cardude714

Hello All
I have a 71 or 72 455 engine (history unknown) that is in good running condition except it does not want to tune correctly. it will not idle well at the factory timing marks. I have removed the distributor and confirmed that it is properly installed with #1 piston at top dead center. I i set it at the factory 6 degrees with vacuum advance plugged it idles terribly vacuum is low and if I place my hand over the airhorn it idles up and smooth with good vacuum. I have checked for vacuum leaks all over cant find anything, tried a different carb with rebuilt primary shaft bushings no change also the idle mixture screws have little affect on idle quality or vacuum. am I missing something? is it an internal engine problem? intake leak underneath?
the engine has tremendous torque of the line but appears to be a dog at higher RPM'S ?
Thanks Rick

joe_padavano

Have you verified that the balancer scribe mark is actually at TDC? The outer ring can slip.

oldcutlass

What distributor is on the car? If its an Hei, the stock timing settings are N/A and you need to bump your timing up to around 14/16.

cardude714

I did check the harmonic balancer, i used a piston stop and the marks where only off by about 1 deg, the engine appears to be stock it has a stock points distributor?

Vintage Chief

Firstly, what EXACTLY is the current vacuum as measured with a vacuum gauge in Hg"? Then we can best determine if you have a vacuum leak. You should be pulling a steady ~17" Hg. What is your vacuum?

rickw30

Had a similar problem with a MSD in my BB. Had other symptoms but mostly bad idle and vacuum. Turned out to be all distributor related. Bad gear, bad shaft, wrong advance springs.
I would check balancer and TDC then take a closer look at that distributor.
There is more to a distributor than just setting TDC.

Amplitude

Everything you have described with the carb(s) sounds like you have a pretty good vacuum leak. Assuming the carb with the bushed throttle shafts was properly rebuilt and has no leaks, I would start looking at all vacuum connections and accessories, and the PCV if it has one or someone has mistakenly hooked it up like there is one. I have seen people connect standard valve cover breather tubes to the PCV port on the carb thinking that it was actually a PCV valve with check ball. I would also check your brake booster, there is always a chance that the fitting is leaking or the diaphragm has ruptured and air is entering from the seam. Just plug every single vacuum port on the thing. If you haven't found any problems with that, then I would start with the old standby tests. Use a propane torch (I like this, but use a really cheap torch head with a piece of 1/4 tubing adapted), starting fluid, brake clean, or gas in a small squeeze bottle and go around the intake while the engine is running, slowly spraying every gasketed surface and even bolts or plugs. If the engine idle changes as you do this, that should tell you right where the leak is. Rough idle, your hand over the choke horn smoothing it out, and the idle screws not responding are both classic signs of intake/ vacuum leak(s). Also, if the needle on your vacuum gauge is fluctuating quite a bit, that is often also a sign of an intake leak.

I would also remove the points distributor and install a new quality piece from MSD, Pertronix, Davis Unified Ignition (D.U.I), or these guys Progression Ignition. If you must go HEI, I would do a DUI over any other option. Make your own timing marks on the balancer with a sharpie, paint pen, or something else that is obvious to see. You can use basic geometry to determine the circumference of the balancer. Take the diameter, multiply that by Pi, then divide that by 360. That will give you the distance for each degree of crankshaft rotation, take that measurement and make marks wherever you need them. I like to do short marks for every 5deg BTDC and long marks for each 10 deg increment. A flexible tailors tape works alright for wrapping around the balancer and marking your locations. For something slightly more precise, especially if you have a measurement like .631, I'll use my calipers to make marks on a piece of heavy card stock paper or a strip of poster paper.

joe_padavano

Why? There's a lot less that can go wrong with points than an electronic unit. If the symptoms are consistent with a vacuum leak, why introduce new potential problems by making an unnecessary change. If you REALLY need an electronic distributor, get the car running FIRST, then make that change. One thing at a time.

Amplitude

Very true, I'm just very comfortable and used to modern electronic ignition systems. For me it removes a variable. I don't know points at all. I know the basics of how they work, but have never had to mess with them. Now, maybe my faith in modern electronics is a false sense of security. That's why I always carried a spare coil, pickup module, and had quick connects to bypass the MSD CDI box in my boat. I'm planning to go EFI this winter with a new crank triggered ignition system. But I needed a Vacuum advance disty for my olds, so I bought the Renegade Chinese knock-off of an MSD RTR as a temporary solution. Hasn't given me a lick of trouble yet. But If I go on any long trips, I'll take a spare.

Ironically I do actually have all the tools to file, adjust, and test a points ignition system. Just never done it.

joe_padavano

But... points are just an on/off switch.

Seriously, both systems work by opening the circuit to the primary side of the ignition coil to collapse the magnetic field in the coil and initiate the spark. There's no magic here. The plugs neither know nor care if that switch is a mechanical switch or an electronic one.

cutlassefi

So electronic ignition doesn’t have any variables? Bad modules, pickups or maybe Ign boxes don’t count? Really?
.

joe_padavano

You'll notice I didn't comment on this:

In my cars with points, I carry an emery board. And you haven't lived until you've set point gap with a matchbook cover on the side of the road.
Of course, just maintain the points properly and they work fine. No drama, no spare parts needed. And yeah, I'm aware of the Chinesium condenser problem.

Andy

My uncle was an old school mechanic and taught me the matchbook trick back in the 70’s.. gets you home every time, he even used the striker pad as an emergency points file if necessary..

joe_padavano

Exactly!

Amplitude

Reasons I carry spares and wire CDI boxes so they can be bypassed if possible. While I've never had anything fail on me (knock on particle board) I have heard plenty of stories, and have had distributor pickups, CDI boxes, and crank triggers fail on friends. However, with a decade doing 12v work professionally as my 9-5 with all sorts of marine and race car electrical on the side. All before transitioning to my current career as a Commercial AV and control systems design engineer. I think I've accrued the knowledge on how to properly install these systems to avoid all of the common wiring issues and mistakes that damage or prematurely destroy the electronic ignition components on other peoples cars.

Guys, I was born in 1984, what do you expect? I didn't grow up on points. Yes, I've heard of the matchbook trick, and people using all sorts of common items to fix points. But, until I own a concourse car, I don't think that I'll ever mess with them unless it is to help a friend.

Prior to my 68 442, the only carbureted vehicles I've personally owned for any length of time are my 69 Mustang, Velocity Power Boat with a 454 Mag, and my awesome 77 Volare station wagon that had power everything and 50k original miles. The Velocity and Volare both had stock electronic ignition systems, the Mustang had already been converted over to a Mallory system when I got it.

I've always added MSD coils and CDI boxes to every vehicle I've had with an a distributor. And have replaced the distributors with one from MSD on every performance car I've ever had. Yes, I wire up a bypass plug in case the CDI box does fail, and as I said, I carry spare components and some basic tools with me just in case. On my boat I carried a spare cap & rotor, a few old plug wires, a distributor pickup, coil and replacement timing module for the Mercruiser Thunderbolt IV ignition system. But that's a pretty common thing to do on a high performance boat. Moisture and running at 4500-6300 RPM for extended lengths of time is hard on just about everything you can imaging.
My fast cars were all EFI so no points there. They were also built to shift anywhere from 6500-7200RPM and I've always heard regular points don't like high RPMs. Not saying that they can't be made to work well with modifications, as proven by the racers in the 50s and 60s. But not out of the box.
I do see the advantages of points when properly maintained, in how easy they can be to diagnose and cheap to fix with just a glovebox worth of parts and tools. Or even a simple nail file or matchbook.
But sometimes we all just stick with what we know. I know that a digitally controlled ignition system using either magnetic, hall effect, or even photo optic trigger will be more precise than a points system. On some, timing can be externally controlled, and In theory, they also won't need continued maintenance and adjustment after installation. Yes, if the distributor pickup or an external Ignition box that fully control all aspects timing goes bad, you will be left stranded unless you have spares. In that latter example of a full-on ignition system with a locked out distributor with external controller, I'll always carry a cheap HEI in the trunk just as a roadside fix. I'm probably making the switch to a Holley MPFI this winter, and I might just carry a carb, some fuel line, and an HEI with me in-case the ECU ***** the bed.

Part of my job is to help our field techs diagnose and solve issues. So, when someone asks for help troubleshooting, I have to start from a base that I know, and remove as many variables and devices in the chain of that system (in this case, a running engine) as possible. Then, once I get it to a stable state, I have them slowly start adding things back one at a time.

I'm sure we are all in agreement that timing is not his main issue. He definitely has either an intake or vacuum leak somewhere. Could be an impropper breather connection, a split or missing vacuum cap, a blown out gasket. Any number of things causing the majority of his symptoms. But timing does play a vital roll in the running quality of an engine. In my opinion, putting a solid modern ignition system on it is a good move towards making a stronger base that could have continued diagnosis. It just happens to come with added benefits. I don't know that I've ever heard of a unit from Davis Unified Ignition (DUI) going bad. But that was all just my opinion from personal knowledge and experience. I would gladly defer to the knowledge of CutlassEFI as I know his reputation and have no doubt that he does more engine builds, tuning work, and troubleshooting in one month than I have done in my entire life.
Quick note: If you noticed, most of my original post was about disconnecting vacuum lines, and different ways to check for intake leaks. Not preaching the benefits of a full MSD ignition system.

joe_padavano

You didn't grow up on musclecars either, so do you put ricer motors into them? Sorry, that's a lame excuse. Complexity does NOT increase reliability. Again, points are a mechanical switch. What's to understand. They're two pieces of metal that open and close. This is NOT rocket science.

Since you were born in 1984, you also don't realize that electronic ignitions were NOT developed for performance applications. They were developed to meet the new EPA requirement for 1975 that all cars had to meet emissions levels after 50,000 miles without any servicing. HEI exists because the high voltage was needed to fire crusty 50K mile plugs with eroded electrodes, and the Hall effect sensor was the only way to avoid needing to replace points at 12,000 miles. Most of the cars we're talking about here will be lucky to see 12,000 miles in a decade, yet everyone MUST convert to electronic ignition because it's "better" than points, then they have to carry a glovebox full of spare modules and parts for when the electronics crap out. Yeah, how's that better reliability thing working for you?