Fuel Starvation Problem

[Marty Rogan]

I was at Road America on Sunday for a lapping day. What a great track! It was BIG-TIME FUN!! Got in 120 miles of track time. The car performed really well until it got down to about 1/3 tank of gas. Then it started stumbling and sputtering. I put in 3 more gallons of 110 octane race fuel and that cleared it up for most of the rest of the day. I didn't want to fill it up at $6/gallon!

My guess is that the gas is being sloshed away from the pick-up. I had the tank out this summer to replace all the vent lines and to eliminate the non-essential ones, per the advice on the boards here. The inside looked very clean, so I don't think it is plugged up in there.

Would and electic fuel pump help with this situation? Or do I just need to keep the tank full?

Looking forward to you recommendations.

Marty

[gundee]

That must be your yellow Z I saw on the SpeedSeekers site.

Wish now I would have driven over there on Sunday. I was at their April event to see what it was all about. If I get some good "stickys" I will sign up for the next one.

How did your front pads hold up?

[Marty Rogan]

Steve,

Yep, that would be me. It was a fanatastic event. Very well run. We got 5 - 20 minute sessions. Too bad you didn't stop by, it would have been great to me you.

RA can be VERY tough on brakes. A couple of the Vetts suffered cracked rotors. One of them broke and seized, causing a horrible crash. The driver broke some ribs and puncured a lung, but was ok. The car was a total.

My car has the Toyota 4 pot upgrade with vented rotors and ceramic pads. Stock shoes in the back. Brakes performed great all day with no fade at all. This set-up had 3 previous (but less demanding) track days. I haven't had time to check pad wear since the event, but my feeling is that they would have minimal wear on them. I can't say enough about this set-up and would highly recommend it.

Have you been out on the track at RA? We could use another Z out there! My buddy Bill came along with his '73, but it blew its rear main tranny seal as we pulled up to tech inspection. He had to bag the day and limp home. What a bummer!

So, by all means, sign up for April. I will definitely try to get there again. It was a blast.

Marty

[boltmans]

I had the same thing happen to me with my '73 during a track day at Gingerman. I had the factory electric pump and the mechanical pump so I don't think that just adding a electric pump will help unless you put some sort of reservoir after the pump. it is just easier to take extra fuel and add it during the day.

The other choice would be to add a fuel cell with foam and an electric pump. That's what I have in my 72 ITS 240 and I have come off track with less than half a gallon in the cell and the engine never skipped a beat.

Bret

[Marty Rogan]

Hi Bret,

I was afraid it probably wouldn't help, but was not sure. This is an early '71, so I am trying to keep the mods to a minimum. That would rule out a fuel cell. Looks like I will just need to keep it filled.

Thanks,

Marty

[Chino 240Z]

Sounds like a blast, Marty! Long sweeper turns can do that to some cars too. Its amazing the amount of fuel you can suck down when your foot is in the carb for 30 minutes. I have a 12gal. cell and it is empty in 2- 20 minute sessions. We have a Nov. 9th opentrack day coming up soon, I get dry mouth just thinking about it! :lick:

[Marty Rogan]

Craig,

It was a blast. I am hoping to make the next Speedseekers event, but that is not until April. :disappoin Our season is over now. Damn, I hate the long winters around here. Oh, well, I have the winter to collect parts and do some projects. Going to put in PU bushings and POR 15 the whole suspension. I plan on replacing the tie rod ends and ball joints while its apart. Koni's are still good, so those will stay. Have not found the right spring rate combo yet, so I might just keep what's on there. I think they are stock, but the car still corners pretty flat with the beefy sway bars (1"frt/ 7/8"rear).

I went through about 11 gallons in 120 miles. It did have the most trouble after the 2 long sweepers on the track. It suprised me how long it took to recover though. You would think it would come right back when you hit the straight, but it didn't.

Enjoy that open track day!

Marty

[Chino 240Z]

Are you running SUs, Webers or other? Lack of fuel in long turns is also a carb-fuel bowl problem too. I never had the problem with the SUs, their round fuel bowl & bottom feed design is a benifit. But others have found this problem with the Webers having the fuel to one side of the bowl during long hard turns, opposite of fuel pickup side. Yours seems to be tank issues though.

[Marty Rogan]

I am running the stock 4 screw SU's. The PO had them rebuilt and I haven't noticed any other problems with them.

Marty

[260DET]

A fuel injection type pickup arrangement or complete fuel injection tank would help a lot. Either that or a separate surge tank and two electric pumps.

Extra fuel only slows you down, plus it sloshes from side to side which would not help rear end stability.

[Marty Rogan]

I am reviving my own old thread since the problem has not gone away, and in fact is getting worse!!!!

Here are some details on the car and what has been done to it for a baseline.

Car is an early '71, blt 1/71.

The engine is the stock L24 with 78K original miles

MSD coil and Pertronix installed

Carbs were rebuilt by PO 10-15K miles ago (several years ago though)

Eliminated the excess vent hoses in fuel tank, connected like non-U.S. spec cars.

Under normal driving conditions it runs fine. It also starts easily and idles smoothly.

The last track day the car ran good in the first session or two. The problem started showing up again, so I filled the tank, thinking that would solve the problem. It didn't. Now it starts bogging down badly any time it is under hard acceleration, even on the straights.

After the track day, I changed the fuel filter. On cutting it open, I found a fair amount of crud in the screen at the top. Took it out and terrorized a local clover-leaf on the express way at about 55 mph several times and it had no problems at all. I thought that had solved the problem. I drove it to work yesterday, and one hard acceleration off an entrance ramp set it off. It lost power and started making a droning sound. Once I backed off a while it drove fine again.

I have been thinking it may be a vapor lock problem? Would that explain why it only acts up under a heavy load? The early 71's really aren't known to have that problem though, like the 73 & 74's.

What do you guys think?

Marty

[jmortensen]

The one time my 70 vapor locked I was at the Streets of Willow and it sounded boggy at the end of the straightaway in top of third shifting to 4th. It got to the point where I didn't even shift into 4th the last time around. The weird thing was this was the only place on the track that it did anything unusual. All of the slower tighter corners were fine. Then when I came into the pits I popped the hood and it idled like crap for a couple minutes then died. Really vapor locked. Left the hood open for a while and it would start up just fine, run just great until towards the end of the next session where it would start bogging at the end of the straight again.

I felt the fuel rail and it was HOT. I felt the mechanical pump and it too was HOT. I decided to remove those things from the system, and I ran a rubber hose from the filter across the rad support back to the SU's and installed an electric pump. My theory is that even if you wrap the fuel line with some heat shielding you haven't disconnected it from the head, which is damn hot. So the heat just travels up the mounting tabs right under the heat shield. Anyway, I never had a problem with vapor lock again. I just dead-headed the fuel system, no return line. Since it worked great with no return, I can surmise that the fuel wasn't boiling in the float bowls, but was boiling as it went through the mechanical pump and fuel rail.