i have a '72 240z and when i start it up, it's fine, but when i open the throttle and let up the clutch, the engine rpms will drop, and it will either die, or hover around 200 rpm until it goes back up to around normal.

i have the choke open, so that's not the problem..

does anyone have any idea what's going on, or how to fix it?

Pretty hard to say, Matt, without either more details or being able to experiencing it first hand.

You profile says you're in Redmond - is that Redmond, WA, Redmond, OR or ??

There may be someone close to you who might be willing to help.

sounds like flooding or maybe fouling plugs

have you checked your timing?

Mechanical Fuel Pump? Carbie issues?

Redmond, Washington.

Dave (Zs-ondabrain) has already come out to help me once with my headlights, but it was a long drive, so im not sure if he'd come all the way out here again.

i think that flooding might have been some of the problem, i made the mixture leaner and it ran better, but that's not all of the problem.

fouled plugs was my other theory, so i'll check that out and get back to you.

Here's a couple of thoughts...

When you floor the throttle, the butterfly opens max, and the piston rises to accommodate the change in air demand. Double check that there's oil in the damper (and that the piston spring is in there) so the piston doesn't rise too quickly and contribute to a lean condition.

Along the lines of airflow and leaning out the mixture, if you have old carbs an air leak can occur at the throttle shafts. You can richen it all you want but fighting an intake vacuum leak is like chasing your tail. Check for other sites of potential vacuum issues

Thirdly, IIRC the vacuum advance on your distributor is actuated when the car is rapidly put under load. This advances the timing until the mechanical advance can "catch up," so to speak...if you have a worn out vac advance, or the advance plate/bearings are stuck it will stumble when you go to WOT. Put 15-20 inHg on your vac advance and see if it holds the vacuum. If yes, then take off the distributor cap and see if the vac advance mechanism (attached to the vac advance diaphragm via a spring) is actually moving about 1/4" when placed under vacuum.

As usual, the typical suspects of an old car apply...good spark, good timing, good fuel, good fuel delivery etc.

Good luck,

Steve

ok,

so i tried it again, but this time i just tried revving the engine, and it worked, but it didn't rev as fast or as high as it normally would..it almost seemed like it would lose power the more i opened the throttle.

so..would that be a vacuum problem?

Hell you know, it's those cheap Datsun engines. They just can't take it. :stupid:

Hard to say, especially from 3000 miles away. My impression has not changed--have you acted on my suggestions? Before going randomly over the car trying to chase down what ails it, you need to do some reading and learning about SUs, ignition timing and some searching on the forums for other threads where people have had similar problems. There are some good websites for the above subjects as well, so do that if you can't/won't buy the books.

I recommend:

ZTherapy's SU videotape

"How To Build and Power Tune SU Carburettors" by Des Hammill

"How To Build and Power Tune Distributor-Type Ignition Systems" by Des Hammill

Buy a MityVac and read the manual.

http://www.teglerizer.com/sucarbs/index.html

http://zhome.com/ZCMnL/tech/su.html

Good luck,

Steve

His Z has points, aftermarket plug wires and I did'nt check the plug brand while I was there working on his headlights.

His choke cables are missing the cable clamp so they engage fine but may not dissengage as easy. It's my guess that the carbs need a good going thru.

If I get a chance this week, I'll head out his way and check the carb oil, needles, his fuel filter and timing. Roughly, he's a teenager who's siked about getting his Z on the road and may be in a bit of a hurry to put in the time and patience that his Z needs.

Wednesday I have 4 harness's to make, Thanksgiving is thursday, Friday is the day of Digestion (OH YES, I will eat TOO much turkey) and I have Adams 280Z coming out to my house on Saturday for a headlight upgrade harness that'll be hard-wired in. Maybe sunday, like we did earlier this week.

I'll bring the 20 weight,

Dave.

so i replaced all of the intake vacuum hoses and put on a new filter, and that seemed to actually make a lot of it better, but once the engine started heating up, it had the same problem. the RPMs dropped and the car almost died.

His Z has points, aftermarket plug wires and I did'nt check the plug brand while I was there working on his headlights.

His choke cables are missing the cable clamp so they engage fine but may not dissengage as easy. It's my guess that the carbs need a good going thru.

If I get a chance this week, I'll head out his way and check the carb oil, needles, his fuel filter and timing. Roughly, he's a teenager who's siked about getting his Z on the road and may be in a bit of a hurry to put in the time and patience that his Z needs.

Wednesday I have 4 harness's to make, Thanksgiving is thursday, Friday is the day of Digestion (OH YES, I will eat TOO much turkey) and I have Adams 280Z coming out to my house on Saturday for a headlight upgrade harness that'll be hard-wired in. Maybe sunday, like we did earlier this week.

I'll bring the 20 weight,

Dave.

alright, sunday sounds good.

i sent the check today, sorry about it being a few days late.