My 77 f150 with a 400M is having some issues while driving under a load...it has no power at all and backfires from the carb. So I got all new fuel hoses a new filter I re-routed the fuel hoses all the way to the carb and installed a pressure gauge. At an idle its about 6.5 to 7 PSI sooo if anyone knows what the pressure is supposed to be so if anyone knows what the pressure is supposed to be? All i can think of is the (electric)choke is maybe sticking or I need to adjust the carb(edelbrock 650 cfm thunder series).

 

6.5 to 7 psi is good for a mechanical fuel pump. The lack of power and backfiring through the carb tells me that you have a timing issue.

 

My 400 was doing the same thing and it turned out the advance in the distributer was seized up from sitting around to long. Hope this helps.

 

Odd it shouldn't have any timing issues i just got it back from the mechanic about a month ago because i couldn't even get it to idle due to timing. So the timing should be good. According to my edelbrock troubleshooting guide lack of power while under a load would most likely be due to a clog or something in the fuel hoses (which is why i replaced all the hoses and added a fuel pressure gauge to see if that was the issue). Also it said the carb might have some debris in one of the jets or something. Also a guy down the street from me thinks its my choke because like I said it idles fine and its okay in 2nd gear but 3rd gear sucks and i cant even get to 4th because the lack of power LOL!

 

7-8 PSI is about all the mechanical pump will output. However, Edelbrock recommends no more than 5.5 PSI at the carb, on most of their models.
Unless the PSI is dropping severely under load, I doubt the issue is fuel supply related. Could be an internal fuel clog somewhere in the carb.
Timing is a much more likely suspect.
If the choke is not opening, that could also be part of the issue. Pretty easy to adjust, or just wire it open for testing purposes.