Jump to content

HEI ignition conversion

Recommended Posts

A few years ago, I converted an older street bike to a GM HEI ignition. Got the module (7 pin, but a 4 pin will work, too) at the junkyard for $7. Rigged it to the pick up coil, then to the primary side of the coil and to ground following a simple schematic. It worked great. 12 volts DC into the module is all that is needed which was easy on a street bike. Well, this weekend I experimented on a dirt bike. Disconnected the CDI system completely. Rigged leads from the pick up coil, and to the ignition coil, and hooked up a simple 12v battery to the HEI module. Guess what? It worked. Engine fired right up and ran crisp. This is an option if the CDI system ever fails. The only problem I can see, is that an HEI needs a 12v DC source. The stator alone produces AC, which is converted inside the CDI module. So either a separate battery would need to be rigged or a voltage regulator/rectified for the stator output to DC and then to the HEI. Hey, always an option if we need it. Wonder how long a separate small battery alone (with no charging system) would last powering only the HEI system; maybe all day or so?

HEI 7 pin diagram.JPG

  • Like 1

Share this post


Link to post
Share on other sites

Interesting and good to know that the Honda CDI sensor will drive the HEI module. When I was researching a Microsquirt system I was concerned about the Honda CDI sensor being able to drive a Microsquirt, or any non Honda system.   The Honda CDI has a very weak spark so opportunity for improvement.  One of my concerns is the life of the Honda CDI coil working with an inductive ignition system. There is an Australian company that sells AC and DC CDI module kits for small engines. 
Another option to the coil is a "coil on plug" unit.   Some doing Microsquirt conversions have used VW COP units and driving them a HEI or other suitable inductive unit. My CRF250X has a CDI system with COP but it is too long to hang onto a XR200 spark plug. I believe the VW unit is short enough, and with your experiment could work on a XR200. 

The ignition section in the alternator should have enough power to drive an inductive ignition and as you said would need rectifier/regulator to convert the AC to DC. Could use a capacitor as a battery substitute. 

Edited by Chuck.
  • Like 1

Share this post


Link to post
Share on other sites

I'm kinda confused about all this. The cdi ignition has been working on these bikes just fine for 40 years or at least almost 40 years. What would be the advantage to changing to one of these systems you guys are talking about? To me it just sounds like acquiring more parts, and more things to figure out how to hook up and make work. *shrugs*

Share this post


Link to post
Share on other sites
1 minute ago, Daniel627 said:

I'm kinda confused about all this. The cdi ignition has been working on these bikes just fine for 40 years or at least almost 40 years. What would be the advantage to changing to one of these systems you guys are talking about? To me it just sounds like acquiring more parts, and more things to figure out how to hook up and make work. *shrugs*

My experiment was in case CDI ever fails, or becomes obsolete, or a replacement is way expensive due to being rare. It's nice to know there is a back up. HEI is very common. Many hot rodders have fitted it to their Mopars, Jeeps, Ford's. I have seen Honda CX and GL's converted and Kawasaki KZ's converted also.

Share this post


Link to post
Share on other sites

The CDI is a very tried and true ignition. I was just experimenting with another system, just in case.  I know of people, and their are videos, of people who repair their CDI unit. Most often the capacitors start leaking or the solder joints crack; both easily repairable. The toughest part is breaking the epoxy to get to the circuit board.

Share this post


Link to post
Share on other sites

As I mentioned the XR185/200 CDI provides a very weak spark, And it is often not visible in sunlight. The plus from lower voltage spark is less risk of arcing to ground because of moisture.  But a stronger spark would help ignite marginal mixtures and could reduce flame outs and make starting a flooded engine easier.  I use fine wire spark plugs because they can provide a spark in adverse conditions. 
My pursuit of alternate ignition had more to do with the limitations of the mechanical advance mechanism for a modded engine than anything else, a 3D spark lead map can provide a more optimum spark lead and better engine performance than a mechanical advance system.

From what I've read on forums it is the Honda DC powered CDI ignitions that have the solder joint issues, not the AC powered units on our little XRs.
A CDI system sends  high voltage (could be 200volts) to the coil and the expanding magnetic field induces the high voltage spark.
The induction systems (Kettering style) cut the 12 volt flow to the coil and the collapsing magnetic field induces high voltage  spark.  So two different methods, and different coils. The CDI systems have a faster rise time for the spark which can blast thru a fouled spark plug, so are good for 2T engines.

Share this post


Link to post
Share on other sites
On 8/25/2017 at 2:36 PM, Daniel627 said:

I'm kinda confused about all this. The cdi ignition has been working on these bikes just fine for 40 years or at least almost 40 years. What would be the advantage to changing to one of these systems you guys are talking about? To me it just sounds like acquiring more parts, and more things to figure out how to hook up and make work. *shrugs*

 

Another big advantage is the readily available parts and reliability. You can get a GM 4 pin or 7 pin HEI module at any auto parts store for less than $20. By comparison, many CDI units are becoming harder to find, and when you do find one, they are $200 plus, and is 50/50 that it will work well for any extended period of time. I guess you can buy a universal CDI and modify it to fit....??

Share this post


Link to post
Share on other sites

I've done some testing of the stock CDI ignition on a mule engine and there is no spark until about 200rpm and then it is very weak; might be nice to avoid kick backs but IMO not a good spark for operation.    My thoughts are a stronger spark would help ignite a non optimum mixture, and trail riding seems to produce a lot of those events. :banghead:  So a stronger CDI, or HEI,  would fix that. [The mule engine has a crank. piston, cam, alternator, etc, but no valves, rings, clutch, or tranny. I drive it with a variable speed drill motor and use an optical tach to measure speed.]

I've thought of some CDI  mods but the weather was so good this past Summer that I spent all of my free time riding. :ride:    I probably won't be able to do more testing until next Spring. 

Some other Honda have coil on plug CDI system, and some VW have a usable HEI coil on plug.  One issue with mixing Kettering style parts is controlling dwell, which is the "on time" for current flow in the coil; too long and the coil overheats, too short and the magnetic field won't be large enough at spark time to produce a usable spark. Different controllers have different ways to control dwell, and different coils have differing tolerance for too much dwell.  Longer than needed  dwell consumes more power without producing a spark. CDI avoids the issue because it just zaps the coil with a couple of hundred volts for a spark. For those interested there is info on the web.

One of my alternatives for Microsquirt ignition was to use the MS to control spark via a HEI controller, and a VW COP. But the MS can also drive a CDI box.
And HomerDodd has shown that the Honda CDI sensor can also drive a HEI module.
 

Share this post


Link to post
Share on other sites

Chuck: 

If you do some Google search's on HEI, you'll find that the older 4 pin HEI modules (used in the mid 70s) had dwell control built into it. The 5 and 7 pin do not, as it was then controlled by the car's PCM. You can still buy new 4 pin HEI's at the auto parts store. Just find a mid 70's Camaro or similar that had the HEI system. One thing about HEI in place of a CDI is the bike will now become fixed ignition timing, as the HEI does not advance/retard the timing. If there is no mechanical or vacuum advance, then the best thing is to do is slightly advance the timing and leave it fixed. A few guys with older CB650's, 750's and Kawi's have done just that with good results. A bit of power may be lost in the upper end, but lower end and mid range is OK.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×