Ok I have read and studied all of the printed literature I could find but have not found the piece that has made the concept "click" in my mind.
Help me understand advanced and retarded timing. Does timing advance mean that the spark happens sooner, farther away from TDC? And then retarded means that the spark happens later and closer to TDC?
Or is it the other way around.
I got my 550 running last night. Started on the first kick. I used a SAE dial guage to set the timing and have not used a strobe yet.
The book calls for a timing distance of 3.37mm, or 24 degrees, or .132 inches.
I ended up at .130 inches and the book gives a tolerance range between .112 and .166 or +3 and minus 2 degrees.
According to the optimal spec, is .130 retarded slightly? I don't want to run advanced since I have the added compression head on the bike.
By the way My bike seems to start and idle fine but did not have the opportunity to get it up to full operating temperature to do much testing or tuning.
Timing question....help me understand.
Moderators: oldjapanesebikes, H2RICK, diamondj, Suzsmokeyallan
-
jaybob
- To the on ramp
- Posts: 326
- Joined: Sun Oct 19, 2008 4:44 pm
- Location: Cedar Rapids, Iowa
Timing question....help me understand.
Last edited by jaybob on Fri Jun 12, 2009 2:58 pm, edited 1 time in total.
-
Craig380
- Expert racer
- Posts: 1250
- Joined: Mon Dec 01, 2008 2:52 am
- Location: Manchester, UK
Yep, advanced is further BEFORE TDC, retarded is closer towards TDC.
2 thousandsth of an inch is pretty damn close to being spot on. Although remember the factory spec is only a spec, different bikes like different settings. For example my own stock 380 pings a little at the factory timing settings, despite using 98 octane fuel. So I run mine about 0.5mm retarded.
Ride the bike for a bit then check the spark plugs. Also listen for pinging from the top end.
Look very closely with a magnifying glass at the tip of the centre electrode. If you can see any tiny silvery balls there, the plug is telling you the timing is too advanced. Retard maybe 0.5mm and try again.
In practice and in stock trim, the Suzi triples are not very sensitive to timing anyway. Remember to keep the fiber heels of the contact breakers lubed -- a spot of grease on the cam and a drop or two of oil on the felt wick.
2 thousandsth of an inch is pretty damn close to being spot on. Although remember the factory spec is only a spec, different bikes like different settings. For example my own stock 380 pings a little at the factory timing settings, despite using 98 octane fuel. So I run mine about 0.5mm retarded.
Ride the bike for a bit then check the spark plugs. Also listen for pinging from the top end.
Look very closely with a magnifying glass at the tip of the centre electrode. If you can see any tiny silvery balls there, the plug is telling you the timing is too advanced. Retard maybe 0.5mm and try again.
In practice and in stock trim, the Suzi triples are not very sensitive to timing anyway. Remember to keep the fiber heels of the contact breakers lubed -- a spot of grease on the cam and a drop or two of oil on the felt wick.
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
-
Craig380
- Expert racer
- Posts: 1250
- Joined: Mon Dec 01, 2008 2:52 am
- Location: Manchester, UK
Jay, if you've got a higher-compression head I would suggest retarding the ignition, somewhere around the 0.112" before TDC setting.
I doubt you would feel any difference when riding, as the Suzi triples do not seem very sensitive to timing changes (within Suzuki's specified range, anyway).
The retarded setting will give more margin for avoiding pinging. Too much advance and higher compression could lead to holed pistons
I doubt you would feel any difference when riding, as the Suzi triples do not seem very sensitive to timing changes (within Suzuki's specified range, anyway).
The retarded setting will give more margin for avoiding pinging. Too much advance and higher compression could lead to holed pistons
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
-
water cooled
- Yeah Man, the Interstate
- Posts: 704
- Joined: Thu Oct 23, 2008 3:23 pm
- Country: USA
- Suzuki 2-Strokes: 1974 Suzuki GT750
- Location: Medina OH
Jason,
I had the same problem when I was selecting the MSD ignition system for the dragbike. Eventually, I looked closely at a degree wheel and was able to figure it out as this particular one showed advance and retard timing on the wheel.
Here is some info that I came across in the MSD multichannel instructions that might help a little. Go to page 6 regarding timing recommendations.
http://www.msdpowersports.com/pdf/frm21258_pn42351.pdf
I had the same problem when I was selecting the MSD ignition system for the dragbike. Eventually, I looked closely at a degree wheel and was able to figure it out as this particular one showed advance and retard timing on the wheel.
Here is some info that I came across in the MSD multichannel instructions that might help a little. Go to page 6 regarding timing recommendations.
http://www.msdpowersports.com/pdf/frm21258_pn42351.pdf
-
pjmcburney
- To the on ramp
- Posts: 342
- Joined: Tue Feb 17, 2009 1:20 am
- Country: Australia
- Suzuki 2-Strokes: T20 GT750L RE5A GSX1100S RG500G GSX-R1100N
- Location: QLD
Think of it like this...
The fuel(gas)/air mixture in a non-compression ignition internal-combustion engine, doesn't explode when ignited by the spark from the spark plug - it actually burns, much like when you light a trail of gas on the ground.
And, you want it to burn rather than explode because you get a lot more out of it for a longer period of time.
Now... because it burns rather than explodes, it takes a (small admittedly) period of time to combust completely in the combustion chamber.
To efficiently utilise this process to force a piston back down a cylinder, you have to time the spark to start the burn (ignite the fuel/air mixture) before the piston reaches TDC so the maximum amount of energy is extracted from the combustion (burn) process.
If you time the spark for right on TDC the piston has come and gone before the burn is finished and you're wasting combustion energy.
If you time the spark for after TDC - well all you're doing is burning the fuel/air mixture in the cylinder and imparting less and less energy onto the piston.
If you time the spark for too far before TDC, the burn process is over too soon and again, energy is wasted, and you run the risk of over-heating (because of the too-quickly increasing compression in the combustion chamber, what with the burning fuel and all) and compression-igniting the remaining burning fuel/air mixture. This is pre-ignition or 'knocking', 'rattling' or 'pinking' and has a detrimental effect on pistons and combustion chambers over time, not to mention you're wasting fuel by exploding most of it and not extracting the maximum amount of energy out of it.
I you time it just right, the maximum amount of burn energy is imparted onto the piston.
So... ignition timing is a fairly critical thing. It even has to change over the rev-range of an engine (especially a four-stroke engine) to extract the most energy from the fuel in relation to the burn time.
As revs rise (generally) you have to advance the ignition timing more and more to compensate for the fact that the fuel takes a finite time to burn, but the interval between each piston stroke decreases.
Having said all that - a Suzuki two-stroke is in a fairly mild state of tune and can tolerate a fairly wide ignition timing range before there's any noticeable change in output.
Let's face it, there's a significant amount of the unburnt fuel/air mixture getting blown out the exhaust port most of the time anyway...
Hope this explanation helps...
Cheers
Paul
The fuel(gas)/air mixture in a non-compression ignition internal-combustion engine, doesn't explode when ignited by the spark from the spark plug - it actually burns, much like when you light a trail of gas on the ground.
And, you want it to burn rather than explode because you get a lot more out of it for a longer period of time.
Now... because it burns rather than explodes, it takes a (small admittedly) period of time to combust completely in the combustion chamber.
To efficiently utilise this process to force a piston back down a cylinder, you have to time the spark to start the burn (ignite the fuel/air mixture) before the piston reaches TDC so the maximum amount of energy is extracted from the combustion (burn) process.
If you time the spark for right on TDC the piston has come and gone before the burn is finished and you're wasting combustion energy.
If you time the spark for after TDC - well all you're doing is burning the fuel/air mixture in the cylinder and imparting less and less energy onto the piston.
If you time the spark for too far before TDC, the burn process is over too soon and again, energy is wasted, and you run the risk of over-heating (because of the too-quickly increasing compression in the combustion chamber, what with the burning fuel and all) and compression-igniting the remaining burning fuel/air mixture. This is pre-ignition or 'knocking', 'rattling' or 'pinking' and has a detrimental effect on pistons and combustion chambers over time, not to mention you're wasting fuel by exploding most of it and not extracting the maximum amount of energy out of it.
I you time it just right, the maximum amount of burn energy is imparted onto the piston.
So... ignition timing is a fairly critical thing. It even has to change over the rev-range of an engine (especially a four-stroke engine) to extract the most energy from the fuel in relation to the burn time.
As revs rise (generally) you have to advance the ignition timing more and more to compensate for the fact that the fuel takes a finite time to burn, but the interval between each piston stroke decreases.
Having said all that - a Suzuki two-stroke is in a fairly mild state of tune and can tolerate a fairly wide ignition timing range before there's any noticeable change in output.
Let's face it, there's a significant amount of the unburnt fuel/air mixture getting blown out the exhaust port most of the time anyway...
Hope this explanation helps...
Cheers
Paul
-
jkevinlilly
- My new bike is "IRIS"
- Posts: 1002
- Joined: Tue Oct 14, 2008 8:33 pm
- Location: Suburbs of Centralia, WV
-
tz375
- Moto GP
- Posts: 6204
- Joined: Mon Nov 03, 2008 10:47 am
- Location: Illinois
To add a little to Paul's post, the peak pressure from the burn occurs at roughly 15 degrees after TDC and it takes say 40 degrees to burn, so we light the fire at 25 before TDC.
Anything that causes the air/fuel mix to burn faster means we have to back off the timing a tad and conversely, anything that makes it burn slower requires more advance.
Things that increase flame propagation rate include:
Motor running hot,
High ambient temperatures
Faster burning fuel
Higher turbulence (squish heads)
Plugged exhausts
Lean mixtures
Higher CR
Etc.
As paul explained, if the fire is lit too early, the combustion chamber pressure rises too fast and the piston is still rising so it makes the motor work harder for less useful output.
Too early and the motor overheats and too late and we waste fuel and power. It's a narrow range and the higher the state of tune, the more crucial it is.
Fortunately, a 50HP 750 is not highly strung and is quite tolerant of timing .
Anything that causes the air/fuel mix to burn faster means we have to back off the timing a tad and conversely, anything that makes it burn slower requires more advance.
Things that increase flame propagation rate include:
Motor running hot,
High ambient temperatures
Faster burning fuel
Higher turbulence (squish heads)
Plugged exhausts
Lean mixtures
Higher CR
Etc.
As paul explained, if the fire is lit too early, the combustion chamber pressure rises too fast and the piston is still rising so it makes the motor work harder for less useful output.
Too early and the motor overheats and too late and we waste fuel and power. It's a narrow range and the higher the state of tune, the more crucial it is.
Fortunately, a 50HP 750 is not highly strung and is quite tolerant of timing .
-
ja-moo
- Yeah Man, the Interstate
- Posts: 554
- Joined: Wed Apr 01, 2009 11:47 pm
- Location: NM USA
- Contact:
A couple of other things,
The speed the fuel burns is a constant, so the timing is "really" just a comprimise on these old bikes.
At lower rpms, there is more time for the burn. Advancing the timing (reasonably) gives more torque, as it sets the major expansion of the gasses where it is needed on the down stroke.
As rpm rises mid range rpm, a bit of advance compensates for the shorter time the piston is around TDC.
Now at high rpm things change when you have expansion chambers when compared to stock exhaust. Heat in the expansion chambers increases the speed of the sound waves, which in turn make the pipe "act" shorter which increases the rpm ceiling, making more power.
Even with 4 strokes now, there are computer maping ignitions which change the timing every 500 rpm or less for optimum power.
The speed the fuel burns is a constant, so the timing is "really" just a comprimise on these old bikes.
At lower rpms, there is more time for the burn. Advancing the timing (reasonably) gives more torque, as it sets the major expansion of the gasses where it is needed on the down stroke.
As rpm rises mid range rpm, a bit of advance compensates for the shorter time the piston is around TDC.
Now at high rpm things change when you have expansion chambers when compared to stock exhaust. Heat in the expansion chambers increases the speed of the sound waves, which in turn make the pipe "act" shorter which increases the rpm ceiling, making more power.
Even with 4 strokes now, there are computer maping ignitions which change the timing every 500 rpm or less for optimum power.
Visiting from the "K" camp...........
-
tz375
- Moto GP
- Posts: 6204
- Joined: Mon Nov 03, 2008 10:47 am
- Location: Illinois
Er JA-moo,
When you mentioned that fuel burns at a constant rate, are we referring to pump gas here or all gas?
AvGas for example burns very slowly by comparison to some race fuels in the same application. VP and Sonoco make race fuels with different burn rates.
Flame propagation rates are also a function of fuel droplet size. The smaller the drops, the larger the surface area:volume and the more surface area is exposed to vaporize and burn, hence faster and more complete burn.
When you mentioned that fuel burns at a constant rate, are we referring to pump gas here or all gas?
AvGas for example burns very slowly by comparison to some race fuels in the same application. VP and Sonoco make race fuels with different burn rates.
Flame propagation rates are also a function of fuel droplet size. The smaller the drops, the larger the surface area:volume and the more surface area is exposed to vaporize and burn, hence faster and more complete burn.
