240z stalling at speed - fuel pump or ignition?

[escapedan]

My 1973 240z (2.6L engine; no smog equip) initially starts and runs normally. It runs fine for 5-10 minutes then, for lack of a better description, the engine starts cutting out at about 65 mph (any gear). I can hear the carbs "sucking air", but it seems to be starving for fuel and/or spark. With the clutch depressed, it will rev to ~4,000 rpm and again cuts out. It gets progressively worse until pull off the freeway.

Once I get off the freeway and drive on the side streets, it seems to work fine again so long as I dont get above ~45mph. Also, it then rev's all the way to redline as if nothing was wrong. I'd sure appreciate any suggestions before I go buying fuel pumps, ignitions, etc....

Here are some basics:

- 240z chassis, 2.6L engine (emissions equip removed), SU carbs, standard 240z distributor with points (ok, stop laughing), upgraded coil, 5-speed trans, headers, etc.

[MikeW]

That sounds like fuel to me. Will it keep running fine with the clutch in, i.e., the problem is only under load? I'd check for a partially clogged fuel filter first as that's easy to do and cheap to replace.

[escapedan]

Great suggestion - I'll definitely start simple and check the fuel filter. It does run fine with the clutch in. In fact, once I pull off the freeway and/or slow down a bit, I can rev it to redline with the clutch in.

On a side note, while I'm in there working on things, what do you think about getting rid of the points with a petronix or Crane or something?

[Curtis240Z]

Pertronix would be the easiest conversion. Crane ignition is gone.

[vercingetorix]

Mine was doing the same thing last year, Turned out to be the fuel filter.

HTH

Best,

H Houghton

[escapedan]

That's great news. I was thinking I would have to end up pulling the fuel pump or upgrading the ignition, but just wasn't sure where to start. Ideally, I should ditch those points anyway...

[five&dime]

My 510 did a similar thing which also ended up being trash in the filter.

[Diseazd]

Points are fine if you keep 'em set correctly........gives you something to do from time to time!

[Walter Moore]

I had that same problem and it turned out to be a bad fuel pump.

I went electric, but a good mechanical pump probably would have fixed it.

[beandip]

You may have a in line filter back by the gas tank also. Did this problem just start or has it been like this for a while. If you have been working on the Carbs you could have changed the float level or levels. The fitting right at the carb where the fuel line attaches to the carb, this is the ''banjo'' fitting. It has a screen that could be clogged , one on each carb.

first change the filters weather or not this is the problem , they are cheap and may need changing anyway. If you know anyone with a gage check the fuel pressure. Should be between 3 and 5 Psi.

Gary

[escapedan]

UPDATE - My 73 is still having the "Stalling at Speed" issue, but I believe I've found the cause. For some reason it is pulling massive vacuum between the brake master cylinder and check valve - so much so that it causes the vacuum hose between the brake master cylinder and check valve to literally collapse. Important note - this began shortly after installing rear disc brakes, but not immediately after. Once it gets to the point where there is no free flowing vacuum, the car dies while driving. It will rev (sometimes) with the clutch in, but will not accelerate at all with the clutch out. I performed a "tracheotomy" on the road by puncturing a hole in the vacuum line and inserting a relief valve, which got me home, but is clearly not a permanent fix.

So, question is has any experienced similar vacuum issues? If so, was it a faulty brake master cylinder? Booster? Any help would be appreciated!

[Curtis240Z]

Did you change the brake master cylinder? If you did....did you make sure the freeplay clearance between the brake master cylinder piston and Master Vac plunger is still the same? The most popular upgrade is to use a 280ZX master cylinder, but the indention depth between a 240Z and 280ZX is different. If you don't get the clearance correct the Master Vac could be applying your brakes, thus stalling at speed. Puncturing the vacuum line would release your brakes, which would let you go again.

Edited November 17, 2009 by Curtis240Z