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still having rough idel probelms!

1678 Views 11 Replies 6 Participants Last post by  kiowamec
its seems that on my 79 425 (after putting true duals on her) the drivers side idels a bit rough and spits from time to time. i had the carb professionally tuned and it still does it. I replaced all wires, gapped plugs again, rotor cap, bla bla bla but no improvement. any help?
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You might have a build up of gunk in the engine. I always get good results by flushing the engine. I use a couple cans of B12-Chemtool in the tank and a spray can of B-12 down the intake. For the spray, I get the engine up to temp, get the revs up, and spray down the intake until it starts to die, get the revs back up, wait a minute and start again until the can is gone. It will smoke quite a bit while it is burning off the gunk. Always helps to stay away from cheap gas also.
The breather filter inside the air fitler assembly can get clogged and cause symptoms like that. Stupid, cheap and I guess worth bringing up.
Sticky valves???? I have ran the Lucas Extended oil treatment to the oil along with some seafoam through the tank. It may take a couple of times, but change the oil at 2k after the 1st treatment, the give it another treatment, you should notic a difference right away. Just a couple of tricks I have used on my 500ci. Good luck. C
Marvel Mystery Oil in the oil and the gas works well too.

Plug gap correct?
Wires on correctly? Not laying on a exhaust manifold.
Coil weak?
Valves not sealing?
Are you sure the idle jets are set correctly?
EGR valve coming off the seat?
Correct plugs?
Vacuum hoses on correctly?
No malfunctions in the vacuum system?
Distributor performing correctly?

Personally, I would fill it with MMO and run the snot out of it for a while.
It could be just gunked up.
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Have you put a vacume gauge on it? how about a compression check? These can tell you if there is a problem with your valves...
it was the freakin vacuum advance.
Vacuum advance has zero effect AT idle on the GM design. Part throttle yes.
Vacuum advance has zero effect AT idle on the GM design. Part throttle yes.
Unless it is leaking...
Sorry, GM design uses ported vacuum of which there is none at idle.
The only cadillac motors that had ported vacuum on the Vaccum advance were the California Motors. They had ported vaccum with a thermo switch that kept the advance down until coolant temperature reached 120 degrees F. 1977 Federal motors had a thermo switch set to 120 degrees F. 1978 & 1979 have the vaccum advances plugged directly into the intake manifold. Therefore there is advance at idle and part throttle application. It is your mechanical advance that does not come out until 1300-1600 rpm.

I hope this helps,
Then I stand corrected. Humble pie anyone.
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