Rough idle

[crash113]

Not sure if I'm in the right forum so I apologize in advance if I'm not. I just bought a 66 plymouth sport fury over the winter and I've finally been able to work on it lately now that the weather is getting warm. It's a hardtop with a 318 automatic with 77k original miles. I just put a refurbished carb on from classic industries and did a complete tuneup except plug wires which are on order and a new coil which I just plain forgot. I just got it running for the first time in quite some time and it starts just fine but it idles incredibly rough but when I get into it a bit it smooths right out. I'm figuring a lot of it has to be that it just needs to be run and get the rings to re-seat. I'm a good mechanic but this is my first classic car and it's twice as old as me so undoubtedly there are some things I wouldn't think to check. Just wanted to get a few opinions on where to start looking. Thanks for any help.

 

[polara71]

....... to the board.......

My first look is at the old wires grounding out, then the carb adjustments BUT I am not the mechanic on the board..


By the way.....we need pictures

 

[tallhair]

you appear to be in the right forum .. welcome and head over to the welcome wagon and introduce yourself and your cruiser.

 

[crash113]

Thanks guys. I had a bunch of pics but I have a new phone and lost them all. I'll post some tomorrow after work.

 

[Mr C]

Need more data: I'm assuming the original Poly 318 with points? During the tune up were new points/ condenser put in? Finish off the tune up (wires at least...you may not need a coil) and see how it runs then. I'd also go through the fuel system (blow lines, new filter) to ensure that you're not throwing old debris into that fresh carb.

 

[Bryan]

+1. From you description, it sounds like it has been sitting for a while. You could well have a bunch of old, dirty gas.

 

[crash113]

Yep 318 with points. Put in a new cap, rotor, points and condenser. Plug wires will be in Tuesday so can't replace those till then. I can pick up a new coil or I do have a brand new MSD blaster 2 coil could I use that or do I risk burning up the ignition with the extra juice?

 

[crash113]

Oh and forgot to mention I'm actually feeding the carb through an IV with fresh gas

 

[Mr C]

Yep 318 with points. Put in a new cap, rotor, points and condenser. Plug wires will be in Tuesday so can't replace those till then. I can pick up a new coil or I do have a brand new MSD blaster 2 coil could I use that or do I risk burning up the ignition with the extra juice?

I'd leave the stock coil on there for now...I think the MSD would throw out too much juice and weld the points together...but it's been a long time since I ran points.

 

[Mr C]

Oh and forgot to mention I'm actually feeding the carb through an IV with fresh gas

Good. Be sure to go through that fuel system next once you've sorted out the tune up.

 

[crash113]

One other thing I'm doing an oil change tomorrow and I picked up 5 quarts of quaker state defy oil and a can of restore. I just realized that the oil is actually synthetic and I remember a few people telling me with an old engine that's sat a long time dont use synthetic oil because it keeps the rings from reseating. Is that true or just old mechanics telling tall tales?

 

[1978 NYB]

It doesn't matter if you use synthetic or conventional oil. These engines were designed to run on high zinc oil and Brad Penn is one of the few oils still made that way.

http://www.penngrade1.com/

 

[moper]

Welcome Crash - I live in Columbia CT - about 20 minutes from you if that. If you've only been alive since the 90s then I'm assuming you don't have a lot of carbureted car experience. The idea of bolt on and it works really doesn't apply to much on these cars anymore. Between the wear, the evolution of fuel, and the intermittent quality control you have to accept that everything you do tuning wise will require some extra thought and effort. The carb may need internal adjustments but with a good service manual you should be able to get it good enough to drive it around. On the points - if you set them by point gap you only did a rough install. The finish work is setting them with a dwell meter. Again - reference the service manual. On the coil - use the MSD. The primary side of the coil (the terminal the ignition wire goes to, and the wire to the points) only sees at most about 1V under battery voltage when starting, and normally around 9v when the car is running. The secondary side is the high voltage and that goes to the plugs if alls working properly.
If you want a hand and are patient I'm close by. I'd be happy to help but my schedule can be a bit crazy at times.
Welcome and go have fun with it. The ice is finally melting (until next week...).

 

[440Sled]

What's your timimg set at?

 

[saylor]

check idle circuit on carb. if it runs good at rpm, the wires, coil, etc are ok. still change them to new, but thats not the issue.
if it runs good at rpm, i say the timing is ok. check base idle timing just in case, but im not feeling that is the issue either.

i had a same issue, and ended up getting a 2nd carb from summit. the 2nd carb bolted on and worked.

the first carb the idle circuit would not adjust correctly, so i never was going to get it to run right. it was not rebuilt correctly.

just putting that out there.

saylor

 

[ieman]

Yep 318 with points. Put in a new cap, rotor, points and condenser. Plug wires will be in Tuesday so can't replace those till then. I can pick up a new coil or I do have a brand new MSD blaster 2 coil could I use that or do I risk burning up the ignition with the extra juice?

MSD "requires" the use of their .8 ohm ballast resistor if you want to use the Blaster 2 with your points ignition. The factory is .5 ohm due to the lower turn ratio of the factory coil. That being said, you could use the Blaster coil with your factory ballast resistor at the cost of shorter points life. If it were my car, I wouldn't hesitate doing it because an electronic ignition would be on my to-do list anyway. Then if you decide to swap to electronic, you can ditch the ballast resistor all together.

 

[crash113]

I talked to a rep at Classic Industries and he said the carb I bought is tuned to original factory specs the only thing I should be touching is the idle screw. I was told if I play with anything else it means something is out of whack in a stock application which I'm running. My plug wires come in tomorrow and I still need to check my timing so hopefully that helps. I love playing with this sort of stuff but I'm seriously thinking of doing a points eliminator swap so I don't have to deal with it. I don't plan on doing anything too fancy right now because I plan on doing an engine swap anyway. And thanks moper I might take you up on that offer. Thanks for all the input guys I'm only 29 and I've been playing with cars since I was a little kid but I can definitely use a little expertise here. But my dad raised me right, on tire smoke, cubic inches and cam 2 haha.

 

[78Brougham]

Just a quick thought. Check out the condition of your vacuum hoses. These older cars have lots of issues with dry rotted, split, and loose vacuum lines. Being that it idles rough and then smooths right out when you blip the gas, it could be something that simple. Manifold vacuum is greatest at idle and could be sucking lots of air in. Recently I screwed up myself when changing the valve cover gaskets on my T & C, had to move tons of hoses and wires and forgot to plug one of the vacuum lines back in. Started it up and it ran like crap at idle too. Might be something to look at before getting in too deep.

 

[70bigblockdodge]

MSD "requires" the use of their .8 ohm ballast resistor if you want to use the Blaster 2 with your points ignition. The factory is .5 ohm due to the lower turn ratio of the factory coil. That being said, you could use the Blaster coil with your factory ballast resistor at the cost of shorter points life. If it were my car, I wouldn't hesitate doing it because an electronic ignition would be on my to-do list anyway. Then if you decide to swap to electronic, you can ditch the ballast resistor all together.

Ditch the ballast resistor and do what put 12 volts to the coil, or put some bastard parts in there that you can't find except at summit or jegs no thanks! I will do the time honored true mopar guy thing and put a extra ballast resistor in my glovebox.

 

[ieman]

Ditch the ballast resistor and do what put 12 volts to the coil, or put some bastard parts in there that you can't find except at summit or jegs no thanks! I will do the time honored true mopar guy thing and put a extra ballast resistor in my glovebox.

Simply in response to his question of if he "could" use the MSD Blaster 2 coil. And yes, 12 volts to the MSD coil "if" the ignition conversion is done. Eliminating a component with a known high failure rate seems like a good idea to me, just my .02, and I did use the "if it were my car" disclaimer...