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Just purchased a '67 Coronet 440, and it's slow...

I just purchased my first classic Mopar, a 1967 Coronet 440 with 87k miles, a stock 383, 4bbl carb, 3 speed 727 torqueflite, and a 8 3/4 rear end.

This was originally a 2bbl so I believe it was originally rated at 280hp. However, right now it feels more like 150hp. The first gear acceleration is "fine", but it feels the car starts to become sluggish after 30mph and acceleration decreases. I'm not expecting it to perform like a modern car but I think this motor can do better.

Last night I checked the numbers and the intake is a Chrysler unit from a 440, with number
3830949. The carb is a Rochester Quadrajet 17086046. This is a GM carb that came on 4.3l trucks. https://www.carburetion.com/CarbNumber.asp?Number=17086046

I'm not an expert here but I think this intake and carb combo is not the most efficient. Are there any power/torque gains to be had with a different carb? I know it's a stock, tired engine with a 3 speed but I'm sure it can do better.

Any suggestions?
If it is a 440 manifold there's your problem. It has to be sucking air and oil into the cylinders from the valley. Forget your plugs see if they're only. Take your carb off look inside the manifold for oil. If there's oil in the manifold get rid of it and get a 383 that is a low deck put it on and put the car back on. The carb is not too big it is a spread bore with tiny primaries. Vacuum secondary is only going to allow the engine to pull as much fuel and air as the engine needs in no more. Change the manifold for the right one put it back together and you will probably be fine.
 
Speaking of gaps, I think i should check and adjust the valve clearances too.
What gap should it be? And again, what’s a good source for this kind of information? A shop service manual?
Please stay away from that engine until you read up on it. It is a 383 that was a 2bbl, hydraulic flat tappet, no adjustments.
 
If it is a 440 manifold there's your problem. It has to be sucking air and oil into the cylinders from the valley. Forget your plugs see if they're only. Take your carb off look inside the manifold for oil. If there's oil in the manifold get rid of it and get a 383 that is a low deck put it on and put the car back on. The carb is not too big it is a spread bore with tiny primaries. Vacuum secondary is only going to allow the engine to pull as much fuel and air as the engine needs in no more. Change the manifold for the right one put it back together and you will probably be fine.
Read through the posts, the correct manifold has already been determined.
 
Go through the steps..

#1 compression test because nothing will help if it doesn't have good compression.

#2 ignition timing

#3 carb tuning

You can Google and find all of the specs or order a copy of the factory service manual but more often then not trial and error usually finds the best settings.

The amount of performance gains to be found through proper tuning can make a HUGE difference. I went through this on mine, started off with a Mallory distributor with a one size fits all setting.. after a week of trying different things it went from being a slug off the line to being a tire shredder. Same with my first carb, couple days of jetting, power valve swaps etc and it started pulling hard through the rpm range.
 
I just purchased my first classic Mopar, a 1967 Coronet 440 with 87k miles, a stock 383, 4bbl carb, 3 speed 727 torqueflite, and a 8 3/4 rear end.

This was originally a 2bbl so I believe it was originally rated at 280hp. However, right now it feels more like 150hp. The first gear acceleration is "fine", but it feels the car starts to become sluggish after 30mph and acceleration decreases. I'm not expecting it to perform like a modern car but I think this motor can do better.

Last night I checked the numbers and the intake is a Chrysler unit from a 440, with number 3830949.
Edit: People have suggested below this is from a 400, not a 440.
The carb is a Rochester Quadrajet 17086046. This is a GM carb that came on 4.3l trucks. https://www.carburetion.com/CarbNumber.asp?Number=17086046

I'm not an expert here but I think this intake and carb combo is not the most efficient. Are there any power/torque gains to be had with a different carb? I know it's a stock, tired engine with a 3 speed but I'm sure it can do better.

Any suggestions?
IMO....
The Dodge 440 is a model description not the engine size. IF the engine, as you noted, is in fact a 383 with a 2 bbl carb, then the intake manifold with the Rochester Q-jet, is likely from a '73 or '74 400 B block engine with a Carter Thermoquad carb.
Depending on how much origionality you desire, then retire all your present stuff....manifold, carb and all the shoemaker adaptors stuff including the rubber fuel line and opt for what Mopar installed origionally. The origional carb was a Carter AFB, and minimal emission control devices. If interested, I can provide thd original AFB number. The Qjet number you noted # 17086046 and the model M4MEA was an electronically controlled step up piston unit.....not necessarily on the 4.3 L engine or ????. Its no wonder why is running poorly. Just my opinion of course.
BOB RENTON
 
If it was a 2 barrel then it wasn't an AFB.
(Aluminum Four Barrell)
But again a COMPRESSION test first
 
Why is everyone going round n round on "if" it was a 2bbl n what intake. That part was resolved early on. The 383 was originally a 2bbl. The intake is now a TQ 4bbl from a '75-'77 400 with a non original TQ on it.
 
Ok so here’s the bad news: all cylinders reported 130-140 except cylinder 5, which was at 60. I tested it multiple times and it came back the same.
I put some oil in there and that changed the pressure to about 70.
I haven’t inspected the valve springs and rockers yet.

Oh and all the spark plugs looked in great shape.
 
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I checked the stamping on the head: it looks like 2406518. Those are supposed to be the max wedge heads.
But realistically, it’s probably a 516.

I took off the rocker cover and took a quick look. Nothing seems out of place or obviously damaged/bad. Should I attempt to take off the springs and check the valve guides? Or better to take whole head off?
 
Supposed to be Max Wedge heads?

1 huh 2.png


Uhhh....

1 laugh 4X.jpg


No. Max Wedge heads were never fitted to a 440.
 
Or better to take whole head off?

Probably this. The head will need to come off if you want to repair the low cylinder pressure.

But it might be worthwhile to now determine the source of the low cylinder pressure. If you add compressed air to the cylinder, similar to conducting a leak down test, you may asertain if it is rings or valves, and which valve. This way you'll know now if it is a motor rebuild or just cylinder heads.
 
A dial indicator on the rocker. Turn the motor over with a bar. Compare with another cylinder.
 
I just read this thread. It sounded from your description of the problem that it's not even performing up to par for how it's equipped. A restricted fuel filter was already mentioned and I believe you replaced the inline filter. Did you know the quadrajet carb originally came with a small paper type filter in the inlet fitting? If you haven't already, you might check for it's presence. They are normally removed when an inline filter is installed but maybe it wasn't. Sounds like the previous owner had rust/debris issues hence the tank/fuel line replacement. You said above 30 mph the car reduced acceleration. Without driving it I can't say for sure if it's a fuel, ignition problem, etc. but usually a fuel starvation issue will get worse the faster you go probably to the point of dying. When letting up on the throttle a little it will usually pick up rpm's. Other fuel starvation problems could be a restricted "sock"/ strainer in the fuel tank, (attached to the sending unit), a kinked line, fuel pump problem, trash in carb, etc.
A word of caution....be careful when removing and reinstalling the fuel inlet fitting on the carb. They are notorious for galling or stripping the threads. Be sure and don't crossthread it. You didn't say what your fuel leak was but that could be it. They used to make fittings to repair them but if that's the case you might consider replacing the carb. They do make adapters to convert a spreadbore intake to a squarebore if you have the hood clearance.
There were many good comments in this thread about improving performance. With 60 psi on one of the cylinders it will never run to it's full potential. That should be addressed but just thinking you have more problems than that. Yes a rear end gear change would make a HUGE difference if you have the 2:76's. Best of luck!
 
This is where the leak was. I think the PO epoxied this just before selling the car and didn't clean it. It was much worse when I got it, but I cleaned it up a week ago and it's almost dry.

The fuel inlet says FILTER with an arrow. Is the paper filter supposed to be in there?

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One dead cylinder is about a 25% power loss.
That needs to be top priority.
I wouldn't spend any time on that carbeurator.
 
This is where the leak was. I think the PO epoxied this just before selling the car and didn't clean it. It was much worse when I got it, but I cleaned it up a week ago and it's almost dry.

The fuel inlet says FILTER with an arrow. Is the paper filter supposed to be in there?

View attachment 1132153
Yep that would be where it is if someone hasn't already removed it. There was a filter and spring in there from the factory. No harm in leaving these out as long as you have the inline filter. Just hoping for your sake it's still there and restricted. The leak issue at the plug someone epoxied isn't uncommon for a Quadrajet. I used to rebuild a lot of these back in the day. Normally taking a small hammer and peening (flattening) the lead around the outside of the plug would fix it but using quick set epoxy was also a common thing. Yes it needs to be clean!
 
One dead cylinder is about a 25% power loss.
That needs to be top priority.
I wouldn't spend any time on that carbeurator.

I’m talking to local shops now. Hopefully will get it sorted in a couple of weeks.
 
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