GM HEI: Cheap and Extremely Effective Ignition Upgrade

[Pinhead]

what if I used this ignition...

http://www.cb750ignition.com/CB450.htm

it says it uses a hall affect sensor, could I use that in conjunction with the HEI unit and DIS Coil?

another idea...
What if on the stock ignition I used two hei units and two coils, I'd have to cap off one wire tower on each coil but it would be worth it I think if it worked.

Long story short I work at GM in Michigan and would really enjoy riding to work on a GM coil. The guys at the office would get a kick out of it.

Plus my coils currently are fried and I don't feel like spending 60 dollars on a stock looking and performing system.

Cheers, thanks for the insight, obviously I'm a newb.

All of the triggering and dwell control in the Pamco ignition system is on the ignition plate. If you were to trigger the GM HEI module with the Pamco ignition, you'd get the same dwell specs as with the Pamco by itself. Unfortunately the dwell is non-adjustable and too long for the GM coil.

[elballoonrat]

so is the hei unit just a "signal booster" then? it doesn't affect dwell or resistance in a way that you can run these coils on a bike tha would only work with 3 ohm or higher coils?

cheers for the explanations. sorry about the ignorance on my part

[Pinhead]

so is the hei unit just a "signal booster" then? it doesn't affect dwell or resistance in a way that you can run these coils on a bike tha would only work with 3 ohm or higher coils?

cheers for the explanations. sorry about the ignorance on my part

In this configuration, yes, the HEI module produces dwell according to the reluctor signal.

The 4-pin modules has "dwell control" to give a longer dwell time as RPM increases to compensate for the short charge time a single coil has to fire 8 cylinders on a V8. This produces too much dwell on our bikes that spin past 8,000 rpm and, as such, is bypassed when installed with the CB650's ignition.

HERE is the notes about the 4-pin HEI module. It can seem kind of technical and hard to understand at first but it helps to understand just how this system works.

If you'd like to use HEI modules with your points ignition system (to make the points last longer and give slightly better spark), look no further than HERE. I would suggest starting a new thread about it, however, so you can get the full attention of the conversation.

[Spike]

Hello everyone first time post. I have installed the HEI system on my '79 cb650 with 4 pin modules (new) and gm coils (new). However i'm having the same problem as member "sicj" where the bike only runs when the pick ups (negative side) are not grounded but wired together. have tried other configurations as suggested to no avail. Any solutions to this or insight would be much appreciated as i do not want to damage my engine.

[klougnot]

Hi Spike I am in the process of modding the mod for a CB750 using the 4 PIN and the idea of just connecting the 2 wires with the white selves together does not seem right to me either.

I don't think it will damage the engine as the HEI are grounded to the aluminum heat sink which is connected to the frame. Does it run it the two blue / white and yellow / white sleeve wires are not connected to each other. I bet it does which would mean they do nothing on the 4 PIN setup. Can you give it a try and let us know what happens?

Also, I am having trouble hooking up my coils I know the C terminal goes to the left side of the C849 so what goes in the other slot. I am hooking this up tonight and help help would be most appreciated. Thanks!

[klougnot]

Hi Pinhead,

Only got to wire up the coils and I should be good to go. From the diagram C goes to one slot in the C849, but what goes into the other slot.

Thanks!

-Kyle

[klougnot]

Hi spike I think I got an answer to what the white blue, and yellow wires with the white band are used by the stock ignitors. Here is an excert the creator.

Stock ignitor uses the white-band wire as the input and thus triggers on a negative going voltage to start the dwell.
The stock ignitor requires a main signal that goes negative then positive.

The HEI only need a positive from the reluctant not positive then negative. My guess is that grounding them shorts out the circuit and keeps the signal from traveling into the HEI.

Full article text can be found at http://home.comcast.net/~loudgpz/GPZweb ... nNotes.txt.

Hope this helps!

[Spike]

Thank you for the help, as far as the coils the signal comes from the HEI module to one side of the coil the other side gets the 12v ignition power from black wires with white stripe. My bike will only run with the white tube wires connected but not grounded.

[klougnot]

So which side does the black wire with the white stripe, (12v+ positive) attach to left side or right? Also, the diagram show the 12v + b/w wire going to the HEI first then to the coils is this how you have it. Thanks!

[MattD]

Actually got a chance to work on the bike a bit this past weekend... finished up mounts for the HEI units, ford regulator and a generic rectifier.

CB650HEIandVR04.jpg (102.01 KiB) Viewed 8566 times

CB650HEIandVR01.jpg (102.03 KiB) Viewed 8566 times

Everything fits neatly beneath the factory seat pan and airbox. Need to finish up mounts for the coils this week and then wiring.

[Pinhead]

The polarity going to the coil, itself, doesn't matter; I'd hook up the GM coil just like the stock coils were hooked up (ignoring polarity).

As for the wires coming from the pulser coils, have you tried reversing the polarity?

Once the engine is running can you ground the negative side? I had some trouble initially getting the bike started, but once it was running it could be wired as stated in the diagram. Adding the "signal booster" solved the non-start issue.

[Spike]

Thanks Pinhead! I didn't think of that, yes I can ground the negative side after the bike is running but will not start when grounded. I have not added the signal booster circuit yet hopefully that will cure my issue. When i ground the negative reluctor wires after the bike is started it revs cleanly.

[klougnot]

Pinhead,
I made a little progress and got it to spark last night. Good news! The cam crosses the pickup's trigger just at the F mark. There is no way to statically time that I would know of since the pickup generates a small amount of voltage to signal the HEI. If the cam is moving at a snails pace it won't generate the voltage to trigger the HEI so no static timing here. At least the marks are linning up.

I'm really interested to see if the timing can be set correctly (if the timing plate fires in the same position as the points). If so, this is kind of a big deal!

Bad news is that I think I am going to put this project on the side burner till the rest of the ridding season is over. I want to take the bike to rice-o-rama and need to have it in ridding condition.

In the meantime I need to figure out of to cut aluminum to make heat sinks and brackets. Thinking of getting a jigsaw with a metal blade? Much thanks for finding this and all the help. Can't wait to see it in action on my bike!

[Loudhvx]

Hi all, Thought I'd post a quick note...

In order to get the proper dwell for the GM coils, the pickups have to be referenced to ground. The problem with this is that the signal is then a little weak for starting if the crank is turning too slowly. Some bikes will have the problem, some will not. Other factors will also affect the signal strength such as the distance between the pickups and the rotor and the strength of the magnets. There is also the possiblility that not all of the pickups are wound the same. There may be some manufacturing variations that will affect the signal during startup.

All of these minor differences in the pickups signal can make a big difference on whether it starts or not. Once it's running, the minor differences will be negligible.

By lifting the pickups from ground (by removing the ground connection, but leaving them connected together), the average DC level floats up to what the HEI terminal G floats to. This then makes the pickups have enough voltage to trigger the HEI. The problem then is that the dwell will be too long for running, and as the RPMs go up, the HEI's dwell extension will start to come into affect and raise the voltage too high. There may also be considerable crosstalk between cylinders. I would suspect the result will be backfiring and stumbling.

To avoid all of this, a temporary boost was devised to come in just during startup. That is what the diodes and resistors are for. They need to be tied to the start button to get 12v during startup.

http://home.comcast.net/~loudgpz/GPZweb/Ignition/CBheiModCavCoil.html

[Loudhvx]

Here are some of the notes I took on the 750 ignitions in case it helps to identify if the 650 is the same.

http://home.comcast.net/~loudgpz/GPZweb/Ignition/CBstockIgnitionNotes.txt