Fuel Tank-Fuel Starvation in left turns

[gira]

Hello,

 

We have a new/old Chump Car that we've got almost ready. In testing last week at Homestead Motor Speedway, we found the engine would stall because of fuel pressure or lack thereof, in left hand turns. My track fix was to pour more fuel in it. It would run normally with 16 gallons in it, but after 5-10 laps the problem would reoccur. The track runs counter clockwise so this is quite a problem. Essentially, we are able to use about 3 gallons of fuel if we're filled up. We have an SU Carb set up with a 1978 fuel tank, running the return system for the fuel to return to the tank. We were able to get fuel pressure and run the new engine in the garage with only 3 gallons in the tank, so I feel we at least have the pick up plumbed properly.

 

I have run many street cars on the race track and never had this problem. 

 

Any ideas for me to check?

 

Thanks,

greg ira

[BluDestiny]

First thought would actually be crud in the tank. The next thing I'd look at is the baffling if it broke off or something

Edited January 25, 2017 by BluDestiny

[gnosez]

Fuel filter(s) could be an issue but it's more likely the pick-up tube.

With the car sitting flat in a garage there is no way to tell the effect of a hard left hand turn. I suppose you could jack up one side and see if the engine sputters.

 

Fuel cell suppliers and Holley sell a variety of pickup feeds (duckbill, sheet, etc.) if you determine it's the fuel being thrown away from the current location of your pickup.

 

We had the same thing happen with our 13 gallon fuel cell and we went to dual pickup located on both sides of the tank and two pumps. The triples suck a lot of fuel in a hurry on the track.

[JMortensen]

I wonder if you couldn't just put a really big fuel filter on it and use it like a surge tank. Or an actual surge tank would probably cure the symptom if you don't want to dissect the tank.

[NewZed]

The left hand turn problem has been described before, but not so bad as yours.  1/3 - 1/4 tank is the more common level where it starts.  I think it was one of the first problems I asked about on this forum.  Swirl pot/surge tank was the suggested solution.

 

Apparently there's also a pickup tube inside the tank that runs up and then back down (what gnosez is talking about, I assume) to the exit point, that sometimes gets holes rusted in it at a high point.  If the holes are submerged they don'r have an effect, but when exposed they suck air.  Could be why you have a worse problem.

 

Here's some pictures of the inside of a 77 tank.  You can  see how the pickup tube rises up before dropping back down to the exit point.  http://atlanticz.ca/zclub/techtips/fuel/gastank/index.htm

 

Aren't modifications prohibited in Chump?  

[seattlejester]

If it is only on left turns I am also thinking a pickup problem or in a rare case the floats shutting off the fuel flow since their pivot is towards the right, that usually has to combo with poor fuel delivery though.

 

Inspection of the gas tank would probably be the place to start, checking for crud, looking for holes in the pickup.

 

Next is the fuel pump making sure the contacts are good and that it is rated for a carb not EFI

 

Then the lines, having a hole or a kink or even stretching the rubber lines as the engine leans over during the turn can cause fuel starvation. Not to mention that if it is using the old lines they aren't rated for the ethanol and can gum up/deteriorate and clog themselves.

 

Then the carbs, a cracked or ill set float can cause issues on turns although usually a cracked one will cause problems all the time. A sticky valve can cause fuel starvation seemingly randomly which can just coincide with turns. 

[beermanpete]

On our '73 the pickup tube in the tank cracked or rusted through and caused fuel starvation even while the tank was mostly full. Our solution was to abandon the original pickup and install a new one through the fuel gauge sending unit port using a home made plate and an AN style bulkhead fitting. The plate is the same size as the sending unit and works with the original lock-ring and o-ring. The free end of the new pickup tube is located near the internal baffle and works well. Obviously, this eliminated the fuel gauge.

[Zipper]

Struggling with this issue with my early 260z - starvation and fuel pump cavitation at anything under half a tank at track days (with my modest street tire G's).  But no real problems on the street unless a very hot day - can go to below 1/4 tank no problem.  I'm suspicious of pinholes/leak in my pickup tube.  My tank is coated.

 

Our solution was to abandon the original pickup and install a new one through the fuel gauge sending unit port using a home made plate and an AN style bulkhead fitting.... Obviously, this eliminated the fuel gauge.

 

Have been thinking of a solution like this, but trying to keep fuel gauge sender - like a replacement pickup via bulkhead next to the sender for wrench access - maybe a Holley hydramat on end of pickup.  Are bulkhead fittings reliable?  Next option is significant rework of tank - chopping, drop-in pump with baffles, etc.  A lot more work.

Edited January 25, 2017 by Zipper

[gira]

Gentlemen,

 

Thanks for all the great suggestions. This tank was in pretty good shape but I am leaning toward the issue of leaks in the pickup tube. If I added a new fuel pickup line, I'd like to utilize the baffle somehow. 

 

Thanks again.

Greg

[gira]

NewZed,

 

Super pictures. So, the pickup tube that goes to the engine enters the baffle pretty high up, like 3"+ if I had to guess. Do we know if it turns down inside there? It seems we would have better luck using the return line, as it enters the bottom of the baffle and would have a better chance at emptying the tank. Am I looking at this wrong?

 

Greg

[NewZed]

Those pictures are from Blue, the guy who put together most of that web site.

 

Beermanpete knows more, he's been in there.  The return line might bend up inside the baffle, with the opening up high.  Same problem.

[beermanpete]

I don't remember what the return line looks like inside the tank. The return line is smaller than the supply line and may not support enough flow for sustained full throttle operation. Greg's car is a is a '78 (or the tank is at least) and is therefore different than ours. The photos on Blue's website show the sender port on the top of thank where ours is on the front. The sender itself and the lock ring look the same so the technique should work. Position the free end of the pick-up near the baffle and bend the end so it is parallel with the floor of the tank and touching the floor or very close at least to it at least.