jonesolds442

RE: Rallye 350

Hello everyone,

Upon purchasing this car, it idled roughly. It had been in storage off-and-on since '90. Therefore, I had the carb rebuilt and did a complete tune-up, including a coil replacement. The car still idles abnormally rough, but it smoothes right out when the RPMs are increased. Actually, it runs wonderfully above idle: pulls strong, doesn't surge or cut-out, doesn't die or sputter. One of my cohorts suggested that one of the previous owners may've snuck in a hotter cam, but the car seems to vibrate too violently. I have a rumpty-rump pro-gas 468 BBO, (542/560 on a 286/292 with a 112). The Olds that housed that monster didn't shimmy like this Rallye does. The rough idle seems so indicative of a vacuum leak that I've re-checked and replaced all the vacuum lines, as well as re-checked all the manifold and carb vacuum ports, but to no avail. I could make a milkshake at idle, but the slightest acceleration smoothes her out like glass.

Another cohort suggested a possible design issue with the top plate on the intake-he regailed tales of SBCs with a recess (allegedly) between the primary and secondary port runners on the top plate that would necessitate a specific carb gasket that would plug that recess and therefore, fix a supposed vacuum leak (rough idle). Well, after pulling the carb, the top plate on the Olds is perfectly flat, with no recessed areas. I'm at my wits' end regarding this rough idle. I'm inclined to contact the guy I bought it from and ask him if it's always idled this rough, and/or if he knew of a hotter cam having been installed.

What are your thoughts?

oldcutlass

Which distributor, carb, intake are you running? What is tune set to, dwell, timing, idle speed...?

jonesolds442

Oldcutlass,

Stock dist, carb is Q-jet from '72 455, stock intake, dwell is at 28 degrees, timing is advanced at 14, and idle speed is set at 700 in gear.

Rickman48

Try doing a 'Hand Choke'! Maybe somethings stuck in the jets.
Remove the air cleaner, rev it up to about 4000, and use your other hand on the carb to manually choke it, 'til it almost dies. Do it 5-6 times and see if it helps.

oldcutlass

Dwell should be at 30. After you reset dwell you'll have to reset your timing. I used to run my 330 @ 12. When you set your idle A/F mixture screws are they pretty close to even right and left, turn them in until the engine stumbles one at a time, and then back them out until you have the highest vacuum or rpm. See if that smooths it out?

Rickman48

On the above post - if you use a vacuum guage to the highest point, you'll get even better results!