stumbling

[donm]

Hi all,

My '80 non-FI Spider runs great around town but when I call for the engine to pull hard, like when I'm on an entrance ramp pulling hard through the gears geting up to speed it just quits and stumbles on me until I back off and feather it a bit. Then I can ease my way up to 65-70 mph and it's fine.

What would cause this kind of behavior? This is a sports car. The plugs and fuel filter are new. The timing is on the money and the vacuum advance is working.

Any suggestions? Thanks in advance, guys.

Don

[majicwrench]

That is quite classic lack of fuel. Inlet in the tank may be clogged, pump may be weak. Any number of things. First test. If it was in my shop I would "T" in a pressure gauge and go for a drive. If the pressure drops at all under a hard pull, there is something wrong.
Keith

[So Cal Mark]

even the lack of integrity on the inlet side hoses can cause an issue without leaking.

[donm]

Thanks for the quick response, guys. So the first thing I'll do is check the inlet in the fuel tank to make sure it's not cloged.

If it's OK, then you suggest I should check for fuel pressure. I put a T fitting in the line just before the carb and then check the pressure under hard acceleration? What should the pressure be?

I'm not familiar with fuel pressure testers but I assume I can borrow one from Auto Zone. May sould like a stupid question, but how do I take a reading while I'm driving?

[racydave]

Don, the carbd models with a mechanical fuel pump will not have alot of pressure. I would use a 10lbs gauge. Expect the numbers to be very close to where it is at idle. I tape my gauge to the windshield, closing the hood should not collapse the hose. Im thinking you should expect around 6 to 8lbs? If that shows nothing out of the normal I would wonder about the secondayy carb function, and check the accelorator pump opperation also.

[donm]

My car has an electric pump mounted underneath the car. It looks fairly new.

At any rate, I pulled the inlet from the tank this morning and it was absolutley clean so I guess my problem isn't as simple as I had hoped. Also, I pulled the line from the carb and there seems to be plenty of fuel flowing; I was able to fill a mason jar in just a few seconds. I'm guessing that means there's no point in taking a pressure reading(?) What do you think?

Re the secondary carb funtion, I was told if I had a problem with that the car would have very little pick-up and that's not the case. How do I check the accelerator pump operation?

Thanks again for the response.

Don

[majicwrench]

The accelerator pump will not cause the issue you are having. If accel pump was bad, you would have a hard time taking off from stops. Or accelerating at all.
I would still test fuel pressure. "T" in gauge before carb, with enough hose that you can pin gauge under a wiper arm or tape it on to base of windshield. Close hood. NOw go for a drive. Exactly what the pressure is does not really matter, it should be above 3lb and below 10lbs just to throw some numbers at you. What you are looking for is the pressure on hard pulling, it should not drop....at all. If it starts out at 4lb, that is where it should stay. If pressure stays up as car bogging, then we need to look elsewhere.
First things first, test fuel pressure.

[donm]

It seems you guys were right about this being a classic case of fuel starvation. I had mentioned that the fuel filter was new but I negleted to notice there was another filter attached to my Facit pump which was partially clogged. I could tell when I tried to blow through it, compared to the new one I just installed.

The car runs great now and I can't duplicate the stumbling problem. It pulls hard, all the way up to 80 without any hesitation. I found out these pumps only put out about 2-3 psi so they're susceptible to any kind of blockage, I guess.

Thanks for all the good advice.