Race start.


74 replies to this topic
  • rbn14

Posted November 27, 2007 - 09:10 AM

#41

I took another look at the circuit diagram for the WR and took a look at the one for the YZ. The neutral switch does indeed close 2 circuits on the WR. One is to prevent using the e-start if it is in gear and you dont have the clutch pulled in, The other grounds the "sky blue" wire, same as with the yz. I will have to take your word for what this wire does as I dont yet have a WR to play with but I am sure you are correct and it has the same function as in the YZ. But... the blue/white wire circuit is only closed when you push the e-start button.

I also looked at the wiring diagram for the 03 and it is EXACTLY the same as far as starting the bike goes although this doesnt mean the effect of the circuit closing is the same. But I have a hard time seeing how a backfire would strip out the starter gear. Among the reasons is that a backfire is simply the flame front traveling out the intake tract. This can happen when timing is too far advanced but it appears timing is only retarded when the bike is in neutral. So, if you start your bike in gear with the clutch in you are still "risking" backfire.

  • grayracer513

Posted November 27, 2007 - 03:48 PM

#42

"Backfire" may be being confused with "Kick Back", which is a different event, even though it may be accompanied by a backfire in some cases. Normally, it wouldn't be, though. Kick back is when the engine fires and the crank takes off in the wrong direction. This can be because the timing is too far advanced, or the engine developed enough power on startup to overcome its forward momentum, for some other reason. For those who have never had one of the YZ/WR450's turn on them like this, it's an event you won't forget. Mine nearly broke my foot right through my A-Stars.

But, as I said, the starter clutch is designed to be torque limiting, so if it gets bad enough, it will theoretically skid before the engine breaks the starter.

As to the wiring diagram, the one I have available to me shows the US version using two separate leads at the neutral switch, one sky blue (s/:thumbsup: for the starter circuit, and one blue white (L/w) for the CDI neutral signal. The two leads are grounded by the switch simultaneously in neutral, and since the starter circuit is isolated from the CDI neutral signal wire by a diode, the starter circuit cannot become a ground for the CDI NS lead. The fact that they share the same ground in neutral is, electrically speaking, moot. In fact, in the Euro version, the two leads are spliced outside the switch and share a single contact in the neutral switch.

It's easy enough to establish the truth here. All you have to do is connect the coil to a test plug and check for spark on the first TDC with the bike in neutral, and in gear (or with the lead disconnected, if you prefer).

The only reason your bike would start any better in neutral with that wire disconnected than in gear is that it likes more advance, and your clutch drags too much.

  • Thumper_Bloke

Posted November 27, 2007 - 09:43 PM

#43

Grayracer, sorry but you are incorrect. The blue/white from the cdi is connected to the starter relay circuit and detects if the starter button is being depressed. Using an oscilloscope, i see two complete dead revs before the capacitor discharges on the trailing edge of the pickup. With it disconnected, the cap discharge (aka SPARK) happens immediately.

I have been riding like this for a long time now, i love it. And my neutral wire (Sb) doesn't seem to do much in either state.

For racing from a dead stop, you might want to use the kicker to get the piston just past TDC compression, then it will have a good complete rotation before the next compression stroke. It still will seem like an instantaneous start, but might help guarantee the starter can rotate the engine into enough momentum.

  • Thumper_Bloke

Posted November 27, 2007 - 10:14 PM

#44

I am referring to the L/W wire closest to the #20 CDI (as it leaves the ignition)

Posted Image

I do see the Sky Blue (Sb) transition to L/W at the connector. That is indeed the neutral sense, but not the one that gives an e-start delay.

  • grayracer513

Posted December 01, 2007 - 10:27 AM

#45

Grayracer, sorry but you are incorrect. The blue/white from the cdi is connected to the starter relay circuit and detects if the starter button is being depressed. Using an oscilloscope, i see two complete dead revs before the capacitor discharges on the trailing edge of the pickup. With it disconnected, the cap discharge (aka SPARK) happens immediately.

I have been riding like this for a long time now, i love it. And my neutral wire (Sb) doesn't seem to do much in either state.

For racing from a dead stop, you might want to use the kicker to get the piston just past TDC compression, then it will have a good complete rotation before the next compression stroke. It still will seem like an instantaneous start, but might help guarantee the starter can rotate the engine into enough momentum.


I am referring to the L/W wire closest to the #20 CDI (as it leaves the ignition)

Posted Image

I do see the Sky Blue (Sb) transition to L/W at the connector. That is indeed the neutral sense, but not the one that gives an e-start delay.

I think I see where the confusion is; the harness colors don't remain consistent across the connector to the leads built into the components.

If I now understand you correctly, you are talking about disconnecting the blue/white ( L/W ) lead at the CDI from the blue/black (L/B) lead in the harness at the 6 wire connector where they meet. The really fun part of this is that the L/B lead runs from there to the starter relay diode, where it meets another L/W. If what I have said above is correct, then I was mistaking you for meaning that you were disconnecting the L/W harness lead from the neutral switch at the two-wire connector near the diode. That one runs, as you said, to the Sb lead on the CDI.

That being the case, you are then doing something different than what I mentioned, and while what I said about that circuit (neutral signal) is still true, it does not apply to what you are talking about.

Sorry about the confusion. :cheers:

  • Thumper_Bloke

Posted December 01, 2007 - 03:06 PM

#46

Yep, its funny the wire colors change when entering the harness, gots to be careful we are all talking about the same wire. Just enough to confuse all of us. Could be worse, at least they arent all black wires.

  • grayracer513

Posted December 01, 2007 - 04:39 PM

#47

Could be worse, ...

Saw a section of a B-52 fuselage at the Air and Space Museum Annex once. Running along the starboard side were 4-6 2" conduits stuffed full of 16-20 gauge wires,....every single one was white.

  • snakesausage

Posted December 03, 2007 - 05:10 PM

#48

I suggested this mod to a friend who races and he ran it by his mechanic. He came back with the following:

"Do not cut that wire. My mechanic says it allows the starter to wind the motor past the backfire point. If it is disconnected and the bike backfires it may strip the starter gear. He kicks his WR at races."

What do you guys think? I remember the broken starter gears the 03's had when they backfired. The Yamaha engineers must have had a good reason for designing this feature in.


I think that your mechanic may be correct about the backfire issue. My bike seems to backfire much more when using the e-start after I removed the blue/white wire. It does not seem to kick back though because the e-start does not stop turning over or load up, it only backfires, so I am not sure if it will cause any damage on the 04+ e-start gears. Like you said, there is a reason that the engineers added the delay so modify at your own risk...

To repeat my previous post:
Just to clarify to anyone else that tries this, there are two blue/white wires that are associated with the CDI, one that comes straight from the CDI and enters the connector next to the gray wire (that most of us have disconnected) and another wire that exits the CDI as sky blue and changes to blue/white at another connector (at least on the 05' US version).

This mod requires that you disconnect the blue/white that directly exits the CDI and enters the 6 pin connector next to the disconnected gray wire.

Snake

  • rbn14

Posted December 03, 2007 - 08:48 PM

#49

Kicking back and backfiring are completely different. A backfire is when the flame front of the combustion event exits the intake valves. I cant see how this could do anything besides start your air filter on fire if you remove the screen. In top fuel dragsters it can blow off the intake manifold but thats a different story. Ofter people call what is actually an afterfire a backfire but this is simply unburnt fuel igniting in a hot exhaust system. I fail to see how anything could happen to any gears in either case. Finally, the bike kicking back will not hurt the starter do to the design of the starting system.
I'm not saying that this is a risk free mod, which is why I like the idea of using a switch so that the only time it is used is for an actual race start and after the bike is good and warm. But, I don't think any of the concerns I have heard so far are legit. You have to think about what the difference is between pushing the button and kicking it and what difference a couple of dead strokes accomplishes. My guess is just more consistent starting. Every bike I have ever kicked has started better when first given a couple "clean out" kicks. Hell, the manual says to do this if you drop it and it wont start.

  • Thumper_Bloke

Posted January 28, 2008 - 07:13 PM

#50

Well, hundreds of starts and hundreds of miles later and i STILL have my blue/white wire at CDI disconnected. however when i ride, i find myself roll starting if i can, or i try the kicker for fun, but most of the time is using E-start, spark first rev mod works great. The starter does work HARDER, i can hear it struggle sometimes. Nothing that alarms me, but i think longevity is concerned, so i will reattach the wire soon.

I like the idea of a switch, you can have instant e-starts with no deadrevs for the green flag, but then switch it to dead-revs mode aka "save the starter motor & battery" mode after your riding is underway.

:busted:

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  • SXP

Posted January 28, 2008 - 07:20 PM

#51

Well, hundreds of starts and hundreds of miles later and i STILL have my blue/white wire at CDI disconnected. however when i ride, i find myself roll starting if i can, or i try the kicker for fun, but most of the time is using E-start, spark first rev mod works great. The starter does work HARDER, i can hear it struggle sometimes. Nothing that alarms me, but i think longevity is concerned, so i will reattach the wire soon.

I like the idea of a switch, you can have instant e-starts with no deadrevs for the green flag, but then switch it to dead-revs mode aka "save the starter motor & battery" mode after your riding is underway.

:busted:


Huh?! You've got me confused. How would you be stressing the starter more by making it rev less? If the blue/white wire mod makes the motor fire instantly, i.e., fewer revolutions of the starter, then that to me means less stress and wear and tear on the starter, right? This is desirable, at least to me:excuseme:

  • Thumper_Bloke

Posted January 28, 2008 - 07:22 PM

#52

oops, not "rev less" but Crank Less.

  • SXP

Posted January 28, 2008 - 07:33 PM

#53

oops, not "rev less" but Crank Less.


I'm still not following you (but then, I'm not the sharpest knife in the drawer).

With the wire connected the starter spins (or cranks) the motor about three revolutions before it fires.....(equation 1)

With the wire disconnected, the starter spins (or cranks) the motor maybe one revolution, and the motor fires.....(equation 2)

So, equation (1) minus equation (2) equals a saving of two revolutions to make the motor fire, or in other words less wear and tear on the starter motor. So, blue/white wire disconnected is a good thing, no?

  • grayracer513

Posted January 28, 2008 - 08:45 PM

#54

If Yamaha went to the trouble of building this feature into the bike, it was done for a reason, and that reason is most likely to allow the starter time to bring the engine up to a higher speed before spark occurs, which would lessen the likelihood of the engine kicking back at the motor.

  • Thumper_Bloke

Posted January 28, 2008 - 09:03 PM

#55

yes, greyracer is explaining it better then i can. the starter sometimes struggles with this wire disconnected. But i have it disconnected ALL THE TIME, so all my starts are nearly instantaneous. However, sometimes the piston is in a bad spot and the starter struggles pushing it past the hard spot. Kinda like if you kick it slow, sometimes its hard to get the kick started until the compression lets go. Other times, you can just put the weight of your foot down on the kick lever, and it turns over effortlessly. Hope this helps for racing starts with a dead engine.

  • SXP

Posted January 28, 2008 - 09:12 PM

#56

If Yamaha went to the trouble of building this feature into the bike, it was done for a reason, and that reason is most likely to allow the starter time to bring the engine up to a higher speed before spark occurs, which would lessen the likelihood of the engine kicking back at the motor.


I buy this explanation for why this feature was originally designed into the bike.

yes, greyracer is explaining it better then i can. the starter sometimes struggles with this wire disconnected. But i have it disconnected ALL THE TIME, so all my starts are nearly instantaneous. However, sometimes the piston is in a bad spot and the starter struggles pushing it past the hard spot. Kinda like if you kick it slow, sometimes its hard to get the kick started until the compression lets go. Other times, you can just put the weight of your foot down on the kick lever, and it turns over effortlessly. Hope this helps for racing starts with a dead engine.


The engine being difficult to start, sometimes requiring rocking of the bike to get the piston past the hard spot, is completely independent of the blue/white wire. It will happen with the wire connected or not and just depends on where in it's stroke the piston stops when the engine is switched off. I believe it even happens on the YZ450s and is manifested by difficulty in getting the kick starter going (Grayracer has posted an explanation for why this happens on the YZ side).

  • Thumper_Bloke

Posted January 28, 2008 - 09:25 PM

#57

OK, we are definately on the same page, it's real world riding that tells me the flywheel likes to get a little inertia by spinning a couple of times before the cdi lets a spark occur WITH the e-start button pressed. I think we can conclude the life of the starter motor and included mechanicals couldbe increased by leaving this wire connected (stock)!

Anyone else like this mod for everyday use?

  • grayracer513

Posted January 28, 2008 - 10:08 PM

#58

Getting back to the race start situation for a second, those using the e-start would do well to set the bike up for the start by pulling the bike back in gear until it comes up against compression. This will give the engine 1 1/2 turns and a fresh intake stroke before it hits compression, and should help it get lit quicker.

  • WR_Dave

Posted January 29, 2008 - 05:01 AM

#59

Getting back to the race start situation for a second, those using the e-start would do well to set the bike up for the start by pulling the bike back in gear until it comes up against compression. This will give the engine 1 1/2 turns and a fresh intake stroke before it hits compression, and should help it get lit quicker.



That's one of the reasons I got in the habit with my 426 of turning the engine up against the compression everytime we stopped on the trail and everytime the bike sat for any length of time. It also has the benefit of the valves being all closed while the engine sits and reducing the chance of a stuck open valve. On the '07 it's hard to find with the leg , but if you trun the engine by hand with the kickstart it is easy to find. :busted: WR Dave

  • SJMC_DON

Posted January 29, 2008 - 11:23 AM

#60

Anyone else like this mod for everyday use?


Yes I do...

:busted:




 
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