engine miss mystery

Sean Griffin wrote:

On Jacks pre ignition  problem - This sound like it may be related to fuel type. Do you use AVGas? If so, there may be a lead build up that is the root cause of the preignition.

Walt - You added an additional oil cooler - what were the oil temperature  (Climb Out & Cruise) before you did that and now after?

I have a blog at waltsrv12.com, I have more detail on the second oil cooler there, plus other stuff. 

Kevin Stewart wrote:

I would suspect a fuel problem. I would drop the carb float bowls and just check for debris that could be sucked into the jets momentarily blocking it giving a misfire. I have experienced this in the past and found small black particles in the bowl. I cleaned it all out and the problem went away.

I will check this for sure. It will be Saturday before I can get back to the hangar. I would suspect a fuel feed issue would be more of a “stumble” in the running and what I feel is a “bump”. 

alejandro zapata gordillo wrote:

Do you have a fuel return line with pilot jet 35 restrictor?

Yes, a return line and restrictor. Also this plane has an engine driven fuel pump plus an electric fuel pump at the tank. The electric pump runs all the time. I am able to turn the electric off in flight for testing and I have to prove both pumps are working at the proper pressures. 

Sean Griffin wrote:

Hi Walt,

Good answer to all questions. Not quite ready to give up on water - I have never used an ethanol blend(E10) so the next bit is speculation:

I have heard that ethanol can separate from the base petrol and is hydroscopic.

Separation may change the RON (octane rating) - I think this may be an urban myth

Being hydroscope it attracts water - this is correct and may have a bearing on how you manage the fuel in storage, especially the fuel in the aircraft tank, which is open to atmosphere (water vapour).

You check the fuel from the bowser for water & ethanol % - do you check the fuel in the aircraft?

37 Gals (140L) E10 -

  Does it all go into the aircraft ?

  Do you fuel after flight or befor?

  What quantity might you store?

  For how long?

What sort of container(s) do you use and are they air/gas tight?

When E10 comes in contact with water the ethanol will allow the fuel to absorb water.  The fuel can reach a saturation point and that is the principal on how to test for ethanol % in the fuel. At the saturation point the alcohol/water mixture separates from the fuel.

With 100LL a drop of water will not mix and will fall to the bottom of the tank, the resulting problems of that water being first into the engine are obvious.

My fuel for the past 4 years comes from the same auto gas station. I have 6 gallon polyethylene jugs that I transport and store it in. I use about 20 gallons a week so my trips to the gas station are frequent about every 2 weeks. The gas doesn’t sit long in the hangar. The plane is fueled before each flight, the amount I fuel depends on the expected flight time. I fly 4-5 days a week. This procedure and equipment is the same for the past 4 years. 

I would try a tank of 100ll with Decalin to scavenge the lead. Much less chance of fuel boiling in float bowls. The gas pump changes the recipe for winter use, and that change

makes it more susceptible to boiling, which has been discussed here in previous threads.