I believe you have two problems BEJ.
1.) Your mechanical advance springs are too weak for an idle over about 850 to 900rpm. So what happens here is you set the initial timing at say 1100 rpm or like you say betwen 900 to 1200 since it's hunting. Now some mechanical advance is kicking in. You think you have 16* initial but in reality you only have maybe 8* or 10*. So now you drop it into gear and the rpm drops and so does you mechanical advance that should not have been present in the first place and the engine rapidly dies. Put in stronger mech advance springs. You only need to have full mechanical advance by 3000 rpm to get good performance.

2.) your vacuum advance can cannot provide full vacuum at your current idle, in gear rpm, vacuum. You may have 15" of vacuum at a 1000 rpm and the vacuum advance unit can provide full vacuum at this level. But once again you put it into gear and the rpm drops and so does you vacuum advance. So now you have only maybe 8* to 10* of intial timing due to the mechanical advance problem and the loss of vacuum, and that's it. It's gonna die every time.
The reason it's hunting is due to the combo of fluctuating mechanical and vacuum advance. It's gonna idle like crap.
You need a vacuum advance can that will give you full vacuum at the vacuum your car can provide at 700 to 800 rpm. Your probably only getting around 9" of vacuum at that rpm.
This can is available at NAPA auto parts stores and will meet your needs better more likely.
VC1843
This can will give a total of 15* of advance and is fully advanced by 9 - 11" of vacuum. It starts movement at 3-5" of vacuum.
Or another one is the VC1825
It provides 18* of advance and provides full advance by 6-8* of vacuum.

So to summarize; stronger mech advance springs, and different vacuum advance can. 95% chance this will fix your problems.

 

Scott,

Thanks for the reply. To answer your questions, all gaskets are Felpro and all vacuum lines are new. The hard line from engine to trans is the original, but while it was out of the car, I cleaned it thoroughly and noted no areas of wear or holes. Regarding the lifters, I can't answer that directly. I had the engine built by someone else. He told me that he consulted Howard's Cams and installed lifters to their specs.

Bryan

 

REELAV8R,

Interesting, and this makes sense to me. I have hunted for vacuum leaks and haven't been able to find one. I am going to give this a whirl and see if it helps. Thanks for the reply. Much appreciated.

Bryan

 

Your loss of vacuum when the rpms drop is not due to a vacuum leak, it's due to the increased overlap on your cam vs the stock cam.
As duration increases on the cam the overlap period also increases for a given lobe separation angle ie 110* 112*, whatever you have. This reduces your vacuum at idle and vacuum falls off at a greater rate as you reduce your idle rpms. so with your 270 duration cam you now have less available vacuum.
If the vacuum can you are using is still stock it was designed for higher levels of vacuum. Stock was more like 19" of vacuum at idle. Now you have 15" at idle and maybe 9" or 10" once it's in gear. You know the effect unplugging the vacuum can at idle has on the engines rpm. You are essentially doing just that when you put it in gear and drop the vacuum below the threshold level to actuate the stock vacuum advance can you are using. Now once in gear you have no vacuum advance or very little. To compensate for this you increase your idle out of gear to maybe 1200 rpms to get something sort of stable. Well that unfortunately may be starting to advance your timing due to mehcanical advance springs allowing timing to advance. So you set your timing with the light at 1200rpms by twisting the distributor to 16* lets say, only not really. You set maybe 10* distributor and 6* was due to mechanical advance. A vicious cycle that leaves you cranking down on the idle screw and getting very stinky rich exhaust at idle.

 

Your last sentence makes me believe that you have been in my garage recently. This makes so much sense. Admitedly, I'm something just below a novice when it comes to this but your explanation seems perfectly logical. My local Napa/Advance/Autozone doesn't carry a vacuum can in stock so I am going to just order a kit from Summit or Jegs that have new springs and weights included with the new can. Hopefully have it up and running by this weekend. If our paths ever cross, I'll have to buy you a beer (or beverage of your choosing).


Bryan

 

Glad to help Bryan.

I do have one more option for you if you want to give it a shot and have a little time and a few items/tools.

You can mod your current Vacuum can to start actuating whenever you want with a $1.20 spring.
The spring I used can be had at an ACE hardware store. Spring #157. It's 1 3/4" total length with the coiled section being 3/4" long with a diameter of about 3/8". any spring around this size will work.

The idea is to reduce the effort required to actuate the rod that advances your timing. In order to do this I used the spring to counteract the internal spring inside the vacuum can. It ends up looking like this.

[IMG][/IMG]

The black line represents where the dist cap comes down on the vacuum can. The hole it's hooked into is inside the distributor area.
On the 90* bend I ground in a small groove with a dremel tool for the spring to sit in so that it does not fall out. I suppose a file would do the trick too just as long as the spring sits down into the slot securely without compromising the integrity of the rod.
Looks like this.

[IMG][/IMG]

Now you need to figure out how long to make the spring to get the specs your looking for. To do this you could use a mighty vac hand pump or a simple setup like this with some vacuum hoses temporarily taken off the engine, a vacuum tee, and a vacuum guage, to get this set up.

[IMG][/IMG]

So if you know that you have 9" of vacuum at 800 rpm then you'll need to cut and bend up a new loop on the spring until you can get the rod to move full throw by 9" of suction. You'll be using your mouth to provide the suction and observing the movement of the shaft. You also don't want the shaft to move before about 2" to 3" of vacuum maybe 4" to be safe. This way at full throttle there is no vacuum advance being supplied to the engine. At full throttle your engine has almost no vacuum at all.

The next issue is often the vacuum advance provides too much advance so that at cruise your car is over advanced and causes jerkeyness or pinging at light acceleration. You can figure out your vacuum advance by observing the difference between your intial plus mechanical (with vacuum unplugged) at 3000 rpm (assuming mech advance is fully advanced by this rpm) vs the total timing with vacuum plugged in at 3000 rpm. Ie if you have 36* with vacuum unplugged at 3000 rpm and then plugged in you have 56* that would mean your can provides 20* of advance at 3000 rpm (cruise rpms)
One way to solve this over advancing problem is to cut a small section of 1/4" copper tubing and slip it over the end of the shaft that is bent up. Like this.

[IMG][/IMG]

This solution can be problematic as it can drag on the slot on the sides and make it harder for the shaft to move negating your efforts with the spring mod. So one other way to make the total movement adjustable is to egg out the rear mounting screw hole. Now you can slide the can back to shorten the total movement of the shaft. I'm still experimenting with this as this movement to the rear would affect my initial timing and require twisting the dist farther towards advance to negate having rotating the magnetic sensor in the distributor towards retard.

My current set up looks like this.

[IMG][/IMG]

One note of caution; make sure that when the rod is fully retracted the spring still has tension on it. You don't want the spring coming off and flailing around in your distributor. One could even glue the spring ends or safety wire the spring to ensure that they stay put if they were really worried about it. There already is a couple springs that spin around under there as it is and they don't come off so probably not a great concern as long as the groove is wide enough for the spring end to sit down in it securely.

 

That's quite a setup you made there. I just bought this (http://www.summitracing.com/parts/mrg-6011) from Summit. As you said, the springs on the weights probably need to be a little stiffer. Figured I might as well just go ahead and give the distributor the full treatment. Nonetheless, that is certainly an impressive bit of engineering.

 

Probably the only parts you'll need on the re curve part of that kit are the springs. Don't use those weights they are junk. Bushings maybe. If yours are worn out or missing.
The vac advance can is adjustable which is good. I have the same adjustable can with the extra spring set up. It probably won't adjust down to what you need, mine wouldn't and I'm using a 270 duration cam. Spring mod may be in your future.

 

Well if the can wont be sufficient then I will jus cancel the order and get the springs separately. Cheaper that way anyway. Of the two from Napa that you recommended, which would be more likely to work best?

Thanks

 

I don't want to quote him, but Lars reccomends 36* of timing without vacuum advance. That would be your initial plus whatever your mechanical will give you.

On my car my mechanical advance is 20* to this I add 16* of inital for a total of 36* without vacuum. In reality I started with 12* and the timing light with engine at idle vacuumadvance unplugged, ( make sure you plug the vacuum line with something) then reved it up to 3000 rpm and rotated the distributor until I had 36 degrees. Initilal ended up being what ever it was. I checked it afterwards and it happened to be 16*.
Also Lars reccomends 52* total for cruise operation. so 52*-36*= 16* of additional timing needed for cruise operation. That is optimum, realistically maybe between 50 and 52.
He also mentions some may tolerate up to 18* of initial and may tolerate up to 54* of timing at cruise for high altitude operations.
so if I were to buy one of the cans it would probably be the VC1825.
This one comes in a little earlier (6" to 8" of vacuum) and gives me the flexability of more advance if I want it. I can always adjust it down (with a bushing or some mod) I figure, but hard to add what isn't there.
You need to establish how much mechanical advance your distributor is giving you. That may be your limiting factor for how much vacuum advance your car can tolerate.
Do you have a digital timing light? If not, get one. They are worth their weight in gold when it comes to timing. They incorproate a tach with the timing. $100 at sears for one. They are pretty much that everywhere. You can get it a little cheaper on line, but then shipping will bring it up to that.
The Mr gasket re-curve kit can usually be had locally at a auto parts store. Only parts I used were the springs.
Ideally you would like the mechanical advance as early as 2500rpm without ping, but no later than 3000 rpm as long as mechanical advance is not skewing your timing efforts at idle. If you ignore initial and do as I outlined above then set idle at 950 out of gear you should end up with 850 or so in gear (with appropriate vacuum advance can) and mechanical advance won't mess with things.
Right now I got my mechanical fully advance by 2850. I'd like to get it a little earlier. So I'm still experimenting to bring that down.
Spring tension is only one factor. The mass of the weights being used is another.
You are using full manifold vacuum now or still ported vacuum?

 

I'm gonna have to retract my previous statement about discarding the weights with the Mr gasket kit. It's possible that the mass of those weights may be less. I don't have mine apart right now to check. This would allow the rpm to be higher with a given set of springs and still not have any mechanical advance at idle yet it still may achieve full advance at or near 2500. So it may take some mix and match to get just the right combo to achieve the desired results.

This just might be the solution to my own advance scenario. One could always grind metal off the Mr gasket weights to achieve different results in combination with the supplied springs.
Maybe one OEM weight and one Mr gasket weight.

 

Ok, that is good info. I will pick up the VC1825 and get on it this week. I don't have a digital timing light but I do have an inductive tach that I use to monitor rpms while tuning. A little more clunky but it works. And, manifold. I switched it over. Once I get everything in and get the timing done I will report back with results.

Thanks Again,
Bryan

 

So you have a non adjustable timing light or one with adjustable timing? If it's non adjustable then have you put a line on your harmonic balancer at 36*?

 

I have a non adjustable light but have marks on my harmonic balancer.

 

Reelav8r,

After some delay, I finally got around to installing the new springs and vacuum can. Here is what I did and the results achieved.

Pulled the distributor cover, and rotor. Wrapped a rubber band around the weights, replaced rotor and distributor cover, started and ensured initial timing at 16*. Done, good to go. Nice solid, steady idle.

Shut it down, removed distributor cover, rotor and removed springs and stock weights. Cleaned the weights up and reinstalled. There were no bushing on the weights and neither of the pair supplied with the Mr. Gasket kit would fit them. Anyway, reinstalled as found and put on the yellow springs. From what I understand they are the heaviest. Reinstalled everything, started, checked initial timing, perfect at 16*, no centrifugal advance, increased RPMs to about 3k and advance came in right at 36*. Up to now, very happy.

Also, during the above, maintained a relatively steady 15" vacuum.

Shut it down and connected vacuum line from manifold port off of carb, right beside the port for power brakes. Before I get to that, I also installed new vacuum can which I checked with a Mighty vac pump. At the lightest setting, the can moved all the way through its travel by 14". I decided to try it first without the spring trick. Started the car and got the same results as before. Idle searching like crazy.

Shut it down again, installed spring and checked with pump. Started moving right at 5" and finished around 13". Installed everything, started, reverified timing without vac advance, still good, hooked up vac, and all looked good, timing coming all in at 52-54*, can't be perfectly sure but right there. Adjusted idle down to about 900, searches a little but not as much as before, played with idle mixture screws to smooth it out a little. Jumped in, put it in gear. F&%#.

No dice, died right away. So what next? Do I need a strong enough spring on the Vac can to have it come in well before 13"? Or, could there possibly be a different problem?

Thanks,
Bryan

 

Well it sounds like you got The timing ironed out pretty good. The weights on the dist should have plastic bushings to fit the pins well. Your HEI a stock unit as far as you know?
Yes the advance can needs to be all in at around 9" or so to maintain the vac advance. Shorten the spring or get a stronger spring. You can mosify the length to what ever you want.
Are you using an adjustable vac can then?

My vac advance can is all in by 9" of vac. I modified it to only pull in 18". Originally it pulled in 22", which was too much. It also starts moving at 3" of vac.
You want to achieve an idle with at least 9" of vac. That should be about 700 to 800 rpm. You may need to set the out of gear idle at 1000 or so to achieve this. Most important is keeping the vacuum at the point where the vac can is all in.

This means your mechanical advance is 20*
It's possible you may need to shorten that later on or your initial plus vac plus mechanical may end up in the 54* to 56* range.
I know that less vac advance could do the same thing, but mine likes lots of vac advance at idle.

You could try ported advance for the vac and see how that works. The frustrating thing is that each engine is a little different. By connecting your can to ported vac and tune it that way, you may experience less loss of vac once it drops into gear because you tuned it with less vacuum to begin with. This might mean you'll end up with 18* initial advance.
I've had to modify my initial set up a little to achieve better running.
I ended up at 18* initial with 18* of vac advance and modifying my mechanical advanc down to 16*. This gave me a 52* combined timing at cruise.

The other half of the equation is carburetion . The carb needs enough fuel to idle and it may not have enough for your cam on the idle circuit. What carb are you running? Timing is half the battle then there is carb if you want really seamless running.

It took me two to three days to hone in on my timing and get it right where the engine likes it. I still may make some tweaks but for now it's good. Patience and beer....lots of beer.

 

One other thing I discovered is that the springs in the Mr gasket kit are just a little too long to provide tension on the weights to keep them fully retracted. Check yours to see if there is some slop in your weights or not. They need to be snugly held fully retracted until rpms stretch the springs to extend them.
You can slightly shorten them by making the loops on the end of the springs smaller with a a pair of needle nose pliers. This will shorten them just enough to keep the weights tight. You ned to kind of roll the open end of the wire on the loop in toward the spring. It will just fit on the pins when your done.
If there is any slop in the weights then they are adding advance when you adjust the free idle and then will drop it (retard) when you put it in gear, which will excessively drop your rpms.

 

Reelav8r,

It occured to me that I never responded to the questions in your last post. I have shortened the spring to bring can all the way in by 9", shortened the distributor weight springs ever so slightly and changed the weights out to the once included with the Mr. Gasket kit. I thought the slightly lighter weights might help in keeping the mechanical advance from coming in too early. Haven't had a chance to check the results yet, hopefully tonight after work. I'll let you know what happens.

[QUOTE=REELAV8R;1584820795]Your HEI a stock unit as far as you know?

Yes, it is the stock HEI.

Are you using an adjustable vac can then?

Yep, using the Mr. Gasket can.

The other half of the equation is carburetion . The carb needs enough fuel to idle and it may not have enough for your cam on the idle circuit. What carb are you running?

I am running the original Quadrajet. It was recently rebuilt by Lars.

Thanks,
Bryan

 

Excellent! Did he rebuild it for this cam or for the stock cam?

 

I gave him the specs for my current setup (dual 2 1/2 exhaust, no cat, 64cc aluminum heads, this cam, no egr, etc)