I need help with ignition timing.....

[ghwallice]

The Zane is 750S renowned for a tuning glitch at about 3500 rpm.
These are 3D graphs of a stock 750S ignition timing files. If one of you is experienced at reading them, please speak up, 'cos I am Not.
The 2nd one is "normal" view, and the 1st is rotated and tilted so we can see the "back of the ridge".
What really stands out to me is that at the current throttle position (7.36%) the advance curve is at 23degrees at 3500rpm, and is at 39degrees at 4000rpm.
That's a BIG change for 500rpm. I could well imagine an engine hunting on deceleration, and flicking between 23 and 36 degrees, which would cause an engine to glitch and hunt some more???

I am considering editing the map so that the rpm gradients were much more "parrallel", uniform, thus reducing the change in timing in the 3000 rpm to 5000 rpm range to much smaller changes like the rest of the map. I'm a bit worried about creating preignition, but if i'm careful to not actually advance the timing at any given rpm i should be ok? I hope...This exercise is solely to see the impact on the glitch, I'm not worried about improving performance at present.

I'm only just starting with all this, so any opinions, support, learning opportunities, constructive criticism ect gratefully accepted. I have looked at a Ducati 916 map, and it looks uniform and even compared to these.

Regards, Greg

 

[Vince]

Purposely done to pass emissions or sound tests?

 

[ghwallice]

I would say yes.....

 

[arancia]

I'd understood the mappings and the final gearing as delivered in the US models were entirely driven by need to pass US noise regulations, will try to find the specification for the tests but think it's something like a drive by at around 50mph with full throttle.

 

[GregT]

If you can adjust the curve, yes, more advance earlier will help. I'd even suggest that full advance should be reached at around 3000 RPM.
In my experience Four valve heads will run very well with quite a lot of advance from low down.

An example quite similar. The Kawasaki EX500 (4V heads - 74mm bore )gets full advance at 4000 RPM. Put big cams and carbs in and raise the compression and they're dead in the water below 4 grand. An aftermarket box with full advance at 2500 wakes them up nicely.

 

[ghwallice]

Greg. Thanks for the response. Most carb preinjection motors top out about 36 degrees? This thing is topping out at about 60 btdc. I havent got a knock sensor, so im fearful of advancing the timing at any rpm. I just want to smooth it out from about 3k to 5k to so that timing variance in this range is more stable, (for a start.....)

 

[GregT]

There are possible points in the rev range vs throttle position where it might go to an extreme advance to get over a hole in the fueling.
Most 4V heads now top out around 40 - 44 degrees. the Kawa quoted above is 42deg max..

The extreme case of this is the 5 valve Yamahas. Two peaks in the curve - 4500 and 8500. 42 and 48 degrees respectively. The 5v chamber just doesn't want to burn fuel at some points in the range. The OW01 is worse - 48 and 52 degrees

Personally I don't have much experience remapping this stuff. All i can suggest is comparing a map from something similar - and later.
There are several injected twins about this size on the market, a few even have aftermarket tuning adaptations - the 650 Kawasaki for one.

 

[Laverda SF]

None of this makes sense to me ;o(

I have enough issues trouble shooting Coil packs, Crank Tiggers on Boche EFI Lamba Systems and OBD2 Codes ;o(

Just put a distributor and points in her - Eat the Best and Forget the Rest - What's this World coming to ?

 

[arancia]

I'd understood the mappings and the final gearing as delivered in the US models were entirely driven by need to pass US noise regulations, will try to find the specification for the tests but think it's something like a drive by at around 50mph with full throttle.

The US EPA sets the maximum noise emissions levels by measurement under a testing procedure (SAE J331a) to recreate the vehicle's maximum noise levels while under heavy acceleration for all motorcycles manufactured after December 31, 1982 which were for sale in the U.S.

J331a establishes the testing procedure and the calculation of the engine rpm for the test which will depend upon the maximum allowable rotational speed of the motor and the overall crankshaft to wheel ratio.

So a motor performance curve resulting from its ignition timing and fueling together with the gearing can be manipulated such that the exhaust noise remains within the permitted 82dB level at the engine speed range that will be used in the testing procedure over a short distance approaching, passing and going away from the sound testing meter.

Take a look at the specification of the test and you'll see why the quieter "flat spot" is there at the specific range of rpm in the test so that the bikes could meet the noise regulations.

 

[Dellortoman]

I've never seen anything like 60° ignition advance before. I note that it's at high revs and closed throttle so it would pretty much be on the overrun while slowing down. Perhaps it's intended as some kind of engine braking.

 

[ghwallice]

The US EPA sets the maximum noise emissions levels by measurement under a testing procedure (SAE J331a) to recreate the vehicle's maximum noise levels while under heavy acceleration for all motorcycles manufactured after December 31, 1982 which were for sale in the U.S.

J331a establishes the testing procedure and the calculation of the engine rpm for the test which will depend upon the maximum allowable rotational speed of the motor and the overall crankshaft to wheel ratio.

So a motor performance curve resulting from its ignition timing and fueling together with the gearing can be manipulated such that the exhaust noise remains within the permitted 82dB level at the engine speed range that will be used in the testing procedure over a short distance approaching, passing and going away from the sound testing meter.

Take a look at the specification of the test and you'll see why the quieter "flat spot" is there at the specific range of rpm in the test so that the bikes could meet the noise regulations.

Interesting....

 

[ghwallice]

I've never seen anything like 60° ignition advance before. I note that it's at high revs and closed throttle so it would pretty much be on the overrun while slowing down. Perhaps it's intended as some kind of engine braking.

Its 32 degrees at 44% throttle and 8000rpm, and climbs to 61.5 at 8500rpm and 11% throttle. I am not going to play with that part of the curve until i understand it.......

 

[ghwallice]

It worked! No more 3500 rpm Glitch!
It now runs and works properly from about 2000rpm through the dreaded 3000, 3500, 4000 rpm zone up to red line.
No issues on acceleration, slow or fast, deceleration, slow or fast, or cruising, at whatever rpm.
I have, as compared to OEM map in the last post, just smoothed it all out.
AFR is also reasonable, much much better than it was before.
I won't be looking for anything better until I do a lot more study. It'll do me for a while!

 

[arancia]

Greg. Thanks for the response. Most carb preinjection motors top out about 36 degrees? This thing is topping out at about 60 btdc. I havent got a knock sensor, so im fearful of advancing the timing at any rpm. I just want to smooth it out from about 3k to 5k to so that timing variance in this range is more stable, (for a start.....)

I imagine that the high advance with low throttle at high rpm is similar to the vacuum advance mechanism that cars with distributors had in an attempt to get decent mpg at cruising speed with light load.

 

[Ventodue]

The US EPA sets the maximum noise emissions levels by measurement under a testing procedure (SAE J331a) to recreate the vehicle's maximum noise levels while under heavy acceleration for all motorcycles manufactured after December 31, 1982 which were for sale in the U.S. <snip>

Lothar has reported finding similar for Europe. I'll leave him to fill in the details.

 

[Dellortoman]

Well done. Comparing before and after maps, it's only a subtle change. I'm surprised that it made such a big difference.

 

[ghwallice]

Its a digital system, not analogue, so an rpm change from 3950 to 4050 would give a 16 degree change in advance, and possibly the change would cause an rpm decrease back down to 3950 and hence a 16 degree reduction in timing. And probably the same between 3450 and 3550.
My target was to reduce the magnitude of the changes to something about equal between rpm bands. Knowing the impact of different degrees of advance would help, but i don't, so it was just suck it see......

 

[Dellortoman]

OK. That seems a bit crude. I'd have thought the electronics would interpolate and apply a ramp between the set points, rather than jump from one setting to the next.

If you start the bike with the computer connected, can you watch that blue dot move around the landscape of the map as you rev the engine? I've done that with Ignitech ignitions and the little cursor showing the actual advance travels along the line between the set points, working out the intermediate advance as it goes.

 

[piranha-bro2]

It gets very complex when the CPU on a full digi system alters ignition curve based on throttle pos and rpm ... and probably other factors as well. Our Ignitechs when used on our clunkers are just an advance curve set to rpm.

 

[Dellortoman]

Ignitech has the ability to receive an input from a throttle position sensor or inlet air pressure sensor (as well as engine revs) to produce a 3D advance map. I've not done it myself, but others have.