5000 rpm, Falls on its face

[1969911T]

A clogged fuel filter would limit fuel flow.

[1QuickS]

Yes, clogged filter, be wary of the screen in the fuel tank!

[tom1394racing]

Does it cut out at 5000 RPM with the car sitting and no load, or is it only when driving? If it occurs with no load, you could connect your timing light and observe if the flashes disappear when the car dies above 5000 RPM. It could help you eliminate either ignition or fuel.

I just had a similar problem on my newly restored '70E. The engine would die intermittently and seeming randomly both without load and while driving. Observing the timing light with the car idling allowed me to pinpoint an ignition problem. Swapping in a replacement CDI seems to have solved the problem.

[Arne]

I've even done this test while driving. My cheap timing light has leads long enough to snake out the side under the deck lid and in through the quarter window. A bit of duct tape to hold the trigger down and drive it while watching for the flashes.

[edmayo]

a broken valve spring can cause that symptom

[t6dpilot]

I was just going to suggest a broken valve spring, but Ed beat me to the punch. I had the exact same problem when I first got my 69 hotrod 15 years ago. We found a broken valve spring. Replaced that and it fixed the issue.

[dmaddox]

Well, I finally had some time to review and investigate the stumble at 5000 rpm.

The first thing I did before digging into the volume was just to test the PSI at the carbs. 1.8psi. VERY low. So, I jacked up the front end and put it on stands. I then pulled the steering cover off to discover a nest of fuel line and wires. An electric fuel pump was installed (and subsequently the fuel pump removed from the engine bay) up front.





I then read some reviews of this pump - which I am finding is not even designed to be used as a running fuel pump. Most people use this little pump as a transfer pump on diesel applications, or for home use to transfer fuel from tank to tank, etc.. Not on cars. Your experience with these may be different.

Three things.

1. The return line is blocked off. Fine, but why it was done like this, I don't know.
2. There is no pre-filter to the pump, which after investigation appears to be what did it in.
3. There is MANY feet (no joke) of fuel line jammed up in the steering area, I am surprised there weren't other issues.

In short, I installed this: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

A few things to note on this pump:

1. It actually FITS in that area under the cover.
2. It is very quiet.
3. Easily regulated at 3.5psi - and oddly, I measured 3.8 at the carbs. Perfect, out of the box.
4. It comes with a pre-filter, has great reviews AND....is 40 bucks. I bought two in the event this dies, I have a spare.

My only complaint is the location - sucks working up under there....and not convenient to swap on the side of the road in any safe manner whatsoever.

In the end (finished the install last night) - the car is even better yet now....MUCH MUCH smoother all the way up the RPM band....no hesitation, no stumbling.

Cheers,

Dallas

[Xavier PJB]

Well done.