318 running bad

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74valiant

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im new to carb'd cars, and mopar, so im hopin for a little help. i have a 74 valiant w/318. 150k on the motor. just bought recently and decided id tune it up and change the oil. the oil was old and worn, as were the wires and plugs. i replaced cap rotor plugs wires oil and air filter. i pulled the coil out to get the new wire to fit, but it still doesnt fit tightly. after this the motor ran fine for a day. now it seems to misfore and backfire. it hesitates when throttle is applied, and sometimes stalls. i know the wires are in the correct order, so what else?? any help would be appreciated
 
Tired timing chain? plugged fuel filter/line, bad gas in the tank? cracked/leaking coil...it's got 150k and 34 years on it.
 
anyone in san diego want to help diagnose for some beer? i want to know more about this motor, so hands on would be the best.


thanks jason
 
Or check your timing. My 318 was stumbling and popping through the carb badly until I bumped up the static ignition timing. When I first checked it it was 5* AFTER TDC, I bumped it to 10* BTDC and now it runs like a champ!
 
Also check to make sure you are getting good voltage at the coil. When I had the high miles 318 in my car it had almost the exact same problem.(before I yanked it for a 360) It turned out I was only getting 4volts at the coil! Bad/Old cracked wiring can cause issues like this also.
 
ok, so i checked the timing and it was at 10*atdc. i set it back to 10 before, and it runs much better.however, it doesnt have the same power as it did before the tune up. the timing chain is worn and does vary the timing a little. is the chain the culprit, or should i change the timing to something else?
 
74valiant said:
ok, so i checked the timing and it was at 10*atdc. i set it back to 10 before, and it runs much better.however, it doesnt have the same power as it did before the tune up. the timing chain is worn and does vary the timing a little. is the chain the culprit, or should i change the timing to something else?
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It is not neccessarly the main culprit, but it very well could be and more than likely is playing a part in the issues. The nylong timing gear wears down over time and the link chain stretches out, making for erratic time. Eventually, if it gets weak enough, the teeth will strip off, either at higher engine speeds or during start up, leaving you stranded and possibly with some bent valves. I dont mean to sound pessimistic, but this is good info to know about 318s. This is there one main reliabilty weak link, per say.

This can be cured by replacing with a double roller timing chain and steel gears.

Also, do the systems of power loss and or rough running occur more frequently when the motor is warm, cold, or both?
 
cuda91 said:
did you check if all push rods are working? or it might be fuel pump or fuel filter.
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i had that problem with my car once, i later discovered only three valve out of 6 was firing, i replaced all the bent push rods. and now it runs good
 
74valiant said:
im new to carb'd cars, and mopar, so im hopin for a little help. i have a 74 valiant w/318. 150k on the motor. just bought recently and decided id tune it up and change the oil. the oil was old and worn, as were the wires and plugs. i replaced cap rotor plugs wires oil and air filter. i pulled the coil out to get the new wire to fit, but it still doesnt fit tightly. after this the motor ran fine for a day. now it seems to misfore and backfire. it hesitates when throttle is applied, and sometimes stalls. i know the wires are in the correct order, so what else?? any help would be appreciated
Click to expand...

i just got other idea, maybe check your disturbor.
 
A new timing chain would be a real good idea if it's the original. Anything with that many miles has to be pretty worn and can leave you setting at any time like MoparJ said. That may not be the only problem though since it has so many miles on it. Run a compression test and that'll tell you how sound the rings and valves are. You might have some leaking valves. If the compression test shows decent I'd look at the carb. next. Might have sucked up a piece of dirt and have one of the jets partially clogged.
 
74valiant said:
im new to carb'd cars, and mopar, so im hopin for a little help. i have a 74 valiant w/318. 150k on the motor. just bought recently and decided id tune it up and change the oil. the oil was old and worn, as were the wires and plugs. i replaced cap rotor plugs wires oil and air filter. i pulled the coil out to get the new wire to fit, but it still doesnt fit tightly. after this the motor ran fine for a day. now it seems to misfore and backfire. it hesitates when throttle is applied, and sometimes stalls. i know the wires are in the correct order, so what else?? any help would be appreciated
Click to expand...
Welcome to mopar
 
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