Fuel Starvation Problem

[Chino 240Z]

If you open the fuel bowls of your SUs and they are clean, and your needles jets are clean, then I would say your stock mechanical fuel pump is not keeping up with the demand of fuel you are consuming on the straights and long hard acceleration. I wouldn't have believed it myself, even after spending 2 hours on a dyno to hunt this same problem down. I already had a electric fuel pump regulated down to 3.5psi like it should be, but still not enough fuel until I cranked up to 5psi. No more problem until that elect. fuel pump started to fail, problem back but really bad (leaking from a weep hole). New fuel pump and no more problem. I bet your car runs just fine at idle and screams to about 5200-5500 then comes the sputter, like no spark, no go, just like a rev. limiter kicking in! So did ours, crazy fuel pumps. If you stay with stock you might want to borrow one for a test, or get a new one?

I was hoping you were going to tell us it's fixed. :tapemouth

Craig

OH ya, the Petronix is good to 11K (so they say) we had ours bench tested to 8K and was just fine, I know they work perfect on the track to 6500 to 7000.

[Marty Rogan]

I started thinking about ignition too. One of our wiser members here once said "If you think you have an electrical problem, it's probably a fuel problem. And if you think it is a fuel problem, it's probably electrical". We were discussing that at the track. We concluded that if it was electrical, the car would have trouble at low RPM's. The car pulls like a train till about 5,500 and then starts to stumble.

I'll have to check the dizzy shaft.

With the tank done, I should be getting really clean fuel. I don't have a pressure gage in-line, so I can't tell what pressure I am getting.

Marty

[ChrisA]

Craig brings up a good point about the mech pump. Worth checking.

I had a 200SX with a built L20B in it. Once while really flogging the car, it would just sputter and loose power. If I backed out she came back to life, but over a certain RPM it would just flounder like it was down two cylinders. Found the dizzy shaft was wobbling and was simply killing the car. New dizzy, no more problems at high RPM.

Good Luck Marty, you'll get it I'm sure.

Chris

[240ZMan]

Marty, when you came off the track did it have problems idling? I ask because I had the exact same symptoms as you at our last track day where it was at least 95. First few laps of each session were great, but after about 10 minutes I had to short shift. Turns out for me the front carb is percolating the fuel. Event though I have a large home-made heat shield over my header, the front gets too hot.

I've been able to recreate the issue at home on a warm day letting the car idle in the sun. The fuel level in the front float rises, and sometimes the fuel percolates. One time I quickly pulled the domes off the carbs and I could see the fuel spurting out through the nozzle.

I've checked and double checked my float levels, and I have a fuel pressure regulator turned down to about 2.5 psi. What surprises me is that I can put my bare hand on the carb when this is happening and while it's hot, it's not so hot I have to pull my hand away.

So far I haven't found a way to solve this completely. I've tried routing the fuel lines around the front of the engine compartment (over the radiator support) as an experiment to see if it was heating up too much on its way to the carbs. Made no difference.

I did find that stuffing some fiberglass insulation between the carbs and the heat shield slowed down the rate of the problem occuring, but I get the same problem when I come back to the car after driving and letting it sit for a few minutes.

I've confirmed it is NOT vapor lock. Taking the cap off the fuel tank makes no difference either.

I'm going to be switching to some Weber DGVs to solve a tuning problem and am hoping that they aren't as sensitive.

FWIW, I have a 4 core radiator, fan shroud, and splash pan. Part of me wonders if removing the shroud might help by blowing the air in a different path under the hood? Haven't tried that yet. What drives me crazy is that I read about people driving their early Z's in Arizona in July with no such issues while where I live in CO 90 is a hot day!

Anyway, I don't mean to hijack your thread, just letting you know you're not alone (in case that makes you feel any better).

Daniel

[Marty Rogan]

If you open the fuel bowls of your SUs and they are clean, and your needles jets are clean, then I would say your stock mechanical fuel pump is not keeping up with the demand of fuel you are consuming on the straights and long hard acceleration. I wouldn't have believed it myself, even after spending 2 hours on a dyno to hunt this same problem down. I already had a electric fuel pump regulated down to 3.5psi like it should be, but still not enough fuel until I cranked up to 5psi. No more problem until that elect. fuel pump started to fail, problem back but really bad (leaking from a weep hole). New fuel pump and no more problem. I bet your car runs just fine at idle and screams to about 5200-5500 then comes the sputter, like no spark, no go, just like a rev. limiter kicking in! So did ours, crazy fuel pumps. If you stay with stock you might want to borrow one for a test, or get a new one?

I was hoping you were going to tell us it's fixed. :tapemouth

Craig

YES, I was hoping I could tell you it was fixed too!!!

You got it. Starts easily, idles smooth and screams to 5200-5500.

You are thinking along the same lines. We were discussing draining the float bowl from the bottom drain to see if anything came out. If yes, then a real good cleaning is in order. Cleaning may be in order anyway, as I have not had the carbs apart myself. The PO had receipts for a rebuild something like 10K miles ago, so I have been hesitant to open them up again.

It seems strange that a new mechanical fuel pump would not be able to supply enough fuel for a totally stock motor. It's possible the new fuel pump may have gone bad in the last 5K miles. I'll have to see if I can borrow a buddy's known good fuel pump.

What brand electric pump do you use?

Marty

[Marty Rogan]

Marty, when you came off the track did it have problems idling? I ask because I had the exact same symptoms as you at our last track day where it was at least 95. First few laps of each session were great, but after about 10 minutes I had to short shift. Turns out for me the front carb is percolating the fuel. Event though I have a large home-made heat shield over my header, the front gets too hot.

I've been able to recreate the issue at home on a warm day letting the car idle in the sun. The fuel level in the front float rises, and sometimes the fuel percolates. One time I quickly pulled the domes off the carbs and I could see the fuel spurting out through the nozzle.

I've checked and double checked my float levels, and I have a fuel pressure regulator turned down to about 2.5 psi. What surprises me is that I can put my bare hand on the carb when this is happening and while it's hot, it's not so hot I have to pull my hand away.

So far I haven't found a way to solve this completely. I've tried routing the fuel lines around the front of the engine compartment (over the radiator support) as an experiment to see if it was heating up too much on its way to the carbs. Made no difference.

I did find that stuffing some fiberglass insulation between the carbs and the heat shield slowed down the rate of the problem occuring, but I get the same problem when I come back to the car after driving and letting it sit for a few minutes.

I've confirmed it is NOT vapor lock. Taking the cap off the fuel tank makes no difference either.

I'm going to be switching to some Weber DGVs to solve a tuning problem and am hoping that they aren't as sensitive.

FWIW, I have a 4 core radiator, fan shroud, and splash pan. Part of me wonders if removing the shroud might help by blowing the air in a different path under the hood? Haven't tried that yet. What drives me crazy is that I read about people driving their early Z's in Arizona in July with no such issues while where I live in CO 90 is a hot day!

Anyway, I don't mean to hijack your thread, just letting you know you're not alone (in case that makes you feel any better).

Daniel

The car runs and idles fine after coming off the track.

The car has a 280Z radiator, fan shroud, and flex fan. It never runs hot, even after flogging it on the track for 20 minutes, it never goes past the "M" on the temp gauge. It doesn't have a header either to throw extra heat in there.

I have a rebuilt dizzy on my '70. Maybe I'll swap that in to see if it makes a difference.

Marty

[Chino 240Z]

Well, I would remove the top fuel bowl cover, the gasket my tear on you if it sticks? I bought a bunch from ZTherapy to keep on hand. Lifting the cover, do it slowly so not to knock the floats out of whack, they might need to be bent alittle more to run a tiny bit more fuel in the bowls. The float is only a rough adjustment anyways, then you fine tune your fuel with the nozzle adjustment at the bottom of the carbs. You can just lift the cover some to peek in and besure you don't have sediments or something that gets sucked down over the hole in the bottome of the bowl. If they are clean, and your car runs like you have your carbs adjusted pretty much the best you can? I would consider the mechanical fuel pump next.

I think the Holley red pump at the tank and a regulator at the firewall works great. I picked up a Holley blue pump which I think is 14psi, and again I knock that down with the regulator. They should come together in a kit. Summit had a good price. But my local AutoZone kicked their butt in price when I got mine.

Here is an idea...

http://store.summitracing.com/default.asp?target=partdetail.asp?part=HLY-12-802-1

http://store.summitracing.com/default.asp?target=partdetail.asp?part=HLY-12-801-1

[Marty Rogan]

Well, I would remove the top fuel bowl cover, the gasket my tear on you if it sticks? I bought a bunch from ZTherapy to keep on hand. Lifting the cover, do it slowly so not to knock the floats out of whack, they might need to be bent alittle more to run a tiny bit more fuel in the bowls. The float is only a rough adjustment anyways, then you fine tune your fuel with the nozzle adjustment at the bottom of the carbs. You can just lift the cover some to peek in and besure you don't have sediments or something that gets sucked down over the hole in the bottome of the bowl. If they are clean, and your car runs like you have your carbs adjusted pretty much the best you can? I would consider the mechanical fuel pump next.

I think the Holley red pump at the tank and a regulator at the firewall works great. I picked up a Holley blue pump which I think is 14psi, and again I knock that down with the regulator. They should come together in a kit. Summit had a good price. But my local AutoZone kicked their butt in price when I got mine.

Here is an idea...

http://store.summitracing.com/default.asp?target=partdetail.asp?part=HLY-12-802-1

http://store.summitracing.com/default.asp?target=partdetail.asp?part=HLY-12-801-1

Yep, I think a peek into the float bowls is in order.

The Holley Blue pump looks like a good buy. Only $12 more than the red and it comes with the regulator. The regulator probably cost more that $12. Did you get the safety shut-off switch?

I am not so good with wiring, so if I end up going that route, I have to get with you on some detailed instructions or tips.

Thanks Craig!

Marty

[Chino 240Z]

With that regulator you can also run a pressure guage from one of the 2 outputs. I mounted the pump on a bracket next to the tank and ran power from a switch on the dash to the pump, then the ground wire of the pump to the frame at the pump. Now, I have a emergency cut-off switch on the cowl outside for someone to cut-me off from the outside if I got into trouble, or I can kill a master switch from the inside on the dash, or I switch off the fuel pump with it's own switch so I can run down the gas level in the fuel bowls. This way it won't have alot of gas in it to boil if it got hot, or to store it in the garage it won't have fuel setting in the bowls. Just before I fire it up I let the fuel fill the bowls a come up to pressure a few more seconds before I excite the starter.

If you go that route, let me know if you need info. on this stuff and I shoot it over to ya.

[240ZMan]

I too am running with a Holley Blue. Just be aware that it's a bit loud. You are going to hear it inside the car at idle. In fact, you're going to hear it outside as well.

[Chino 240Z]

Oh yea, 240ZMan is right. You can hear it inside the car. I like to hear sounds like this, adds more to the excitement. If you use a 1/4" rubber pad as an insulator under the mounting clamp, the noise in the car is reduced. If it's a street car you would need to think about this. I think I only notice it in the pits or in the grid lanes. After that everything is too loud!

[Marty Rogan]

I was running short on time, so I broke down and dropped the car off at my local Z Speciality shop. He traced the problem down to the rear carb insulator gasket was blown. Apparently, under heavy acceleration, it was sucking too much air in. It would have taken me a lot longer to figure that one out! So put that one in your Z memories banks if this ever happens to you.

Well, I went to an open track day yesterday to test her out. She ran like a champ all day! Woohooo!! I really ran her hard too and had no problems with fuel. I kept the tank full just to be sure.

It was a fantastic day. About 87 degrees, with a light breeze. The event was put on by a local dealer that is a Charter member of the Autobahn Country Club. http://www.autobahncountryclub.net/index.html

I was surrounded by some pretty fast company: plenty of Feraries, Maseratis, a 911 Carrara a Lotus Elise and a couple of Alfas. The old Z held her own out there though. It's a real hoot to see a Ferari pull over and give you a point by. I passed the 911 too. I am sure this is mostly due to these guys having more money than driving talent, but it was fun just the same. I may have had the cheapest car out there, but it wasn't the slowest!!

The owner's son brought a Ferari Challenge car. Man was that car fast!! He's winning his class in the SCCA, so he had the talent to back it up.

I put in 5 -30 minute sessions and 1 shorter one for about 140 track miles.

Man I love these open track days!!

Marty