Chris ~ ["I'm not completely familiar with the mechanical fuel pumps, but does anything regulate the flow?"].

Yes.

The 280 had only an electric fuel pump with pressure regulation.
The 260 had both an electrical pump with regulation and a mechanical fuel pump.
The 240 had only a simple mechanical pump, but they regulate themselves internally.

The line pressure for the 240 mechanical pump (btwn the pump and the carbs) is expected to be from 3.41 to 4.27 pounds per square inch at any engine speed.

When the carbs are full and the float bowl needle valves are closed (not allowing any more fuel in) mechanical pumps 'disconnect' themselves internally.

Once the line charges with fuel, backpressure holds the diaphragm down and disengages its actuating rod from the pump arm by holding it beyond the pump arm. The pump arm continues to work of course (it's riding the cam eccentric), but the diaphragm is temporarily held away from it, so the diaphragm doesn't move and no fuel movement results until it's needed.

I can't find a diagram, so picture the diaphragm looking like an open umbrella. The only thing the pump arm does is pull the "umbrella" handle down against spring pressure, then releases it. That downward action pulls fuel into the pump thru the inlet valve and fills the chamber with fuel. If the fuel can't move out of the chamber (carbs are full), the fuel holds the umbrella down against spring pressure. While the diaphragm is held down, its "handle" is no longer in contact with the pump arm. The pump arm goes on pumping, but it isn't touching the 'handle' while the umbrella is held in the DOWN position. No fuel moves until it is called for by the carbs; then the spring pushes the diaphragm back up (pushing fuel thru the OUT valve) and re-connecting the 'umbrella handle' to the pump arm.

I was taught in actual practice the system reaches a delicate "flutter" balance where the carbs let a constant little 'sip' of fuel thru the needle valves, and the pump does the same, instead of any dramatic "OPEN/CLOSE" scenario.

Yes, the 240Z had a return line but I never considered it vital to operation, and always considered it to be an emissions control device. I might be wrong. Bryan or Paul could tell us about that with more authority.

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1970 240Z

In terms of emissions, a return line is considered worse if I'm not mistaken. Many vehicles nowadays are dead-head setups for this reason. For the Z's the return system was more for controlling the heat of the fuel and preventing hot start issues from what I've read.

Edit: And experienced to an extent...

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-Chris

Ahhhh....so the fuel return was sort of a 'gasoline cooling' device? Thanks.

I knew the flattops had severe vaporlock and afterboil problems, and owners went to real extremes trying to live with them. I don't know if Datsun made the fuel return on the later 240s different than on the early 240s. I know my original '70 240 never gave me a fuel problem ~ always restarted fine hot or cold, so whatever they did first, it worked as advertiZed.

REF: the cam; I saw this car when it had the 4Bbl on it and the cam sounded so lumpy that it might not idle much slower than it does now in the video. I think someone put a big stick in there to use the Carter carb but then didn't know how to tune it. It's idling much lower now than it did with the 4Bbl, but I suspect the problem is something very basic (like a mis-timed cam or improperly adjusted valves or an ignition problem). Also, the car is missing one muffler, so we're hearing a single glass pack and a single straight pipe, which makes it hard to determine how smooth or rough the engine is running. I can't get any straight answers from anybody about the timing light test I recommended 3 weeks ago, and there's little sense in continuing without that, so I've pretty much given up trying to analyze this case.

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1970 240Z

After that one encounter Ive never turned the cam in the opposite direction and gladly go the extra turns if it keeps from putting unnecessary strain on the chain.

Ive tried a lot of spark plug orders, advancing/retarding timing, and even different distributors. Turns out the reason my battery crapped out on me is because I reconnected the previously disconnected ground from the battery to the firewall. Disconnected it and after a couple of drives everything was back to normal. No idea why this worked but it did!

The return line just seems like its rusted shut so nothing gets through it, but I wanted to get a return line on there because I feel like the blocked return puts more stress on the fuel pump, and I really dont want the plug to pop off the return while im driving.

The car is idles between 1k-800 depending on when I look at it. I can get it lower but it already sounds like a popcorn maker and makes me nervous when the idle drops so low. The exhaust projects exactly what the engine feels/sounds like in the car at idle. It doesnt sound as crazy as it does in the video when I tap the gas, but the lope is spot on.

The reason I havent used the timing light is because I knew the timing was out of whack and I feel like it would just reinforce that. I was also away from home for 5 weeks and didnt have a timing light with me(turns out I bought a remote starter!). Did get my hands on one and tried to take a video of what I saw. You can briefly see towards the end that the timing notches are far below the arrow on the front cover. Im going to get the engine to TDC tomorrow and see what the first piston is looking like.

Heres the video: http://www.youtube.com/watch?v=P87PwwXPw94
Youll probably have to look very closely if youre not playing it in HD and youll still probably have to keep your eyes peeled in HD also.

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71' 240Z: HLS3040666

Has the difficult part just ended or is it just beginning?

Pulled the valve cover and #1 plug out to see where my TDC actually was.
The cam and distributor agree and make everything seem normal:





But actually feeling for TDC through the #1 showed that TDC is:






And the other:





Guess this means im going to have to take off the timing chain and set it properly?

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71' 240Z: HLS3040666

No ~ it looks right. Your piston reaches TDC twice during each 4-stroke cycle and when the 'bunny ears' are down (opening the valves), that's the top of the exhaust stroke. When the ears are up, that's TDC on the compression stroke. THAT's when the distributor cap must point at plug #1.
And remember, #1 is at the front of the engine.

Show us a picture of the front of your camshaft gear, showing detail of your timing chain. There should be some marks (dots) which line up if you turn everything far enough.

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1970 240Z

You DO know that your engine has a hot(ter than stock) cam in it, right? Hence it will sound less smooth, and possibly "popcorny" at idle...

What do you mean by "feeling" for TDC, with feeler gauges through the spark plug hole? Looking at the timing mark on the crank pulley? The are TWO types of TDC, compression stroke and the exhaust stroke....

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-Chris

I do but its hard to tell if the popcorn sound is from the cam or improper timing. The first time I floored it I almost redlined because after 2000rpms it pulls like my 260 never did.


I felt with a plastic tube. Like when setting the valve clearances I knew I was at/very close to TDC when the tube would fit and slide snugly in over the piston.


I thought the cam and crank were not in sync because my #1 isnt at either of the spots the rotor is pointing. I based where #1 should be on the distributor cap on the direction the rotor was pointing when I initially checked the cam, but the piston is showing the TDC is a little earlier than I thought. The rotor is pointing at a post one spot below the where I have #1 set up in that picture. Perhaps I just need to try messing with the plug wires again and try setting it close to 17 degrees with the harmonic balancer? Hoping this will work because I really dont want to take the front cover off.



Valve cover is back on right now and the cars hidden away but here are some old pictures of it:

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71' 240Z: HLS3040666

1. Loosen your distributor body slightly and twist it back to where the timing mark indicator is set in the middle of the scale. Leave the dizzy lose enough to turn by hand.

2. Do your thing again with the plastic straw, putting #1 piston as perfectly close to TDC as you possibly can, with the cam lobes facing up.

3. Where ever your distributor rotor is pointing then, make that #1 spark plug. Arrange the other wires in the proper 153624 firing order, counter clockwise.

The car will run with that basic setting.

4. Now hook up your timing light and unhook your vacuum advance hose at the distributor. Stick a screw in the hose to keep it from leaking.

5. Twist your distributor body until the timing light shows about 12* BTDC, then tighten your distributor down and reconnect your vacuum hose.

That should give you full timing. Your cam is so lumpy (a radical hot grind) that you should expect it to idle a bit rough and you might need 1,000 rpm for a smooth idle. You have "enough cam" for that old 4Bbl and probably for triple Webers or Mikunis. It looks even lumpier than my old 3/4 race cam was in my Charger. Surprising to see such an aggressive grind in a street Z. It might actually require you to advance the timing more than 12*, but that's where I'd start. Does your Tach work with that electronic ignition distributor?

if you decide to run the RPM up, you'll want to replace the cam cover back on when you do, just to prevent spraying oil all over your engine bay and manifold.

Chris, have you ever seen a Z cam that radical? Do you think it might be a full-race?

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1970 240Z

I'm not an expert on cams, only just started studying them closely relatively recent. But no, that's not the hottest one I've seen. The really radical ones I've looked at have the circular portion of the lobe (terminology escapes me) ground nearly or completely flush with the diameter of the camshaft. Check out this D.L. Potter remake:

http://item.ebay.com/viewitem?sbk=1&nav ... 1229992363

If only he didn't keep the duration a secret until you bought it, I'd like to know all the specs before I dropped that amount of money on something like that. I suppose lift is more important however.




Porkbun I'm giving you a hard time because when you felt for TDC the pictures you took were of the WRONG TDC (not compression stroke). Rotate the crank another 360 and you'll be at the correct location (crank spins TWICE for every full rotation of the cam).

Like Frank said, the two front lobes of the cam should point UP, like rabbit ears, when at TDC compression.

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-Chris

But I felt and took pictures of both TDC's! Looks like you missed the 3rd set of pictures in that post. Doing a bunch of work all around the car and decided to pull the plugs. What do these plugs tell you?

Going to try and get to testing the timing today or tomorrow depending on how much I get done today. Bunch of new parts that should be coming in today!

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71' 240Z: HLS3040666

That plug tells me I wish mine burned that cleanly. It might be a slight shade too warm but that's better than being too cold and carbon-y.

It should be an NGK or a Bosch, by the way. What heat range did you buy?

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1970 240Z

If all 6 plugs look like that I would leave the fuel mixture alone. It might be a little lean, but not by much. The carbon on the plug looks like it was there before you made the last adjustments.

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Rob
1971 240z

I "missed" it because of the wording, I realized you had pictures of both TDC's but you sounded confused to me. Feeling with a plastic tube isn't exactly a precise system of measurement, you'd be amazed at how much/little the engine moves with each degree of rotation on that pulley. A dial indicator on the piston dome is the best way to view this, compared to that feeling with a plastic tube is like pushing a small button with a hammer. If you took pictures of the notch/window on the cam tower that you can see through the cam gear holes you'd get a better idea. My guess is that your mechanical timing is probably just fine, maybe you'll have to move the cam gear to another position.



Looking closer though, how much did you twist the body of your distributor between the first and third picture (and did you run it like that)? Between #1 and #2 it looks like nearly 90 degrees.

Your sparkplugs look perfectly fine.

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-Chris

I don't know, that plug looks to clean, color distorted. (btw, NGK or Nippendenso, no others will do imo) I'm coming in late on this, just busy, but think simple.....air, you got, (unless you got a rat nest,) then fuel and air. Then you have timing and valve clearance. This all has to be perfect. btw, it's a straight 6, 1-5-3-6-2-4 so unless it's rusted, it aint dying.