Outboard Motor Ignition Ideas

[HarleyJack17]

Yes this waaaay off topic but I know there are some pretty smart folks on here, and maybe this will be a thread with a lot of info/learning. Or it may die in the interwebs hahaha.

Motor: Suzuki Outboard DT25 Horse Power circa 1990 (3 cylinders) 3 Carburetors
Ignition: CDi with Rev Limiter and electronic Throttle Position Sensor to control timing

I am wanting to build a hot little two stroke out of this outboard, assuming I can.  However, I am going to hit a wall with the rev. limiter.  The rev limiter is built into the cdi unit and is around 5700-6000 rpm.  Porting and modifications really predict the need to turn the motor to a higher RPM beyond this to get max gains and meet my goal(6,500-7,000).  There used to be a company that could "crack" the rev limiter but many times it resulted in killing the CDI unit....it is potted and I suspect that removing the potting was the risky part. That company no longer exists and cdi units are obsolete.  In short, the rev. limiter is the wall and will negate any port work.  I can make it faster, but not as fast as wanted due to this.

As I am told(some I know) the design is 3 points under the flywheel(triggers), a TPS on the center carb that shows reduced voltage.  The cdi handles the charge, but the voltage from the TPS handles the timing, to a point. TPS spec is .47-.5 volts at idle and above 2.7 at full throttle.  Since bypassing the rev limiter is a risky ordeal, if even possible, I am wondering IF, or HOW one may could build a system around what is in place.  Online there are plenty of cdi units, but very few operate on a 3 cylinder design.

Just curious as to how to approach eliminating the OEM and building something that would work.  I estimate timing needs to be 2.5/5 degrees at idle and 27 ish at top end.  Since it seems much like a car, and I know many have done things for FI etc. on this forum, why not ask. 
I did have the thought to take a design from say a Yamaha and see if I could adapt it, and eliminate the TPS all together and use manual timing events. Limitations on that route would be the crank end, flywheel differences, fab work, and most likely not possible. Ideally an electron bolt, or possibly programable solution would be best.  The items are in place, but I have no clue on what is available.  Cost is somewhat a factor as it would be irrational to sink $1000 into it. A few hundred however is easily doable.

On one hand it makes for a performance modification, on the other it opens the window to fill a gap in an obsolete part. Plenty of these motors running around and they are sought after due to restrictions on state owned lands etc. As always, we like to go faster and push limits.

Open to ideas and opinions.....something different for the forum but in my opinion a good test/project.

[RustyCrankshaft]

Ditch the OEM CDI and swap on an aftermarket CDI. Most 2 strokes are wasted spark (not all) so it makes using a different CDI a bit easier.

I'd probably lean towards using a 12vdc dirtbike CDI, many of which can be had programable if you want specific timing control. Ditch the TPS and run a micro switch to switch timing maps from low RPM to full send.

There are also some 3 cylinder 2 stroke snowmobile and old outboard/jetski CDI's that you could use if you don't need a bunch of features.

[MeanGene]

Ah, that triggered (pardon the pun) a memory from 1972- my buddy worked at the Ski-Doo dealership, had a 797 Blizzard race sled, with triple Tillotson HDs with no chokes. I would help him get it started by putting my mittens over 2 of the carbs while he cranked it, would start on 2, then cover the 3rd for a second. I also got a chance to play with a 72 775 T'NT for a week, the intake roar could be heard echoing off the hills lol

[RustyCrankshaft]

Ah, that triggered (pardon the pun) a memory from 1972- my buddy worked at the Ski-Doo dealership, had a 797 Blizzard race sled, with triple Tillotson HDs with no chokes. I would help him get it started by putting my mittens over 2 of the carbs while he cranked it, would start on 2, then cover the 3rd for a second. I also got a chance to play with a 72 775 T'NT for a week, the intake roar could be heard echoing off the hills lol

I didn't start playing with sleds until the 90's, but did have a few hopped up 2 stroke sleds. EFI, turbo, etc.

Still have and ride (on occasion) a 75 RD350 that I've done some work to.

And a bunch of dirtbikes, quads and outboards. Still love my old Tower of Power Merc's. The eco Nazi hippie dock fishers not so much!

[HarleyJack17]

Rusty,

Any ideas on some part #'s? I have searched A LOT and can't seem to come up with anything that would work on 3 cylinders. It seems something is specific about that as there are plenty for 2, 4, etc. I suspect it has to do with it phased at 120 degrees(theory).  The timing control is an issue, as it is done with the TPS, and no mechanical parts or ways to make it mechanical without major modifications. I like the idea of switch, that would be easy to fab brackets on this aspect. Question is where can I find info on how to approach this. I see drop in CDi units, but not for this application, not programmable for timing.  Good info, but can you point me in "A" direction.....Again, this is a bit of new to me system.  Not much like the old school mechanical advance on outboards.....like they were in between injection and carb only in the day. But they made one for of the fastest small outboards.

I looked at the block a bit this weekend trying to figure out how to port, any advantages....sure seems that any porting to be done would be very minor. Exhaust is about as big as it can be...you may could widen the ports a total of 3/16" before digging into the Aluminum block...but don't see any major gain from it based on the design. If you built a hedder, then yes. The bottle neck I see is pushing all the exhaust through one hole the size of of one exhaust port, when there are three.  The intake side, you could open up but I have not used a scope or pulled a sleeve to see how much. Again, all of it is null if I can't bypass the current cdi.  If this falls dead, then I will clean and hone the cylinders and sell it.
The other aspect is maybe if solving the cdi riddle, being able to give people an option since it is obsolete, problematic, etc. Not really for profit, but simply to support other DT 25 owners.

[RustyCrankshaft]

The simple, but basic, solution would be a 3 cylinder sled CDI. https://cdibox.com/ Ran some Firepug's back in the day and have retrofitted them to other stuff. There are LOTS of 3 cylinder 2 strokes, just not many current production. As long as the outboard you're running is a magneto ignition it makes using a sled or bike CDI very easy. Could use the CDI for a points delete on a H1/H3 Kawi, or Suzuki water buffalo, 3 cylinder banshee, etc. Something from those applications will be useable for your outboard.

For timing control (no need for your stock TPS) you can run a programmable CDI. I've run a bunch of different models, tried this one when I was sand drag racing my 3 cylinder Banshee:
http://www.fastfromthepast.com/z-pdci-31

Also ran Mach Z and Mach 1 Skidoo sled's and those CDI's are readily available - the early ones had no rev limiter and early on with my 3 cylinder banshee I ran one of those as well. I had tried some programmable CDI's on my Mach Z but I don't recall who made them at this point and at least with the sleds I found I didn't need to control the curve, I just slide it ahead a little.

As for the porting/exhaust issues. You can widen the exhaust port and pick up a bit of power, but the big changes will be the top and bottom ends of the port and the taper which controls port timing, but the issue with an outboard is first, you are likely not able to run a pipe with expansion chamber to be able to tune the exhaust which is were a significant amount of power is actually developed from port work - not the port work itself. The second is the physical restriction you have to deal with to get the exhaust to the prop hub (if it's thru hub exhaust which is better than thru plate).

If you can't tune the exhaust you are very limited on what you can do with the porting without hurting one end or the other. You could make more power but hurt the bottom end so much it can't pull hard enough off idle to get the boat on step anymore. You do have some room to work, 2 stroke outboards were really the only kind for decades and were raced frequently. Back in the day there were even some off-shore boats that ran tunedup outboards.

To make up for it you can force air in or give it a spritz of drugs and run the more aggressive porting.

[HarleyJack17]

Rusty,

Thanks for the info. Agree with all you said.  Sled stuff is new since I am in the south. I have an uncle in AK and some of the stuff he tells me about seems crazy. Around here the only two-stroke scene has mainly been outboards.  Since this one needs a piston(some cleanup) I want to try my hand at making a little more power. I also have another one, on the boat now, and the CDI info is good stuff. Sad that you can get all the parts but that. I will dig into the info and see what I come up with.  Main thing is not going overboard. I know I can do some custom stuff to make power, like a hedder, but then it is 100% useless minus for racing and I could never recoup a dime around here.  I will say I was surprised at how well designed internally the Zuke is from a performance standpoint. I have been into a 25/30 Yamaha on the front half and saw more than a few things that could help if one wanted to spend the time....not that way on the Zuke.  I could make a customer tuner and gain a lot I feel. Like I said, the exhaust EXIT is very restrictive. Ports not so much. But that is me looking at it.  Not a porter per say, but I did stay at a Holiday Inn Express one time HAHA.
Thank you again.

[HarleyJack17]

Rusty,
I just looked at the Zeel....I see no reason that would not be an option. Reading up on it, seems to be exactly how it works now, minus the TPS.  Never knew this stuff was out there.
Question would be how to go about programming a base timing map.  In theory you could take base and max and work a curve into those points and limit advance at RPM. But we know that is not the best method.....may not even work worth a darn. I would think some kind of steps, or slower curve would work.  5 Min and 27 Deg. Max is common on the same iteration in a Yamaha, but again mechanical and base on throttle...wide open=max throw on moving timing...crude but works.  Likely one reason the Zukes do so well on low rpm hole shot...better timing curves.
Neat stuff. Thanks again.

[RustyCrankshaft]

I'd start with the stock curve if you can find out what it is (a lot of the outboards will at least give you a few points on the map). Keep in mine that marine stuff, 2 or 4 stroke, the load is essentially fixed. At x RPM you will have X amount of load, you are essentially driving a water brake dyno around (not an exactly since there is prop slip, etc, but the example gets you in the right frame of mind). With that in mind you are really tuning for whatever peak RPM/timing needs to be and below that all you need is enough timing to accelerate to operating RPM, you don't really ever run in between.

The Suzukie's do benefit from the more advanced timing curve, but it doesn't have to be anything crazy. Start with your 2 points and refine driveablitliy at low RPM. Unless you are fishing and trying to fast troll on the main. And from what I've seen watching the output from those CDI's, a lot of the map is really just to help starting and off idle transition. Maybe some of the later ones had more complicated maps, I haven't played much with outboard boats in a while. So the middle of the curve really just needs to be good enough.

It will probably take some trail and error to dial in if you do any port or exhaust work.

Also, just to be sure we're using the same terminogly, when talking 2 stroke ports that typically refers to everything from the cylinder liner surface to whever the exhaust "hooks up". EI pipe, muffler, etc. Also keep in mind that unlike a 4 stroke car engine, the combustion chamber tends to typically also include about the first 4 or 5 inches of exhaust "port".