timing adjustment

[crazymater91]

Has anybody messed with advancing the timing just curious?

[greg737]

First, a disclaimer: The following is TMI (too much information), do not continue reading beyond this point. Consider yourself warned.


I don't think you'll find anyone who's done this (yet, or ever). Reason being it wouldn't be an easy operation to perform.

Start by reviewing the stock setup on the EX-250: The bike's CDI is rather dumb, using only a pre-determined, hard-coded map (just a single 2-dimensional curve, really) of values to set the advance based only on a single input parameter: Current RPM. It is programmed to set spark at 13 degrees BTDC at idle and it graduates to 42 degrees BTDC at 4,200rpm and remains at that advance for the remainder of the engine's operating envelope.

You wouldn't want to simply "advance" the timing curve on an EX-250. The factory curve was pretty well thought out (by really smart Japanese engineers) and delivers good (but not great) characteristics from idle to redline. Any wholesale change (shift) of the factory curve would leave the engine with bad performance somewhere in it's operating envelope. Although, if you're not concerned about passing EPA tests like the manufacturers have to be, you might be able to draw a bit more performance out of a re-drawn 2-dimensional, hard-programed curve.

For example: the worst part of the EX-250's current ignition timing curve occurs at about 4,200rpm when the spark advance reaches 42 degrees BTDC. At this (relatively low) engine speed this much advance is a bit of a compromise. It makes the engine very fuel efficient at this rpm in a low-load, non-accelerating situation (emmissions would also be lower for EPA considerations), but at that same rpm, in a situation where the the rider is rapidly rolling on the power for acceleration this is really too much advance which hurts performance. A lot of riders have noticed this little "hesitation" or "stumble" in the EX-250 at around 4,200 (and many blame it on carb settings).

The change you're probably looking for would be to make the bike's ignition system "smarter" like the ECUs on modern fuel-injected cars and motorcycles. They take into account things like throttle position, throttle rate-of-change, manifold temperature, manifold absolute pressure, manifold absolute pressure rate-of-change, fuel/air ratio (actual vs. programmed via an O2 sensor in the exhaust), and sometimes even engine-knock sensors. With all this information the ECU can rapidly change the spark advance to be both extremely aggressive when called upon to produce maximum power (without causing detonation) and the next moment it can be all about fuel efficiency at low load.

So you'd have to replace the CDI with some sort of programmable aftermarket ECU like the Microsquirt or Megasquirt ECUs. They're designed as a way to change a car or motorcycle over from carbs to fuel injection, but you could use only the ignition control portion of the module if you wanted to.

If you google Microsquirt or Megasquirt you'll find that there's a very, very deep rabbit-hole of information to fall into. You may never surface.

[Racer x]

Do some serching on the Brt-tis. Ignition system .They are for 2008 and up bikes and they work very well. There is also a thread from when I adapted an 88-94 icu to the new bike giving 7 deg of advance and raising the rev limit.
Other than that you are somewhat limited to what you can do on first gen bikes . 42 deg is a lot when you start raising compression.

One big problem is the stock pickups won't talk to a power commander. When I go to microsquirt I will use the universal pick up . That involves movinh the pick up points on the stator.

[crazymater91]

Thanks y'all did some searching found some stuff out but unless I start racing I think I will shy away from it and again. Thanks

[greg737]

yeah.... an interesting topic with obvious performance benefits, but a really high degree-of-difficulty to implement.

[Racer x]

With the adjustable timing you just have another tuning tool. Alone it dose not do much. But once you do pistons carb exhaust .you need to tune the ignition timing just like you need to do more with the carbs than just jeting. It not only makes more power but it is smooth usable power. Not just peak power. Without the ability to adjust the timing you loose a lot of options.

[crazymater91]

I agree I would love to have adjustable timing but can't really justify the the cost for a daily rider the reason I asked the question is the guy I was talking to said it was about a 30min job just some adjustments. And I was thinking a little more power As I see now that's not the case

[crazymater91]

By the way the brt-tis would not work on a pregen am I correct. Thanks

[Racer x]

I think it could be made to work. The only benefit would be to retard the timing for hi compression,nitrous or a turbo.