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2003 YZ450F Coil Pack Retrofit to 400/426
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Posted by: biglou---------------------
2003 YZ450F coil on plug mod for 98-02 YZ400/426F:
First things first-Why do this? Well, first and foremost, because we CAN! Secondly, it is a very clean-looking aplication that also serves to allow you to rotate the carb so you can directly access the bottom of the float bowl. This makes rejetting a snap. And, it really cleans up the looks of the bike on the right side. There is currently a popular mod which involves modifying a coil pack from a 99 Lincoln Continental into a coil on plug pack for the 400/426's. This mod is no different, with the exception that is is a more compact unit that doesn't interfere with the head stay at all. Note that I had that 99 Lincoln mod in place when I started this new mod. I also elected to link to my pictures so as to preserve the highest possible picture detail (read: larger pictures).
Here's how I did it:
Here's what things look like in stock configuration: Click.
Here is the current popular coil on plug mod (details can be seen on Motoman393's website: http://motoman393.thumpertalk.com/ ) as compared to the 2003 YZ450F coil pack: Click.
As you can see by the next two pics, the reach is just short on the new 450 coil. Compare it's reach to the 99 Lincoln Continental coil's reach: Click 1, Click 2.
To get around this, the boot at the top of the new 450 coil can be trimmed to allow it to slide farther up the coil pack and giving it more reach down into the head so it firmly engages the spark plug. See the following series of three pics on how to modify the boot:
First, just pull the boot off the bottom of the coil pack: Click.
Next, trim about 1/8" off the top of this boot: Click.
Last, slike the boot back up onto the coil pack as far as it will go: Click.
When you push the coil pack onto the plug, be sure it is seated firmly, then push the boot down so it seals the opening in the head against any dirt or debris. Here is what the finished product looks like: Click.
Electrical info: The connector should be available at any Autozone type parts store. I used the same connector that I got when I bought the parts to convert the Lincoln coil. I think this is a fairly standard automotive industry 2-pin connector. Run one lead to a ground, either where the old coil was grounded (there's a grounded terminal there already from the TPS) or on the head stay somewhere. Take the orange wire that pushed onto the spade terminal on the stock coil and connect it to the other lead on the plug to the new coil pack. As you can see, I soldered and heat-shrinked my connections. Don't forget to slide some heat shrink on the wires BEFORE you solder them! 
Coil info: Yamaha p/n 5TA-82310-00 (mine was $71 before tax).
Let me know if I've forgotten any important info or if you want to know any other details. Unfortunately, I didn't get to ride it. The weather here in the Midwest has been absolutely abismal for the past 2 weeks. Looks like the closest I'll get to riding this thing in the near future will be to change the oil or sit on it and make "vroom-vroom" noises... 
Posted by: Treejumper---------------------
Nice work Lou! :thumb:
Posted by: BSWIFT---------------------
That last pic proves you rode at Cooperland. Nice work.
Posted by: Lorin---------------------
I'm curious, with all of time and money spent, did this mod improve performance in any way or was it done to improve the appearance and access to the carb?
Posted by: biglou---------------------
The latter. It is functional in that matter. Plus it looks very "works"! That alone is worth a couple bucks! For the record, Dr. D ran a Hayabusa coil on his 426, and, word is, that other than fashioning the electrical connector, it is a direct plug in-no modding to the coil pack necessary. Granted, my mods to the coil were extremely minor.
Posted by: ohvrider---------------------
I'm wondering...did you check the resistance of the Ford coil against the stock resistance of a Yamaha coil? If there is less resistance in the Ford coil it could overheat the cdi box after a good ride. If it has more it would be less load but also less voltage at the plug. I put a Mallory Promaster coil on a Ford once and burned out the module because I didn't use a resistor inline. It ran fine for about an hour or so before it messed up. I'm gonna show the pics of this awesome mod to my friend who has a 426. I don't know if he wants to buy a 450 coil when he's thinking of buying a 450 anyway. Did you use the little bolthole in the Ford coil to hold it down better? Nice work... Actually I'm a mechanic and I think I have one of those coils off a 5.4 somewhere :thumb:
Posted by: biglou---------------------
The Ford coil mod has been around for some time. I have a buddy here locally that has been running his hard, roughly three times a week since February and he has had no problems. I talked with Doug Dubach at DirtWeek for a while about some of the technical aspects of the new 450, and while we didn't talk exact resistance numbers, he did mention that he had indeed run a Hayabusa coil in his 426, and that the new 450 coil should do the trick on the 426 just as the Hayabusa coil did. There are probably dozens of folks over at ThumperTalk that are running this coil setup (the Ford setup) and none have reported problems yet. I suppose I could grab all three coils and do a resistance reading on them for comparison. I'll get that posted first thing after work tomorrow.
As far as the bolt hole in the Ford coil, I didn't see one, and I don't think I could have bolted it anywhere. It is a tight squeeze under the headstay/frame spine with the Ford mod. Granted, you can't see it with the tank on, but it was still kinda crammed in there.
One last thing, now that I think about it. Seems like the 99 Lincoln Continental coil pack was chosen because of its relatively close resistance reading as compared to the stock YZF coil. I do remember that it was a bit less, so it may run a little hotter. I'll see if I can confirm all this tomorrow. Right now the bikes are wedged into the back of the garage as I am staging for a trip this coming Thursday. I'll pull them out tomorrow and take some readings. Thanks for bringing that up. :thumb:
Posted by: biglou---------------------
Here's what I came up with:
Stock coil 0.7 and 22.2k ohms
Ford coil is 1.0 and 5k ohms
The 450 coil, well, I can't seem to get the connector off with the tank in place, and, like I said, the bikes are jammed into the back of the garage. I'll get to it within a week and post back here. Sorry, but I just don't feel like rearranging the garage and pulling the seat/tank again this week!
Posted by: the bigfella---------------------
You guys truely have way to much time on your hands!
Lol
But I love your work!
Posted by: biglou---------------------
Finally got around to measuring the coil from the 03 450. 0.6 Ohms. For the life of me, I cannot get a reading through the secondary. Not sure why, but I cannot read anything (open) from the plug contact to either pin at the head of the coil pack. Oh well, it runs!
Posted by: Humai---------------------
BigLou,
Thanks for the informative post and follow-ups. I saw a guy kicking and cursing his 01 WR250F the other day for fouling plugs. I wonder if this mod would help deliver a more powerful spark in cases like this.
Posted by: OldassKDX---------------------
Maybe it could, but he'd be a lot better off jetting his bike properly.
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