240Z resurrection

SacCyclone

Club Member
Do you have a uni-sync tool to balance the carbs??

Similar to this:
https://www.summitracing.com/parts/...MIuN_yuou64wIViddkCh2_rghqEAQYASABEgJ8f_D_BwE

The float level is very critical and a pain in the arce to get correct.

Spray some carb cleaner around the intake and fittings while the engine is running to check for a vacuum leaks.

when you apply the brake pedal at idle, do you get an increase in rpm.....would indicate a bad brake booster.

Check that the carb slides inside the bell are sliding up and down freely....the SU needles will bend very easy if care is not taken, the slides will not operate properly.

and and and the list goes on.....
 

tyroguru

Club Member
Do you have a uni-sync tool to balance the carbs??

Similar to this:
https://www.summitracing.com/parts/...MIuN_yuou64wIViddkCh2_rghqEAQYASABEgJ8f_D_BwE

Thanks for the tips Mike. I'll hopefully be able to find some good time at the weekend to look at all this so I'll bear this all in mind and report back on how I get on.

A do have a Airflow meter to balance the carbs with and I have a Gunson Colortune plug winging its way from Amazon as we speak (https://www.amazon.co.uk/dp/B0012MB4VE/ref=pe_3187911_189395841_TE_dp_1). I don't need much of an excuse to by tools especially ones that let you see the color of the fire in the hole!
 

SacCyclone

Club Member
One last thing...for now....
If at idle the engine runs really rough, push up on the main jets at the bottom of the SU's with your finger. Some times these mains will hang open and cause a really rich idle and popping backfire etc.
 

tyroguru

Club Member
One last thing...for now....
If at idle the engine runs really rough, push up on the main jets at the bottom of the SU's with your finger. Some times these mains will hang open and cause a really rich idle and popping backfire etc.

I'll take a long look at the carbs this weekend but I had a very quick look last night. I hope I'm getting the terminology right here! The front carb is the one which seems to be running very rich and if I manually operate the check mechanism the jet moves downward but doesn't move back up when I release the choke - it stays stuck open (at the bottom anyway). I disconnected the choke cables (they are incredibly stiff anyway) and the result is the same - the jet stays down and has to be manually pushed up.

I had a quick search around and people are suggesting a range of things including the needle not being centered, the fuel hose being old and stiff but I'm sure there are many other possible reasons. I'll report back what I find.
 

toopy

Club Member
I'll take a long look at the carbs this weekend but I had a very quick look last night. I hope I'm getting the terminology right here! The front carb is the one which seems to be running very rich and if I manually operate the check mechanism the jet moves downward but doesn't move back up when I release the choke - it stays stuck open (at the bottom anyway). I disconnected the choke cables (they are incredibly stiff anyway) and the result is the same - the jet stays down and has to be manually pushed up.

I had a quick search around and people are suggesting a range of things including the needle not being centered, the fuel hose being old and stiff but I'm sure there are many other possible reasons. I'll report back what I find.

If the above suggestions fail or only partially work, remove the jets from the carbs and very carefully with very fine emery paper, rub over the entire jet a little at a time by wrapping the paper around it, use carb cleaner afterwards, then re-fit in carb, hold by hand and move gently manually, dont worry about the linkage for now.
You should start to notice an increase in movement/smoothness pretty quickly, obviously slow and steady being the order of the day :)
 

uk66fastback

Club Member
It's a five minute job to get the carbs off the car ... I'd have them on the bench while you've got this problem and take the choke mechanism apart and reassemble fully lubed up. My choke mechanism was completely fouled up it's a wonder the thing worked at all ... I think from memory I suspended the twin cables from the ceiling and dripped oil into them overnight ... (probably overkill) Careful with the choke lever in the car - they are old and brittle now and have been known to break easily (either that gives or the plastic centre console to which they are mounted).

Further improving that, I bought one of the metal pieces you can bolt to the tunnel and then attach the choke lever and mechanism to that, instead of the actual console. 40-45 year old plastics have a habit of breaking suddenly ... !
 

uk66fastback

Club Member
Which plugs did you use Mike? I have an assortment that of 3 different types so would look better if they were all the same.

I used these ones from ZCarDepot ...

Exhaust Manifold Air Smog Pipe Plug ... x 6

https://zcardepot.com/products/exhaust-manifold-air-smog-pipe-plug-240z-260z

I think you might well be able to find these at RS Components though in the UK ...

Fwp2LUJJ.jpg
 

SacCyclone

Club Member
I'll take a long look at the carbs this weekend but I had a very quick look last night. I hope I'm getting the terminology right here! The front carb is the one which seems to be running very rich and if I manually operate the check mechanism the jet moves downward but doesn't move back up when I release the choke - it stays stuck open (at the bottom anyway). I disconnected the choke cables (they are incredibly stiff anyway) and the result is the same - the jet stays down and has to be manually pushed up.

I had a quick search around and people are suggesting a range of things including the needle not being centered, the fuel hose being old and stiff but I'm sure there are many other possible reasons. I'll report back what I find.
Yes, thats a big problem and it won't run right at all.....that main jet is spring loaded as I remember and it should spring back up after the choke is released. You might try some WD40 type oil first as this has worked for me several times in the past...just spray all around the main jet and work it up and down without choke cables attached. If you have the time you can disassemble, emery cloth, then assemble with some lube.
 

tyroguru

Club Member
Taking the advice of Mike and Mike I removed the carbs and got them on the bench. In hindsight this was an excellent piece of advice as I wouldn't have been able to inspect at that level of detail with them still on the car (thanks guys!).

I guess it's obvious to say this and I'm sure people have seen a lot, lot worse but everything was a bit messy and tired looking. The car is nearly as old as me though and that charge could and is leveled at me quite often so I think that's probably par for the course...

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The insulator blocks were welded on and had to have some rubber mallet persuasion to get them off!

I'd reported that the jet on the front carb was sticking and not returning when choke was applied. This looks to be because of the inner torsion spring on the choke mechanism (see annotated photo below) and it seems to have lost its stiffness - in the hand it feels loose and doesn't contract or expand well when force is applied. On the carb if you compare the choke mechanisms in operation, the rear carb snaps back when force is applied but the front one hardly returns and this is without the load of the jet on it.


IMG_9670.JPG

I'd also reported that the jet on the front carb didn't return even when no spring was attached but this seems to have been resolved by a real good clean and I didn't have to resort to friend grit sandpaper (thanks toopy for the suggestion!).

As a temporary workaround for this weak spring I have hooked up a spring from the choke linkage to the heat shield as shown in the photo below and it seems to work fairly well.

IMG_9717.JPG

A few other things I noticed while cleaning the carbs was that the needle in the rear carb float chamber doesn't shut off very well at all - it has to rise quite a bit higher to cut off the fuel into the chamber (blowing into fuel lines to test that is seriously unpleasant :) ). I adjusted the floats as well as I could but I'm not convinced that the float levels are correct. I'm also not convinced that the pistons are traveling as freely as they should but I'll revisit this as I go along I'm sure.

Anyway, I got the carbs back on the car, wound the mixture screws down two turns from the top, backed off the idle screws to the top and turned them one and a half turns down, backed off the balance screw and started her up and... she tried to start and backfired through the inlet manifold! What??!! Of course, as the choke cables were not attached and I was holding the choke mechanism up with my hands this caused a sensitive flower such as myself to nearly poop! After reading around the general consensus was to look for vacuum leaks but as I couldn't get her started I torqued every bolt on everything on the inlet side to what it should be and added butterfly clips to any pipe that was in that area (I should have done this already). Anyway, this didn't improve things so I left it for a few days.

When I got back to the car I was feeling a bit fed up with diddling with the carbs so thought I'd adjust the valve lash as its been on my list and everyone says it's one of the first jobs you should do anyway. Obviously, I couldn't do this hot at the minute so just did it cold with the reduced clearances (0.008 inlet and 0.010 exhaust). I'd not done this before so it took my ages! Most of the exhaust clearances were too small and quite a few of the inlet were too large (yes, I was making sure I had the inlet and exhaust the right way around!) . Here's a gratuitous photo of the first few cylinders worth in case any of you experts out there can see something horrid looking:

IMG_9638.JPG


With a fresh set of eyes I inspected everything on the ignition side of things and noticed that the HT leads had been mixed up! N00b mistake. I disconnected them all and put them all back carefully according to the diagram on P12 of "How to Rebuild your NISSAN/DATSUN OHC Engine". She fired up slightly but soon died again! What the Flip??!! I then noticed that the diagram of the distributor on P12 was numbered differently to the firing ordered listed on the same page. The distributor in that diagram is labelled incorrectly (though the firing order is correctly listed next to it). Sheesh. According to the Internet Overlords this is a known issue with that diagram. I couldn't see an Erratum published for this book though - come on California Bill, you can do better than that!

With HT leads on in the right order (d'oh!) she fired up but it doesn't sound quite right - as though the engine is not firing on all cylinders at all times - a bit rough. I let her run for a about 5 minutes or so and switched her off where she duly ran on for a few seconds. Hmmm. Timing maybe? I have a timing gun but I've never used one before so I'll see if I can figure it out this weekend...

While the engine was pretty hot I used the opportunity to do a quick compression test as I'd not done one before and I'd bought a compression tester so why not?! I'd also bought a remote starter to make things like this easier - I love it!

I took all the plugs out and made sure it was WOT and the numbers I got were:

Cylinder 1 - 160
Cylinder 2 - 150
Cylinder 3 - 152
Cylinder 4 - 152
Cylinder 5 - 152
Cylinder 6 - 155

I've got more faffing to do with the carbs I know - setting mixtures, balancing etc. so I'l try and do that this weekend or some time next week if time allows.
 
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tyroguru

Club Member
I forgot to add to my carb related activities above. People rave about the reman service that Ztherapy have for these SU carbs and I was very pleased with my Euro style balance tube so I contacted them and Bruce said the current waiting list is 5 months!! Might be a nice Christmas present for myself though :) . At a cost of 680 dollars + shipping (and I've no idea how much that is) I figure that I may as well get myself a set of triple Webbers as they're only a bit <cough> more expensive than that... I'm joking there (kind of...).

I gather they wouldn't do anything much for performance without a host of other additions. They'd go well on that Rebello engine I'm dreaming about though :) .
 
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uk66fastback

Club Member
Good work tyro. Mine are coming back from ZTherapy in the next week or so. Shipping by DHL is about $140. I can be more accurate with the costs when I get them back ...

I sent them in March ... !
 

toopy

Club Member
That close up shot of the front carb shows quite clearly the aged condition of the fuel pipe that connects the float chamber to the jet. It should be nice and supple to allow smooth movement of the jet. Something more to worry about! :D

I replaced mine a few years back with motor bike fuel hose, which is nice and flexible and thus far has worked well, although as you can see in the pic below, it to has stiffened in use over time, and was replaced again late last year.

IMG_0064.JPG
IMG_0065.JPG
 

tyroguru

Club Member
Good work tyro. Mine are coming back from ZTherapy in the next week or so. Shipping by DHL is about $140. I can be more accurate with the costs when I get them back ...

I sent them in March ... !

Who knew there were so many people needing carbs refurbing! I'd be really interested to know what the total cost is when you get these back and also what you think of them. Everyone seems to be really happy with this service but another view is always good.
 

tyroguru

Club Member
Victoire! Well, for today anyway.

As I mentioned earlier, the plugs were totally sooted up after no time at all - a couple of minutes of extremely poor running at best although that's being extremely generous as the engine hardly ran at all. The more I read around the more I was convinced that this just had to be a vacuum problem but for the life of me I couldn't see where. Various Youtuber's said to either use carb cleaner or propane to check for leaks but I'm way too much of a baby for that so went for the least efficient way: water spray! As the engine dies pretty quickly I started it and started spraying around the inlet manifold like crazy. The engine stopped even faster than normal when I sprayed the front of the inlet manifold. Turns out that there is a 8-10mm hole in the side of the manifold from a bolt that was no longer there!! How did I miss that?! I'd check a 100 times for anything like this. What an idiot... I found a bolt that plugged the hole:

IMG_9725.JPG

Not surprisingly things seemed a lot happier with this hold plugged. Things were still running rough though but at least we could run it long enough to get the engine up to temperature.

The tach isn't working and I can't be bothered to find out why at the minute so I bought a digital tach off Amazon and it's fantastic (photo below) . We were idling at ~1200 so backed off the throttle adjustment screws on the carbs to get it down to around 800. We'd be back to the idle numerous times while we got the timing and carbs setup but it's really nice to get a really accurate measure easily (OK, I'm assuming it's calibrated well but I'm prepared to trust on that!).

IMG_9724.JPG

Next onto the timing. To be honest, I'm not quite sure what timing figure I should be going for as I couldn't see my distributor listed in the Haynes manual or from a cursory glance on the web. However, at idle she was running at ~25% advanced so we retarded the timing and at ~12% @ 800rpm it seems OK. Please chip in if that is wrong.

Now to balancing the carbs and making sure the mixture was right. I bought a carb flow meter a month or so ago and I also got a Gunson Colortune to help us set the mixture up - I have no idea what things should sound like so I need as many tools as I can get that tell me something about what's going off! I'd love a PicoScope but that might be a bit much even for me :) .

IMG_9723.JPG

It took a few iterations but we eventually got the carbs sucking the same amount of air at an idle of 800 rpm with a mixture that looks OK according to the guidance Gunson lay down in the user guide. The amusing thing is that they say a good mixture should make the Colortune look a "Bunsen Blue" in color! They obviously never saw my comprehensive school Chemistry report. I reformed myself later in life but my Chemistry lessons were taken up doing anything and everything apart from Chemistry!

We did have a serious job trying to get the mixture set correctly on the front carb though. Basically it is a poorly boy: (1) the throttle adjusting screw is very imprecise and hard to tune with - totally different action to the other carb although I suspect this is a problem with the throttle mechanism on that carb. (2) as described previously the spring in the choke mechanism has no tension and therefore leaves the jet stuck down (short term remedy with my additional spring I added in) . (3) the jet adjusting nut doesn't move the jet downwards very well - 2.5 turns means nothing as it hardly moves!You just have to keep going until the jet starts moving down. I'll keep my eye on this I'm not sure the jet will stay in the position it is currently in.

Anyway, we went out for a quick drive and it sounds and responds so much better than it has done until now. It's coming along!
 

SacCyclone

Club Member
So both the main jets are in the up position now, that's great.

This just happened to me a few days ago with a new to me 240Z. After we got the car started it ran rough, like missing a couple cylinders. We also found that when we depressed the brake pedal the idle increased by a few RPM. Found we have a bad brake booster diaphragm, confirmed by plugging the vacuum line from the balance tube to booster. This vacuum leak will lean out the 4,5,6 cylinders. Once we replaced the brake booster, all was smooth.....yeah!!!!
Mike
 

tyroguru

Club Member
So both the main jets are in the up position now, that's great.

This just happened to me a few days ago with a new to me 240Z. After we got the car started it ran rough, like missing a couple cylinders. We also found that when we depressed the brake pedal the idle increased by a few RPM. Found we have a bad brake booster diaphragm, confirmed by plugging the vacuum line from the balance tube to booster. This vacuum leak will lean out the 4,5,6 cylinders. Once we replaced the brake booster, all was smooth.....yeah!!!!
Mike

Nice one Mike! I'm not convinced that I've got a great vacuum so I think I'll revisit that in the future - it can go on the ever growing list of jobs. I've got three weeks away from the car now with vacation and work travel but that's not bad as I need to figure out a game plan for what to do next. We've been working toward the point of having the engine running well (for some loose definition of "well" anyway) and I feel we're about there now. Hopefully when I'm back we can do a few miles and see how things go. One thing that needs attention for sure is the suspension as it creeks, groans and bangs like crazy especially at the rear. If you push on the rear end then it makes some shocking noises! Some fun coming up :) .
 

tyroguru

Club Member
Away on holiday in the UK this week so managed to sneak a few tools into the boot while packing so that I could carry on with some tool organising when allowed... I'm using foam inserts from ShadowFoam (https://www.shadowfoam.com) and it's pretty nice stuff. It could be a bit tidier but that would take forever!

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