The car bogs down and stalls right around 50 mph (4rth gear). It'll crank right back up and runs great up until that point, but I cannot quite figure out what the problem is. I suspect it's a carb issue, but if so, I cannot seem to tune them correctly. Do any of you have any suggestions?

 

Check your fuel filter. Then your fuel pump. Next your float/bowls. Sounds like it is running out of gas.

 

I had a similar issue with my 72 SUs. Turns out the throttle shafts wore out and was leaking a vacuum behind the needles. After driving see if their wet with fuel on the outside if they are the bushings and maybe the shafts themselves need replaced.

 

Fuel filters are clean and have been replaced (I have one up front and I added one near the tank in the back). I'll double check them again just to be sure, but I think I might need to go through the carbs again. I was hoping not, but their rebuild is several years old (car has been doing a lot of sitting while being restored). Good suggestion about the throttle shaft issue. I'll check it out also.

 

Ya if it would hold a tune the throttle shafts are probably your issue then.

 

OK Bluekitsune, that's the direction I'm going to go. A Z Therapy rebuild kit and throttle shaft bushings.

Thanks for the help