I built tanks before and know how to test them. I am sure they don't leak now as they are quick build tanks and I am pretty sure they are tested prior to shipping, but judging from all the leaking fuel tank threads, quick build tanks are prone to developing leaks after some time. I would rather do a preemptive strike now before they are installed and painted. Since I am increasing capacity anyway, I am going to open up every bay and put some decent fillets on all the ribs and rivets. Like I said, looking inside I don't like what I see. People complain a lot about the fuel vents dripping and siphoning off fuel after filling their tanks, even after leaving a margin for expansion. I checked out the vent line end on one of my tanks with a flashlight and mirror and there is almost 1/2" gap from the top of the vent tube to the tank top skin. I can almost get the tip of my finger between them!.. No wonder some weep/drip/siphon fuel and create a mess. I will re-work or replace the lines while I am in there and have the ends turned up and beveled so there is just a 3/32-1/8" gap between the beveled open end of the vent line and the tank skin. This should eliminated dripping as long as I don't over-stuff the tanks with fuel. I did this building my -10 tanks and never had an issue with dripping fuel after filling the tanks as long as they were not stuffed. The RV-10 vents just come straight out of the tanks with a 90* bend down and out through the wing root skin. None of that routing through the cabin stuff like the RV-9. I am using the Rocket vent mod with the wing root loops then straight down and out. I already ripped that mess out of the cabin.

Dave,
What is the rocket vent mod?
Thanks
Dave

Like this. Tank is vented at the outboard top edge, to a 2-or-3 loop coil of 1/4" tubing, and then vented through the bottom of the wing. I did this with my outboard tanks, and the outboard vent into the inboards for flow-through venting. None of that cabin vent line noise.

http://websites.expercraft.com/airgu...y&log_id=38573

http://websites.expercraft.com/airgu...y&log_id=33889

My inboard tanks are standard except for the vents, and I built the outboard leading edges into another tank, 15.5 gallons per side.

Here is a pic of my -7A. Not quite finished but you get the idea.

Nice Ray. What are you using to separate and hold the coil in place? I want something that will not allow the coils to bounce around. I was thinking I would fabricate a split loom out of aluminum with snap bushings or rubber grommets and then have the loom fastened to the fuel level sender cover plate.

drifting the thread a little but in another thread about vent lines it was pointed out that low points could collect water, then ice. what's the story with these vent loops?

I used large, opposing tie-wraps, which is what you see in the photo. One around two tubes with another wrapped around the middle of the tie-wrap between them. You could also use a short piece of rubber tubing in between.

Beyond that, the connection to the tank and wing root fairing do a fine job of stabilizing the assembly. I'm in the middle of my first CI now and will be opening the wing roots for inspection to ensure all is well.