YZ426 Pulse Per Revolution

After tearing up a rod in the original TZ project with a clapped out WR400 motor (big end came apart and sheered the rod in half, remarkably didn't affect the case or the head!) I have found a shift light that works with the A/C current of the YZ (current heart of the Hybrid). But I am having problems figuring out how many times the coil is firing per revolution. The light seems to come on fairly early when I set it how I think it should be. Any help would be greatly appreciated. Thanks.

C'mon now...hook a brother up!

One more try....

I'm not sure where you're hooking up to but I'll see if I can help. There are 6 connections to the magneto on the YZ450 (probably the 426 as well but I don't have a manual). The white and red wires go to the pickup coil which I believe is the trigger to fire the ignition coil. I haven't verified this but I think it fires once per revolution which means it is firing on both the compression and exhaust strokes. Basically if the pickup is on the crank (like the YZ) the ignition will fire every revolution but engines that trigger off the cam will only fire the ignition once every other revolution. The other wires in the bundle go to the magneto source coils and those output AC to supply the CDI unit among other things. Their frequency is a function of engine speed times the number of poles on the coil but I'm not sure what that is. On a WR it is on the order of 100hz at idle. Tapping of the signal to the ignition coil is probably a better choice. In any case it looks like the coil fires on every revolution (compression and exhaust). If the tach your using is calibrated to count 2 revs per firing which is the more traditional method you will read twice the actual rpm. Does that make sense??? :thumbsup:

Thanks for the info. Using my multimeter the two places I found a signal were the pink wire from the Magneto and the orange wire to the coil. Both volatages where similar...low! I originally had a sweet Stewart Warner Light/Tach but it needed a clean, strong (over 10 volts) D/C signal. The light I bought from Hi Speed Tech needs less than 5 volts and doesn't care whether it had been rectified. I am using the orange wire set at 2 pulses per revolution. I know the rev limiter hits at 10,500 so I won't be able to test it unitl I hit Road Atlanta over the 4th but I think I am good. Using my multimeter (kind confusing as it only gives me 4, 6 or 8 cyl inputs) and a low shift point (3000 rpm) I think I have a direct correlation. We will see. Thanks again for the reply. Some validatiaon is nice.

Hey, I just noticed you have a 426 in a TZ frame :thumbsup:. I have one in my Aprilia RS-50 frame that is street legal and my buddy has a TZ426 that he races down here in the Southeast CCS races. There's not too many people out there with single cylinder hybrids. How has yours held up so far? Does it compete well for you? My buddy pulls Aprilia RS250's out of the corners but they can run him down on the straights where the top end power comes in.

Very Cool!! I went and checked your pics out last week. So far not so good. The first motor I used was a tired WR400 motor. I seperated the big end of the rod at Nashville in March and it spit me on my head. Not too bad as I was in the rain. $1450 later I have a built YZ426 motor that came from at ATV race team. Fresh rebuild and runs strong. I am running it at Road Atlanta next weekend and will have more info then.

Who is your buddy...Jason Clay? He has helped me quite a bit with mine.

Here is a link to some pics of mine. It has not been updated with the new oil tank and the bodywork is still rough but you get the idea.


Out for now...

Yeah its Jason Clay. He is running the WR motor in his bike. I am the one who helped him get his bike put together and helped him find the parts and stuff he needed for it :thumbsup:. Your bike looks great so far, but why did you make the oil tank so big? How much oil does that thing hold? How much does your bike weigh with fuel and oil?

Let's just say in my first iteration and I thought biggger was going to be better with the oil tank. It didn't turn out so well. The second version ( I will update the pics this weekend) is made from thinner material and mounts on the right side where the coil would have monted on the original TZ. It weighs about 25% of the original and is much more functional. I had the fabricator weld in oil filler and suction line from a raptor oil tank. So now I have a decent fill hole and a screen in the bottom. My best guess on weight (using the two bathroom scale method) full of oil, water and about a gallon of gas is 224lbs.

I am racing with Jason over the 4th. I look forward to meeting him and viewing your guys handy work!

Yeah that sounds good. Have you had any venting problems with your oil tank so far? I have mine mounted in the tail of the bike with a vent in the top but I didn't have it vented properly so it would spew oil all over the tank. I found out it is supossed to be routed off the oil tank to the breather tube on the valve cover so it can suck it back into the engine. I don't want to take too much credit for Jason's bike though, he did all the work and I just kept in contact for advice :thumbsup:

So far I have not had any problems. I have the small hose vented from the valve cover to the tank and then the big hose I have vented to a catch can that holds about a pint. So far I have not had any oil in the can...well...I should say from the old motor I didn't. I don't expect any from this one. I am also careful to to overfill and leave a good air pocket in the top of the tank. I use the Raptor dipstick as a go-by. I will pst some pics tomorrow and email the link again so you know its updated.

Tell me about the Aprilia conversion. How does the frame handle the motor? Does it flex alot? That would be a hoot to ride.

Actually the Aprilia frame is holding together very well. At first I was worried about the structural integrity from the added weight and power but it is doing fine so far. The main thing that takes most of the abuse is the swingarm pivot. I am glad I was able to retain the stock mounting location in the swingarm for the 426 motor. Without that mount the motor would definitely put too much stress on the frame and probably twist it loose. I added a reinforced brace in the swingarm also so it is very strong now. It's just a very time consuming project because I want everyting to be functional. All the stock dash lights, new custom built tachometer, speedo and temp guage have all been painstakingly hooked up so they all function like stock. My goal is to make the bike as factory built as possible so its not just a pieced together bike with a big motor stuffed in it. I also mounted a custom radiator setup in it with a fan to keep it cool in traffic. The stock headlights were too small also so I made a custom plasma halogen setup with dual 50 watt bulbs for night riding along with an LED strip mounted in the tailpiece. I am also having the flywheel machined down soon to give it more bottom end snap. Since the WR flywheel I installed is heavier, I am having it lightened but it will still run lights. One major pain in the ass on the bike was building the kickstart assembly so it would clear the frame. I had to buy two complete kickstarts and weld both knuckles together so it would be spaced far enough away to clear the frame on the downstroke. After a little welding and grinding, it fit perfect and just clears the peg when fully engaged :thumbsup:. Here's a few pics.




It just looks so clean and smooth!

My TZ was pretty beat up when I bought it. I am plannin, if the project stays together, to paint it and re-polish up the frame over the off season. The last motor I bought came with an ATV kickstarter that was extended a bit so if you run into hassles let me know. I will ship it to you for a try. I had to grind about an 1/8" off the starter shaft on mine to get it to clear the frame.

I have been over to the local shop a few times to check out the new YFZ450 ATV motor. It has electric start and looks like it wouldn't interfere with anything on my bike. I might try and serach for one of those motors next year.

I finished mounting up the shift light and put on some new pegs tonight. I have local machine shop that has been doing my machining for really sweet rates. They machined me four pegs for $60. I need to swap out the rear sprocket and re-safety wire a few items and I am ready to go to Atlanta next weekend. If the weather holds up I will get some pics.

Cool, definitely get some pics of the bikes in Atlanta. Yeah, I also thought about the YFZ motor but its only 38hp stock :thumbsup:. It would be sweet if it had the same specs as the bike engine. However, if I do another hybrid project it will be with a CRF450 motor. No oil tank or lines to deal with :awww:. I was looking at those kickstart extensions for the quads and they were like 200 bucks :devil:. I figured I could make one for less and see how it worked first. If it doesn't work, I would definitely like to try out the extension though. Keep me posted on your progress. I would love to know how much power your motor is putting out. I figure mine is right at 48hp with the 450 cam, UNI filter and 117 octane race gas. Jason's bike is 47hp with a Lectron carb but the WR's don't make as much power as the YZ motors.

I seriously thought about using the CRF motor for this project. I think you can get pretty decent horsepower out of a CRF (you have one...you would know better than I!) but I worried about the four speed tranny. There is a fella that races WERA with us, Matt Blashfield, that has a CRF in a Honda Hawk chassis. Jason whoops up on him but Jason could be a better rider. Either way he did a sweet job with the install...a ton of machined billet mounts. Mine are all hand fabbed mild steel...by me.

I put some updated pics of the new oil tank on my pic site. Sorry they are so dark but I took them in the garage. I can't wait to paint is so it looks worthy. I took it up the street with the race gearing, 16/35, and it sure is tall. But that should be right for Road Atlanta.

She is lubed, wired and ready to go. Will post more when I get back from the races!!


The CRF motor is a 5-speed and the only reason Jason was able to beat him is because the Hawk chassis weighs a lot more than his TZ. At least that is what he told me. So you are running 16/35 gearing :devil:. That is huge, I didn't know a 16 would fit. I am running 14/38 gearing on mine and it still runs 100mph. Definitely get some pics from Atlanta though :thumbsup:

Wow...didn't knwo that the CRF was a 5 speed, guess I should have researched it more! Next time that might be the way I go. I like the single camshaft.

Email me and I will send you a spreadsheet that I made up to figure gearing. It is pretty cool. You put in your tire circumference and you can see how each change affects speed in every gear. I locked the cells and forgot the key but you can chnage the secondary ratios to get an idea of what the gearing does. I have it set to compare the TZ, WR and YZ. The gearing that I am running now matches what Jason is running (WR vs YZ). We will see.


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