need help diagnosing intermittent drip

[urbanti]

After some flights, but not all, this 1965 M20E drips 100LL at a rate of about 1 drop per 12 seconds from the frontmost drain tube, located ahead of the nosewheel on the pilot's side of the nosewheel.

The drain tube is a combined drain for the mechanical fuel pump, and for the intake tract.

The leak has nothing to do with the electric fuel pump, which drains from another tube located four or five inches rearward of this tube. Also, we flew repeatedly w/o using elec boost pump on landing and made no difference.

Shutting off the fuel selector has no immediate effect on the rate of the drip, which continues for a long while after the plane is shut down, but stops eventually.

The engine runs great, has perfect fuel flow without using the boost pump, and climbs/cruises very fast.

Any ideas?

thx,

Tim

[rbridges]

I think someone else had a thread about this.  It may be a leaking fuel pump.

 

http://mooneyspace.com/topic/12774-first-flight-on-my-m20e-and-i-have-a-maintenance-issue/?hl=%2Bleak+%2Bpump#entry162407

 

 

nevermind, I just noticed you said it wasn't the fuel pump.

[carusoam]

RB,

This might be the one you were referring too?

http://mooneyspace.com/topic/12796-induction-drain-valve-drip/?hl=sniffle#entry162660

The description seems to be familiar.

Tim, see if the description of their drip fits what you are seeing?

Best regards,

-a-

[1964-M20E]

Sounds like what would happen if you overly flooded the engine.  If it is the forward tube that connects into the bottom of the intake you may want ot check the adjustments on your fuel servo.  It could be allowing fuel to flow after the engine is shut down.

[Hank]

It may be the fuel selector itself. There's a long glass piece down there with an aluminum seat, and they wear out of round and out of flat. Seems that my IA used some lapping compound on a wooden pencil eraser to go down inside and improve mine. She now drips very little.

[urbanti]

Thx very much for all of the replies.

I'll talk to an A&P and see what we can discover!

best

Tim

[PLN_FXR]

Sounds like a diaphragm is going bad in your engine-driven fuel pump.  This assumes you are shutting your engine down by pulling the mixture (I have to verify this; every now and then I run into someone who shuts them down by turning off the mags).

[urbanti]

Yes I am pulling the mixture to shut down.

Pls explain why you suspect the engine driven fuel pump?

Thx

Tim

[guppy]

Fuel pump membrane, when it cracks, will leak fuel out the normally dry side of the pump. I had this happen many years ago in a 64 chevy

[kerry]

I agree with the above.  When the fuel pump is dripping fuel it's time to replace.

[Guest]

I would suggest that you sepparate the two lines to determine which is the source, the fuel,pump vent or the intake drain valve.

If its the intake drain valve you may have an overly rich idle mixture, check it at shut down, typically no more than 25 RPM. If the dripping stops it may just be raw fuel draining. Lean the idle mixture and see if it stops.

If the fuel is dripping from the fuel pump vent line one of the pump diaphragms has failed or is failing. You may be able to test this by turning on the electric pump with the throttle and mixture closed, this would pressurize the system and show the leak.

Clarence

[urbanti]

Update from the OP: After 30 hours of experimentation, it seems that the fuel pumps are fine.

If I lean the mixture all the way out after landing and taxi, and then choke the engine out while performing the idle cut-off, no post-cut-off drip occurs.

Or, if one occurs, its only a coupla drops.

So perhaps I was not sufficiently leaning the engine for ground operations and loading the intake manifold with fuel.

regards,

Tim