fuel blockage/restriction?

 

The float level certainly fits this thought process, but what are your thoughts about it being ok on the electric pump?

 

 

[planesmaker]

DeadstickQuestion: If the float level was the problem, would not the problem also occur with the electric pump???

Also if an obstruction such as the finger filters was the cause would it not also occur with the electric pump??

 

I'm certainly open to suggestions - just checking if my logic is right.

 

Given the problem did not exist before the new installation my thoughts are something other then fuel blockage/restriction?

 

The float level certainly fits this thought process, but what are your thoughts about it being ok on the electric pump?

Hi Frank this may not help you as I don't have any answers to the problem. A friend had same problem with his jab it would falter on takeoff with elec pump off. I am not sure what he eventually found I know the Carby was rebuilt and filters changed.

 

Can I suggest you change the electric pump as it maybe restricting flow somehow, or bypass it and do gravity fuel flow check with and without elec pump inline to see if it is the problem. Tom

 

 

[Peter008]

Is it a one of miss on climb or is it all the time? Have a look at this cobra head modification that fixed the issue on my 230. I spoke with Jabiru and they suggested I try it when I discussed with them.

 

http://www.jabiru430.com/EngineCoolingimages.html

 

The site has a good write up on it but my miss was at full power on climb and only on cool days. Always gave me the impression that there was carby ice from taxi movement.

 

 

[deadstick]

DeadstickQuestion: If the float level was the problem, would not the problem also occur with the electric pump???

Also if an obstruction such as the finger filters was the cause would it not also occur with the electric pump??

 

I'm certainly open to suggestions - just checking if my logic is right.

 

Given the problem did not exist before the new installation my thoughts are something other then fuel blockage/restriction?

 

The float level certainly fits this thought process, but what are your thoughts about it being ok on the electric pump?

Hi frank, I understand what your saying, if it's starving at full power there's not enough volume of fuel being supplied, the gravity feed is effected by the finger filters being partially blocked, there is a minimum requirement for the mechanical pump to work( it's in one of the manuals) have you done the gravity flow test? The float seat is a long shot and it does behave slightly different under pulse flow( mechanical pump) and constant ( facet boost pump) if it's set just a touch lower than standard it has the effect of leaning the mixture slightly, if it gets lower and the flow isn't enough to keep the head of fuel available you get a lean cut. Just about every jabiru that has minimal fuel in the tanks ( no head pressure)will flash the fuel PX light on mechanical pump alone. Can you blow through the fuel tank vents in the fuel caps as a blockage can cause poor gravity flow? Check all the basics first ( vents fuel tap fully open etc) then check for flow as per the manual. Check the fuel level in the header tank. Where are you located? I'd've happy to assist if your nearby.

 

 

[deadstick]

Frank, I have a brand new carb here factory jetted for the 6 cylinder, if you want to try that.

 

 

[frank marriott]

Thanks everyone for your input. And thanks for the offer deadstick.

 

Following the above advice and fuel flow checks I discovered that the new pump was not fitted and the original was refitted!!!

 

Both being new and looked the same i.e. No old oil etc.

 

Fitted new pump this morning and all good. Did half an hour over the top at 3200rpm indicating 135kts on engine pump alone.

 

The problem for anyone who has not been down this road before (like me) the engine will give 2800rpm on gravity alone (at least with full tanks). I was assuming engine pump was working and some other problem existed when in fact it was running on gravity alone until the electric pump was turned on.

 

Certainly learnt more details about the fuel system on this aircraft in the last week then I ever intended. At least now I know both engine pump and electric are delivering 60ltrs/hr capacity.

 

 

[deadstick]

Congrats mate.

 

 

[Oscar]

Frank - great that you have sorted the problem, but I have a question: if the Type 1 fuel pump was re-installed, was that with the longer push rod? If so, then I think we can assume that the mechanical pump diaphragm was not being allowed to settle properly back to its 'empty' position, so not sucking enough fuel in to pump forward. That makes me wonder - if the longer push rod was used, has the cam lobe been damaged?

 

 

[frank marriott]

Oscar

 

Both pumps were type 2, 74mm pushrods.

 

 

[Oscar]

Aha, well that's all good then! If the old pump was running ok on the old engine, it'd be interesting to know why suddenly not on the new one though, to add to the sum of Jab knowledge around!

 

 

[frank marriott]

No, no old pump involved. The new engine was complete with pump which had a restricted/jammed/faulty movement. It had some movement but not enough to work. The difficult thing was without having seen one is to know what is normal movement for the particular pump type.

 

I can't see what is broken/jammed without complete strip and have to return the faulty unit as part of the warranty exchange.

 

 

[Oscar]

What a bugger!.

 

 

[Bruce Tuncks]

Lots of good stuff on this thread... Some years ago a Jabiru was landed on the Stuart Highway near Coober Pedy. The engine had started to run rough, and the pilot switched on the electric pump and it came good for awhile.

 

The cause was found to be that the fuel line wedged under the tank. It vibrated into the spot where it squashed closed.

 

I've wondered about putting in a fuel-pressure meter to help if this situation ever developed. But its hard to find a meter with a 0-5psi range.

 

Bruce