[Vid]

First, here’s the relevant hardware:
4.210 stroke 457 cu in, 10:1 squeeze, Edelbrock RPM heads, RPM intake, FST 850 cfm carb, HEI upgraded with Davis module and coil, Lunati hft 704 cam (carefully degreed in), ATI Super-damper, manual transmission.

Here’s what’s happening. Got the engine fired up and the cam broken last night, in2200rpm minimum for three 10 minute heat cycle sessions. 14° initial advance. No leaks, no issues, no pinging, no overheating, everything went relatively well. Motor sounds like you’d hope it would, great.

Spent time this morning attempting to get it dialed in. Set the timing using the method where the advance springs are removed from the diz. Plugged the vacuum adv hose. Cranked the motor just upwards of 2750rpm and adjusted the timing to 37° all in. Seemed fine. Shut it down, reinstalled the diz springs and vacuum advance. Started it up and checked the initial timing. It’s reading about 6° retarded. That can’t be right? Also the idle rpm doesn’t seem to want stabilize. I’ll adjust it to around 850rpm, blurp the throttle and it comes to rest at a much faster rpm, maybe 1100rpm.

Any ideas? (PS don’t judge the sloppy plug wires, they’ll get tidied up soon )





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[johnta1]

What's the problem? (or symptoms?)


I don't know why you would take advance springs off though?

[Formulas]

if you had vac adv plugged in when you checked for the 37 thats your problem .

the whole purpose of springs out timing check is to set total timing with full mech adv only and you dont have to rev the engine up to get there then reinstall the springs and your initial is what it is memorize that for future use, then plug vac adv in

[Vid]

Originally Posted by Formulas

if you had vac adv plugged in when you checked for the 37 thats your problem .

the whole purpose of springs out timing check is to set total timing with full mech adv only and you dont have to rev the engine up to get there then reinstall the springs and your initial is what it is memorize that for future use, then plug vac adv in

Sorry, not clear on that answer. Plugged, or “plugged in” as in connected and functioning? The vacuum advance was plugged (closed off) to check the 37°. I’ll try it again.

I’m also not sure why the idle doesn’t go back to where it was set, there is no interference anywhere that I can tell and the dual throttle return springs are strong. I’ve never experienced that problem before. I’ll pull the carb off and look for clues.

Thanks for your responses


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[Vid]

Originally Posted by Formulas

if you had vac adv plugged in when you checked for the 37 thats your problem .

the whole purpose of springs out timing check is to set total timing with full mech adv only and you dont have to rev the engine up to get there then reinstall the springs and your initial is what it is memorize that for future use, then plug vac adv in

Sorry, not clear on that answer. Plugged, or “plugged in” as in connected and functioning? The vacuum advance was plugged (closed off) to check the 37°. I’ll try it again.

I’m also not sure why the idle doesn’t go back to where it was set, there is no interference anywhere that I can tell and the dual throttle return springs are strong. I’ve never experienced that problem before. I’ll pull the carb off and look for clues.

Thanks for your responses


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[Formulas]

Sorry i read over the sentence to fast where you implied non functioning vac adv.

dist weights and cam number? is the cam installed numbers up or down? everything moving freely?

your carb butterflies could be hanging up somehow on the intake opening or gasket look down it for clues

[steve25]

Your advance shaft in your HEI is hanging up more than likely due to dried out grease.

This can seem to take place all of a sudden on these old units, where they’re ok one day and after the motor sits for a week it all goes to hell!

Remove the gear ( but first note how it needs to be oreintated go back on) slide out the inner shaft once you removed the advance springs and flush out the old grease, clean it up off the shaft and then lube the shaft hole up well again with synthetic wheel bearing grease.
Run the shaft in and out a number of times to check that it’s getting lubed up well.

Of course if the shaft is showing signs of getting worn, or the whole deal is wobbly already then it’s time for a rebuild or a whole new HEI.

Here’s a personal example as to what can happen.
If your timing is jumping around higher then what you set it , like up above 4500’rpm then the motor will knock and kill itself and you likely will not hear it until it’s too late.
This takes place when the advance springs are too light and the advance limiter bushing is gone.

[Formulajones]

The HEI may need to come apart. Every one I've messed with needed help. They are also notorious for over advancing as the stop bushings are always missing. That could be your issue. Setting timing the way you did would get your total right, but if it's over advancing then coming back to idle would show a very low initial timing setting.

There are several ways to go about correcting the advance limit on an HEI, none of which are easy to explain on a forum. Also as Steve mentioned they typically need serviced with grease and possible bushing replacement as well. Almost every OEM unit I've had in my hands was just plum wore out and sloppy.

At which point it may just be easier for most to buy a new aftermarket piece.

[steve25]

I can’t put enough emphasis on checking your total timing with out vacuum advance hooked up at 5000 rpm to confirm that it’s not over advancing on you.

[Sun Tuned]

The part where you removed the springs and set timing at 2750 is where this got messed up.

You cannot do this with an HEI, unless it’s been modified for a positive stop,. It won’t work right doing it in that manner. The slots in the shaft plate are about twice as long as they need to be.

You got the total set alright that way, but the pins were against the end of the slots. When you put the springs back on it placed the whole deal in its normally parked position and that’s why it was retarded.

Procedural issue.

[Cliff R]

You cannot do this with an HEI, unless it’s been modified for a positive stop,

+2

I'll also add that welding or making a positive stop for an HEI is NOT an option. They are designed to stop the advance curve when the "flats" on the weights meet the "flats" on the center cam. With the stock HEI (or really strong springs) springs this will stop the advance at that point. However, if you try to use light springs, or spin the RPM's high enough the weights overcome the spring tension they can, and will add a BUTT-LOAD more timing......

[zippy]

Originally Posted by Cliff R

You cannot do this with an HEI, unless it’s been modified for a positive stop,

+2

I'll also add that welding or making a positive stop for an HEI is NOT an option. They are designed to stop the advance curve when the "flats" on the weights meet the "flats" on the center cam. With the stock HEI (or really strong springs) springs this will stop the advance at that point. However, if you try to use light springs, or spin the RPM's high enough the weights overcome the spring tension they can, and will add a BUTT-LOAD more timing......

Not an option as in it is a must do? I haven't made a positive stop on mine yet. But just about to give the dizzy a complete go through.

[Vid]

Thanks for all the helpful responses. I basically just started from scratch again with the timing using the traditional method instead of “springs off”. She’s purring like a kitten now (likes 875-900 rpm idle) and the initial timing sounds pretty happy right at 15°. Starts right up when the starter gets bumped.

The throttle issue seems to have corrected itself as it goes right back down to 875 rpm after lifting off.

I might swap the 190° thermostat for something 10 or 20° cooler and a small amount of valve train noise makes me want to go back and check the pre-load on the rockers. Besides that, I’m in pretty good shape and will be ready for Hot August Nights!

Thanks again to everyone on this wonderful forum for their feedback. You guys point me in the right direction every time I have questions and it’s greatly appreciated.


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[indymanjoe]

sweet ride! enjoy it.

[steve25]

Glad to hear it's better, but why did you break in the Cam in 3 ten minute sessions ?

I have never done less then a straight 20 minutes.

Even on hot day and with running the motor unloaded it will take 5 minutes for the oil to start to flow and get kicked around up to the Cam like it should.

[Cliff R]

"Not an option as in it is a must do?"

Yes, HEI's are designed to stop the mechanical advance when the "flats" on the weights reach the "flats" on the center cam. The factory springs are strong enough to keep the centrifical force from allowing them to "roll out" on the tips and add a butt-load of timing.

There is no "stop" for the advance pin as Sun Tuned mentioned. This is a serious design flaw in HEI's and has been since they were introduced.

If the springs get weak, or you install lighter springs it's going to add additional timing at high RPM's. I'll stop here for a moment and add that there are a few HEI's that don't operate in that manner, but they are rare and not Pontiac units.

Anyhow, there are many methods to adding a positive stop outlined in various threads and on Forums. Just don't wonder over to the Chevelle site like I made the mistake of doing once and "poke the bear". He'll run you off the board and chase you all over the Internet telling EVERYONE what a STOOPID useless POS you are and that you don't know anything about building distributors or tuning these engines......FWIW.....

[Formulas]

Some HEI cams are more resistant to over advancing than others,

My own testing in a garage with only a timing light, some cams would reach full desired advance stop advancing for about 1500 rpm then start advancing again, Some other cams would add desired advance then stop and would not add anymore up to the point i didnt feel comfortable reving it anymore

So my personal experience is theoretically all HEI cams could over advance but some cams, springs,weights need more RPMs to over advance than my 462 operates at so its not an issue

I did however add stops to my higher RPM 433 HEI, have not spun it yet to verify curve

[JSchmitz]

Yep, I observed the HEI over-travel on my engine. Had to weld up the pin slots. Then, dead on repeatability.

[JSchmitz]

This has been said thousands of times I'm sure. But, NEVER EVER EVER waste your time trying to get aftermarket HEI advance weights and cams to work! Tried many years ago. Moroso, Mr. Gasket, etc. will NOT function properly. Unless someone has produced something since I attempted. Aftermarket springs and factory weights and cams are the way to go. This is after you disassemble the distributor, repair, clean, and lube it.

[ZeGermanHam]

Glad you got this sorted out, Vid! I'm always impressed by the knowledge on this forum.

Also, totally separate thing, but I noticed in your photo that your valve cover bolt spreaders are installed upside down. :-)