1973 Custom Classic 454 (Loss of Power)

[savatreatabvr]

I've got a 73' Custom Classic that originally came with a 350 but the previous owner replaced it with a 454. Throughout the years I've always worked on my own vehicles but this 454's got me scratching my head because it just doesn't have much power and it idles rough. I'll list the obvious problems first, the Quadrajet (17057213) is missing all four washers to the mounting bolts, it's missing the linkage that opens the secondary butterflies and the spark plug for cylinder #6 has issues, see pics. I'm thinking my vacuum advance may also be an issue but with the truck in park it seems to rev up fine and smooth so will just replacing the plugs and using washers on the bolts have that much of a dramatic effect on power?

[Your41Plague12]

The plugs should make some difference. I'd also check the vacuum lines; it seems that when you shift the transmission into gear and the difference in vacuum is created, something gets funky there. If you have a TH400, check the vacuum modulator. Mine needs replaced too. For more power, definitely hook up the secondaries. Judging by what this website says, it looks like you have what they cal "Ash (Lead)" deposits building up. This website describes the symptoms and what can be done to fix it.

http://www.classictruckshop.com/club...park/plugs.htm

It claims it can cause minor misfiring, which would explain it running rough. It seems to me like replacing the plugs would be a great starting point. Get back to us once it's done and maybe we can come up with a different conclusion if that doesn't fix it.

[savatreatabvr]

CORRECTION: I went to Autozone for spark plugs and they gave me the wrong plugs, I told them I had a 73' 454 but after searching for 30 minutes they found the right plugs and supposedly I don't have a 454, I have a 409. I always thought the 409 had a very distinguishable valve cover, see pic, not like the straight rectangular valve cover of the 454, see pic! What's going on here?

[savatreatabvr]

By the way, replacing the plugs made a world of difference! It still idles a bit rough but at least I've got the power back!

[Your41Plague12]

No chance you have a 409. They have the oddly shaped heads like you said. Your 454 might be a different year, but it's definitely a BBC of some kind, not a 409. Just take one of your old plugs back there and see if they can get the part number for it. That will tell you a variety of engines it possibly could be.

[notyo_cheez]

Check/replace the fuel filter while you're at it. Pick up a few feet of various sizes of vacuum hoses and replace them all for good measure. Always do simple and cheap first.

[savatreatabvr]

So until I get the casting numbers off the back of the blocks it could be a 366, 396, 402, 427, 454 or 502? The casting numbers are easy enough to decipher I'm just having a hard time reaching them with my little telescopic mirror and flashlight! I think I need a brighter flashlight!

[notyo_cheez]

Get a crayon and a piece of paper and rub the casting numbers. Make it easy on yourself.

[savatreatabvr]

This may be a stupid question but can not having a choke at all affect it's performance once it's warmed up?

[savatreatabvr]

Hey, that's an idea!

Originally Posted by notyo_cheez

Get a crayon and a piece of paper and rub the casting numbers. Make it easy on yourself.

[notyo_cheez]

Originally Posted by savatreatabvr

This may be a stupid question but can not having a choke at all affect it's performance once it's warmed up?

No choke when it's warmed up shouldn't matter. If the choke doesn't work you might want to do something to get it working again, on a 4bbl the second stage should open when you push the pedal naturally. Choke thermostats are common failure points on the old Rochesters.

If your budget allows for it look at an aftermarket Edelbrock or Holley and get rid of that Quadrajet. They worked well when new but when they wear out they're more trouble than they are worth. All the GMs I ever owned with Roch carbs always had problems.

But before you take out a second mortgage on the house to fund your repairs check all your vacuum lines, get a manual for your truck and look for the specs for choke/carb adjustments and if you feel plucky get a rebuild kit and tear it down. Most of the time cracked vacuum lines will wreak havoc with engine behavior so insure you are all tight where you need to be before you start turning screws.

[cjlinkster]

Is your engine running at the correct operating temp? I suggest that you may want to check your thermostat.

On my 454, the prior owner took out the thermostat, and the engine wasn't warming up past 160 degrees.

Mine's a 1984, its vacuum advance source is from a line connected to a temperature switch on the front of the engine. Without having the engine operating in the correct range (190 to 210), it's timing seemed to be off (low power, etc..). I suspect that the vacuum advance wasn't working correctly or even at all.

With the new thermostat, it is running a lot cleaner and seems to have more power.

[motornut]

speaking of vacume advance check the dizzy weights move freely

[savatreatabvr]

You know what, you're right!!! You jumbled my memory, back in Okla I had a 72' Chevelle with a 454 when I was 17 years old, 25 years ago, and it had a huge radiator just like my truck does now but the Chevelle wasn't getting up to operating temp so I'd put a piece of cardboard in front of the radiator to get it to run hotter and it solved my problems. I'll try the same thing on my truck and see what happens! Thanks cjlinkster!

Originally Posted by cjlinkster

Is your engine running at the correct operating temp? I suggest that you may want to check your thermostat.

On my 454, the prior owner took out the thermostat, and the engine wasn't warming up past 160 degrees.

Mine's a 1984, its vacuum advance source is from a line connected to a temperature switch on the front of the engine. Without having the engine operating in the correct range (190 to 210), it's timing seemed to be off (low power, etc..). I suspect that the vacuum advance wasn't working correctly or even at all.

With the new thermostat, it is running a lot cleaner and seems to have more power.

[savatreatabvr]

Another good tip, I'll check it out in the morning!

Originally Posted by motornut

speaking of vacume advance check the dizzy weights move freely

[savatreatabvr]

I've learned to not overlook the simple things that I think are insignificant to the issue I'm have with this 454! I mentioned before that it had no power and ran rough well after replacing the plugs, wires and Quadrajet kit it ran better but it ran great after I simply moved the Accelerator Pump linkage from the lowest hole to the top hole of the arm the actually pushes the plunger down into the carb. I may be getting ahead of myself because I haven't started it yet today but I've got high hopes so thank you all for the excellent troubleshooting ideas.