Ben's 75 260z

[ben92]

On 11/14/2021 at 10:24 PM, CroS13 said:

Hey mate great work and upgrades on the car, I like how your modernising everything.

Where did you get the fuse box to replace the fusible link set up?

Rudi. 

Hey Rudi! Sorry, I only just saw this post - not sure if it's helpful anymore but here's the fuse box I installed:

https://au.mouser.com/ProductDetail/Littelfuse/04980933X?qs=sGAEpiMZZMvShe%2BZiYheii%2FeEXsvxFUx9RjL22D3SL0%3D&countrycode=AU&currencycode=AUD

And here is the rest of the order I made at the same time with the part numbers for the fuses:

 

[ben92]

So, unsuprisingly, a new set of carbs didn't magically get the car running decently. After installing everything and trying to dial in a baseline tune it ran worse. A lot worse. Backfiring from the carbs and the exhaust, idling at 800, then 1600, then dying, it was all over the place. I tried all the usual things - adjusting timing with a timing light, attempting to sync the carbs, adjusting idle screws, running it with / without the aftermarket electric pump, checking for vacuum leaks...but no success. Putting a syncro over most of the air intake tubes killed the thing and it was so hard to keep it running consistently that I couldn't work out what to even attempt. I gave up for 3 months, apparently, figuring that I'd have to send it off to someone who knows a lot better than I do.

But now, with a house move to a place that has an incline driveway looming (meaning the car needs to be driveable to be able to get it up the driveway to store it), I figured I'd do a last run of somewhat methodical tests.

The first idea was to drain the (possibly) old fuel, just in case all it really needed was fresh fuel. When I unplug the fuel send port on the tank, the fuel almost just dribles out. The return post sends fuel flying out as you'd expect. So, first question - is that to be expected? I've got a late model 260z tank, so as far as I can see the send port is driver side, return port is passenger side.

Ignoring that, the second test was to work out what sort of fuel pressure I was getting - perhaps inconsistent pressure was causing inconsistent running. I'd bought a PSI gauge, so may as well use it. With the key in the 'ON' position, the aftermarket electric pump makes a big racket, but does functionally nothing. I tried switching tank outlet ports, fuel lines, fully charging the battery, and also blowing compressed air down the lines / tank ports incase there was a blockage (there isn't, as far as I can tell). The electric pump should definitely be able to prime the whole fuel line on it's own though, right? Even with air in the lines, it should still be strong enough to push fuel from the tank to the carbs with decent pressure? Or am I asking too much of it?

Not knowing the answer or wanting to buy another electric pump without doing more testing, I decided to take off the pump and blow / suck air through it. I wanted to know if I had the pump wires disconnected, or the pump was broken, was it actually blocking the line and stopping the mechanical pump from doing it's job? Turns out I could blow air through it, but it makes a sort of trumpet noise at the start - like there's a bit of resistance but then a gate stays open once the fuel is flowing. I could probably look into how these things work but for now the tests continue.

Next test - seeing as the triple carb set up has never been trialled without the electric pump after the tank, how would running just the mechanical pump go? Plenty of cases of people just running the stock mechanical pump with triple webers it seems, so worth a shot. After a long while of turning the engine over (side question - is it bad to keep the engine turning over without it firing up? How much damage have I already done over the years?) the single, dead head line was primed with a consistent 5 PSI. Eventually I throttled the carbs and it fired right up - revving straight up to 2000 rpm, sitting there and backfiring a little. Not wanting to touch anything and hear it backfire all over the place today, I've turned it off for the day to try and work out the best way forward again. I've got to wait a day for the threadlocker on the fuel pressure regulator ports to set, so I'll charge the battery again over night and adjust the idle screws on the carbs a little before firing it up tomorrow hopefully. If it runs consistently, then perhaps I can at least start to dial in a tune? I also realised I got distracted and never ended up draining the tank, so it may still have stale fuel.

So - last question - can I install this non-bypass, dead head fuel pressure regulator between the mechanical pump and the carbs like I've got pictured below (with the routing of where the clear hose goes, just with everything connected properly)? Supposedly the webers want 3-3.5 PSI, and the mechanical pump seems to be giving them 5 PSI. Originally, I planned to use the FPR with an electric pump installed after the tank and a return line just coming out of the third carb to keep the fuel lines cool in traffic. Will the FPR mess with the mechanical pump? I imagine the mechanical pump will push fuel regardless based on RPM, but if the FPR is restricting flow right after it, then how will the pump respond?

One day I'll be able to post simple updates, but for now it seems all I've got is questions and more questions, so if you've made it this far then sorry, and thanks! As always any help is really appreciated.

[1600dave]

If you think its a fuel problem, keep the troubleshooting simple. A mower tin of clean fuel, stick a length of fuel hose into that to feed the mechanical pump and then send that straight to the webers. Plenty of Datsuns didn't have a return line from factory and run fine (my 1600 for instance). If it runs OK like that, start working backwards to see where the problem lies in the fuel system. 

Also, a tip - if that's how you intend to leave the fuel lines set up, be very careful routing them around the front of the engine like that. I did at one stage and suffered an engine bay fire when things came slightly adrift and the radiator fan put a cut in the fuel line.

 

 

Edited February 19, 2022 by 1600dave

[datsunrally]

Just read through this and a couple of questions come to mind: 

• What sort of electric pump do you have, what is its PSI output, check it's a carby pump, not a high pressure one for injection
• Why do you have the mechanical pump connected as well? 

The electric pump should easily be able to prime the fuel line to the carbs by itself. When you turn the key to 'ON' you should hear it clicking / whirring away, when the pressure builds up sufficiently, you will note the sound changes a little.

I would bypass the mechanical pump for now, connect the electric pump to the regulator then turn the ignition to 'ON' and get a reading of the fuel pressure at that point. Then start the car and see what the pressure does. In the ideal world, you would then drive the car around a bit and observe the fluctuations in the pressure under light and heavy throttle applications, then set the pressure at a point that maintains the required pressure range under full load.

Do you know how to adjust the Malpassi pressure regulator? They're very easy, if there aren't instructions, then unscrew the little dome nut and you will find a threaded pin with a notch for your screwdriver. From memory (it's been a little while) screwing it down a little will reduce the pressure reading on the gauge. You will need to experiment a bit, you'll get the idea. About 3-3.5 PSI should be good for your Webers. 

Jumping from poor-running SUs to poor-running Webers was probably a step too far, but it's done now.

Did you say in an earlier post that when you took the hose off the tank very little fuel came out? Clearly that's a problem, unless there's no fuel in there, which in itself is a different problem…

Jeff

[ben92]

On 2/20/2022 at 9:16 AM, 1600dave said:

If you think its a fuel problem, keep the troubleshooting simple. A mower tin of clean fuel, stick a length of fuel hose into that to feed the mechanical pump and then send that straight to the webers. Plenty of Datsuns didn't have a return line from factory and run fine (my 1600 for instance). If it runs OK like that, start working backwards to see where the problem lies in the fuel system. 

Also, a tip - if that's how you intend to leave the fuel lines set up, be very careful routing them around the front of the engine like that. I did at one stage and suffered an engine bay fire when things came slightly adrift and the radiator fan put a cut in the fuel line.

Cheers Dave for the suggestion, definitely should have tried that first really. I did try doing exactly that this afternoon with a can of fuel I got today, and I got the car running, but still not well and not a noticeable amount better than before. Which leads me to believe the old fuel could use replacing, but the tank / old fuel / lines definitely aren't a huge problem and causing poor running.

The  dodgy fuel lines in the engine bay are definitely for testing only - I'll make another proper hard line setup once I figure out which set up to go with 

On 2/21/2022 at 11:41 AM, datsunrally said:

Just read through this and a couple of questions come to mind: 

• What sort of electric pump do you have, what is its PSI output, check it's a carby pump, not a high pressure one for injection
• Why do you have the mechanical pump connected as well? 

The electric pump should easily be able to prime the fuel line to the carbs by itself. When you turn the key to 'ON' you should hear it clicking / whirring away, when the pressure builds up sufficiently, you will note the sound changes a little.

I would bypass the mechanical pump for now, connect the electric pump to the regulator then turn the ignition to 'ON' and get a reading of the fuel pressure at that point. Then start the car and see what the pressure does. In the ideal world, you would then drive the car around a bit and observe the fluctuations in the pressure under light and heavy throttle applications, then set the pressure at a point that maintains the required pressure range under full load.

Do you know how to adjust the Malpassi pressure regulator? They're very easy, if there aren't instructions, then unscrew the little dome nut and you will find a threaded pin with a notch for your screwdriver. From memory (it's been a little while) screwing it down a little will reduce the pressure reading on the gauge. You will need to experiment a bit, you'll get the idea. About 3-3.5 PSI should be good for your Webers. 

Jumping from poor-running SUs to poor-running Webers was probably a step too far, but it's done now.

Did you say in an earlier post that when you took the hose off the tank very little fuel came out? Clearly that's a problem, unless there's no fuel in there, which in itself is a different problem…

Jeff

The electric pump is aftermarket supercheap junk as far as I know. No brand or marking on it, and it was doing functionally nothing at all last weekend when I ran all my tests. I might get around to bench testing it on the weekend just out of curiosity, but for now that's why I've removed it for now and only have the mechanical pump  installed. This wasn't the original plan, but at this stage it doesn't look like switching out the mechanical pump for an electric one would really change anything in terms of trying to get a smooth, healthy idle in the garage anyway.

 

The best I could manage tonight was getting a somewhat consistent idle, albeit still with a lot of popping and backfiring that sounded too unhealthy for me to want to let the car run long enough to warm up. I don't know how much damage all the sputtering and exploding is doing so I don't want to over do it? Revving still gives a bunch of different results; sometimes it hangs for a few seconds, the fan usually kicks in hard, there's usually a lot of backfiring and occassionally it would kill the car altogether. To get it to idle consistently-ish I adjusted the timing and the weber's mixture screws and seemed to be going in the right direction, but yeah, all the excessive banging concerns me too much to let it just idle for too long.

I've definitely set the webers idle correctly, that's simple enough. Every tuning guide mentions that for the weber's mixture screws you start with 2 turns out from 'seated' - but I don't have the slightest clue where 'seated' is. The springs are the only thing that seem to be adding resistance to that screw so the mixture at the moment is pure trial and error and with the messy idling it's pretty hard to gauge whether turning in / out is making the idle better or worse.

The fuel pressure from the mechanical pump is still at a solid 5 PSI - still can't figure out if putting the regulator after the mechanical pump with no bypass is a good idea, so I haven't tried that either. Could the extra 2 PSI cause running issues?

I could fire it up again and attempt to re-set the timing with a light if the idle stays in a good range. I could also get yet another fresh set of spark plugs and see if that helps, and play around with the mixture / synchro tool some more. Perhaps going through everything another time could give better results, but at this stage, unless I'm missing something, this is all stuff I've tried a lot over the last few years, so I'm tempted to find a local mechanic that actually knows what they're doing and might be able to diagnose something I can't?

[AndBir]

On 2/24/2022 at 9:45 PM, ben92 said:

I've definitely set the webers idle correctly, that's simple enough. Every tuning guide mentions that for the weber's mixture screws you start with 2 turns out from 'seated' - but I don't have the slightest clue where 'seated' is. The springs are the only thing that seem to be adding resistance to that screw so the mixture at the moment is pure trial and error and with the messy idling it's pretty hard to gauge whether turning in / out is making the idle better or worse.

Edited to say this only applies to the 152G model weber carb with the 4 progression holes.

Assuming you have the Weber 45 152G model and the correct idle jet, emulsion tube etc. etc then the sequence of setting the idle should be :

1) Disconnect the throttle linkages from the carbies so you can accurately set the position of each carbies throttle plate via the idle speed screw

2) Remove one of the screws covering the progression holes on each carby

3) On each carby, adjust the idle speed screw so that the edge of the throttle plate is covering the first progression hole

4) Replace the progression hole plate screws

5) Gently screw in the idle mixture screws until you feel them "tighten" and then screw each one out 2 turns

6) You can now reattach the throttle linkages making sure that when you do they do not move the position of the throttle plate previously set.

7) With things now set up check that if you depress the accelerator pedal it does not try to move the throttle plate beyond the maximum opening (adjust the bolt under the accelerator pedal to limit the travel of the pedal).

8  ) Now try to start the engine (after fully depressing the accelerator pedal 3 times)

Edited February 28, 2022 by AndBir
only applies to the 152G model Weber 45

[ben92]

On 2/27/2022 at 4:00 PM, AndBir said:

Assuming you have the correct idle jet, emulsion tube etc. etc then the sequence of setting the idle should be :

1) Disconnect the throttle linkages from the carbies so you can accurately set the position of each carbies throttle plate via the idle speed screw

2) Remove one of the screws covering the progression holes on each carby

3) On each carby, adjust the idle speed screw so that the edge of the throttle plate is covering the first progression hole

4) Replace the progression hole plate screws

5) Gently screw in the idle mixture screws until you feel them "tighten" and then screw each one out 2 turns

6) You can now reattach the throttle linkages making sure that when you do they do not move the position of the throttle plate previously set.

7) With things now set up check that if you depress the accelerator pedal it does not try to move the throttle plate beyond the maximum opening (adjust the bolt under the accelerator pedal to limit the travel of the pedal).

8  ) Now try to start the engine (after fully depressing the accelerator pedal 3 times)

Hey Andbir, cheers for the write up! Just checking, is this what it should look like when you say 'throttle plate covering the first progression hole'? I've shone a light down the intake to work out where the plate sits. I haven't seen any guides that mention setting the idle like this, I'd only heard of going in 1/4 or 1/2 from where the idle speed screw starts activating the arm. Setting it like I've done in the photo is about a full 2 1/2 turns in opposed to 1/2 a turn in? I'll report back once I've been able to fire her up again but I wouldn't have thought to increase the idle speed when I'm already idling pretty high and rough.

[AndBir]

On 10/30/2021 at 7:21 PM, ben92 said:

I ended up going with the Weber 45 DCOE carb / manifold / linkage kit from Recarb

Apologies, when I read you got a new set of triple Weber 45 I assumed they would have been the later Weber 45 152G as these have the 4 progression holes whereas the 152 model only has 3 progression holes.

As yours have the 3 progression holes please ignore everything I advised in my post above as this is how I set up my 152G weber carbies.

I will edit my post to say it only applies for the 152G type.

Edited February 28, 2022 by AndBir