Jump to content

eloZada

New member introduction - My 76' 280Z in Atlanta

Recommended Posts

 The engine revving freely, but not when it's under a load is lack of fuel. Not much to tear down. Pull the chambers and pistons, clean everything and be sure the pistons drop freely. Pull the float chamber tops, The needle and seat (fuel valve) is under the top. The trickiest part is setting the floats.

Thanks, I had already cleaned and checked the pistons. They do drop freely, an I changed the oil on the dampers and put SAE 20 engine oil, as it says in the Haynes Manual. I will now try to clean and adjust the float.


Sent from my iPhone using Classic Zcar Club mobile
  • Like 1

Share this post


Link to post
Share on other sites

Hi guys,

The other day I had a little time and I cleaned the float bowls, adjusted the floats (at between 3,5 and 4 mm), changed the filters and changed the gaskets at the float chamber. Unfortunately I have no change in the behavior of the engine. It still sounds like it doesn't get enough gas. I'm going to put a clear filter on the line to see when it stops getting there, because in the beginning it always seems to run ok, but after it heats up a little it starts running bad again.

Here is a brief video of the issue I'm having, it actually sounds worse now than before the first time I opened the float chambers:

I will check the spark plugs again just in case it's just not firing correctly anymore, but last time they were fine and It has not run that much since either.

Any other ideas?

Share this post


Link to post
Share on other sites

Sounds great when the RPM go up.  Firing order and timing seem right.  Any way to just turn up the idle speed to keep it running, so that you can mess with it?  I don't know SU's.

  • Like 1

Share this post


Link to post
Share on other sites

 Any service manual or Phil's "Quick and Dirty SU Tuning" will show the screw. It's pretty easy to find by studying the linkage.

  • Like 1

Share this post


Link to post
Share on other sites
4 hours ago, eloZada said:

Any other ideas?

I don't remember much from my carb days but I do know that if it runs well at higher air flow levels but has problems at low air flow, that's usually a sign of a vacuum leak.  Vacuum leaks get over-powered at high air flow levels.  This is true for EFI also.  So I might focus on small air leaks.  With carbs those can be at the mounting gasket surface, or the intake runner to head surface.  I know somebody that spent a lot of time with similar problem and it was a cracked base plate on the carburetor.  That was a late-model Chevy V8.

A test the EFI guys use will also work with carbs I think.  Get the idle speed up just enough to keep it running.  Then spray carb cleaner or starting fluid at the places you think might be letting air past the carbs.  If the air doesn't go through the carb it doesn't pick up any fuel and you'll get a lean condition, with stumbling and poor running.

  • Like 1

Share this post


Link to post
Share on other sites

Thanks ZedHead, yes, I will turn up the idle and try the carb cleaner thing. Although I always wondered how that works exactly. I imagine the idea is that the carb cleaner will get sucked in if there is a leak?


Sent from my iPhone using Classic Zcar Club mobile

Share this post


Link to post
Share on other sites

 Curious about something? In the video, when you rev the engine, was that an intentional slow rev? In other words, does the engine respond instantly when you give it throttle?

Share this post


Link to post
Share on other sites
2 hours ago, eloZada said:

Thanks ZedHead, yes, I will turn up the idle and try the carb cleaner thing. Although I always wondered how that works exactly. I imagine the idea is that the carb cleaner will get sucked in if there is a leak?


Sent from my iPhone using Classic Zcar Club mobile

Since carb cleaner or starting fluid is flammable, your engine treats it as fuel. If you have a vacuum leak along say a gasket at the insulator blocks, that leans out the engine. When the carb cleaner gets pulled in through that leak, your mixture isn't as lean.

Another method I've used in the past was an unlit propane torch. You barely crack it open, and when you get near the source of the leak, you'll hear the engine speed increase.

  • Like 1

Share this post


Link to post
Share on other sites
3 hours ago, Mark Maras said:

 Curious about something? In the video, when you rev the engine, was that an intentional slow rev? In other words, does the engine respond instantly when you give it throttle?

I didn't rev it up completely because I didn't want to damage anything if it was not working correctly. But it does respond instantly. It's not easy to see in the video, but I step on the gas and it revs up, but without letting go of the pedal, the engine starts loosing power and you see the rpm going down even though I'm still stepping on it.

Share this post


Link to post
Share on other sites
1 hour ago, SteveJ said:

Since carb cleaner or starting fluid is flammable, your engine treats it as fuel. If you have a vacuum leak along say a gasket at the insulator blocks, that leans out the engine. When the carb cleaner gets pulled in through that leak, your mixture isn't as lean.

Another method I've used in the past was an unlit propane torch. You barely crack it open, and when you get near the source of the leak, you'll hear the engine speed increase.

Thanks Steve, I will try that then and see if I find any leaks. Looking forward to finally solve this issue and get the car on the road again.

Share this post


Link to post
Share on other sites
37 minutes ago, eloZada said:

I didn't rev it up completely because I didn't want to damage anything if it was not working correctly. But it does respond instantly. It's not easy to see in the video, but I step on the gas and it revs up, but without letting go of the pedal, the engine starts loosing power and you see the rpm going down even though I'm still stepping on it.

Now that's a horse of a different color.

If you hold the throttle at a certain position and the engine doesn't maintain speed, it's likely that the engine is running out of fuel. You need to check

  1. Fuel pressure
  2. Float levels

Since you say you have already set the float levels, you might want to check fuel pressure. Here's the gauge I have in my car: https://www.amazon.com/gp/product/B000CIH38M. You will also need this adapter if you are running standard fuel lines: https://www.amazon.com/gp/product/B00093CL3M. You should be running about 3 to 3.5 PSI IIRC. If you have enough pressure, then you probably don't have your float levels set properly.

If the pressure is low then it's probably 1 or more of these:

  1. Weak/undersized pump
  2. Rust/pinholes in the pickup in the tank
  3. Kinked fuel line
  4. Partially blocked fuel line.
  5. Fuel filter that is getting loaded up with crap from the fuel tank.

If you get to a point where you want to throw your hands up, I can refer you to a number of people in the area I would trust to resolve your problem.

  • Like 2

Share this post


Link to post
Share on other sites

Thanks SteveJ, that is great help. I haven't quite gotten to the point when I'm giving up yet, although I admit I'm getting close. But this car is supposed to teach me a lot in mechanics and it certainly is doing so, together with you guys, of course ;).

I'm going to try the fuel pressure gauge and also I'm going to check for vacuum leaks. If I have no new findings after that, then perhaps I will start considering contacting you about referrals.

Share this post


Link to post
Share on other sites

Hello again guys,

So I followed some of your instructions, although I just realized I haven't checked for leaks yet. But I did add a fuel pressure gauge and I put in a new clear filter in order to better see what's going on, so I hope this gives us a little bit more insight.

Everything went good at first, right after adding all the stuff the car ran properly for a while, as shown in this short video. You can see it's pumping plenty of fuel and the gauge marks between 3 and 4 psi. The car sounds and revs normal.

 

After a while though, after I drove the car briefly around the parking lot it started loosing power again, as so:

 

Next thing I'm gonna check for leaks with the carb cleaner spray, as I admit I completely forgot the other day, but I do suspect it will also have something to do with soot in the tank and line, mainly because of the look of the old filter.

IMG_3720[1].JPG

I'll let you know once I have checked for leaks, and after that I guess I will have exhausted all possibilities.

Share this post


Link to post
Share on other sites

I agree with the cruddy tank. Try a few more tank fulls but I'm thinking it needs to be cleaned. Not as hard for a 280 as a 240. Lots of us have done it so just ask and you'll get plenty of info.

  • Like 1

Share this post


Link to post
Share on other sites

i found on my tank, the tube that the fuel pump hooks to was about 95% plugged with rust. i would bet between that and your fuel line, thats your problem

  • Like 1

Share this post


Link to post
Share on other sites
On 7/25/2017 at 9:24 AM, sweatybetty said:

i found on my tank, the tube that the fuel pump hooks to was about 95% plugged with rust. i would bet between that and your fuel line, thats your problem

I agree with this, it may be the fuel line. Better check on that as well.

  • Like 1

Share this post


Link to post
Share on other sites

You can hear the fuel pump struggling. The other thing you want to move it to just off the tank. I'm not aware of fuel pump that is designed to suck.  Especially that distance. 

 

 

Edited by JSM
  • Like 1

Share this post


Link to post
Share on other sites
17 hours ago, JSM said:

You can hear the fuel pump struggling. The other thing you want to move it to just off the tank. I'm not aware of fuel pump that is designed to suck.  Especially that distance. 

Thanks, I will have to figure out where to get the power from, but I will consider this. I imagine that would help, but I believe it should not be the cause of the problem I'm having right now, because it used to work fine before.

 

 

Share this post


Link to post
Share on other sites

Yeah likely crud. Your car should already be wired for the fuel pump. Should be pretty easy. 

Share this post


Link to post
Share on other sites

If there was only someone in the Atlanta area who understood the 76 280Z wiring diagram to help you locate the factory wiring and safely modify it to work...

  • Like 2

Share this post


Link to post
Share on other sites

I started draining the tank through the screw at the bottom in order to blow through the line and remove any possible blocking. This is what came out with a gallon of gas.
IMG_3751.JPG

Also, I saw these cables down there. Yiu think that might be the wiring for the pump?
IMG_3756.JPG


Sent from my iPhone using Classic Zcar Club mobile

Share this post


Link to post
Share on other sites

Never seen anything like that. Looks like the bottom of a boat, barnacles. You will most likely have to drop the tank and clean and coat the inside. Cost me $50 or so on my '77. Google "Red-Kote application instructions" to familiarize your self with the procedure. It's not hard just time sensitive and will take a week to fully cure the liner. I can offer plenty of tips, I've done two so far just let me know.

  • Like 1

Share this post


Link to post
Share on other sites
Never seen anything like that. Looks like the bottom of a boat, barnacles. You will most likely have to drop the tank and clean and coat the inside. Cost me $50 or so on my '77. Google "Red-Kote application instructions" to familiarize your self with the procedure. It's not hard just time sensitive and will take a week to fully cure the liner. I can offer plenty of tips, I've done two so far just let me know.

Thanks siteunseen, I think I will have to do that. Right now I want to clean it enough to be able to get it out of the parking place where it is and take it somewhere where I can work on it properly. I'm guessing this might be my main problem right now. Still have to check for leaks though, haven't been able to do that yet, mostly for fear of hitting something that can catch fire without having a fire extinguisher closeby


Sent from my iPhone using Classic Zcar Club mobile

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.