Ignition timing for modified engines

[zrx1100]

After reading the Smedspeed site's section on modified engines—particularly ignition timing advance—I started thinking about their advice. The recommendation is to use more advance at low rpm, less full advance, and a slower ramp to 3500 rpm for performance builds (https://www.smedspeed.co.uk/tech.html). While reducing advance is often discussed (https://www.xs650.com/threads/xs650-ignition-timing-revisited-are-we-too-advanced.45197/), extending the ramp isn't covered as much. Smedspeed suggests bending spring posts, which seems drastic. Are there other ways to achieve this, like using stiffer springs or modifying the existing ones?



For reference: the stock advance curve

The Smedspeed advised:

I also tried mapping the advance curve on my bike using the tach reading and a rudimentary degree gauge below.

I have the timing set at idle at the lower range of the spec. It seems that my springs (10 year old from Mike’s XS) are a bit weak as the full advance is reached by 2500rpm.

Here are all the maps super imposed.

 

[Jim]

To be honest, I don't think the ramp up is that critical for our application. Just speaking for myself, i seldom lug the engine below about 3000 revs. Even puttering around town, I'll drop gears to stay above that.

About the only use I see for a slow ramp up to 3500 would be coming out of a hairpin with someone hot on my ass. Beyond that, how often are you running down that low?

 

[Jan_P]

Jim was quicker

Not done the reading about this
But perhaps of interest the first XS 650 I had . The springs was sloppy and the advance weights contact surface had groves
Worn .. I had the plan if the bike lasts one year it is OK
But the bike ran like a scolded rat .I could never figure out why but it did .
Points -- stock intake and exhaust I believe it had stock jetting

I did not know that the advance rod should be greased back then So I went to Boyer Bransden
Since the advance unit was worn anyways.
But I still feel it ran better before.

Did more dynamic riding back then ON --OFF
Say I had idle at 1500 --I believe say it again believe --the weak springs made the ramp instant
But with the dynamic riding the 1500 to 2000 2500 was a quick transition to full advance
So If no other argument like knocking and so I dont think an prolonged ramping is wanted
or useful.
Past that with the correct jetting it pulled strongly.

A tuned engine perhaps for the more power Maybe it is a quick transition to higher rev the main jet opens and so

The idle advance I set for simple kick starting .. and perhaps a little tweaking listening about rev change adjusting + and -

The added ethanol fuel can affect .. I feel a bit later at the top makes it run with less noise.
I rarely drives the same Dynamically way nowadays. have a sports bike f I want that.

 

[Signal]

Use and Ignitech programmable ignition. You can design your own curve on a dyno.
The hard part is setting up the crank triggers.
I have fitted three of them and the ignitech is great.

 

[GLJ]

You could play around with different advance springs and other changes to match Smedspeed's suggested advance curve. Or set you engine to his total advance setting. Then when you feel racy change your shift points to where you don't fall below 3500 rpm.
Under normal riding on the street how often how often do you fall below 3500 rpm and try to accelerate as fast as you can. I know if I needed to I would just knock it down a gear or if in first feather the clutch.

 

[zrx1100]

You could play around with different advance springs and other changes to match Smedspeed's suggested advance curve. Or set you engine to his total advance setting. Then when you feel racy change your shift points to where you don't fall below 3500 rpm.
Under normal riding on the street how often how often do you fall below 3500 rpm and try to accelerate as fast as you can. I know if I needed to I would just knock it down a gear or if in first feather the clutch.

Any suggestion for where to get stiffer springs? I hear you about just shifting to get past 3k

 

[GLJ]

Any suggestion for where to get stiffer springs? I hear you about just shifting to get past 3k

Sorry I do not. I run a Boyer ignition set for 38 degrees total advance. Works well for me.

 

[Jan_P]

Any suggestion for where to get stiffer springs? I hear you about just shifting to get past 3k

I remember trying to make my own springs .Formulas of springs are available and spring wire also
Here it was difficult to find a so short having the correct end loops.
If suitable machines like a lathe. It helps .Making an axle and then wind the wire around it
End loops with pliers

 

[zrx1100]

Use and Ignitech programmable ignition. You can design your own curve on a dyno.
The hard part is setting up the crank triggers.
I have fitted three of them and the ignitech is great.

following a path of less resistance, i have been eyeing Sachse https://www.elektronik-sachse.de/manuals/Z10-XS-3.23-en.pdf

their curve 5 looks interesting

 

[Signal]

I agree with Jim its not an area of the rev range that gets used much.

The Sachse has some nice features and gets rid of the steam era springs and weights so win- win.

 

[zrx1100]

I agree with Jim its not an area of the rev range that gets used much.

The Sachse has some nice features and gets rid of the steam era springs and weights so win- win.

maybe i ride wrong, but i use the range quite a bit and the bike is fine there as it is, but if thre is an opportunity to improve, it is always fun to think about it

 

[zrx1100]

had a good chat with Rick Forte from Smedspeed. After learning about my motor configuration, he confirmed that "max advance should be around 36 deg @ 3000-3500rpm". He is not sure about bending posts to increase tension on springs and is going to check with Howard. He did recomment TRI spark and Ignitech. TRI spark seems like a very solid setup and goes out to 3500rpm. It has been discussed here extensively (https://www.xs650.com/threads/installing-a-tri-spark-ignition-system.62687/). Ignitech is fully programmable, but does not seem to have an optimized mounting kit for the street. Rick says they are close to offering something like that. @Signal, maybe you can post your experience.

As for me, I just ordered some OEM (hopefully) springs from eBay to measure spring constant lol....

 

[Signal]

I have fitted ignitech to a RD 350 based race engine and 2 XS 650 race engines.
All cases were total loss with modified alternator rotors and GN 250 pick ups. So not much good for a street setup.

With the XS engines the Ignitech was used as it was intended to use methanol in the future.

The Ignitech is able to be triggered from the crank or the cam.
I honestly think if you have a working ignition use that and that for a road bike the ignitech is overkill.

But if you really want to get your bike timed well, connect a throttle position sensor to the ignitech and that opens up 3D ignition mapping options and that I know little about.
If you want to use the Ignitech I am willing to help you through the process.

 

[zrx1100]

I have fitted ignitech to a RD 350 based race engine and 2 XS 650 race engines.
All cases were total loss with modified alternator rotors and GN 250 pick ups. So not much good for a street setup.

With the XS engines the Ignitech was used as it was intended to use methanol in the future.

The Ignitech is able to be triggered from the crank or the cam.
I honestly think if you have a working ignition use that and that for a road bike the ignitech is overkill.

But if you really want to get your bike timed well, connect a throttle position sensor to the ignitech and that opens up 3D ignition mapping options and that I know little about.
If you want to use the Ignitech I am willing to help you through the process.

i'll grow into it Next stop for me to see if I can get stiffer springs in there.

 

[zrx1100]

From TriSpark: Our Compass system for the Yamaha XS650 (not rephased) follows the same advance range as the original factory system, but with more subtle transitions. The advance begins at approximately 1400 RPM and reaches full advance by 3500 RPM, with most of the advance occurring before 3000 RPM. Half advance is achieved at 2000 RPM. This design provides excellent low-end throttle response, a stable idle, and reduced risk of pinging or knocking. 24 degrees of advance

So per this description, their curve loos like this (the gray line):

It is a nice curve with a lot more advance than stock at lower rpm and a softer approach of full advance. Steve from TriSpark further advised that the plate of the sensing unit can be rotated to move the advance up or down, similar to the stock timing plate

 

[zrx1100]

Sachse, on the other hand is a bit puzzling. Even though they say that the reduced advance is better, the curves are way retarded and I know that my bike would idle very poorly with that much retard from 12-15 degrees.

i imagine, that the timing plate on Sachse can be rotated to move the curves up and down. With that assumption, curve 3 with additional 6 degrees looks very interesting

the tri-spark would still have more advance around 2500rpm and would level out nicely toward 3500 rpm

i like that Sachse allows selection of a number of curves to try, but my exhaust/cam overlap has an overlap at 2500rpm, where there is not enough oxygen in the mixture and more advance would help. So TriSpark may be better. If anyone has thoughts on these option, let me know.

 

[Jan_P]

Not read through but the stock have a 5 ish degrees more advance . At higher rpm perhaps it makes a
difference
I had a set up with poor worn advance unit bike running like a scolded rat everything stock
That I have not experienced later Boyer and Aftermarket exhaust
The modern fuels can make less advance at higher revs better
But sachse looks off.
Good work

 

[gggGary]