oh holy mother of acceleration/timing question

Well tonight I had an urge to get the moped out and ride it despite the 20something degree temps here in chicago. I hadnt ridden it since sometime in november (i usually ride it to school and i can NOT stand cold temperatures in the morning). Previously, before i had put it in the garage last, i had been playing with the timing (by screwing with the point gap). when my flywheel flew off when i first got the bike, i tried to put it up so that the timing mark matched peugeot's specs of 1.5mm BTDC (its a peugeot 103sp btw), but i somehow screwed it up and its about 10 degrees off. So i've been screwing with the timing, trying to get it to line up to an artificial timing mark i painted on (the true timing mark cause the other one's not lined up right). Previously i hooked the bike up to a timing light and started it, observed the marks, adjusted, etc. This time i used a multimeter to tell me when the points seperated exactly without having to start the engine. when i had it about right, i took the moped out, put on my heavy jacket (us army field jacket with warm-as-hell wool liner) hat, gloves and all and started it up. oh my goddamn.. its perfect now. my main complaint with the moped previously was that the acceleration sucked ass.. acceleration this time was perfect. Top speed was the same, 30mph (found this out because a friend of mine just happened to be driving around my neighborhood at 1am and saw me and followed me). Perfect.

And now a question: can anyone tell me what different characteristics different timings might give me (so i dont have to go try them all). I know too retarded or two advanced will both give less power, but what would advancing or retarding the timing a degree or two do?

Re: oh holy mother of acceleration/timing question

There's 3 kinds of ignitions with different timing caracteristics; retarding, fixed and advancing.

Most 2-stroke peds have a fixed or a retarding ignition. Advancing ignitions are usually illegal because it increases the performance of your bike dramaticly.

You can best compare the ignition timing to pushing someone on a swing. If you push too late it'll hardly have any effect and if you push too early you're going to be in trouble.

-The fixed ignition:

The timing of the iginition is the same at all revs, this makes setting the timing fairly easy. If you set the timing too early the feul will be ignited before it is fully compressed. Your bike won't go faster than 5 Mph and ride really jerky. This'll destroy your piston in the long run, it's called "detonation". If the iginition is set too late you'll have less power.

-The retarding ignition:

A retarding ignition delays the spark at higher revs. So when you go faster the ignition timing will be set later, so you'll lose power and will not be able to go any faster. So the retarding-mechanisme is a revlimiter. The caractreristics of setting the timing are the same as those of the fixed ignition, except that the ignition cannot be too early at high revs.

-The advancing ignition:

An advancing ignition does the opposite of the retarding ignition. When you go faster the piston will go up and down much faster, so the feul has much less time to fully ignite. If the ignition would "advance" at higher revs, the spark will come earlier and the feul will have more time to fully ignite. Correctly setting the ignition timing on an advancing ignition is tricky. If you set it like a fixed ignition, the spark will come too early when the ignition is advanced, wich will cause "detonation", only this time at higher engine speeds. When setting the timing on an advancing ignition you must give the ignition room to be able to advance, so at low engine speeds the engine will be sluggish, but when the revs start to rise the power will really increase. This ignition also allows the engine to run at much higher revs, sometimes with the ignition advanced as much as 30 degrees. I have one of these ignitions myself, the engine does 11000 revs instead of the original 8500. If I adapt my cilinderhead it'll be able to go all the way up to 14000 rpm, but the clutch of my bike cannot handle such enginespeeds and will explode above 12000 rpm so I'll keep it at 11000.

Re: Hmm

Reeperette /

So which kind does a Tomos Targa mount, and can I get my hands on an advanced one ?

That's the one upgrade I've never really tried, but since I got everydamnthing else on it...might as well go all the way.


Re: Hmm

hmmm well the tomos targas have cdi ingition so u would have to get a reprogramed one or something... tell me where i can get one!

Re: Hmm

For racing-CDI units got to:




The Takegawa Hyper CDI-unit is a cheap ($50) racing CDI with a good performance. These three manufacturers also have highly tuned CDI-units, but those cost a lot.

These CDI-units are originally made for a Honda 4-stroke, they might not work propperly on a 2-stroke. I think you'd best try your local moped-dealer first.

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