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Discussion Starter · #1 ·
I read the posts regarding vacuum advance, but still having problems. I just installed a new HEI in my 225 and it runs better without the vaccum advance, and I can't figure out why. It stumbles off idle pretty bad with the vacuum advance, which I have ported. Is there away to delay the advance off idle? I confirmed that the HEI is an odd fire. The pole piece has 3 tabs, then 6 on the ouside that are evenly spaced. I am running the the 2G, but I need to confirm that that I have a return fuel line that is not blocked and going back to the tank.

FYI, It was running pretty rough just after I installed the HE, with a new coil. After it ran awhile, it stalled and I lost spark. Turned out I had a bad new coil. I really hate problems like that. Also took the fan off while installing the HEI and I figured that I could just use the Hayden to keep it cool. Noticed that when I walked by the grill, that it almost blew my hat off. Seems that that my pusher came from the factory as a puller. New parts are not making this any easier!

Thanks.
 

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If you have six on the outside that are evenly spaced, then you might have a combination of odd & even-fire parts in your HEI. Click http://tellico.off-road.com/wwwthreads_uploads/12-411290-ODDEVEN.JPG to see RRich's artistic impression of odd and even fire differences, (thanks to RRich for posting this).

Make sure you have all the correct parts first. Then have the distributor re-curved by a competant tune-up shop. The 231 was designed to take more mechanical and vacuum advance than the 225, so without recurving the mechanical and replacing the vacuum advance can, you'll put stress on the crank of the 225. Make sure that the distributor is installed correctly as it will run if it's off a cog from where it's supposed to be. It will also run if the plug wires are off as I found out yesterday when trying to get a 225 running better, (previous owner had wires crossed).
 

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Tim you hit it dead on the head. 6 evenly spaced around the outside is definatly an even fire, but the 3 points on the shaft are an odd fire. It will trigger as an even fire. Take it back to where you got it, as Tim said, the parts are mixed.

Funny, I read it, but it didn't "click."

Also, just installing a stock HEI isn't enough, it will stumble as you said.

The 2G carb has too strong a vacuum for the HEI. The carb originally used with the HEI has a weaker ported vacuum.
What's happening now, in addition to timing 3 cylinders wrong with the above, the advance comes in way too fast, causing a bad stumble. It runs better without any vaccum to it.

The cure is easy, costs about $20. (After you get the right distributor.)

1. Get a Crane Adjustable Vacuum Advance for it. If I remember right, you need to turn the adjusting screw all the way counter clockwise - to the LEAST SENSITIVE position. Verify with the instructions - they show the slowest curve, use that one.
It's been awhile since I've done one, so I might have said it backwards. The least sensitive position will be perfect for the strong ported vacuum on a 2G.

2. Second, and A VERY IMPORTANT STEP. The Crane comes with a little cam, a limiter, that goes under one of the mounting screws. The Crane without that limiter will give about 30 degrees of vacuum advance, waaaay too much. Intall the limiter so it only moves about 1/2 way, or slightly less, or about 15 degrees.

3. Use the stock advance weights with the stock advance springs. Do not follow the advice of the kid at the parts house trying to sell you a weight kit, that's good for drag racing, but not off roading with an oddfire.

I've done quite a bit of experimenting on a dyno, scope, exhaust anayzer, and distributor machine to make sure that's the right curve. Turns out it's simple, takes less time than it did to type this.

(Same goes for putting an HEI on an old SBC too. Done that quite a bit.)

Soooo - You need a different distributor WITH THE RIGHT PARTS IN IT, and a Crane Adjustable Vacuum Advance and 10 minutes to "dial it in."

Enjoy.
 

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Rrich,
Is the vaccuam on the 2G to much for any HEI? or just for the 225 conversion? I went back to a 2G on my 4.1L. I never did get my HEI curved for my motor. The distributer is a 79 231 in the 83 4.1L. Is this grounds for recurving, or are the years bout the same for the distributer cureves?

I got all the ignition stuff put in the jeep and it runs real good now. It does stumble and cough when i stomp in the gas, but it seems to only happen at a stop. And it seemed to happen when the engine wasnt that warm. Also with the stumble it will pop inside the carb/air filter housing? I had that problem before with my 225, but i forgot what i did to stop it. It will come back to me at sometime.

Dan Stewart 1963 CJ5 "Caloosa Jeepers" member
 

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Yes.

The ported vacuum source's curve is a characteristic of the 2G, not the engine itself.

The 2 G was used on lots of smaller motors in those days, the days preceeding HEI, even as big as 283 V8's and possibly 327's, not sure on the 327's though. It was a very popular carb. But it's days were before HEI.
When HEI started as common production in 1975 carb's had changed significantly, the ported vacuum had a lighter vacuum. At that time they were trying to run everything, heater, AC, headlight doors, etc. off of vacuum. Strong vacuum was getting scarce.

The older carbs had a strong ported vacuum. The end result is at idle the vacuum is around 3 or 4 inches. At just slightly off idle the stronger ported vacuum of a 2G goes to about 8", then as the throttle is opened further it increases as the plates open more, peaking at about 14-15" at about 1/3 open throttle.

The newer carbs had near 0 at slow idle, then slowly increased to about 8" - 10" at 1/3 throttle.
The HEI was designed to fit that curve.

So you can see the older carb would "slam" the HEI to near full advance way too soon, causing what's called "tip in" stumble.

When accelerating you don't want much advance.

It's not commonly known, but more than 1/3 throttle the curve goes down again to near 0 again at full throttle. 1/3 throttle is cruise with light load, like freeway driving. When you punch it, you need LESS advance for power, the vacuum goes away, then the only advance left is the mechanical advance system.

Sooooo - the 2 advance systems are curved for different purposes. The mechanical system is curved for maximum power, it's always there no matter what, and advances about 15 degrees from initial till about 2500-3000 RPM.
Then after the mechanical is established, the vacuum curve is added on top of that - usually about 15 degrees more at about 3000 RPM - to maximize efficiency under normal light load conditions - essentially to increase fuel milage. That curve is determined by fuel consumption measurements and emissions. Lower emissions means better efficiency.

When you punch it, you don't care about mileage, the ported vacuum goes away, reverting to the max power curve of the mechanical.

In no event should it go much over 35 degrees total advance. Yes race cars, especially drag cars go way over that figure, but they aren't trying to get 100,000+ miles out of them. 2 or 3 1/4 mile passes are all they are looking for. I've dyno'd several that we ended up with a fixed 52-55 degrees - no advance system, just initial is also final. Max power at 8000-9000 RPM. (Yes, Starting was a problem, you get it spinning with the starter as fast as possible, then switch on the ignition - they idle about 3000 RPM, but they do their "running" at the high R's.)
Stock engines don't see that speed and can't take the cylinder pressures created by that much advance, it blows the rings right off.

Back to stock:
The idea is advancing as much as possible helps mileage, but too much causes destructive ping.
On late model systems with Electronic Spark Control (EST,) electronic timing, the computer keeps trying to advance the timing as much as it can (once it's in closed loop.) There's a tiny microphone on the intake manifold called the "Knock Sensor" that listens for ping. Whenever it hears ping or knocking it pulls the timing back, (less advance,) about 5 degrees each time it hears a knock. Then the computer tries on each subsequent firing to advance it another little bit - till the knock sensor hears another one, then back it goes again.
The result is the system is staying as advanced as possible without ping at all times under all loads, creating the best efficiency it can. It's neat and works very well.

One project I've always wanted to develop is an HEI EST system for older cars. It would only require a 7 pin module, a knock sensor, and a control box, fairly easy add-ons. How'd you like to get 25 MPG with your Jeepster? It may be possible with such a device.

Interesting trivia - HEI first came out on 1968 Pontiacs, in very limited production - a different "version" of what we are familiar with. Less than 500 were made, lots of troubles, unreliable, no parts, nobody understood it. All but a few were recalled and replaced with standard ignitions.
They tried another attempt at it in '72 I think, even less issued, then recalled them as well. Then in '75 they became standard equipment on most everything - perfected to the max. There's lots of rumors going around about how HEI has so many problems, spread by folks that sell other types of ignitions, mostly bull!

If you suspect the tip-in stumble is advance related, simply try it without any vacuum on the distributor, --- goes away, that's it!

OK, more than you ever wanted to know, but hopefully it creates a better understanding of advance, and hopefully it helps someone.

By the way, most shops with a distributor machine like to sell you a "recurve" job. As a friend of mine with a carb shop agues with me all the time about it. He puts in a "curve kit" with lighter weights and springs, giving it a much faster curve. He usually ignores the vacuum advance, never tries to match it to the carb at all. Then he has the customer drive it hard on the street, yes, more power revving up through the gears at wide open throttle like a racecar (maybe.) The "tip-in" stumble he creates he gets around by putting a 15 second vacuum delay valve in the advance hose, covering up the problem like a cat does. If the customer still feels a slight stumble, he sells them a re-jet job. Flooding it with more fuel helps cover it up.

 

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Rrich,
Very good info, my measly little mind is still in a flurry of tech talk, but that is just fine. I am getting that ping and i did time my engine. So when you mentioned that if i disconnect the vacuum to the distributer and the ping goes away, Can I run without the vaccuum hooked up? I have a buddy with a 258 6 in his jeep with a big cam and he doesnt run the vacuum advance at all. So if i can run without the vaccuum and no ping, then i am OK? or do i still have to get an adjustable vaccuum advance. The jeep does want to die when i stomp on the gas, when i ease it in, it runs perfect. Interesting.

Dan Stewart 1963 CJ5 "Caloosa Jeepers" member
 

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2G's were used on 350's as well. My Buick 350 Waggie had a 2G on it. Of course the cfm was more than what was used for a 225.
 

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Yup, won't hurt a thing without the vacuum advance hooked up. You won't get quite the mileage you'd get with it set up properly, but could even get more than what you've been getting so far - if the advance has been detrimental thus far. And - drivability will be better and you won't be taking the risk of destructive ping.

If it runs better without it, that proves it's advancing too fast.

Tip-in stumble isn't always due to advance, but yours sounds like it. It can also be carb problems, like accelerator pump circuit, or transfer circuit problems. Even a bad coil wire or coil etc.

Interesting thing - an engine for maximum efficiency needs the max cylinder pressure to occur about 37 degrees after top dead center. That's with only a small "charge" of air/fuel and very light load.
For max power it's somewhere around 25 degrees - with a bigger "charge" of air/fuel.

Since the A/F mixture takes a relativly constant time to burn, the faster the engine goes the earlier we have to light the fire. Like a barbeque, it takes time to get it at max heat, the more coals you pile on (charge), the longer it takes.

The big bad engines are stuffed with a much bigger A/F charge and spin faster, that's why they take so much more lead time.

350? That's kinda small for a 350, but would give great throttle response and efficiency since the velocity is so fast. I'll bet putting a Q-Jet on makes a world of difference!
Seems like someone posted there's 4 different 2G's, but all are a bit small for a 350.
 

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By the way, sometimes vacuum advances act strange with a tall cam. The reason is the vacuum source is "bouncy," the timing ends up "bouncy" too. (The vacuum's bouncy because the carb's constantly switching from the idle circuit to the transfer circuit, then back - due to the "big gulps" of air. The distributor just does what it's told by the vacuum.)

The simple cure, put a 5 second vacuum delay valve in the advance hose to even out the "bounces." Available at most any decent parts house, late 70's Fords used them all over. Or you can use a very long big hose to accomplish the same thing, you just want to "smooth" out the signal.
The idle will smooth out and you'll get better mileage, considering of course the curve from the carb is matched to the distributor. If no help, again the Crane - with the limiter installed, does the trick.

The only time you can run the adjustable advance without the limiter is if you don't have any mechanical advance whatsoever, else it's waaaay too much advance.

The other trick to take out the "rumpity rump" of a big cam is lengthen the transfer circuit slot slightly downward, just a touch. Yes, you can make a big cam purr like a kitten if you want, it takes some - lots - fiddling, but it's possible.

Some folks just put manifold vacuum on the distributor with a tall cam, then wonder why they don't have any bottom end.
 

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I just drove my jeep over to my buddies so they can throw it on thier trailer for our ride tomorrow. i will take off the vaccum and run it like that. I dont know what kind of cam i have, but the timing does seem to bounce, but i have to check it for a loose chain first to get that out of the way.

Tim had that info about the 2Gs pretty interesting about how many varieties there are.
How exactly does the dirstibuter ground to the engine. I as thinking that i need t oground the distributer better, that may be why i fried my last coil.

The jeep was running really good today except the exhasut is a little rich. And It seemed to have some of that PING when i was going over the bridge. Usually i have no problem, but when i replaced all the ignition stuff, the power just doesnt seem to be there, I didnt have that PING when I went over the bridge other times. Hopefully it will go away with the vaccuum disconnected.

Thanks for the help
Dan Stewart 1963 CJ5 "Caloosa Jeepers" member
 

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The ground for the distributor is the housing is bolted down tight to the block. No other ground needed. The HEI module grounds through the mounting screw.

Except - if you have points, you'll notice a braided strap running from the breaker plate to the dist housing inside. Give it a tug, they do break 'cause it flexes every time the vacuum moves the plate. They are available at parts houses cheap. If it's broken, it can also give you a stumble - sorry, I forgot about that.

But, that won't burn a coil. The wrong, or none, ignition resistor will burn a coil on a points system.

HEI uses no ignition resistor, needs a heavy gauge straight 12 volts. But, a poor quality coil's insulation isn't very good, they burn through easy. Whenever possible use Delco. Echlin would be my second choice. Avoid the aftermarket rip off stuff, "pink" as it were, like Accel.
 

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Discussion Starter · #12 ·
I meant to say that the 6 points are "unevenly" spaced, and that I do have a Crane adjustable advance. It was a long day.

I think Rich hit it right on the head with the total vacuum advance being too much and too soon. I forgot to use a hand vacuum pump to check and see how much advance I had so I could limit total with the cam. I also forgot about the vacuum adjustment for sensitivity. I will check it all out tomorrow and report back.
 

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Discussion Starter · #13 ·
I've got the engine smoothed out with the HEI, but still having problems. It is still starting hard when hot, and once I have it running at a smooth idle, it stalls when I put it in gear. This was a problem before the HEI.

The basic timing is set at zero/5 degrees advance and then 10 degrees advance. Idle is set at 800 rpms. Runs smooth and stalls when I put it in gear. Tried a lower flow PCV valve from a Chrysler 4 cylinder, but it still starts/stalls when I put it in gear. It idles much better at 10-12 degrees advance, but will not restart hot. It turns over well, but has a hard time catching, like it is starving for fuel.

I have the vacuum advance set less than half, and I guess that it is about 8-10 degrees. Cam is at full prevent to stop the vacuum advance total. I even tried a bleeder orifice to delay the advance, and it still stalls going into gear.

Any suggestions? I feel like I am close, but I'm not sure what to chase next.

Thanks
 
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