Advanced Timing Question

[cfspawn]

Hey all..
Had something pop into me head before and wondered what everyone thought.
when I replaced my exciter coil on my stator i noticed my timing was advanced by one notch (there are 3 lines) so i reset it back to factory which is the middle line or notch as said in the manual. When i rode the bike it felt a little restricted but had heaps more bottom end. so i put it back to the advanced setting as it gives me more top end. Is this the right thing to do or should i leave it at the factory setting, and does it hurt anything mech wise running advanced? your thoughts would be great as i am thinkin of putting it back to standard.
Thanks guys.

 

[COMBEN]

should be OK if...

You should be OK as long as your bike is jetted good to a little rich, when running more advanced the engine tends to run a little hotter as it does produce more power so any slack on the jetting may raise it's head here...but I'm afraid it's the old story of you can't have both both ways

retarded timing = good low end but poorer top end
advanced = good top end poorer low end..
I think the the KDX has a simple timing map, rev and load related would be great...hole in the market here!!

Richard

 

[cfspawn]

Yeah i realise its probably for personal preference etc but not to sure what the best setting would be for the woods as you dont get a incredible high speed and could use more bottom end to get out of the thick stuff.

 

[COMBEN]

....need low end grunt...well you could buy a 220R ;)

try going to both extremes of the timing marks but the retarded marker will most likely suit the terrain you seem to favour...retarded timing pushes peak torque (grunt if you wish) further down the rev' range, it may even make it even easier to start as a bonus but that should ever be a problem with KDX's!

I don't think they would mark lots of degrees of adjustment on what is a production part and changes maybe negliable, if you can feel them at all?

...this advice is from someone who has never had a 200 only 220's but I know the relationship between timing and engine power/torque curves :ohmy:

cheers

 

[canyncarvr]

retarded timing = good low end but poorer top end
advanced = good top end poorer low end..

Sorry. That is as backwards here as it is there.

Advancing the spark timing will improve low-end response/pull/'grunt'.
Retarding the spark timing will improve hi-end response/pull/'overrev'

Advancing the spark 'tends' to keep heat in the cylinder, retarding the spark 'tends' to put heat in the pipe...thus the above effects.

If you're thinking, 'That can't be right because 4-strokes don't work that way!' .....that statement answers its own question.

 

[cfspawn]

So your saying that its more unsafe to have it advanced rather than retarted i guess if i was to leave it gotta check jetting and if it is running rich or lean.

 

[Rhodester]

So your saying that its more unsafe to have it advanced rather than retarted i guess if i was to leave it gotta check jetting and if it is running rich or lean.

Not to worry with these relatively low compression KDX engines. I'm running 158lbs of compression and am advanced a little beyond the most advanced mark. You'll be plenty safe if you want to experiment a little.

 

[canyncarvr]

re: 'So your saying that its more unsafe to have it advanced rather than retarted'

I said no such thing.

It is more unsafe if it is advanced too much. That is true.

Mr Gorr has written that few 2-strokes benefit from timing advance...more benefit from timing retard. That statement wasn't aimed toward KDXs particularly.

I've had my bike on both sides of 'standard'. I ended up back where I started..on the OEM mark. That's my personal choice, certainly doesn't need to be yours.

An incorrectly timed engine can lead to severe engine damage. Detonation starts tearing things up long before you ever hear it.

 

[matt-itude]

I have advanced the timing on my 03 200 to the factory suggested max position. I use the bottom end much more than the top and it made a considerable difference in bottom end power and snap. So did finaly getting the proper pilot jet in there. My engine is stock except for vforce3, knarly woods pipe (stock silencer) and snorkel removed from air box lid. I run pump premium and have found no problems related to the timing.

 

[cfspawn]

Thanks CC..

 

[COMBEN]

Appologies are due...in Mr Gorr's own words below....well bash my b**ls with an iron bar.... you learn something everyday...I'm OK with diesels though...but only the 4 strokes, don't take my advice if it's a 2 stroke diesel :laugh:

"Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe."


cheers