Mjt316

I just recently converted my distributor from points type to hei. I was wondering if the timing settings would be different than with the points type ignition. It's a 1970 Olds Cutlass Supreme with a Rocket 350. The base timing with the points was 10 deg BTC. Would it be the same with the hei. Also it keeps backfiring from the carb when rpms are raised. What would cause that?

Brians64f85

Check your firing order to make sure you do not have a wire crossed, if that checks out bring #1 piston up to TDC and check rotor position, it should be pointed towards #1 cyl. One tooth off on the dist. will cause the backfire. Good Luck. Post update.

Mjt316

Wires are in right. Piston was at TDC when I put distributor in and rotor was facing #1 spark plug when put in. What should I set the timing to?

oldcutlass

I'd set it to 16-18 deg before tdc @650 rpm, with vacuum disconnected. The back fire issue is usually 2 wires swapped, so you might want to recheck it. Did you bypass the resistor wire?

Mjt316

There is no resistor wire hooked up to the distributor. I have a wire going to a power source. I hooked it into one of the wires that was plugged into my Tcs solenoid.

oldcutlass

You need full battery voltage, and at least a 14 gauge wire. Any load on that circuit will make your car run like CACA.

Mjt316

It's hooked up to a full battery source. The wire is 14 gauge. It runs fine until you try to accelerate and then it backfires and wants to stall out.

MDchanic

Just start reading this thread here, and you will see at least three descriptions of how to set the timing on an HEI conversion and why, posted over the past 3 days.

- Eric

joe_padavano

First of all, the timing doesn't care whether the spark is triggered with points or electronically. All the engine cares about is that the spark arrives at the right time for each RPM and load condition. What DOES matter is that the HEI distributor you used almost certainly will NOT have the optimum mechanical or vacuum advance curves for your engine. For optimum performance you need to recurve the mechanical advance and get an adjustable vacuum canister.

By the way, here's one example of why modern fully digital ignition systems are better than even HEI. You can change both the "mechanical" (actually, digitally controlled replication) and vacuum advance curves by turning ***** or adjustment screws, sometimes from the driver's seat, while you drive.

MDchanic

Like in a Model T? We've come a long way!

- Eric

oldcutlass

Eric, now thats funny and very true!

joe_padavano

I think the old saying you're looking for is "there's nothing new under the sun".

Mjt316

I have got the vacuum advance going directly into the intake manifold. Do i have to recurve it to get rid of the backfiring problem?

MDchanic

If you had read my previous post and followed the link to the current thread in which this subject is being discussed, I think you would have the answer to your question, or at least have a more specific question to ask.

- Eric

Mjt316

Should I hook the vacuum advance to the intake manifold or the carburetor. Does it make a difference?

MDchanic

The answers are "Maybe," and "Yes."

Read this and this, and then see whether your questions are answered.

In the end, connect in whichever way it makes your engine run better.

- Eric

Mjt316

Ok so I set the base timing to 10 deg BTC with the vacuum advance disconnected because that's what my repair manual said to do. However this was the setting with the points distributor. When I plugged the vacuum advance in the timing advanced and the rpms raised. Do I go by the old settings or do I slightly change them?

joe_padavano

I'm going to challenge that a little. Ported vacuum uses a timed port in the carb that's upstream of the throttle plates at idle but once uncovered, it's identical to manifold vacuum. The only difference between ported and manifold vacuum is at idle (with throttle closed) and slightly off idle. I've always found my cars to run better with full manifold vacuum, but that also depends on the initial timing and the advance curve in the vacuum can.

MDchanic

So long as it's just a little...

I agree with all of this, and prefer direct manifold vacuum myself, but in answer to Part II of his question, "Does it make a difference?" I'm afraid the answer is "Yes," especially if he's got an off-idle hesitation.
Connecting it to direct instead of ported vacuum may improve the hesitation in this case.

Okay, I know I'm beginning to sound like a jerk (mostly because I am one), but did you actually read this when I asked you to here?

It is a detailed discussion of exactly your problem with another person who was doing exactly the same thing that you're doing.
In it, it very clearly said, a number of times, to ignore the specifications for the original distributor, since you have changed that distributor to a different one, which has different characteristics and requires different settings.
I am NOT going to repeat all of the detailed information that I posted last week, so you can either read them there or get someone else to repeat them here.

Once you have read them, then you can ask questions about any points of confusion or specifics of your situation.

In response to what I believe your question to be, the manual tells you to set the points, then set the timing at idle (or at 1100 RPM, depending on year and model) with the vacuum disconnected, THEN connect the vacuum and set the idle.
In your case, since you've used a different distributor, you need to disconnect the vacuum and set the timing to about 35°BTDC at about 3,500 RPM, and work backward from there, just like I repeated three times in the other posts I referenced earlier in this thread.

- Eric

Mjt316

How can I tell when it is at 35 deg BTDC. My timing marks don't go that high. I don't have a tach to tell me what the rpms are at.

MDchanic

That is covered in the posts I referenced, of course.

Easiest way is to just use some tape to measure from the 0° to the 12° mark on the indicator, then lay out that distance from the TDC mark on the balancer to 12°, then from there to 24°, then mark that spot, and line it up with the 11° mark at 3,600 RPM and you've got 35° BTDC.

Or you could just get an advance timing light. You know you're going to get one sooner or later anyway.

- Eric

Mjt316

I have a dwell tach and an advance timing light. So where should I set the dial to on the timing light.

MDchanic

That's much easier.

Set the timing light to 35° and align the 0° mark with the timing mark on the balancer,

— OR —

Set the timing light to 25° and align the 10° mark with the timing mark on the balancer,

— OR —

any similar mathematic combination of the above.

- Eric

Mjt316

Should I do this when the engine is warm or cold and should I do it when it's at fast idle?

MDchanic

Always do these things warmed up, and the idle doesn't matter, because you're running it up to 3,500 RPM, which is above any idle.

Once points (when so equipped) and then timing are set, then you set the idle, first the curb idle, then the fast idle.
Fast idle only matters while warming up on a cold day, so if you only use the car in warm weather, it is fairly unimportant.

- Eric

The_Jeremiah

I just wanted to ad my .02 cents here, I have switched a handful of cars over from points to hei, they never have a good curve, you will probably have to have your curved. if its a place like who does mine, they ask you the weight, cam, tires, gears, etc.

Mjt316

Alright so I set the timing mark at 10 deg and I turned the dial to 25 which brings that to 35 deg btdc, but the timing didn't change when I did that. Also my dwell tack doesn't go up to 3500 rpms either. So I need to know the proper settings for the timing when it's at idle and the vacuum advance is disconnected. I know I can't go by the 1970 specs anymore considering I changed the ignition.

MDchanic

Umm... you change the timing on the engine by rotating the distributor, not by turning the **** on the timing light.

This is getting to be one of those "Exactly how much do you know and have you ever worked on a car before?" threads.
We are ASSuming here that you've done some work on cars before in your life.
If our ASSumption is wrong, then please tell us, so that we can give you advice that is at your level of experience, otherwise we and you are just wasting our time.

As I said in the thread I directed you to earlier, the correct timing at idle is somewhere around 20°BTDC, but the important part of the timing is at 3,500 RPM - if you set the timing to 20° at idle, you have no idea where it really is at 3,500 RPM.

Why not just get a tach that goes to 3,500? Most do.
I've bought a number of them for $2 to $5 at flea markets and yard sales.

- Eric