Hi all - just got done with front end build and been running it past couple of days - stopping / steering / riding nice ... today I got in on the highway - around 65mph i could tell it was missing a bit - on the way home from a stop sign it had a major hesitation / lurch - then sputtered / backfired / and stalled - fired right back up but I want to dial it in - here’s the history ... feb last year I rebuilt the quadrajet and the distributor - mechanical advanced was seized - and so was vacuum advance - the previous fall it would barely run - I replaced the points and condenser with blue streak and gaped it with feeler gauge then bought a dwell meter to dial it in - new ignition coil - plugs and wires are from three summers ago but didn’t run it a lot - did away with electric fuel pump and went back to mechanical - have in line filter and carb filter and a pressure gauge - the pressure looks good (not seeing it at highway speeds and it does bounce but I’m sure that’s from the accuator / lobe action) the intake manifold is a performer so no heat stove so no choke - just wired open for the time being - 68 455 c heads - aluminum performer intake - stock exhaust manifolds - 72 quadrajet - points distributor - any ideas? Thanks gang

 

From your write-up:
(1) You set the dwell - but you don't state what degrees you set the dwell. The dwell needs to be set @ a specific degree. Check your CSM and dial this in;
(2) You don't state anywhere you set the timing. You have to set the timing. Again, look in your CSM and dial this in;
(3) You don't state anywhere how you set your carburetor A/F mixture.

There is only one way to tune-up this engine and it must be performed in the following sequence.
(1) Set dwell - dwell meter;
(2) Set timing - timing light;
(3) Set A/F mixture - vacuum gauge.

I'll see if I can dig up some numbers on the 455 bbo.

 

1971 CSM 455 bbo

Slow idle RPM = 650
Fast idle RPM = 1100

In sequence:
(1) Dwell = 30*
(2) Timing = 10* BTDC @ 1100 RPM (You must set timing w/ the distributor vacuum advance disconnected and plugged). Be sure to reconnect vacuum advance before adjusting carburetor A/F mixture screws.
(3) Carburetor = Set A/F mixture screws until you achieve the highest vacuum possible. Turn each A/F mixture screw 'in' then 'out' until the the highest vacuum is attained. Depending on which distributor you have & which vacuum model you have, you should be able to achieve a vacuum of ~ 16"Hg - ~20"Hg.

 

Thanks VC! Appreciate your time - sorry - yeah I set it right on 30* - timing was 10* base (with vac advance capped and off) I forget what i calculated all in at - the 1100rpm was the sketchy part I believe I was close but no working tach in either dwell or car at the moment (I did get a new dwell recently though) - I did have a cheapo harbor frieight reflector tape tach that was difficult to get to aim at balancer but I did get a few readings is how I think I was close - I did the carb with vacuum gauge I was pulling optimal vac (forget what the # was - like 21 to 22?) ... I will go through it again next time I get to the car - appreciate the refresher / I’ll take a peek at the plugs while at it just to see how they are holding up - question on slow idle vs fast idle though - is slow idle achieved with the car in gear? I have a manual - so do I just use the fast idle reading? Or is it a choke adjustment? (Only did this once before so I’m rusty) thanks again - Joe R

 

Yes, slow idle set w/ car in gear. I have an automatic. I set my fast idle, then when I set my slow idle I simply block my tires, set the parking brake and put it in Drive. There's a small delta in slow idle between w/ AC versus w/o AC. I have AC so I bump the slow idle up about ~100 RPM. I think my slow idle is ~750 RPM. You want the delta between fast idle and slow idle to be about what - maybe 400 RPM - 500 RPM? In terms of economy & fuel consumption, with a manual I'd set the slow idle after driving it some so the engine isn't "racing" at intersections - just idling comfortably. If you don't have a tachometer, just ballpark it on sound. High enough slow idle so it doesn't "lope" and stall out when you engage the clutch.

 

Of course, if you have those numbers dialed in - which seem fine to me - I'm not certain we've addressed your issue on the lurch & stall, yet. Others might have a suggestion. I'll dwell on it some.

 

Thanks - it won’t hurt to go back through it again - Maybe I’ll see something - I still don’t understand how to do “slow idle” in a stick though - I believe I just did high idle last time. Maybe it’s time to address an electric choke too - Need to read up more on quadrajets carbs - I know choke is inop - not sure if secondaries are opening either - haven’t gone wot because I also need a clutch soon - it holds decent but if I get on it it will start to slip (next spring goal) I will repost my results - thanks again!

 

And I caught the pun 😜

 

In my mind, I think of slow idle as the number of RPM required to maintain adequate idle under "load". I think of it best when I think of an automatic transmission vehicle. I pull up to the stop sign, and I don't want the engine to stall out or die when I stop. When the vehicle is stopped (under load), it should be able to handle/address the load placed upon the engine. Therefore, what are the items considered under load? Alternator, AC compressor, PS pump, water pump, etc. As each device places a load on the engine, they individually & collectively reduce the effective RPM of the engine. Albeit, an engine w/ AC (turned ON), will place a heavier load on the engine when the vehicle is stopped. While stopped, the AC compressor clutch may engage or not engage; while engaged, it places a load on the engine and reduces the effective RPM of the engine; while not engaged the RPM increases slightly as the compressor clutch is free-spinning (not engaged). Therefore, there's a sweet spot for each engine during a full stop (slow idle) based upon the load placed on the engine. IMO, that's one reason it's critical to tune-up an engine in the proper sequence so as to deliver optimum performance @ WOT and/or slow idle: Dwell>Timing>Carburetor

 

You are correct, which is why there is a different RPM spec for idle RPM of manual transmission cars vs automatic transmission cars.
My book shows hot idle RPM of 650 in D for auto and 750 for manual (out of gear, of course).

 

I haven’t gotten to the car yet - but I don’t think it was necessarily a bad timing issue with the stall coming from the stop sign - it could be timing related - but it feels more fuel / spark related - going for timing first though - I will look at points - cap - plug - filters and all that while at it.

 

You might try this first. You ONLY need one of those items I've identified in the above. Remove both the in-line filter and the pressure gauge. Start driving w/o those items installed in the fuel line. Additionally, ensure the fuel line attachment point to the carburetor is as nearly straight as possible for a minimum of about 3" - 5" before entering the carburetor. I can't tell completely from the image, but it appears there's a rather sharp nearly 90* turn directly after the pressure gauge to rubber hose then the metal line. Remove that 90* turn and ensure a nearly straight-in fuel delivery into the carburetor. I'm not certain I agree w/ you regarding the pressure gauge bouncing around is from the actuator; and, if it is, it shouldn't be bouncing around - you want unimpeded fuel delivery into the carburetor. I don't believe you're buying yourself any advantages w/ an extra in-line fuel filter and a permanently installed pressure gauge in the fuel line. Personally, I'd ditch those items and fix that kink then drive it for a couple hundred miles to see if the problem persists or goes away.

 

Leave the fuel pressure gauge and lose the inline filter. That filter is a fire hazard. You only need the one filter in the carb. You may see a fluctuating pressure as the opens and closes to let fuel into the carb and fuel pump actuator going up and down. As long as you stay around 6#'s of pressure your good. Doubt the 90* fitting is an issue unless the ID is less than 5/16ths. Before spending any money double check your tuneup settings and take a look at the plugs to see what they are telling you.

 

Will do - thanks gang