383 suddenly running bad

Reece Stephens

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I'm completely at a loss here, I have a 67 newport with a 383, I drove it all weekend and it ran great, never had an issue. Monday morning I start it up to drive it and it sounds like I have a massive exhaust leak, and it smells like raw fuel. It cranks over and starts normal and idles fine, I verified that I don't have an exhaust leak, I checked all my plugs, they're not fouled, I've replaced my cap, rotor and coil, the points were replaced about a year ago along with the condenser, and all my plug wires are also good. Has anyone else had this problem? If so what was the fix?
 

Davea Lux

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It's not running like it has a vacuum leak, in fact it idles at about 650 rpm. I also have a clear fuel filter. Any time it comes up off idle it sounds labored.

Have you checked the timing chain? Set the lower pulley to TDC on the timing mark. Now remove the distributor cap and have a helper rock the crank back and forth with a socket installed on the large bolt that holds the harmonic balancer in place. Note how much free play is present before the distributor shaft starts to move. There should be no more than 12 degrees of free play or the timing chain is excessively worn. Labored performance off idle can be an indication of a jumped timing chain especially if there has been an unexplained change to the timing settings.

Dave
 

Turboomni

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Have you pulled the oil dipstick and see if it smells of gasoline?
 

Reece Stephens

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Have you checked the timing chain? Set the lower pulley to TDC on the timing mark. Now remove the distributor cap and have a helper rock the crank back and forth with a socket installed on the large bolt that holds the harmonic balancer in place. Note how much free play is present before the distributor shaft starts to move. There should be no more than 12 degrees of free play or the timing chain is excessively worn. Labored performance off idle can be an indication of a jumped timing chain especially if there has been an unexplained change to the timing settings.

Dave
I appreciate the advice, I'll definitely check that.
 

stubs300

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it sounds like I have a massive exhaust leak, and it smells like raw fuel. It cranks over and starts normal and idles fine, I verified that I don't have an exhaust leak, I checked all my plugs, they're not fouled, I've replaced my cap, rotor and coil, the points were replaced about a year ago along with the condenser, and all my plug wires are also good. Has anyone else had this problem? If so what was the fix?

Help me out here? You've checked & don't have a exhaust leak, it runs fine, but it smells like raw fuel, correct? If so, how are all the rubber fuel lines, how old are they? Any fuel leaks/puddling that you can see? Check to see how tight the plugs are, they can work loose and cause problems like you say. DAMHIK Good Luck
 

CBODY67

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Idles fine, but sounds labored when coming off idle? No exhaust leak? BUT a muffler baffle that has come loose and blocked the majority of the exhaust flow through the muffler, I suspect. To check, unhook the front of the muffler and see how the engine responds, then. Advise . . .

Just some thoughts,
CBODY67
 

Reece Stephens

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Idles fine, but sounds labored when coming off idle? No exhaust leak? BUT a muffler baffle that has come loose and blocked the majority of the exhaust flow through the muffler, I suspect. To check, unhook the front of the muffler and see how the engine responds, then. Advise . . .

Just some thoughts,
CBODY67
I have a chambered thrush muffler, been on the car since may. I suspected it may be exhaust related so I pulled the muffler and the sound actually got worse with no muffler. As for fuel leaks, it doesn't have any.
 

1970cat

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are you sure it's not flooding from a stuck choke or needle? check the fuel pressure before the carb. you could have a cracked fuel pump diaphragm. i've had them go bad and provide enough fuel to run , or dump excess fuel.
 

Reece Stephens

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are you sure it's not flooding from a stuck choke or needle? check the fuel pressure before the carb. you could have a cracked fuel pump diaphragm. i've had them go bad and provide enough fuel to run , or dump excess fuel.
I disconnected the choke, and this is a freshly rebuilt edlebrock
 

stubs300

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How old's the coil? If replaced is it the correct Ohm for your application, maybe it's possibly defective or takin a dump?? Check, clean, grease all & insure all wires are up to snuff & tight. I'm electrically igknat with electrics after that so I can't help any further if that's a/the problem. Good Luck
 

mrfury68

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Like stubs300 posted above, don't overlook the coil. Many years ago the service station owner I worked for told me a bad coil can give you the same symptoms as a fuel delivery problem. That advice saved me a lot of frustration over the years. Good luck
 

mopar440

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Heat riser shut and stay shut? Does disconneting wires 1 by 1 cause a change?
 

Reece Stephens

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How old's the coil? If replaced is it the correct Ohm for your application, maybe it's possibly defective or takin a dump?? Check, clean, grease all & insure all wires are up to snuff & tight. I'm electrically igknat with electrics after that so I can't help any further if that's a/the problem. Good Luck
It's a new coil, I'm running an edelbrock coil. I did try another coil and it didn't make any difference.
 

1970FuryConv

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I agree with Dave. Check timing chain 1st. Factory Plastic cam gear teeth break off.

I also agree with checking the exhaust. If the muffler is mounted too far forward on the midpipe, the baffle can contact the midpipe and cause restriction. This will produce the performance problems off idle. Also, excess back pressure can effect fuel intake.
 

stubs300

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It's a new coil, I'm running an edelbrock coil. I did try another coil and it didn't make any difference.

How tight are your plugs too? A loose plug will give you a exhaust leak sound and cause a bad ground effecting spark reliability! Good Luck
 

CBODY67

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IF it sounds like an exhaust leak, where might the sound be coming from? Raw fuel smell with no obvious fuel leaks?

Check to see if you can feel some hot exhaust gases escaping from one or both sides of the center of the intake manifold/cyl head location? As in IF the steel valley pan gasket might have failed in that area? If it might have failed on the bottom side, the exhaust gases will go into the crankcase, which means that removing the oil filler cap might have more flow coming out of it than just normal crankcase smells.

Please advise,
CBODY67
 

stubs300

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IF it sounds like an exhaust leak, where might the sound be coming from? Raw fuel smell with no obvious fuel leaks?
Please advise,
CBODY67

He's been very vague with both his asking questions, and not answering questions already asked. We can only assume his problem!
 
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