Engine stumbling issue, problem found

[Cluemeister]

I recently had a stumbling issue on my 914 turbo that only occurred on run up.  Once the engine was warm, the problem went away.  I thought it needed a pin adjustment to allow more fuel flow, and brought it to the shop for that work to be performed.

However, when the diaphragms were exposed, it was discovered they were deformed.  Lockwood and others with experience in this area believe some kind of solvent distorted the diaphragm.  Suspects would be something like methanol, which is used to flush out gas lines, or carb cleaner, or some other additive. 

I run exclusively 91E free, with the rare 100LL x country fill up.  I have never put any additives in the fuel.

New diaphragms are on order.  

[Flocker]

Could the deformity have been caused by excessive heat?

[Glenn]

Bummer.  Perhaps you just THOUGHT you were burning ethanol free gas?  Did you ever check it for ethanol?

I'm curious.  How many hours on your carbs since the last rebuild?

[Cluemeister]

The gurus I've spoken with say ethanol would not have an effect. They think it's some kind of other chemical. Joe at Lockwood said he's seen it before, and they think it's some kind of chemical added to the gas.

Nobody mentioned heat, so it's doubtful that's it, but you never know.

The carbs were rebuilt one year ago, about 70 flying hours since then.

[Glenn]

Jan 22, 2019 20:20:45 GMT Cluemeister said:

The gurus I've spoken with say ethanol would not have an effect. They think it's some kind of other chemical. Joe at Lockwood said he's seen it before, and they think it's some kind of chemical added to the gas.

Something the EPA mandates to be in the gas is a REALLY good guess.  

[bravodriver]

You might want to save some samples of the fuel in the tanks and have it analysed. And get another current sample from the source pump. If you have receipts from your pump, and can prove contaminants or wrong blend, you might have a case for reimbursement ( if it's worth it to you) Here is a url for a fuel testing www.fuel-testers.com If the mix from the pump is wrong or contaminants are present, the only way to find out is analysis. You may have to drill down on google or contact the fuel testing companies if they can additionally check for methanol or one of the "zenes" (like benzene, toluene). Fuel truck Tanks and tankers require cleaning and you can be sure they are not scrupulous about rinsing. Remember there is no cradle to grave certification of the process to make auto fuel, just checking at the depot, before it goes into the tanker trucks. Some years ago I owned a Mercedes diesel and I ran into a problem that was caused by Shell Oil inadvertently markedly jacking up the sulfur content in the fuel. This damaged the fuel injection system. Only reason this is was caught was there were hundreds of vehicles damaged and the Dept of Agriculture in Florida forced Shell to pony up. Given the small number of airplane folks pumping, wrong fuel mix would be never discovered.

[Cluemeister]

Tanks being drained and flushed. Not worth it to me to have the fuel tested, so I'm just going to move forward.