914 stalls above idle

It's either the float bowls are over tightened, or they are not sealing properly due to a couple other potential issues such as the one I had.....

I had this happen on my 914 after re-jetting it.... was puzzled for a little bit, took it apart 2-3 times checking stuff.... until I thought about what I had also changed - the float bowl gaskets... to the new black silicone style. It had the green paper gaskets in it when I pulled it apart. Hmmm.. turns out, the black gaskets are about 5 thousandths thinner than the green style. When you tighten the float bowl retaining bolts to 48 inch pounds, it was only putting about 2-3 thou of "squeeze" on the gaskets before the bolts would bottom out... I took the retaining bolts to the lathe, took off 5 thou and bam.. runs perfect.

That is the approx rpm where it starts to pressurize the float bowls over ambient and if there is a leak, it won't pressurize the chamber and force fuel into the engine. Make sure it wasn't overtightened first, and if so, go down that path.. set proper torque, if it still doesn't work the bowls can be warped. But... if the torque was right.. which gaskets did you use? Might have an issue like I did!

Todd,

Over a month later and we are still fighting this problem on the 914UL powered Kitfox.  (The owner did take a 5-week vacation and I took the time off as well to work on other aircraft.)  I don't remember which float bowl gaskets came out of the carbs but after yesterday I know for sure the gaskets that are there now are the black ones.  I'll have a closer look to see if the bowl screw is in need of a shave.  

Thank you

Jeffrey

HELP!!!  Still trying to sort out why this 914UL stalls when the throttle is advanced.  She gets to about 3,100rpm and dies.  If we quickly retard the throttle back to idle the engine calms down and runs smoothly again.  I have checked and rechecked everything from the tanks to the carbs.  I'm almost to the point of starting to replace parts.  (Not the ideal way to troubleshoot...)

Another mechanic (from the race car world) suggested a check of the pump volume.  The chart from the Installation Manual doesn't make sense to me, but then I was a political science major in college, not an engineer and nothing in PolySci made sense to me.  (I wished I had majored in some kind  engineering...)  I have attached the chart to this message.  Has anyone tested the fuel flow volume on a 914 or could give me an idea of how much fuel should flow in a certain amount of time?  I remember doing simple flow tests on automobiles back in the day.  You take the fuel line loose at the carb/carbs/fuel injection system, whatever you are working with, and put the end in a bucket and run the pump for a prescribed time then measure the amount of fuel in the bucket.  Right or am I missing something?  

On the 914 the fuel pumps move far more fuel than the engine requires (something like 30 gallons per hour). If your fuel pressure is stable and within spec, I would not think the fuel pumps are the issue. 

To help interpret that chart into English...

1000hPa = 1 Bar = 14.7 PSI ...

and 120 LPH = 31.7 gph.

Meaning an open fuel hose should deliver 30+ gph or 1/2 gal per minute.

Or with 10psi of backpressure (40" MAP) ... 1/2 gal in 66 seconds.  About 6 times more than the engine will ever consume.

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As Ken Said,  watch the fuel pressure vs the MAP pressure.

When the Boost starts to rise, so should the fuel pressure.

Fuel Pressure = Boost + 5psi. in this Turbo system.

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The float Bowl pressure NEEDS to be identical to the Carb Throat Pressure.

If there is a bowl leak, any leak!, the boost pressure will force the fuel out of the carbs.

Is the engine dying right at the same point the Turbo starts to boost?