RM250 HEI conversion

My '96 RM250 CDI started giving problems last summer. Used CDI units are a gamble, and not cheap. Have read about many street bikes being converted to GM High Energy Ignition (HEI). So I bought a used 7-pin module at the junk yard for $7.00, just for testing for this project, but I will buy a new 4 pin module now that I know it works. 4 pin has the advantage of dwell control. Rigged it to the existing pick-up coil, made a wiring harness and have temporarily rigged it (see the pics; will be a cleaner install in the next few days). Started on first kick. Nice crisp idle and throttle. Slight stumble in the mid range, which may be jetting, but might be an ignition advance problem. The CDI normally controls advance and HEI has no advance capability (done by the car's computer). I have read quite a bit about two strokes and learned they do not need the advance the way a four stroke does, and several earlier two strokes had fixed timing, no advance at all. I am going to slightly advance and retard the timing by trial and error, until I get it sounding good. The stator now sends AC voltage to a regulator/rectifier I bought online for $10. The output is 14 volts DC for the coil and HEI power supply. One of the best advantages of HEI is the readily available modules. Any auto parts store sells theme less than $20. If one goes bad, simply buy a replacement at O'reillys, Napa, Pep Boys or Auto Zone. 

RM250 HEI  6.JPG

RM250 HEI  5.JPG

I gotta give you a thumbs up just for getting this to work!  I am a little concerned about the mounting plate covering up so much of the air filter, possibly restricting too much air flow, but still a very cool project!  Looks like you need to find some dyno time to work on the ignition curve. 

1 hour ago, zig06 said:

I gotta give you a thumbs up just for getting this to work!  I am a little concerned about the mounting plate covering up so much of the air filter, possibly restricting too much air flow, but still a very cool project!  Looks like you need to find some dyno time to work on the ignition curve. 

Could prolly drill holes once the final fitment is known. 

Edited by shrubitup
3 hours ago, zig06 said:

I gotta give you a thumbs up just for getting this to work!  I am a little concerned about the mounting plate covering up so much of the air filter, possibly restricting too much air flow, but still a very cool project!  Looks like you need to find some dyno time to work on the ignition curve. 

 

Hey thanks ! Yes, the airflow is a concern to me, also. I played around with the timing a bit today, played with the air screw and got rid of the stumble. I advanced the timing just a few degrees and it really helped. It rev's clean now. Now that I know it is working as planned, I am going to trim away a large unused area of the mounting plate for better airflow, and install the wiring clean and professional looking.

Edited by HomerDodd
23 hours ago, HomerDodd said:

My '96 RM250 CDI started giving problems last summer. Used CDI units are a gamble, and not cheap. Have read about many street bikes being converted to GM High Energy Ignition (HEI). So I bought a used 7-pin module at the junk yard for $7.00, just for testing for this project, but I will buy a new 4 pin module now that I know it works. 4 pin has the advantage of dwell control. Rigged it to the existing pick-up coil, made a wiring harness and have temporarily rigged it (see the pics; will be a cleaner install in the next few days). Started on first kick. Nice crisp idle and throttle. Slight stumble in the mid range, which may be jetting, but might be an ignition advance problem. The CDI normally controls advance and HEI has no advance capability (done by the car's computer). I have read quite a bit about two strokes and learned they do not need the advance the way a four stroke does, and several earlier two strokes had fixed timing, no advance at all. I am going to slightly advance and retard the timing by trial and error, until I get it sounding good. The stator now sends AC voltage to a regulator/rectifier I bought online for $10. The output is 14 volts DC for the coil and HEI power supply. One of the best advantages of HEI is the readily available modules. Any auto parts store sells theme less than $20. If one goes bad, simply buy a replacement at O'reillys, Napa, Pep Boys or Auto Zone. 

3tcurves.gif

The RM250 there is a PowerJet version with TPS but you get the idea.

Interesting. Please keep us posted!

Looking forward to further updates, dyno tuning....

Edited by BRAAPZ
Typo
4 hours ago, redrider144 said:

3tcurves.gif

The RM250 there is a PowerJet version with TPS but you get the idea.

Based on this chart, I may just fix the timing at about 12-17 degrees and live with it........what do you think?

3 hours ago, HomerDodd said:

Based on this chart, I may just fix the timing at about 12-17 degrees and live with it........what do you think?

15-17 might not be a horrible compromise.  A retard circuit sure would be nice though.  With fixed timing you’ll definitely be leaving hp on the table.

Edited by redrider144
8 hours ago, redrider144 said:

15-17 might not be a horrible compromise.  A retard circuit sure would be nice though.  With fixed timing you’ll definitely be leaving hp on the table.

Good info. I know the  7 an 8 pin HEI include a pin for retard ability known as "EST" (electronic spark timing) which receives an input from the the vehicle knock sensor and retards the timing 10 degrees. I have read somewhere (gotta find it again) that some guys have built a resistor/transistor combination to input into the EST pin and retard the timing below the fixed amount they put it at. That may work as an alternative. I'm going to research it a bit more, as that may be the best compromise, without having to install mechanical or vacuum advance (that would be a pain in butt !).   Here is a good link that explains details of all the HEI modules (except 5 pin, not used much):  http://www.useasydocs.com/details/GM_7pinHEI.htm

 

Edited by HomerDodd

Why could you not have used a chineese  cdi from one of there two stroke scooters, there are even today replica cdi available for yamaha blaster yfs200 which cost a few dollars, I have my doubts how bike specific a 2T cdi actually is,so long as you are using a AC CDI ,its pretty easy to adapt the wiring.

Similarily what you have done is convert to a DC CDI system..so you could have used any dc CDI as well and they are cheap and would think would have adance /retard capabalities.

No disrespect,just that ive been working bikes for more than 40 years and not familiar with HEI... and why you would use it advantage wise over the cheap alternatives available.

Interesting though and please keep us posted, maybe theres something we  can all learn.

2 hours ago, mike levy said:

Why could you not have used a chineese  cdi from one of there two stroke scooters, there are even today replica cdi available for yamaha blaster yfs200 which cost a few dollars, I have my doubts how bike specific a 2T cdi actually is,so long as you are using a AC CDI ,its pretty easy to adapt the wiring.

Similarily what you have done is convert to a DC CDI system..so you could have used any dc CDI as well and they are cheap and would think would have adance /retard capabalities.

No disrespect,just that ive been working bikes for more than 40 years and not familiar with HEI... and why you would use it advantage wise over the cheap alternatives available.

Interesting though and please keep us posted, maybe theres something we  can all learn.

 

I actually gave thought to that. But I was not sure which CDI unit would work, and how to adapt the wiring. I would never want to buy a used CDI, although several people have opened them and repaired leaking capacitors, cracked solder joints, etc. As far as the power, I have made a 14.5 volt battery pack from nine AA NiCad batteries for starting, then the stator charges it from there, so it always starts on the first or second kick. The stator to HEI will not start on it's own without a battery pack or large capacitor. That is one disadvantage, but not really a game changer for me as I made it all fit cleanly. Do you have a specific recommendation or link for a cheap CDI box that I could easily adapt? The HEI was simply an experiment. I may or may not stick with it.

Ahhh... Now that you've mentioned you're running a battery it makes a bit more sense to me. My first thought is how the hell can it even run when every component from magneto to coil, is being used in a way it was never designed, or intended to be used. 

Magneto CDI and induction ignition (while similar) operate under different principles. Induction, (HEI, points, etc,) use low voltage, high current, (think of the coils used in this type as a battery) voltage is introduced, building up a magnetic field, current cut, which collapses field, producing spark.

CDI coils, think of as a step-up transformer. High voltage, low current, is suddenly introduced into a primary winding with very little resistance, causing such a disruption, that secondary windings produce spark. 

You didn't mention if you've rewound magneto, but if not, this I would expect to be the first point of failure. They are designed to provide high voltage, low current. I would think dropping voltage so low by trying to send full current through a HEI to a CDI coil (low resistance) is basically like shorting it out. Will work for awhile, but eventually heat will kill it.

Now you could rewind magneto, or use a step-down transformer (drop voltage-raise current) but you will still need battery, or large cap so a steady current can build up a magnetic field in a inductive ignition type coil. And, in the end, you'll still have no advance or retard.

Sorry to be a "Debby downer", but I think it would be wise to stick with CDI, like what mike mentioned earlier.

I don't know of any cheap Chinese CDIs' that would work, but Zeeltronic makes some pretty awesome high performance universal CDIs that don't break the bank. For under $200 shipped he could make a pre-programmed magneto type CDI, or for about $10 more, a programmable unit, add another $50 for handheld programmer, and you truly would have something that could be dyno tuned to extract every last HP.

Im running a programmable Zeeltronic DC-CDI on my 98 RMX. Love it!! Best mod I've done to the bike..

Post about it is on page 2 if you want to read...

 

Oh, and you need 10 Ni-cad cells for a 12v system. Normal charging voltage is 1.5v per cell, fully charged Ni-cad is 1.25v. Times these #'s by 10 and you get 15v. charging, and 12.5v. for full battery pack. Basically spot on for a 12v SLA alternative.👍 

30 minutes ago, Jeremyf1 said:

Ahhh... Now that you've mentioned you're running a battery it makes a bit more sense to me. My first thought is how the hell can it even run when every component from magneto to coil, is being used in a way it was never designed, or intended to be used. 

Magneto CDI and induction ignition (while similar) operate under different principles. Induction, (HEI, points, etc,) use low voltage, high current, (think of the coils used in this type as a battery) voltage is introduced, building up a magnetic field, current cut, which collapses field, producing spark.

CDI coils, think of as a step-up transformer. High voltage, low current, is suddenly introduced into a primary winding with very little resistance, causing such a disruption, that secondary windings produce spark. 

You didn't mention if you've rewound magneto, but if not, this I would expect to be the first point of failure. They are designed to provide high voltage, low current. I would think dropping voltage so low by trying to send full current through a HEI to a CDI coil (low resistance) is basically like shorting it out. Will work for awhile, but eventually heat will kill it.

Now you could rewind magneto, or use a step-down transformer (drop voltage-raise current) but you will still need battery, or large cap so a steady current can build up a magnetic field in a inductive ignition type coil. And, in the end, you'll still have no advance or retard.

Sorry to be a "Debby downer", but I think it would be wise to stick with CDI, like what mike mentioned earlier.

I don't know of any cheap Chinese CDIs' that would work, but Zeeltronic makes some pretty awesome high performance universal CDIs that don't break the bank. For under $200 shipped he could make a pre-programmed magneto type CDI, or for about $10 more, a programmable unit, add another $50 for handheld programmer, and you truly would have something that could be dyno tuned to extract every last HP.

Im running a programmable Zeeltronic DC-CDI on my 98 RMX. Love it!! Best mod I've done to the bike..

Post about it is on page 2 if you want to read...

 

Oh, and you need 10 Ni-cad cells for a 12v system. Normal charging voltage is 1.5v per cell, fully charged Ni-cad is 1.25v. Times these #'s by 10 and you get 15v. charging, and 12.5v. for full battery pack. Basically spot on for a 12v SLA alternative.👍 

I added a single phase three-pole winding on the empty poles of the existing stator. I used 18 gauge magnetic wire, with about 25 turns per pole, alternating clockwise and counter clockwise. Makes about 16 volts at idle, rises to over 25 volts. Goes directly to the voltage regulator, where the output is 14 VDC. That charges the battery pack. My AA batteries are higher voltage, as nine of them in the pack indicate 13.4 volts. It works the way a lighting circuit on a dual sport would work. Your right; thinner wire exciter coils are for high volts, low amps directly to the CDI. I still have that coil, just not used at the moment, so I can easily revert back to the CDI. The stock Suzuki pick up coil works with the HEI, but is polarity sensitive. Must be connected correctly or it wont spark. Remember, this is just an experiment project. The idea came from guys with older street bikes that converted to HEI, due to discontinued ignition parts for those bikes. I may ride it and see how I like it. If not, easily re-install the CDI. Only a few hours to swap it out, not that I have everything built and tested.

Edited by HomerDodd

JeremyF1 ..great imput ..and sounds overly complicated, in our workshop we often get bikes where there is no parts availability...Im based in Namibia.. so u need to make a plan

CDI super easy to wire up, unles u have a scoot with extras like tps or auto other items like carb fuel heaters etc..  If you have the stock stator on a 2t ,theres only one excitor coil..which is power input black and red wires and then your pulse generator a green and a blue wire (or blue with yellow stripe)  other than that a gound (dark green) and then the output wire ..being black or orange....also a black with white stripe goes to kill switch.....this holds same for 99% CDI

the YFS 200 cdi is commonly available for under 10 USD...can buy on aliexpress im sure or some other importer doing chineese aftermarket parts..check ebay also...cheers

 

Ok. That explains why the magneto hasn't burned up. Good job winding yourself lighting coils!!

Not familiar with AA Ni-cads that are higher voltage. My 10 cell pack will read higher just after charging (surface charge) but settles out to 12.5v.

Pickup coil should work with reversed polarity, only difference should be that it's receiving a +v signal as it approaches trigger, rather than leaving trigger.(maybe not with your setup) Found out the expensive way which way to wire on my RMX. Zeeltronic required (+) signal first. I wired red to red and green to green not knowing this makes (-) signal first. Bam!! Busted kickstart lever. lol. 

 

Also learned it's damn near impossible to start a kick start engine with a timing map. Thought I could get away with not using the direct fire mode (0* advance) the original PDCIS-11T had up to 2000 RPM by programming a conservative timing map. Wrong!! There's just too much RPM fluctuation with only one signal per revolution. Timing was all over the place... Really has to have the direct fire mode. Problem with that is timing was limited by the short trigger. Fixed that by having him program a start retard function. Calculates RPM over the short trigger rather than + to + signal. Works slicker than sh!t :)

2 minutes ago, mike levy said:

JeremyF1 ..great imput ..and sounds overly complicated, in our workshop we often get bikes where there is no parts availability...Im based in Namibia.. so u need to make a plan

CDI super easy to wire up, unles u have a scoot with extras like tps or auto other items like carb fuel heaters etc..  If you have the stock stator on a 2t ,theres only one excitor coil..which is power input black and red wires and then your pulse generator a green and a blue wire (or blue with yellow stripe)  other than that a gound (dark green) and then the output wire ..being black or orange....also a black with white stripe goes to kill switch.....this holds same for 99% CDI

the YFS 200 cdi is commonly available for under 10 USD...can buy on aliexpress im sure or some other importer doing chineese aftermarket parts..check ebay also...cheers

 

Thanks,

You mean the new CDI I'm running complicated?

Yes I did get carried away with having Zeeltronic add all its capabilities, but none are actually required to make it work on any 2t.

Only needs 6 wires connected to perform as a basic DC-CDI.

not overly complicated Jeremy... im an old f#rt and my head gets bemuddled and sore with all the electronic chat & technical engineering stuff and loose concentration.... hee hee!

 

10 hours ago, mike levy said:

JeremyF1 ..great imput ..and sounds overly complicated, in our workshop we often get bikes where there is no parts availability...Im based in Namibia.. so u need to make a plan

CDI super easy to wire up, unles u have a scoot with extras like tps or auto other items like carb fuel heaters etc..  If you have the stock stator on a 2t ,theres only one excitor coil..which is power input black and red wires and then your pulse generator a green and a blue wire (or blue with yellow stripe)  other than that a gound (dark green) and then the output wire ..being black or orange....also a black with white stripe goes to kill switch.....this holds same for 99% CDI

the YFS 200 cdi is commonly available for under 10 USD...can buy on aliexpress im sure or some other importer doing chineese aftermarket parts..check ebay also...cheers

 

Cool ! Do you have a link for this CDI and who sells it?,  Is that wiring color code you described compatible and will mate up with the Suzuki wiring? I might as well buy one of these. Are they fairly dependable for at least a few years? I agree with you on the CDI advantage; they have the timing curve inside, so that is definitely the advantage over HEI. Always nice to have a back up, and right now my HEI set-up runs pretty strong. Will do some track and trail testing and report back.

all cdi  are same basically holds good for most honda/yamaha/eastern bikes, so any similar 2T should be workable

 99% of time as said

green  & blue with yellow stripe are pulse gen

black with white stripe = kill switch

orange(or brown) output to ignition coil

Red with black stripe(or red) power from stator

black ground

if your colours differ, easy to pick up your colour code from your wiring diagram..

on blaster cdi pulse generator is grounded on one end other end methinks is white /red...so ground wire(blk)  will be grounded& PG secondry wire... that could be only difference to yours.( im not sure how your original looks)

https://www.aliexpress.com/item/New-Arrival-HP-CDI-Box-For-Yamaha-YFS-200-Blaster-1996-1997-1998-1999-2000-2001/32739995371.html?spm=2114.search0104.3.9.Dkh7ua&ws_ab_test=searchweb0_0,searchweb201602_5_10152_10065_10151_10344_10068_10345_10342_5660015_10343_10340_10341_10541_10562_10084_10083_10561_10307_10060_10155_10179_10154_10056_10055_10539_10537_10312_10313_10536_10059_10314_10534_10533_100031_5650015_10550_10103_10073_10551_10102_10552_5670015_10553_10554_10557_10142_10107-10552,searchweb201603_17,ppcSwitch_5&btsid=c70e35d9-879e-4b4e-802f-9141c705d3da&algo_expid=39ab9e00-6728-40f3-af10-b1686b0c931c-1&algo_pvid=39ab9e00-6728-40f3-af10-b1686b0c931c

https://www.ebay.com/sch/i.html?_odkw=yamqaha+blaster+cdi&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xyamaha+blaster+cdi.TRS0&_nkw=yamaha+blaster+cdi&_sacat=0

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