Timing advance (where's the beef?)

david f martin /

I've been following the threads with great interest (considering trying it on mine), but so far all seem to be hypothetical... Anyone have real experience slotting the holes (or similar mod)?

david

Bad info is the beef.

As I stated David ... some dirt bikes come with the mounting holes slotted from the factory... that would be Yamaha and Kawasaki... Honda and Suzuki you have to slot the holes.

And it is not just theoretical.... I have altered mine for more low end performance by advancing it a little.... On a modern dirtbike, you advance a little for more low end and less top end. And retard it for less low end and more top end.

Which is the opposite of what you have been reading here by people other than me... which is why I have not agreed with the popular opinion here

On another older 2 stroke racebike... I played with the timing 3 or 4 times... and got detonation (pinging) every time I got away from stock specs very far either way... Both too far advanced and too far retarded caused temperature to rise in a bad way.

That is why my opinion is that pretty close to stock is best.

And I don't believe mopeds are set with "bad" timing on purpose.

Because the BTDC timing measurement is specified by the book... and those measurements are almost the exact same as the older point ignitions on 2 stroke street and trail motorcycles.

Here are some examples

50cc...... 1.6mm

100cc..... 1.7mm

175cc..... 1.7mm

(and those are fixed timing motorcycle ignitions.. no kind of "advance mechanism built in)

And the 2 peds reported here were 1.5mm and 2.0mm.

So they are not "retarded".

I will come back with a link Dave...to a description of how to change timing on a 2 stroke dirtbike from a world reknown 2 stroke engine tuner.

Here it is David >>

http://ericgorr.com/techarticles/basic_two_stroke.html

Cut and paste that into your address bar and go there and read all about 2 stroke tuning.... By the BEST there is.

The part about ignition timing is towards the bottom.

Re: Bad info is the beef.

Ron Brown /

Fred,

That sounds backwards to me too, as automatic advance units allways advance the ignition as rpm's increase. Anyway, I'll try that link and see what he has to say.

Ron

Re: Bad info is the beef.

Ron Brown /

Fred,

OK, I read it and I'm still confused. This guy has to be leaving something significant out of the equation.

I also went back to my old 2 cycle tuning book and it says that higher rpm power bands can support more advanced ignition timing. If this guy is right about losing top end power then there has to be something going on that he is not describing too well.

As an example, as rpms increase, the cylinder volume increases faster, if the burn rate of the fuel/air mixture does not increase, this should lower the cylinder pressure. What does this guy know that he is not telling us in his explaination?

By the way, most peds run at fairly low rpm, which he may refer to as mid-range, so maybe advancing the ignition a liitle is not too bad.

Ron

Re: Bad info is the beef.

OK... There is one thing I left out when I wrote what I did... and that is that those modern dirtbikes already have electronic advances built into their spark curves.

And those are probably already advanced as far as is good for the motor... so to advance it more does not help top end... it actually is fighting itself by lighting off too early.

Anyway... I prefer to follow real world results, not theory.. and you can take what he says there as gospel... in my opinion.

My own experience with point ignitions was as I said... pinging when I advanced it... despite the fact that I was running about 105 octane.

And as you can see by the BTDC timing numbers... the peds are in the same range as the older point ignition 2 stroke motorcycles.

However....If I have time this summer... maybe I will play with mine on a ped.

By the way... you do know the general rule that, the more peformance you get out of a motor... the less spark advance you need? Because combustion efficiency is improved (and faster).

Here is the link to his full site...

http://ericgorr.com/

Re: Bad info is the beef.

Ron Brown /

Fred,

Maybe electronic ignition is the reason.

Anyway, I'm leaving for bike week now.

I know, I'm a little late, but I hear the sun is still shining and I need a ride.

Signing off for a week or so,

Ron

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