Engine rough (miss shots) when idle in flight

[skylor]

It looks like you have the fuel line that runs between the servo and the spider manifold routed from the injector servo all the way to the rear of the engine on the cylinders 2/4 side where I’m assuming it runs up to and through the rear baffle then back forward to the spider. This is a very long and convoluted path that is likely doing you no favors in terms of heating the fuel, in addition to the issues noted by others.

Lycoming normally routes this line up between cylinders 1 and 3 through a grommeted hole in the inter-cylinder baffle, then nearly directly to the spider manifold. This is a much shorter and more direct route for this line that minimizes the areas where it runs near the exhaust system.

Skylor

[olyolson]

Camillo,

As Sklor pointed out, it looks like your fuel line is pretty long. Not the same setup as yours but I have a purge valve on the right side and the fuel line goes down between the #1 and 3 cylinders in the shortest possible length direct to the fuel servo (see picture). He’s right that your fuel line may be too long by going around the back of the engine on the left side.

[Camillo]

Thank-you both.
Yesterday I went flying. Medium temperature spring day (actually, a medium summer hot day). 26° C OAT.
In the first flight all went OK. I idled on final and engine run smooth.
I left the aircraft parked for 10 minutes, then I started the engine again and at 1.300 RPMs, engine started to miss shots. It was an evident vapor bubble issue. After a while RPMs stabilized, thus indicating that fresh fuel was reaching the engine.
So, I believe you are right on the necessity to change the fuel line path.
I will update this post for further news.
Thanks.
Camillo

[Camillo]

As Skylor argued, yes, my line goes from the spider back through the baffle and the fore, under cylinders #2 e #4. It is quite long. It comes close to the exhaust in one location, just before (or after) the outlet from the injector servo.

I will look if the different route through a hole between cylinders #1 and #3 will be suitable.

In the meantime, I rerouted the other hose. Now it comes close to exhaust in two locations instead of three and is way more far from the exhausts than before.