automatic advancing and retarding of engine timing?

**thehollowmen** · 14th June 2005, 21:47

I know this sounds really silly, but how would I tell if the CDI is able to advance or retard my timing automatically?

I pick up a 11.5:1 650 fuel injected V twin tommorrow and I'll get less power on 91 if it retards the timing. On the other hand I could get a small amount of SDA (alcohol + small amount of methanol) from work to boost the octane (the manual says 10% etOH or 5%mtOH in petrol) and if it advances...

happy days for me!

**Motu** · 14th June 2005, 22:10

Advance is built into a CDI by just the way it works...as it goes faster the magnetic flux gets cut earlier or some such...it's only a few degrees,but enough for most engines.You can check it with a timing light if you have a hole with timing marks...but they spray oil out.I've checked enough to know that it just works and don't bother anymore.

[edit] - oh,I see - you are wondering if it with change it's advance curve by itself if you change the fuel????? It would need to be closed loop computer controled ign to be able to do that...and bike systems aren't very sophisticated.

**thehollowmen** · 14th June 2005, 23:39

Thanks for explaining that :-) Motu, karma heading your way.

I think I'll stick with 91 for the time being and give 96 a shot when I can really rev the hell out of it.

**Brian d marge** · 15th June 2005, 03:40

Originally Posted by Motu

Advance is built into a CDI by just the way it works...as it goes faster the magnetic flux gets cut earlier or some such...it's only a few degrees,but enough for most engines.You can check it with a timing light if you have a hole with timing marks...but they spray oil out.I've checked enough to know that it just works and don't bother anymore.

[edit] - oh,I see - you are wondering if it with change it's advance curve by itself if you change the fuel????? It would need to be closed loop computer controled ign to be able to do that...and bike systems aren't very sophisticated.

As far as I know the Cdi works by Hall effect which is an electromotive force which is caused by the interaction of a steady state current in a magnetic field . The magnitude of this emf is proportional to the aount of current flowing and the intensity of the magnetic field . they then switch this by using resistors , or other forms of circuit resistors , to a Scr or a from of transistor , this discharges a capacitor which discharges through the coil a a rapid pace causing a bigger voltage build up in the coil

( i am doing that from memory so ,,,any corrections welcome . )
The advance curve is just made by using differing value circuit resistors, , so at a lower Rpm when the pick up is producing X value Emf by using a lower/higher value resistor the capacitor will dump through the coil earlier/later than before ie advance retard the timing ...
Programable ignitions just use a chip to do the same thing , ( they also sometimes have Knok sensors )
Which is what will happen if you have a higher comp engine and use a lower octane fuel, you will need to retard the ignition to guard against detonation,

Sorry I am watching the 250 race just before going to bed , so any discrepancies sorry bout that , but you should get the drift ...

Good combustion chamber design you can run nearly 13 to one with very little knock on 91 unleaded ...
Most modern jap bike are designed to run on 91 unleaded , if you use 96 in an unmodified engine you run the risk of cold fouling the plugs, They just cant quite burn the crap of and the spark has a hard time

If you were to use methanol in a injected v twin, then the oxygen rich mixture will change the exhaust temp ( usually around 1425 ish ) which will fool the ecu in to injecting more or less fuel ( I cant remember if you use larger or smaller jets in a methonol carb bigger I think ....ie the INjection system will compensate ..not the cdi ......( as motu said the closed loop system will delay signal letting it fire the coil at the most suitable advance/retard position)
The system will run the most suitable advance curve , to guard against detonation , the power loss will be ( I think 9/75 th of not a lot )

Stephen
BTW methanol doesnt like aluminuim I think . becareful ......

**What?** · 15th June 2005, 06:32

Originally Posted by thehollowmen

I pick up a 11.5:1 650 fuel injected V twin tommorrow and I'll get less power on 91 if it retards the timing.

How do you work that out??????
Fuel it with what the manufacturer recommends. These days, most likely to be 91 (which just happens to be more flamable than 96 - higher octane ratings are to reduce detonation, not increase power)

**Motu** · 15th June 2005, 07:18

No Hall Effect in bike systems...no square wave signals,they are more akin to a lawnmower than a car - but then I have never worked on a modern bike ign system.

**thehollowmen** · 15th June 2005, 07:50

Originally Posted by What?

How do you work that out??????
Fuel it with what the manufacturer recommends. These days, most likely to be 91 (which just happens to be more flamable than 96 - higher octane ratings are to reduce detonation, not increase power)

Easy. If it normally runs on 96 at high compression, then that's all well and good and I get my horsepower.

However, if I put in 91 and it doesn't like it, the CDI will retard the timing until it doesn't ping and everything is stable. However in retarding my timing it will give me less power.

*ponders*

logical for someone without a mechanical background... problably more manure to the people with one.

**thehollowmen** · 15th June 2005, 07:53

Originally Posted by Brian d'marge

( i am doing that from memory so ,,,any corrections welcome . )
The advance curve is just made by using differing value circuit resistors, , so at a lower Rpm when the pick up is producing X value Emf by using a lower/higher value resistor the capacitor will dump through the coil earlier/later than before ie advance retard the timing ...
Programable ignitions just use a chip to do the same thing , ( they also sometimes have Knok sensors )
Which is what will happen if you have a higher comp engine and use a lower octane fuel, you will need to retard the ignition to guard against detonation,

(SNIP)

If you were to use methanol in a injected v twin, then the oxygen rich mixture will change the exhaust temp ( usually around 1425 ish ) which will fool the ecu in to injecting more or less fuel ( I cant remember if you use larger or smaller jets in a methonol carb bigger I think ....ie the INjection system will compensate ..not the cdi ......( as motu said the closed loop system will delay signal letting it fire the coil at the most suitable advance/retard position)
The system will run the most suitable advance curve , to guard against detonation , the power loss will be ( I think 9/75 th of not a lot )

Stephen
BTW methanol doesnt like aluminuim I think . becareful ......

Thanks :-) The CDI advancing and retarding timing, I've seen that in some high performance cars almost exactly like you say.

It said it should be ok in my manual, for 5% methanol or 10% ethanol. One of them said something about 'stabilisers' so I might have a good read up again before I put anything into the bike.

**scumdog** · 15th June 2005, 07:58

You MAY have the wrong end of the stick, I'm pretty sure the advance curve is set for 91 which the factory designed the bike for, putting in 96 won't make it 'over-advance' the factory setting to take advantage of the higher octane.

That's why boys who put avgas in their favourite factory tuned toy (normally an old Falcon with 220km on the clock down here!) are tossing themselves off if they think they're going to get 'heaps more power', if it ain't pinking with 91 then it's unlikely to have enough compression and/or timing advance to take advantage of the 100 or more octane of the avgas.

**Motu** · 15th June 2005, 08:14

Yes - unless you have a fully computer controlled system which I doubt many bikes have - you can't ''advance'' timing...only retard,you can't make something happen before it happens.You can build in a lot of advance and then retard it electronicly,but why would the factory build a system like that?...only if the over advanced state was ''normal''.This is how we set up CNG igns back in the old days - overadvance for CNG and then use electronics to retard for petrol,some units had programable advance curves...but as I said,you can only delay and event,not advance it.

**Ixion** · 15th June 2005, 11:09

Originally Posted by Motu

No Hall Effect in bike systems...no square wave signals,they are more akin to a lawnmower than a car - but then I have never worked on a modern bike ign system.

BMW purportedly use Hall effect sensor in the ignition system.

**Paul in NZ** · 15th June 2005, 11:21

Dude... If you want to know anything about electronic ignitions ask this guy!

http://www.jefferies-au.org/MyECU/index.htm

Cliff is a member of AIGOR and I remember when he started doing this. Basically his bikes ignition shat itself and being a clever clogs he thought, well how hard can it be to build one and.... I mean you have to love Guzzi owners eh!

Cliff is a good guy and cleverer than ... well me for one...

Have a look at this site and be amazed what one clever guy can do with a few basic tools, a bit of knowledge and a ton of patience and determination!

Cheers

**vifferman** · 15th June 2005, 11:22

My bike has one of the more advanced EFI systems, with three modes including 'closed loop', but I'm pretty sure it doesn't alter the ignition timing for different fuels. In 'closed loop' (which is only used when running at constant throttle and/or low revs), it uses the O2 sensors in the zorst to alter fueling, but not ignition timing (apart from the normal advancing of the curve as the revs rise). If I use different fuels, I have to reset the ECU to make it store the new O2 sensor readings for 'closed loop'; for other modes, it just makes it up as it goes along. Despite having umpty-zillion sensors, there's no knock sensor, and as far as I know, no bikes have them, so you just have to make sure you're using the right fuel for your bike, which would be 91 in your case, I would imagine.
I've got a similar compression ratio to yours (11.6:1), but I run with either 98 (96 has too much crap in it), or alternate between 91 and 98 so that the octane is somewhere between 91 and 98, as the recommended rating is 92, and it pinks when taking off when it's really hot, if I use 91.

**Motu** · 15th June 2005, 12:06

Originally Posted by Ixion

BMW purportedly use Hall effect sensor in the ignition system.

But they are German though eh...quality before quanity,unlike their competitors,and in bed with Robert Bosch.Hall effect generators are delecte and a motorcycle enviroment is a bit harsh for them....unless of course you are using car technology in your bike like BMW does....I suspect the hall effect will be tucked away under the front cover nice and safe.

**vifferman** · 15th June 2005, 12:10

Originally Posted by Motu

But they are German though eh...quality before quanity,unlike their competitors,and in bed with Robert Bosch.Hall effect generators are delecte and a motorcycle enviroment is a bit harsh for them....unless of course you are using car technology in your bike like BMW does....I suspect the hall effect will be tucked away under the front cover nice and safe.

Don't electronic speedo drives use the Hall Effect? Or is it something similar?