odd dips in fuel pressure, pump problem?

I recall researching this, and determining that the 35 jet is in fact .35mm, though obviously the size alone doesn't describe the flow rate.   My engine doesn't have the stock Rotax fuel line parts, so I wouldn't have anywhere to install a Mikuni jet in my system.  Thanks for the thought though.

Rusty

This is the jet series(all same external shape/dimensions/thread) that I used however there are quite a few others probably with diffrent external dimensions.

I have modified a hose spigot/barb with the correct thread so the restrictor jet just screws in.

I don't think the size of the restrictor is much of an issue here. 

Logically, I have to believe there is a vapor bubble, or possibly air through a leaking fitting under suction.  Since I'm not able to send the vapor bubble back to the tank, it just continues to circulate through the restrictor. Whenever there's liquid at the restrictor, the pressure is normal, and whenever the vapor is going through, the pressure is lower.  It's the only way I can make sense of this.  

Now if the return went back to the tank, you'd likely not see this.  If there was no restrictor, the vapor would vent out through the carb bowl vents, which I consider the single best feature of a carb in this century.  I can also imagine that it takes a while to build up enough of a bubble to start to see the issue, and that probably explains why I don't see it until I've been flying for 15-30 min. 

Here is an excellent example of the fuel pressure fluctuation from Friday. 

Hi Russel,

one thing came across when looking at your recent post. If it takes quite a while to build up an air bubble in the gascolator  to eventually show in your data (which appears to be a very plausible story indeed) what would have happened with no gascolator? Would the super-mini first Mirco-bubble not have gone through the carb with virtually no effect (no building up to a large bubble, no hassle)?

Perhaps you like to try flying about taking the gascolator (bubble accumulator) out of the equation and see how it goes!

Just a thought.

Regards

Peter

I think the next test is going to be to block the return line to the gascolator.  I'm betting that will stop the oscillation by letting small amounts of vapor pass through the carbs unnoticed.  I do worry that it will bring back my old problem of high fuel pressure on descent and taxi. 

Of course I still have no explanation for why this started after so many hours of trouble free operation.  I can only wonder if they did change the fuel enough to cause it.  I've also thought that the firesleeve on the hoses probably acts as an insulator, and is probably what's delaying the onset of the symptoms. 

The good news is that I like tinkering with stuff like this, as long as it's not something that's actively trying to kill me :-)

Rusty