New member introduction - My 76' 280Z in Atlanta

[Mark Maras]

13 hours ago, eloZada said:

Generally it runs freely when it's not under load. I will do as you say, I imagine I will have to disassemble the whole thing to clean and adjust it properly?
I will try to do it as soon as possible so I can give you guys a response soon. (I'm in the process of moving to a new place within Atlanta and there's lots going on). I really appreciate the help!


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 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.

[eloZada]

 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.


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[eloZada]

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?

[Zed Head]

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.

[Mark Maras]

 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.

[Zed Head]

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.

[eloZada]

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?


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[Mark Maras]

 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?

[SteveJ]

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?


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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.

[eloZada]

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.

[eloZada]

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.

[SteveJ]

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.