912UL intermittent rough running

I'm 99.99% sure it's the engine. I have no wheel pants on this plane. This plane is a tube & fabric ultralight. When the "shutter" happens there is a definite indication on the rpms. The rpms drop & I am unable to increase throttle. I can reduce throttle & then reapply & sometimes its fine, other times it still runs rough at high rpms, but is fine down low. At this point all of my focus is on the engine. 

Just reaching a little here. We could use a bit more info.

Maybe blow out the fuel lines? During this does the fuel pressure stay fairly steady? Have you removed the carbs and cleaned them out? You could have some floating debris. Do you have the newer Corona pump or one of the gold colored AC pump?

Did it do this before you change the rubber carb boots? Did you replace the "O" ring behind the carb socket? You maybe sucking air in if not. 

How old are the carbs time wise? Maybe time for an overhaul if they have some high time on them.

So I decided that new floats & new bowl gaskets wouldn't be a bad idea. Ordered & installed. No progress on running better. Although I have peace of mind with the newSaw, blue Marvel floats & rubber gaskets. 

I emptied my tanks & ran a bore scope through them............. yikes! 

The fuel caps had rubber tops4/vents in them. I removed them a bit ago, but apparently not before they broke apart in the tanks........... 

At this point I'm suspecting rubber bits clogging up my fuels lines. 

This is some of what I found while.soing a bore scope of the tanks........ 

Hi Jesse,

We all get "stuff" in our fuel tanks but you seem to have hit the jackpot. 

As Roger Lee advised - thoroughly clean/blow out all your fuel lines. Clean your carburettors again (just in case). Replace in line fuel filters with disposable transparent wall, gauze filters  eg Hengst H102WK, H239WK or H103 WK, Baldwin BF7580, BF7725, BF7863, BF9906

I have a nice high quality fuel filter with a  replaceable mesh filter core. It caught most of the bits going through it. I have already replaced the filter & cleaned the carbs. 

The tanks looked fine when looking through the filler neck, but I can only see a few inches inside the tank that way. After seeing what was in the filter I decided that I needed to run a bore scope in the tank & that's when I found that nasty surprise. The only way to thoroughly clean the tank is the remove them from the wings & wash them out. ???????

At least this is a good path forwards to the engine running good like it used to. I'm fairly certain that the fuel lines are partially plugged & the engine isn't getting enough fuel while flying. That scenario is making a lot of sense after finding this junk in the tank. 

It sucks bad when you can't find any issues, but at least now I have a good lead on the problem. 

I will report back after cleaning the tanks & getting it running. 

Thanks for all the help. Now........... #Back to work