1957 XK140MC Cause of Failure to Launch

Following an earlier thread in which I requested guidance to sort out overheating of my XK140MC OTS, I have now developed a new problem.
After timing, plugs, and carb tuning, the car seems to run nicely at idle and with short bursts of accelerator to ~2000 RPM unloaded. A short test drive to assure that all would be well and to see if the overheating was cured, I endured the shocking embarrassment of dying in traffic less than a quarter mile from my garage. I pushed the car to the side of the road and tried several times to restart. It would start and then immediately die. After 5 minutes of OMG what do I do now, I was able to start the car and very carefully limp back to the garage (low revs in 2nd). I left things overnight and restarted the car this morning. Once at temperature, I increased revs in place and once it hit 2500 rpm it died, precipitously. I am thinking fuel starvation. The pump is new and it activates normally and stops normally after pressurizing the fuel line. Am I correct to be thinking fuel starvation? I have a new filter on the way but is there any other gremlin in this?

Clogged fuel line is the first thing that comes to my mind.

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When resurrecting my E-Type I drove it around on slow secondary roads to make sure everything worked. All seemed fine. Then I took it on the freeway. It soon started bucking and would barely maintain 20 MPH. Not fun. I almost drifted onto an off ramp where I pulled over. After a few blips of the throttle, it seemed to run fine. I then drove it carefully home not exceeding 30 MPH. The culprit was the fuel pump which made all the right noises but could not produce the volume needed to support freeway speeds.

In the standard configuration there are 4 filters.

  1. fuel tank drain plug

  2. inside the fuel pump bottom cover
    LCS Pump

3 & 4. in the banjo bolts on the float bowls

I have had rust sediment that collected down in the tank drain plug and blocked the pickup tube. It never got as far as the plastic inline filter I had rigged up.

I have also found particles that got past all the filters and blocked the drilled passage from the bowl to the carb jet.

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Check if there is still oil in the dashpots from the carbs.

Oh yes, this problem followed a carb turning.

In our MGA race car we were going crazy trying to track down an issue where it would run splendidly, until you hit about 3500rpm on full load. It would sputter and lose power, though unlike your situation it would not completely die. Carbs had been set “per the book” and we went through, had distributor rebuilt, new wires, new coil, new plugs, new filters… Just couldn’t find the issue…

Then I read a stray comment on, I think, a Datsun forum about setting fuel height in the jet relative to the bridge, rather than using the bar under the float fork method. We checked and noted the fuel level in the jet was not visible. We adjusted the fuel level to sit higher in the jet and viola! A properly running car. On the race car this is pretty easy, as there’s no more hard fuel manifold, just a braided flexible hose to each bowl-lid, so you can take the lids off without disconnecting anything else, would be a bit more tedious with the hard fuel line but still might be worth taking a look.

Wowzers. More than worth a try! Very pleased to get this tip. This could explain why when stranded, waiting a minute allowed it to start again. So the idea would be to adjust the forks a bit closer to the Gross jet?
It was a sad outcome not to be able to take the XK140MC to the Reno British motor show this weekend. I took the Mark nine instead. It did do well with first in class. So not all was lost however, it is most embarrassing to be talking about this car and not be able to show up with it running. Thanks again for the tip. I will report the results.

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No guarantee on results, but it seems like similar enough symptom to be worth a try.
Unfortunately, aside from the linked thread on MG forum, I don’t know any “spec” to set the fuel level at in the jet for various carbs, so it may take some experimentation. Of course setting per the factory manual should work, but fuel height in the jet should account for any irregularity in floats, slope of engine etc.

The 1/2" bar is correct for Jaguars. It’s in the manual, page C13

Some other cars such as MG, TR, AH use a 7/16" bar.

This is from an MGA manual.

Thank you Rob. I have the SU carb adjusting tool kit and followed this method explicitly.

Nonetheless, I will do this again as fuel availability could explain the symptoms?