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C3 hard start and rough idle

Old 01-10-2019, 05:37 PM
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Rebuck33
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Default C3 hard start and rough idle

hello all. I have a bone stock 1978. Two problems....

first, and this has happened ever since I have owned it. I have to crank and pump forever to start it. Two years ago when I bought it, it was this way. I had a neighbor rebuild the carb, he used a kit, and we put it back together. Same exact issue. Crank for a minute or two.... then it will fire.

second issue, and this is newer. I have a miss or something. It seems to come and go. It will start but not idle. It throws tons of blue smoke and itís intermittent. It happened off and on over the summer, sometimes after it really heated up or I romped on it, it would straighten out. Other times it would start and idle smoothly after a few seconds at high idle. It has been extremely wet this year so I thought maybe some dampness in the distributer cap. Two weeks ago I had a moment and sprayed WD40 in it, put the cap on and it fired right up and idled great. This afternoon I tried to start it and after cranking I had to keep it at 1500 RPM, blue smoke everywhere and very rough and unresponsive, barely could get it to 2500 RPM. What could cause this? I donít think the plugs, wires, cap and rotor are that old but will gladly replace them if thatís what someone thinks. I canít imagine itís vacuum issues if it happens sometimes and not others.

This has 40,000 miles on it and hadnít been run more than maybe 2 times in a year. Garage kept and I use Stabil and a StarTron in the gas.

Thanks in in advance for your time....
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Old 01-10-2019, 05:45 PM
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Big2Bird
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I will default to Lars on this, but I must say I have seen the filter sock degrade, and pieces get stuck in the fuel pump check valves. This allows the fuel in the line to drain back down to frame level.
I tell everyone to change this sock. After 40 years, they are trashed. If it looks good, it is not.
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Old 01-10-2019, 05:56 PM
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Correct used dry gas in my 77 in 1982 and that **** clogged my sock . I do not place any thing in my cars tank now but gas.Dry gas clogged my carb filter also and it took a week yo get it to run smooth. As far as carb rebuild kits try finding a nos that has the right stuff in it to rebuild it correctly.
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Old 01-10-2019, 06:38 PM
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Is your choke opening ?
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Old 01-10-2019, 08:32 PM
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Choke seems to be working fine. It does this right from the get go and continues to do it.
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Old 01-10-2019, 08:33 PM
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Where is the filler sock?
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Old 01-10-2019, 08:56 PM
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Yes, where is the filter sock?
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Old 01-10-2019, 09:05 PM
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Originally Posted by Rebuck33 View Post
Where is the filler sock?
In the gas tank.
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Old 01-10-2019, 09:13 PM
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Originally Posted by sug View Post
In the gas tank.
Thanks!
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Old 01-10-2019, 10:09 PM
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Old 01-11-2019, 08:14 AM
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Rebuck33
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So no other suggestions on the really rough idle and wonít stay running other than the choke?

also, about this filter sock. Iím gonna look for it and understand how it could mess things up but donít quite get why it would cause long cranking each time sitting for more than a day. I think I understand how it could mess with the valves in the pump and drain the line but will that siphon the carb bowl? It seems to me something is allowing the carb to empty into the engine. My neighbor thinks our first step should be the power valves in the carb?!?
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Old 01-11-2019, 12:04 PM
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Originally Posted by Rebuck33 View Post
So no other suggestions on the really rough idle and wonít stay running other than the choke?

also, about this filter sock. Iím gonna look for it and understand how it could mess things up but donít quite get why it would cause long cranking each time sitting for more than a day. I think I understand how it could mess with the valves in the pump and drain the line but will that siphon the carb bowl? It seems to me something is allowing the carb to empty into the engine. My neighbor thinks our first step should be the power valves in the carb?!?
No power valve in a quadrajet. There are some plugs underneath that can leak down.
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Old 01-11-2019, 03:48 PM
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a couple things stood out
blue smoke,,,,oil
spraying wd40 in distributor,,, moisture.

many sayings about 90% of carb problems are ignition.

what have you done to ignition?
tested? changed parts?
pics of plugs
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Old 01-11-2019, 05:08 PM
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Rebuck33
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Iíve done nothing to the ignition yet. The cap looked new inside and had zero moisture in it. I guess maybe before I go too far I change plugs. Does it make sense to try and run it and check exhaust manifold temps to see if itís just one cyclinder not firing when this happens?
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Old 01-12-2019, 12:32 AM
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yes look at the plugs

yes a temp gun can find a dead cyl

weak spark is bad
could be
corrosion
weak coil
bad wires
plug gap
fouled plugs, oil, heat range
78 has hei
should give a good hot spark.
you need to verify the ign system is good.
set timing
then work on carb
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Old 01-12-2019, 05:32 AM
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Before you start it the next time take the air cleaner off and see if the accelerator pump squirts gas when applying throttle. If it doesn't the carb is empty of gas and will require some cranking to fill up before it starts. If it has been a while between starts the gas evaporated which is common occurrence. If it has not been more than a few days then the gas has leaked out and the carb needs to be rebuilt/rechecked.

Also if you let it sit a while and the engine has bad valve seals oil will leak into cylinders and cause a lot of blue smoke at start up which will lessen as the engine is run.

I'd replace the plugs/wires to see if runs any smoother.
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