Z dies during high speed acceleration

[cj71z]

I spent all day tring to get the car running right. Finally when I thought I got the mixture and timing correct I took the car out for a spin. She accelerates hard through third, then when I shift to fourth and hit the gas she seems to drop dead. Starts running real rough, makes a gurgling noise like it's choking and even if I floor it I can't get anymore speed and even start to lose speed. When I pull over the car drops RPMs like it's going to die, then eventually the idle comes back and the car runs like it did before. I'm thinking this is a fuel issue, but I'm not sure. So far this is what I've done:

Electronic ignition w/ E12-80 timing set to 7 degrees.

Rebuilt SU's w/SM needles, 1 small vacuum leak on each carb at the bushings for the butterflys. 30W oil in piston dampers. Adjusted the mixture according to directions I found on this site, but I seem to have a problem with getting it perfect. Whenever I think it's right it seems to change on me. I could adjust it all day and it never seems to stay in the same spot.

NGK's gapped to .040 are a nice tan color when I check them

Gas tanks been relined, cleaned and full of gas

New mechanical fuel pump

Any help would be great...I can't wait to feel her full potential

Thanks

Chris

[Zedrally]

What does the fuel filter look like?

Seems to be the only part you haven't changed!

MOM

[suspect the filter]!

[zman525]

well i was reading my manual the other day and it said not to use 30W oil in the SU's ( it said it SPECIFICALLY). maybe thats the problem? kinda doubting it though...

[ChrisA]

I would switch to 20wt oil. And check the filters at the inlets of the carb bowls. Fine mesh screens in the banjo fittings.

Good luck.

Chris

[Doehring]

Check the timing, 7 degrees is not enough

[e_racer1999]

ya, my first thought was timing, then carb oil..... 20W or even 10W30 is what i use

[cj71z]

If it was the timing wouldn't I have problems accelerating in all gears? I've read on here of three different timing settings; 7, 10, and 18. What are your cars set to? If I cruise into fourth and leave my foot out of it the car runs Ok, then if I punch it she bogs again. I'm going to change the fuel filter and check the banjo filters. I've read somewhere that early Z,s came with an electric fuel pump near the tank, is this true? I had ATF in the carbs before, but changed it because I thought the carbs were leaning out on acceleration.

I'll post my findings when I get a chance to work on her.

Thanks

Chris

[e_racer1999]

the electric fuel pump to my knowledge only came on 280s.... ATF does cause too lean of a condition, which is why i recommended 10W30 or 20W.....

i have my timing set on the most advanced it can go without pinging. oh, and you won't have problems accelerating until the engine is under the most load, i.e. punching it in the lowest gear.

[ChrisA]

I've read somewhere that early Z,s came with an electric fuel pump near the tank, is this true?

It is true but they were on 73 240Z's. An electric pump near the fuel tank and the mechanical pump on the motor. Your car appears to be made before the electric pumps were put on. Couldnt hurt to look though. There is a filter in the bottom of the pumps cylindrical body that gunks up badly. The electric pump was added I thought to compensate for the bad flat top carbs Nissan installed for emissions.

Much luck,

Chris

[MikeW]

oh, and you won't have problems accelerating until the engine is under the most load, i.e. punching it in the lowest gear.

I would say that punching it in the highest gear is the best way to make sure it's not pinging.

[e_racer1999]

I would say that punching it in the highest gear is the best way to make sure it's not pinging.

i meant lowest gear ratio, i.e. highest numerical

[cj71z]

E racer, what's your timing set to? I was at 10-12 or so, then retarded it when I went to 30w from the ATF. Advancing it will keep the power in the higher gears under a load? I'm assuming that bad fuel flow from a dirty fuel filter would result in my mixtures seeming to change as the fuel pressure wouldn't keep the float bowls full at all times. I probably have a couple of problems that need fixing. Hopefully I'll get a chance to work on her this weekend. Thanks for all the help everyone and keep the advice coming

Chris