240z running oh, so rough!

uk66fastback

Club Member
Hi, I've put a welcome thread in the relevant section ... my car is nice enough but I've now had some time to honestly look at it and it is running like a pig. When the guy took it off the flatbed I thought it didn't sound that healthy - but it kinda sounded like it had a bark from the exhaust and it had been standing for a month on a boat etc so I put it down to that.

Have had some time now to have a look and it is difficult, nigh on impossible to start ... when it does, it just seems to run as though it is on about two cylinders. I started it yesterday and it runs at about 600rpm, then without my foot on the throttle, it'll buzz up to 2000rpm, making quite a noise. then I can blip it and it'll come back down to 600rpm, nearly stall, then go up again etc. I can control the revs by placing my palms over the air intakes. The car won't start at all with the air cleaner ON.

What I know:

Everything is original so I have been told - block, tranny etc - numbers match. I have cleaned and gapped the points. The dizzy looks original. The plugs are clean and gapped correctly. The coil looks old but I have no idea HOW old. The leads all have 1 9 7 2 printed on them in white - so they're original if that's what they had ...

They guy said the engine had never been worked on - maybe that's the trouble - mind you, he is 85 so how much is right or wrong with his fading memory I don't know. Car has only done 3000 miles or so in the last 20 years. 82k in total. The tyres are 20 years old and the spare is the unused original. Tools have never left the cubby hole by the looks of it.

Having read up on the net and various forums about the SU carbs, I thought I'd give them a clean so removed them at the weekend. Read up on SU adjustment - not in the ZTherapy league of course but just the basics. Read about the jet adjustment with the two full turns etc - but when I removed the carbs, they had no adjustment on them underneath? (see pics) One of the jets was low in the carb body, see pics, but I pressed it up from underneath and it is now where the other one is.

Anyway I cleaned up the carbs and put them in and nothing improved but at least you could eat your dinner off them!

Anyone ever seen US '72 carbs like them before with no jet adjustment - I snapped a pic of the serial code on the end of them - and that does translate I believe to a '72 SU/Hitachi carb.

So to recap. Points - fine, plugs, fine, coil - ? (I have a spark - leads - they work but could be breaking down? Timing - no idea?

If you've got this far, thanks for reading - and here's a clip of it I have uploaded to YouTube, which will show what is happening. The frantic tooing and froing of the throttle mechanism in the engine bay is my right foot trying to keep the thing running ...


https://www.youtube.com/watch?v=fvL-_0R7d4c
[YOUTUBE]fvL-_0R7d4c[/YOUTUBE]
 
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AliK

Vehicle Dating Officer
Staff member
Club Member
Have you checked the fuel filter? It seems to a one eyes man such as I it sound like a fuelling issue.
 

uk66fastback

Club Member
I replaced the fuel filter with one of the clear plastic ones ...

Like an idiot after mentioning the pics above - (see pics etc) - I then forgot to add them to the post!

So here goes ...

Front carb and jet



Rear carb and jet (where is it?)



There it is ...



So after viewing loads of YT vids on SU carbs, I removed them, expecting to find an adjusting nut under the carb ... (and under the oil/dirt)



Close up ...



Where is this adjusting nut?



Serial number on the carb ...

 

AliK

Vehicle Dating Officer
Staff member
Club Member
Third pic from bottom has your adjusting nut. Notice it has little notches in it that click into the tab for easy adjustment?

I have the same thing on my Ztherapy carbs but a knurled round nut on the ones that came with the car.
 

Wyn

Club Member
Can't help with the running sorry but it sounds like a canal barge on tick over lol

Does sound like its running very weak mind?
Is that inlet linked and are all cylinders firing ? You could try remove the leads whilst running to check its on all 6 or down on the frt 3 or rear 3 maybe to pinpoint which carb is at fault ? One carb still partly blocked maybe
btw, where's the turbo :D
 

AliK

Vehicle Dating Officer
Staff member
Club Member
Let me dig out my Ztherapy everything carbs CD if I make hit home at a sensible hour any evening this week and do you a screen shot.
 

toopy

Club Member
I had that rising and falling of revs issue, turned out the rear carb and gone slightly out of balance.
Dont know how, one day it was fine, next it wasnt, had a little 'fiddle' and normal service was resumed!
Been fine since :)

Do both jets slide smoothly up and down? any hint of drag/roughness will cause a problem, but that low jet is definitely not helping matters:unsure:

Is there oil in the dashpots?
 

red baron

Well-Known Forum User
do you have electric fuel pump at rear near tank if so check pump working also has filter inside pump assy remove and change filter
 

Albrecht

Well-Known Forum User
Clearly a fuel starvation issue.

I'd check tank and fuel lines as a matter of course on a car that's had so little use for such a long time. Condensation in the fuel tank can lead to rust scale, blocking the pickup. Hard fuel lines (they are steel...) build up layers of rust inside them like sedimentary rock, often quite mobile so they block, unblock, block again depending on how they shift around under suction from the pump.

It's amazing what you can find inside original hard fuel lines. Even ones that look quite good on the outside can be all but blocked on the inside. Most of the crud in there is caused by condensation in the tank mixing with the fuel and sitting in unprotected steel. Most of it doesn't even get as far as the engine bay fuel filter...
 

mattbibbey

Well-Known Forum User
As Albrecht says, and told me too, I had a very similar problem with mine although it would usually happen when overtaking! Mine was as he described, a mobile blockage in the fuel lines coupled with a small fracture in the fuel line. The blockage would move and then air would be sucked in through the crack. It'd be worth replacing fuel lines on an old motor anyway, relatively cheap and will most likely solve your drama here.

Good luck
 

uk66fastback

Club Member
Thanks all. That adjuster I had taken the small screw out to clean it, and then taken the pic. I managed to push the jet up to where the one in the other carb was so whether they're right or wrong, they're the same now!

Pistons and needles slide lovely in the dome, I can push them both up and then they slide down landing with a resounding clunk ... I'm using ATF in the dash pots ... Have read opinions as to the thicker 20 SAE ... The ATF is certainly thinner, but I might find that difference out on the road, it won't be the cause of the bad running. The fuel lines/tank is a good shout, I'll check those, also the rear electric fuel pump if it has one. Were they standard? This car was only used once a month in the last few years it was in Texas. Maybe that, and the boat over, who knows, may have shifted a few bits of muck, rust, scale etc into places we don't want it.

I have put £20 of fuel in so it's pretty fresh.

Can the OEM fuel lines be ordered for a reasonable price or do people usually just make up their own?
 
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mattbibbey

Well-Known Forum User
When I needed to rectify mine, I was just desperate to drive the car like a yobbo so I cable tied braided, flexible fuel line to the original. Chippy yes, but it works. Haha
 

Farmer42

Club Member
Had the same issues with mine when I first had it. You need to systematically go through the fuel feed from tank, forward, disconnecting pipes to ensure you have fuel getting through.

The main pipes to disconnect are:

1. The carb side of the mechanical fuel pump (if you have one)
2. The top of each float chamber on each carb.

Remove the HT lead from the coil and turn it over to see if fuel pumps through but don't forget to use something to catch it.

If you have fuel at both, take the tops off the float chambers and check that the float valves are not stuck which is a common problem especially if some dirt has got through. That was the problem with mine.

I would also drain the tank and filter the fuel back in through a gauze (or if you are brave, nick a pair of tights off your missus!!). This may remove a lot of the sediment from the bottom of the tank - worked for me!

Good luck
 

Gus

Forum User
Hi, sorry this is my first post on here, but I've spent quite a while looking at the threads on here in preperation for hopefully buying a 240 at some time in the future! :)

I have however, used SU carbs on many previous cars, and just to add one thing to all the really good previous answers.. If you take the carb off, and drain the fuel out of the float chamber, the opening where the fuel travels through to the actual carb is quite tight, and as I found on a TR4A (exactly the same carbs), the passageway can block up with old fuel.. But a good squirt of carb cleaner and a toothbrush will shift it no problem! :thumbs: This is especially likely on a car that has been sitting for a long time! Even if it isn't causing your rough-running issue, the car will always thank you for clearing out all of it's fuel passageways! :driving:

Hope you manage to get her running sweetly again soon!
 

uk66fastback

Club Member
Prior to having a look at the fuel tank/lines this weekend, I've gone to turn the car round in the garage so the back of the car is up by the tools/bench and after 10 minutes of trying to get it to start, it's now kicked into life with a renewed sense of urgency but now won't come under 2200rpm. When starting, it jumps up to 1500rpm for about a second then up to 2200 ... Where do I go from here? Is it this fast idle screw I want to be looking at, cos that is fully adjusted ... And you can't back it off any more to bring the revs down?
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
Are there any connections missing off the intake manifold or even the servo pipe split etc?
 
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