Yamaha 92' WR 500

Joined
Nov 29, 2003
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#1
Hello everyone! This is my first post.
I have started racing my WR 500 at the local sand drag track here in Arizona.
I am not familiar with engine performance modifications to 2 stroke engines, I mechanic on Top Fuel Bikes and Funny Cars.
I would like to do some work on the WR engine, but don't know where to start.
The engine is stock, 487cc, and has an FMF pipe and silencer, Boyseen 2 stage reeds, and I removed the stock air box and installed a Uni round air filter.
My best times with the bike, paddle tire and strut, is 5.39 @ 60 mph. The track is 300' and altitude is around 1,500'. I have just installed a 10" over swingarm and lowered the chassis. I will run the bike as is for the next few months, we are starting our winter series. But, I want to start getting advice on what to do engine performance wise. I hope to start engine mods around June/July.
I would like to move up to the MP1 class, which is 4.49 and quicker. I now run the MP2 class, 4.50 and slower.
Thanks for any help!
Patrick
 
Joined
Aug 13, 2000
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#2
Check out my reply to a post on the subject of Maico engines.

Also, come over to macdizzy.com 2 stroke forums. There is a wealth of info there and some crazy folks who race similar machines.

Chris
 

EricGorr

Super Power AssClown
Joined
Aug 24, 2000
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#3
Welcome to DRN, I have a soft spot for the old air-cooled YZ/WR of course maybe thats due to the vibration vibrating my spine into Jello!

My friend Troy Bradshaw won the AMA Amateur Nationals in 1984 on a YZ490 in 1984, the year Kawasaki introduced the water-cooled KX500, supplying a factory bike to Tommy Watts for an amateur race. We enjoyed kicking their green asses that week. I preferred the 40mm round slide Mikuni from the 490 over the flat slide Kehin. There is a ton of porting that can be done to that engine to unleash the beast. Up in the Midwest here, the 490 is still a popular bike in ice racing where power is paramount.
 
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#4
Chris, will check out the Maico posts and Macdizzy forum.

Thanks, Eric. I have been checking out your site and reading the tech articles. I installed an air shifter and the track workers just shake there head when I leave with the front wheel 2' in the air, feet dangling, and hit the button. I have to stay as far up front as possible until about 70-80' because if I move back before that, the bike will try to put me on my backside. However, my 60' times are so inconsistant because I stink at slipping the clutch. Lots of traction with the 5.5" wide 10 paddle tire. Should not have to do that with the new swingarm, wheelbase is 67" and lowered a bunch. If she don't spin the tire, which I don't think she will because traction is not a problem, it should run some low 5's. Next event is Dec 6th. I know there is lots of potential with this combination. If you want to check out some pics, www.photosintime.net
Click on sand drags, click quads/bikes, I'm on page 6. I am the first 5 pics and the last few pics on that page. Several wheelstand pics.
Patrick
 
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Nov 29, 2003
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#6
Looks like the engine will have to come apart before I wanted it to. Had shifting problems all weekend. It would shift fine on the 2-3, but would not shift, under heavy load/full throttle, on the 3-4 or 4-5. It would shift fine under lite load/half throttle.
I did improve in 60' times and ET.
best 60', 1.874
best ET, 5.277-backing out of the power to make the shift