240z hesitation when under acceleration

[jumbobeck]

Hi, i have a good condition '72 240z with a totally stock setup with the exception of electronic ignition. I've had the car since December, sadly my strobe light, dwell meter etc (and my tech knowledge) were consigned to the bin 20 years ago

On three occasions recently (during town driving and immediately after) the car refused to accelerate cleanly, some stuttering and mild vibration were felt. On both days the ambient temperature was in the low 20's. Could this be the fabled fuel vapourisation (I had a 240z 25 years ago which had daily use for years without ever experiencing this problem).

The car has done very little mileage recently due to work and family commitments, the result being that I've used only about 1/2 tank of fuel in 8 months. I've topped up the tank with fresh fuel, but the problem persists.

As an aside, on one occasion before some of the town driving mentioned above, distinct vibration and a reluctance to pull was felt at about 80mph. This may be unrelated, especially the vibration, as the diff has seen better days.

Any advice greatly appreciated

 

[Dale]

At 80 mph, that would be about 4k revs?

When you've been accelerating, does the spluttering happen at about the same revs?

If so, it sound like something I suffered with a while back, and that was bits of debri in the fuel system. Little bits of paint and rust from the tank that build over the years that flow up the fuel system under acceleration that clog up reducing the flow of fuel. The debri will then flow back over, unclogging, when you ease off the throttle and the car will run ok until you accelerate again.

As I remember it always happened at about the 4k mark.

It might also be the reason for the vibration, as you can feel the spluttering and bad firing through the car. It was quite a 'rapid' spluttering, if that makes sense?

 

[jonbills]

Might be worth checking the basics:
when were fuel & air filters last changed?
what do the spark plugs look like - maybe it's running too rich.

 

[260ZG]

What is the electronic ignition, is it an after market one?

I had a system fitted to a 260Z that developed a mind of its own. It would be running fine and then suddenly decide to completely cut out -not funny in the middle of a busy junction after which it was dumped and a 280ZX distributor and coil fitted.

If it is an after market one I would re-fit points and condenser and see if it cured it.

 

[jumbobeck]

Thanks guys, all good ideas . I'll start with the fuel filter and work through your other suggestions this weekend

 

[vrs9]

Had the same problem with my 260z. Fuel filter sorted the problem straight away. Disconnect the current filter and if its looking pretty nasty (which mine was) just put in a new one. My 260 is reving up freely now.