No power up hill or after 45 MPH

[78 Square]

I'm trying to figure out why after about 45 mph (give or take) or even at a slight grade, I struggle to keep moving. Even on a flat grade, I have the pedal floored and I can barely make 55. I just change my plugs and wires, my fuel filter. And yes it is installed the right way. I'm thinking it's because my secondaries on my Quadrajet aren't opening. I don't know much about it but it seems to me there's either something broken or missing from what other people describe. Maybe I'm just missing something. Any suggestions? I've tried looking for other questions that are similar but None of them are like my problem exactly. The truck starts fine. Idles fine and pulls pretty good up until I hit highway speeds

 

[chengny]

Exhaust restrictions?

When you post a request for help with problems of a broad nature like this, I think you'll find that the more background you provide - the more responses you'll get.

Examples:

1. I just bought this truck and it struggles to go faster than 55 mph.

2. I have had this truck for about 10 years. It used to run great but lately it can't even make 55.

3. I recently made (some modifications) and ever since the truck won't reach highway speed.


Anyway, what you describe is a common symptom of insufficient fuel flow. I can assure you that a Q-jet in even just decent condition does not require the secondaries to open in order to reach highway speed. The primaries will easily handle any speed (at even a vigorous rate of acceleration).

Check the operation of the carburetor linkage. See that the primaries rotate to the fully open position when the accelerator is depressed. Do the test using the gas pedal - not the linkage at the carb. This will verify that the entire accelerator system is operating freely.

 

[rich weyand]

Also check your timing. If the distributor was not clamped down tight, it can drag retarded, and performance will be as you say. BTDT.

 

[Joe383]

The spring for the secondary's could have been messed with too and it could be adjusted too tight and not opening.

 

[MadOgre]

Do you drive with both feet ?

 

[78 Square]

This is really the first time I've driven it since I've had it. I had to do a good bit of work to it. I don't think it's the exhaust, I just put the exhaust and the headers on. I just don't understand why at low speeds it runs great until I'm on the highway and hit a slight grade. I loosened to spring the entire way just to see if it would even open. I know it will only bog the truck down if it opens too soon but it won't open at all. Like I said, I don't know much about it but there's a little green piece that lays at the bottom and when I took a screwdriver and moved it up to touché the bottom of the screw, the primaries closed but the secondaries didn't do anything. I was planning on buying a Holley once I bought it but everyone tells me to keep the Quadrajet. It definitely is going to need rebuilt in the near future

 

[78 Square]

I definitely do need to fix the timing. It was way off and I adjusted it but ear shot for now. Just haven't gotten around to using my buddy timing light. Someone told me before that if you open the secondaries by hand while it's running that screws them up and they won't work right again. Is that true? I'd just like to figure out if this thing is just that much of a pig or if there's a reason I can't keep up with traffic when the speed limit is 65

 

[Quadrajet Power]

You have good info from others here already. After you check those things and if your problem still exist, you may have fuel flow issues. Which could be fuel pump or internal carb issues.

 

[Quadrajet Power]

Post a picture of your quadrajet. Do you know the code number?
Make sure your choke is opening all the way. Your secondaries may be blocked from opening by the restricter on the passenger side that engages when choke is activated. Or is could be gunned up and need cleaned off. Your upper air valves will not open unless your bottom blades open with the throttle.

I know lots of people toss the quadrajets and spend lots of cash on a Holley or Eddy, but the quadrajet, when built right, is a great carb.

 

[MadOgre]

This is really the first time I've driven it since I've had it. I had to do a good bit of work to it. I don't think it's the exhaust, I just put the exhaust and the headers on. I just don't understand why at low speeds it runs great until I'm on the highway and hit a slight grade. I loosened to spring the entire way just to see if it would even open. I know it will only bog the truck down if it opens too soon but it won't open at all. Like I said, I don't know much about it but there's a little green piece that lays at the bottom and when I took a screwdriver and moved it up to touché the bottom of the screw, the primaries closed but the secondaries didn't do anything. I was planning on buying a Holley once I bought it but everyone tells me to keep the Quadrajet. It definitely is going to need rebuilt in the near future

Sounds like maybe the linkages are messed up on the Q-jet not allowing the secondaries to open.

Post up some pics !!! Or we wont be much help to you.

 

[78 Square]

Sorry guys, would of posted pictures earlier but I had to wait to get off work

 

[78 Square]

Driver side. Not sure why it's upside

 

[78 Square]

Passenger

 

[78 Square]

Passenger from the front

 

[78 Square]

Passenger from above