Cowling Problems

Jorem

Recruit
Joined
Sep 17, 2007
Messages
3
I recently changed the cowlings on my collector boxes of my twin tunnel 26' Vindicator hullCowling.jpg and now I am experiencing a sharp decrease in power. Both engines were rebuilt this summer and would run at 35-3800 rpms @ 24 knts.

The cowling is the triangular box that sits on a transom plate.Transom Plate.jpg. The cowling is bolted to the stern and sealed to the plate along the bottom. The exhaust enters the box through the transom and exits the port located at the bottom of the plate.Exhaust Port.jpg

The caulk around the old cowlings was blown out in places and the cowlings themselves were cracking and pulling away from the stern. So, I purchased new cowlings and put them on. I sealed them well with 5200. The first time out after completing this job, I couldn't get the engines to climb over 3000 rpm and barely made 14 knts. It seems like I have restricted the exhaust and have inhibited my engines from running at high rpms. Could this one change cause that? Nothing else has been changed? ...not even new fuel!

So I'm wondering - should the cowlings even be sealed around the transom plates? Should some "blow by" be allowed? I have noticed that the transom plates, on which the cowlings sit, are sharply beveled back toward the transom. Beveled Edge.jpg I needed to put in 1/2 to 3/4 on caulk just to fill that space. Maybe exhaust is supposed to exit there are well as the exhaust hole on the plates.

Any thoughts?
Has anyone ever experienced something like this before?

Joe
 
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