Fuel siphoning out the vent tube

SSSammy · #1 (**permalink**) 05-04-2010, 07:50 PM

This is the filler neck vent tube that dumps under the car, and it occurs at the track under high G left turns

I presume the gas is washing over to the right side of the tank and up the filler neck. Yes, a fuel cell would cure this, but is there an easy fix? I got black flagged at Run N Gun for this.

So a couple of us geniuses at RnG decided to join the filler neck vent tube to the other tube that is there to drain the spills from the body indent around the cap. Thus creating a big "U" vent back up to the top of the fender. This sort of works, but when I ran at Harris Hill last month, it just siphoned out of the top of the fender

Seems like it is better if I run with half a tank. Problem with that is, I get fuel starvation in right turns with less than half a tank .. sheee it!

Have we solved this before? I like to track the car, but would not want to do a lot of racy things to it.

Sam

Excaliber · #2 (**permalink**) 05-04-2010, 08:13 PM

Wow, thats an interesting problem, I have an early ERA with the same type of vent system as you describe. Now I've had my car in some extreme cornering with less than half a tank. Never had a spill problem, never had a fuel starvation problem. Go figure...

In fact I like to run "just enough" gas in the tank to get the laps done and no more. MAYBE running more than half a tank IS the problem with spillage?

COBRANIP · #3 (**permalink**) 05-04-2010, 11:39 PM

What about putting a check valve in the vent tube? I would think that should do it.

strictlypersonl · #4 (**permalink**) 05-05-2010, 04:56 AM

Interesting that you're having a feed problem only on right turns. The normal feed system is completely symmetric from side to side, including the tank's central collection area (with one-way doors). Probably just a coincidence, unless one of the doors is not functioning properly.

Assuming the fuel is finding its way up the vent tube, a check valve should stop the leakage. It may make filling the tank harder though.

SSSammy · #5 (**permalink**) 05-05-2010, 08:29 AM

CN and Bob, I'll give the check valve a go. Would this be an automotive part that Summit might carry?

Filling has been a problem since day one. I just hold the nozzle up high enough so I can see if it is backing up. Usually, the slowest setting on the valve is just slow enough that it doesn't overflow. But you have to stand there and monitor it.

On the fuel starvation, I may be thinking it is right turns only and it may be occuring earlier and it takes a few seconds for the air bubble to get to the carb. But I regularly have to come off the track because of this. It does seem to go away on straights.

Thanks for your advice!

Sam

SSSammy · #6 (**permalink**) 10-03-2010, 06:23 PM

Just wanted to post the solution for the record. I purchased a Fuel Safe check valve and installed in in the filler neck overflow line that normally dumps behind the right rear wheel. It had to be mounted right side up to breathe correctly and not interfere with venting. So as the photo shows, I made a loop and routed the "air intake" back down below.

Results, two track events .. no spillage, no fuel starvation either .. but I'm not sure that this solved that. See the photo.

Sam

tcrist · #7 (**permalink**) 10-03-2010, 06:40 PM

Sam,

Do you still have the same problem filling your tank (as far as back pressure)?

SSSammy · #8 (**permalink**) 10-03-2010, 06:47 PM

Quote:

Originally Posted by tcrist

Sam,

Do you still have the same problem filling your tank (as far as back pressure)?

Yes, I have to hold the nozzle partially out of the neck so I can watch for overflow. Some nozzles have a low flow setting that I can lock in, but most of them do not have a low enough setting that I can set and forget.

Sam

tcrist · #9 (**permalink**) 10-03-2010, 07:31 PM

Where does your filler neck tube enter your tank? Mine enters about half way up on the side. I don't think there is any way to fix it unless you change it to a top filler.

SSSammy · #10 (**permalink**) 10-03-2010, 08:09 PM

Quote:

Originally Posted by tcrist

Where does your filler neck tube enter your tank? Mine enters about half way up on the side. I don't think there is any way to fix it unless you change it to a top filler.

I'm guessing the tank vent tube, see upper left of tank, may not be totally clear. You can see the fill tube at the top. It comes in at the top of the sidewall.

Sam

Sam

tcrist · #11 (**permalink**) 10-03-2010, 09:45 PM

My vent tube looks a lot smaller than yours. As I do not have an ERA I really don't know much about their filler tube.

Like I said, my filler tube only comes half way up the side of the tank. Not the best design.