Exhaust Back Pressure

[julian hood]

Going to check for exhaust back pressure on my boat today. Any ideas what causes this?

[roadnsky]

Julian-
It's caused by a blockage or restriction in your exhaust...

"Based on reports over the past couple years, the most common place for exhaust back pressure to build up is where the engine cooling water enters the hot section.
Minerals apparently precipitate out as the engine cooling water encounters the elevated temperature within the hot section and builds up along the ID of the pipe.
A second place where elevated exhaust pressure can occur is within the first several feet of rubber hose just downstream from the water lift muffler.
The inner layer of rubber breaks away from the rest of the reinforced hose until it crumples up on itself and blocks the flow of exhaust and cooling water."

May I suggest you do a search first and read the various threads?
You'll likely find the answers you're looking for have already been posted since this subject has been discussed extensively.
Of course, it's also very likely others will just jump in too and you'll get the info...

[julian hood]

Back Pressure

I pulled the exhaust pipe off today. found no blockage. I did adjust my timing and got more power that way. Beginning to think maybe I have a blockage in the fuel line. Engine is surging about 300 rpm's under load. Will track that down today.

[CalebD]

A fellow A4 owner at our club was having problems with his engine this spring. It would start up fine but would stall if you pushed in the choke. It ran for about 10 minutes with the choke out before dying completely.
I suggested that back pressure of some kind was killing his engine.
Sure enough, he took the water lift motor off the boat and found a bunch of crap had collected in there and once the muffler was re-installed his engine ran fine.
What are the symptoms your engine is experiencing that make you wonder about back pressure in the exhaust?