Kolby66

Do you know the best way to determine, if you have a miss due to carb, or from ignition? Cutlass runs great, but at idle has a miss. When sitting at a light it is stumbling a little, but as soon as you give it gas, no hesitation at all. Stock 72 350 4 barrel qjet.

oldcutlass

I would go through my tuneup specs before doing anything else to start.

joe_padavano

^^^This. Try pulling one plug wire at a time while the engine is running. If the RPMs don't drop, that cylinder is the problem. Also check for vacuum leaks, cracked hoses, etc.

Kolby66

Thanks for your inputs, Last spring previous owner completed a complete Tune up, plugs wires, cap rotor points and condenser. Carb bolts a little loose, tightened them a scoche, replace cruise vacuum diaphragm, (however previously had the vacuum source capped off) no change. I will need to have my wife in the car in drive, to pull plug wires one at a time, that's the most notable (in drive warm at a stop light) never dies, and accelerates after just fine.

Sugar Bear

Pull the plug wires only with pliers that are electrically insulated and designed for that purpose.

69CSHC

100%

As Eric and Joe P stated I would go over everything. By the book ad nauseam, monotonous, tedious, annoying, but you will find the problem.


Same with my 69 350, car still had issues. Tinkered, tinkered, tinkered, took a while but got it to run real nice in my opinion. First thing I learned was that when I tried to lower the idle to close to factory spec the car would stall as soon as the power steering was engaged in a parallel parking type situation. So back up went the idle till I could figure out what was causing this.


But does it struggle ?

My car would do 30 minutes wide open highway casual driving, come to an exits stop and then stall. But it was hit or miss you never knew. Other times it would stumble almost stall catch itself then seem fine till the next time...

In my case plenty of small issues, someone had put the fuel filter backwards, the rubber fuel line locations although minimum in factory setup had dry rot. No significant gas leak but the hoses had cracks. Which I'm guessing allowed additional air into mix on hard acceleration... When car was full tank of gas you had a very small gas drip by these areas that developed. Or that I finally became aware of... So small hard to notice on asphalt, etc, but you could smell a bit. The rubber elbow by gas tank, and another small piece near firewall area iirc on engine end of passenger side.

My car could eviscerate a tire from a stand still but would stumble at WOT on the highway or on the track. Air fuel mixture seemed to be the biggest issue. Got the proper tool studied a YouTube video and went for it. Tinkered with air mix screws and idle screw and eventually got her to run nicely. Initial idle was probably 850 rpm in drive, adjusted down to 750 then drove her that way for a while. Wanted to make sure she was good in all situations. Brutal traffic, hard acceleration, sudden stops, etc. My next adjustment session down to 650. Then the following session finally down to the factory 575 RPM. Runs like a champ, guessing about 90% on the money. Choke still needs some fine tuning... ( Recent timing chain kit replacement has since sped up the idle to 625 RPM in drive, which I have not as yet adjusted down.)

Tune and carburetor where all new, done and replaced by a shop just prior to me purchasing car, I have the dated receipts...

Recapped all ports that where already capped on carb. Previously done quickly with whatever was available. Like the old screw into an open ended hose type cap... or dry rotted rubber. All replaced with new rounded end caps. The longer I think about it the more I remember... Just go over everything, slowly but surely you will cover it. By the book, factory knows best. Unless the car has been modified then you have to reassess.

Kolby66

Thanks I will look at all suggestions, I would say it does not struggle to keep running. just not smooth.

shiftbyear

A vacuum gauge is a great diagnostic tool, it can even reveal a clogged exhaust system.