Spark knock???
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,034
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i do not run voes, i run rpm based timing.
my issue was clutch off ping and nothing would fix it as the voes is trying to force full timing. where i ride, it is in the full adv region which is around 2.7>3.0k rpm.
now when you push an hd engine to its limit, the voes will drop to a lower curve to reduce engine heating. you can adjust the point where this happens. there is a few degrees between the two. at low rpm, the extra timing helps throttle response but not so much near wot.
my issue was clutch off ping and nothing would fix it as the voes is trying to force full timing. where i ride, it is in the full adv region which is around 2.7>3.0k rpm.
now when you push an hd engine to its limit, the voes will drop to a lower curve to reduce engine heating. you can adjust the point where this happens. there is a few degrees between the two. at low rpm, the extra timing helps throttle response but not so much near wot.
HDF Community Team
Joined: Dec 2005
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From: NC USA
What final (max) timing are you running on the curve? And what mods do you have, generally speaking? Just curious...
Last edited by t150vej; Sep 14, 2019 at 10:40 AM.
Seasoned HDF Member
Joined: Aug 2008
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well, i have a heavy past in the old tech stuff, not much for bells and whistles. i have owned BT's but prefer XL's due to their nimbleness and quick performance.
i run the 1974 ch straight up but it isn't a real go getter, i run 38mikuni vm, mechanical adv with compu-fire dual ign.
now the 01 sport is diff. i run a tad over 10:1, cam timing retarded close to 5* and use s&s ht2l lifter spacers set just enough to quite the valve train. this is running basically a solid on a hyd grind andrews n4 cams. if i were to use the voes, timing would be 25>35* but i have rpm base set at 27* but can easily go down to 20* without any loss. the redline is 7.5k but the speedo quits after dropping out 3rd. it starts getting lite at 120 and squirrely at 140. i run the sportgear and international gearing 27/55. the only issue is when ambient temps get high. ironically, it runs best on 87 fuel, higher makes no diff. two screws and easy to change timing. i also have rolled the entire curve backwards via module base plate. the biggest thorn was clutch off, once rolling no issues and it will even run 45mph at 2k without knocking at steady throttle in 5th. if i need to scoot, i can go to 1st if needed as it drops at 60 but rarely needed. if i baby it, near 60 mpg and scooting around 30 mpg, the 200 main likes to suck fuel.
i run the 1974 ch straight up but it isn't a real go getter, i run 38mikuni vm, mechanical adv with compu-fire dual ign.
now the 01 sport is diff. i run a tad over 10:1, cam timing retarded close to 5* and use s&s ht2l lifter spacers set just enough to quite the valve train. this is running basically a solid on a hyd grind andrews n4 cams. if i were to use the voes, timing would be 25>35* but i have rpm base set at 27* but can easily go down to 20* without any loss. the redline is 7.5k but the speedo quits after dropping out 3rd. it starts getting lite at 120 and squirrely at 140. i run the sportgear and international gearing 27/55. the only issue is when ambient temps get high. ironically, it runs best on 87 fuel, higher makes no diff. two screws and easy to change timing. i also have rolled the entire curve backwards via module base plate. the biggest thorn was clutch off, once rolling no issues and it will even run 45mph at 2k without knocking at steady throttle in 5th. if i need to scoot, i can go to 1st if needed as it drops at 60 but rarely needed. if i baby it, near 60 mpg and scooting around 30 mpg, the 200 main likes to suck fuel.
Grand HDF Member
Joined: Apr 2007
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From: Brighton, MI
A VOES enabled ignition module will have two curves, an advance curve that will reach full advance at about 1500 rpms and a more gradual curve that will reach full advance around 2500- 3000 rpms, depending on settings. The advanced curve is not much of a curve, basically full advance all the time.
The slow curve on an ignition on a stock 80" may go to full advance around 2500 rpms whereas a 140" may need go to full advance around 3000 rpms.
When the VOES switch is "on",the switch is closed it allows the control signal to go to ground which tells the ignition module to use the fully advanced curve (full advance 1500 rpms) , so it it more accurate to say the VOES advances the timing, not the other way any more than you would say turning off a light makes darkness. Using a ohm meter you can see when the switch closes, but keep in mind when the switch closes the current flows to ground to tell the ignition module to "advance" the timing. If the switch stays open, the signal does not go to ground and the timing is not fully advanced ( well , not until 2500-300 rpms).
The VOES is designed to fail in the open or "off" position using the slower advance curve. A big exception would be if the VOES wire was bare and grounded somewhere,as this would actually bypass the VOES and the timing would be fully advanced all the time. The switch on the VOES is controlled by vacuum, if you lose vacuum the switch opens and stops the signal from going to ground which tells the ignition module to stop using the fully advanced curve.
You can check the VOES by unhooking the wire from ground at idle , if the VOES circuit is working the idle should get slower because the timing is no longer being advanced. When you ground the wire, the idle will go faster, if neither happens, you can bypass the VOES and ground the wire before it gets to the VOES, when the wire touches ground the timing advances, when it does not touch ground the timing drops back (retarded). You can tape up the wire at this point to keep it from going to ground and ride the bike and see if there is any detonation problems, if there are NO detonation problems with the VOES out of the circuit ( wire taped up) then the detonation problem is associated with the VOES advancing the timing. BTW: You will probably have to adjust the idle up a little if you unhook the VOES. On the other hand if it still has detonation problems without the VOES ( wire taped up) it is something else, as stated earlier, just retard the timing a small amount until the detonation problem is gone, then hook up the VOES up again. If the detonation problem returns after you hook up the VOES again you know it is now being caused by the VOES advancing the timing too soon.
Eliminating the VOES will only affect the engine performance at low rpms, you will not loose any peak horsepower/torque on the dyno. Once the engine hits that magical 2500 - 3000 rpms ( depending on advance curve being used) the ignition is at full advance regardless of what the VOES is doing. I know, many guys insist it retards the timing, but it advances the timing, removing the VOES and taping up the wire so it can not touch ground will use the slower advance curve. You would not install a VOES to "retard" the timing, but removing it will. A VOES that is set up to advance the timing too soon will cause detonation problems, in that case, removing it will eliminate any detonation problems. Many big inch motors do not use a VOES to help prevent detonation problems caused by a VOES set up wrong.
The slow curve on an ignition on a stock 80" may go to full advance around 2500 rpms whereas a 140" may need go to full advance around 3000 rpms.
When the VOES switch is "on",the switch is closed it allows the control signal to go to ground which tells the ignition module to use the fully advanced curve (full advance 1500 rpms) , so it it more accurate to say the VOES advances the timing, not the other way any more than you would say turning off a light makes darkness. Using a ohm meter you can see when the switch closes, but keep in mind when the switch closes the current flows to ground to tell the ignition module to "advance" the timing. If the switch stays open, the signal does not go to ground and the timing is not fully advanced ( well , not until 2500-300 rpms).
The VOES is designed to fail in the open or "off" position using the slower advance curve. A big exception would be if the VOES wire was bare and grounded somewhere,as this would actually bypass the VOES and the timing would be fully advanced all the time. The switch on the VOES is controlled by vacuum, if you lose vacuum the switch opens and stops the signal from going to ground which tells the ignition module to stop using the fully advanced curve.
You can check the VOES by unhooking the wire from ground at idle , if the VOES circuit is working the idle should get slower because the timing is no longer being advanced. When you ground the wire, the idle will go faster, if neither happens, you can bypass the VOES and ground the wire before it gets to the VOES, when the wire touches ground the timing advances, when it does not touch ground the timing drops back (retarded). You can tape up the wire at this point to keep it from going to ground and ride the bike and see if there is any detonation problems, if there are NO detonation problems with the VOES out of the circuit ( wire taped up) then the detonation problem is associated with the VOES advancing the timing. BTW: You will probably have to adjust the idle up a little if you unhook the VOES. On the other hand if it still has detonation problems without the VOES ( wire taped up) it is something else, as stated earlier, just retard the timing a small amount until the detonation problem is gone, then hook up the VOES up again. If the detonation problem returns after you hook up the VOES again you know it is now being caused by the VOES advancing the timing too soon.
Eliminating the VOES will only affect the engine performance at low rpms, you will not loose any peak horsepower/torque on the dyno. Once the engine hits that magical 2500 - 3000 rpms ( depending on advance curve being used) the ignition is at full advance regardless of what the VOES is doing. I know, many guys insist it retards the timing, but it advances the timing, removing the VOES and taping up the wire so it can not touch ground will use the slower advance curve. You would not install a VOES to "retard" the timing, but removing it will. A VOES that is set up to advance the timing too soon will cause detonation problems, in that case, removing it will eliminate any detonation problems. Many big inch motors do not use a VOES to help prevent detonation problems caused by a VOES set up wrong.
Grand HDF Member
Joined: Apr 2007
Posts: 3,693
Likes: 2,988
From: Brighton, MI
What's your setup, and has anything changed recently? What cam are you running, and what ignition? If everything's stock, you could have just gotten a bad tank of gas... that's happened to me several times, and Bertha runs like crap for awhile until I burn it all out. I always run premium, too.
The reason I ask is because I installed a V-Thunder EVL-3010 cam last Christmas, and a Daytona Twin-Tec single-fire ignition. The Daytona instructions said to set the ignition module advance to 7 (out of 10) initially for premium gas, so I did - but she knocked like hell at that setting when I got on the throttle under 3000 RPM. So I dialed it back to 5 and no more knocking. The combo of the EVL-3010 cam, which apparently likes a bit higher revs, and the initial timing advance didn't work very well together. I learned quickly that with too much advance, I had to downshift and run above 3000 RPM before I really got on it, which was a hassle...
The reason I ask is because I installed a V-Thunder EVL-3010 cam last Christmas, and a Daytona Twin-Tec single-fire ignition. The Daytona instructions said to set the ignition module advance to 7 (out of 10) initially for premium gas, so I did - but she knocked like hell at that setting when I got on the throttle under 3000 RPM. So I dialed it back to 5 and no more knocking. The combo of the EVL-3010 cam, which apparently likes a bit higher revs, and the initial timing advance didn't work very well together. I learned quickly that with too much advance, I had to downshift and run above 3000 RPM before I really got on it, which was a hassle...
Seasoned HDF Member
Joined: Jun 2010
Posts: 9,320
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From: Upstate New York
It’s not supposed to be able to fail that way, but it did to me.
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