Finished building my72 390 last year and have not had time to find the problem as I am driving my 71 now.It starts fine and idles but it has no get up and go at all. My 71 300 six runs stronger off the line than the 390. Once the 390 finally gets up to speed it runs fine but still has no power for pulling hills.If I stomp the gas pedal nothing happens(Edelbrock 600CFM4BBL Vaccume seconds.Everything worked great before the rebuild(stock except a mild Comp Cam)it always went to passing gear when the throttle was stomped and now I got nothing,it seems as if the whole engine is in slow motion until it gets up in RPM and then it still has no torque It runs great at highway speeds but bad at stop and go. I have checked the cam timing,installed new tune up parts (all),new air filter,have not changed carb tuning as it was fine before,fuel filter,checked all linkage,even wore my lucky sox, but nothing has helped at all.If anyone has had this trouble before and knows what might be going on or that I have missed something ,it will be greatly appreciated to know what is going on with this 390.This is the second rebuild on this block,new valvetrain to match cam,new everything else inside is new.
"bowties in the rearview mirror"

 

Is the mechanical advance in the distributor working?

 

Sounds like a cam timing issue. Are you sure you are not off 1 tooth ?

 

Thats what is sounds like to me. Did you use a degree wheel or just lined up the marks on the timing set? JMHO

 

Passing gear is a linkage thing isnt it ? Are you sure it's not binding up or possibly got bent and doesnt have the correct throw now ? Just some brain fizzing pardon the igno if it's igmo of me...

 

Or accelerator pump?

Not sure about the "passing gear" thing though - does it downshift and not spin up, or does it not even downshift?

 

I have not checked the mechanical advance yet and will as soon as I can.
The timing marks were lined up on the gears when I put the cover on and I will have to check with the engine shop if they used a degree wheel.I put a new C clip on the passing gear shift rod but I will check to make sure it is still on there.It will not shift down when the throttle is hammered or anything so I guess I will start there,thanks for all the imput and will keep posting with updates,good or bad!
"bowties in the rearview mirror"

 

Finally had to find time to fix the problem as I need the truck for work now.Decided to start with the timing and found it to be set at about one degree BTDC,my fault.I wrenched on the distributor hold down bolt with my distributor wrench and in the process it pushed the distributor over out of time and I didn't catch what I had done.I should have rechecked the timing after it was tightened up but I did not.Reset the timing to about eight and a half and it runs great with lots of power.
I reset the kickdown for passing gear but have not got it working yet ,I might have time this weekend to adjust on it .I adjusted the throttle linkage and it is good and tight with little play then got the kickdown linkage to move it's full throw but will not kick the tranny down. I have not yet been able to get the vaccume seconds to open up so if time allows I will get into that as well.Everything in the distributor is new and working as it should.
On the way home today (60 miles all freeway up n dowh hill) I thought I would open it up and see what happens.Well the good part is it runs up to 65 real good and will run anywhere up hill or down just fine (still no passing gear or secondaries).The bad part is when I ran it up to 75-80 uphill it started to blow back through the carb and started losing power on this uphill run.This went on until it came down to 65 again then runs good like it did before.Is this because the secondaries won't open up and thereby starving the engine of fuel?Well thanks for any ideas as they have all been helpful and I will keep posting results and findings.
"bowties in the rearview mirror"