Struggling to find the problem - air within fuel system?

[Dave G.]

I'll bet it was the hose clamp. Being on the suction side of the system you would not see a leak but it would suck air into the line. Good job tracing that down as those can be a bear to find.

 

[nquigley]

In case it helps anyone, I took photos of the M-25's decompression lever, and tested starting and running my engine in two lever positions. These pics are from aft, looking forward (actually, it's my 'spare' engine in my garage)
- lever at 90 degrees (3 o'clock) position - fixed position
- lever at 45 degrees (1:30 o'clock) position - floating position
- lever lifted to vertical position against the spring tension - decompression position
My engine starts and runs normally in either the fixed or floating position - no noticeable difference in my observations
** Do not try to lift the lever to the 'decompression' position while the engine is running - one immediately feels a rapid bumping sensation through the lever.

I didn't try to turn my engine over in the decompressed position. The bit of string that's still on my spare engine's lever gives a clue to how one might turn over the engine from the start button in the cockpit if you don't have a helper by the engine.

 

[patrscoe]

When I was chasing down my air leaks (OP), I also investigated the decompression lever. Mine also started in the fixed and 'floating' position but the decompression is when you push it all the way over under spring tension. But I remember there was a different sound of the engine when it was in the floating position and I am assuming, if under loadand higher RPMs, the engine would not have provided the power you normally would get in that float position. I didn't want to test that method.

 

[nquigley]

Thanks. I'd love to know if the lever should be left in one or other position for normal use, but I can't find that info. I don't understand why there are two positions that 'seem' to have the same effect :-\

 

[Kenneth K]

I'm not sure how you get the lever into the position shown in the first picture. Mine doesn't go that way (at least, I've never tried to push it over that far). Here is the normal (compression) position on mine:



I've cranked my engine with the lever in the "decompress" position. It sounds just like the starter motor cranking when the solenoid/pinion gear isn't engaging the engine.

 

[Loren Beach]

Looking at the rear of the engine in photo 2, I am wondering how you get to the fill plug/dip stick on the top of the Hurth? (Or am I looking at it incorrectly?)

 

[Kenneth K]

Looking at the rear of the engine in photo 2, I am wondering how you get to the fill plug/dip stick on the top of the Hurth? (Or am I looking at it incorrectly?)

Yes Loren, you have it correct.

I forget which "hole" I pull it through, but I can push it upward from the transmission with one hand and the grab the top of the dip stick with the other hand.