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View Full Version : Timing effect on rich vs lean??


rfranz1952
9th September 2009, 19:30
Does the amount of advance or retard in timeing have an effect on how rich or lean the engine will run at a given carburetor setting?

Just thinking about it, more advance provides more time to burn, so, at least in theory, more of the fuel and oxygen would be used up, and the oxygen sensor will return a leaner reading?

Bone
9th September 2009, 19:47
It doesn't change how rich or lean the MIXTURE is per se. (How rich or lean the air/fuel charge is that is being introduced to the chamber).

But yes, as you point out, it can change (very very very slightly) the amount of the mixture that is burned. I don't know that it's enough to really alter fuel mapping in closed-loop operation on a feedback motor.

Really timing more effects how efficiently you use the mixture (whether or not it is rich or lean in the first place).

And whether or not you will get pinging from too early a combustion.

MAARANDALL
26th November 2009, 17:41
How to you advance or retard your engine. B/c when harley did my 883 - 1200 conversion i dident get the jet kit (yes stupid me) any who it started pinging and then they retarded it and a few days later i got the jet kit put in buy another shop (not harley) and i think my bike might still be retarded. How do i check if its right or not?

biknut
26th November 2009, 18:08
I don't believe timing has much, or any effect on the AFR. If there is, it's too small to notice.

XLXR
26th November 2009, 18:34
There is an interaction between timing and mixture, but generally only guys with modified motors trying to get every bit of power need to try and fine tune beyond stock settings. It is best to start tuning with conservative settings, retarded timing and rich mixtures. The worst case is to have lean main jetting and timing too advanced. Both, or either case can make the motor run very hot. Piston melt down can happen.

On modified motors, when you are trying to tune to the max, you generally have to fine tune both to get the optimum balance.

Carb bikes do not have 02 sensors.

rfranz1952
27th November 2009, 01:33
T

Carb bikes do not have 02 sensors.

They do if you've put one on:smoke

biknut
27th November 2009, 03:03
Carb bikes do not have 02 sensors.

That's true, but you can put one on easy enough. 08 Nightster front pipe on my 88 model.
http://xlforum.net/photopost/data/1215/medium/WBO2_sensor_front_view.jpg

Shu
27th November 2009, 16:30
With the stock HD advance curves you only have the ability to "fine tune" with adjusting the whole curve the same amount. While this may not seem like a lot I can tell you from hours of tuning on mine that there is efficiency and power to be found with slight timing adjustments as well as vibration reduction. And yes since both pistons are on a single crank pin minute changes do affect the cylinders slightly differently. Those with laptop tunable ignitions and a lot of dino time could really dial in ignition timing from idle to red line and find a pony here and there across the board. I guess the question is does it affect the afr and jetting....well yes but as stated before not a lot or enough to alter the right jet sizes. Bore size and chamber size and shape have a huge effect on the proper amount of timing an engine requires.
Maarandall, depending on your exact conversion and ignition when the dealer retarded yours by a few degree he may have done you a favor in terms of power. The stock 883 ignition on a 10:1 compression reverse dome piston stock 883 head conversions tend to like the ignition retarded by three degrees or so. You asked how to adjust. On the cam case under the '5 speed' aluminum cover is the ignition module on your model. You pull that cover and the plate underneath to expose the module which is on a sensor plate. There are two bolts that hold that sensor in place. You rotate the plate to adjust the timing. You will need an adjustable timing light if you are going to try to fine tune it as a regular timing light will only show you the 20 degrees at idle factory setting since the crank isn't marked all the way around.

Don Burton
27th November 2009, 17:33
Shu,

I have a rubbermount and have no first hand knowledge of this but didn't the stock rigidmount 1200s come with a more conservative timing curve than the 883s straight from the factory? I have read many posts about retarding timing after a 1200 conversion.

Shu
28th November 2009, 00:53
Shu,

I have a rubbermount and have no first hand knowledge of this but didn't the stock rigidmount 1200s come with a more conservative timing curve than the 883s straight from the factory? I have read many posts about retarding timing after a 1200 conversion.
Actually the 1200's had a less agressive curve than the 883. I have those curves in an excel spreadsheet somewhere and a link to that online somewhere. I'll try to find that later and post the link.

MAARANDALL
28th November 2009, 03:30
With the stock HD advance curves you only have the ability to "fine tune" with adjusting the whole curve the same amount. While this may not seem like a lot I can tell you from hours of tuning on mine that there is efficiency and power to be found with slight timing adjustments as well as vibration reduction. And yes since both pistons are on a single crank pin minute changes do affect the cylinders slightly differently. Those with laptop tunable ignitions and a lot of dino time could really dial in ignition timing from idle to red line and find a pony here and there across the board. I guess the question is does it affect the afr and jetting....well yes but as stated before not a lot or enough to alter the right jet sizes. Bore size and chamber size and shape have a huge effect on the proper amount of timing an engine requires.
Maarandall, depending on your exact conversion and ignition when the dealer retarded yours by a few degree he may have done you a favor in terms of power. The stock 883 ignition on a 10:1 compression reverse dome piston stock 883 head conversions tend to like the ignition retarded by three degrees or so. You asked how to adjust. On the cam case under the '5 speed' aluminum cover is the ignition module on your model. You pull that cover and the plate underneath to expose the module which is on a sensor plate. There are two bolts that hold that sensor in place. You rotate the plate to adjust the timing. You will need an adjustable timing light if you are going to try to fine tune it as a regular timing light will only show you the 20 degrees at idle factory setting since the crank isn't marked all the way around.

Thank you very much Shu, very informative, ill give it a try.

Don Burton
28th November 2009, 04:25
Actually the 1200's had a less agressive curve than the 883.

Yes. That's what I meant when I said the 1200s had a more conservative timing curve. I believe that it's the same with the rubbermounts as well.

bustert
29th November 2009, 16:13
as was brought out, the timing has little effect on rich/lean issues and even less on a computer controlled engine. the ecm looks at all of the parameters and calculates the needed corrections to a burned in fuel map. the basic map can not be changed unless it is in an e2prom and you have the software to make the changes. if your system uses eprom, can not be changed unless you burna new one and change the chip.

however, how rich or lean does effect the ignition. a lean condition requires a higher firing voltage due to the fact that there are less fuel molecules to ignite. that is why lean burns are set up with high ignition voltages and wide gaps to help ignite the mixture. gasoline in itself will not burn(remember the formula needed for a fire). the burning mixture is a chemical reaction. however, to start the process, an energy source of a higher value is needed and that is the electrical spark. without this higher source, the chemical change can not happen and that is why a weak spark can not sustain a running engine.

on the other side, a overly rich engine causes the flame front to move slowly as there is not enough o2 so the engine either dies or misses.

timing also effects cylinder pressures and temperatures.