Curious if any of you have experienced this. Never did before on this car, even with over half a million miles on it. 1974 Cutlass Supreme, 350, freshened up at 492000 miles, now has 520000. After a recent 1300 mile round trip, it started to stumble when the secondaries opened up. I installed a new gas tank, because I figured I had an obstruction in there, and it had the original tank. The sock was loose in the tank, so I also installed a new pickup and new hoses. Was better, but still there. I installed another carburetor, another distributor (HEI) and it still does it. I am thinking I may have a defective fuel pump. The one on there is only a couple of months old, but it may be crap. Lots of bad parts these days.

 

Check your timing and accelerator pump settings.

 

When I had fuel pump issues the engine would bog at higher RPM and not immediately. It was just an issue when the pump couldn’t keep up with the sustained demand.

 

That is exactly what this is doing. You actually explained my issue better than I did.

 

Everything is ok with that. Not that much to these cars, yet, sometimes you can get stumped with things like this.

 

I'm also experiencing some stumble on hard acceleration (i.e passing on a freeway), but have been told it's old gas. There's less that 2000 miles on the engine rebuild, and the carburetor was recently rebuilt. Before going down any rabbit hole with fuel pumps, what is normal fuel pressure for a mechanical fuel pump and does that number change under acceleration?

 

I believe it is between 4-6 psi. I am going to be checking mine sometime this week. If you do have old gas, I would get rid of it and put in a tank of fresh gas. The old gas will have a lousy smell to it. It should be about the same pressure at all times.

 

Ah, from your first post I thought it happened right when you went WOT. If it starts out fine then falls off after a bit, then it could be fuel starvation.

 

Figured I would let everyone know that I fixed this issue. It was, in fact, a defective new fuel pump. Installed a new Carter pump and it cured the issue.

 

I replaced my mechanical fuel pump w/ a Carter - they make a good mechanical fuel pump, IMO.