A year of speed hill climbing an 04 YZ450F - likes and dislikes.


6 replies to this topic
  • 72degrees

Posted July 04, 2013 - 12:06 AM

#1

The Will Power tuned 04 YZ450F 'supermoto' I bought last year has now done quite a few speed hill climbs in the UK. Mostly in my hands but my lad has ridden it at one event. He will be taking it over as his main ride soon as the 96 YZ250 is showing its age and he is complaining that it's too slow.

Likes:

The power - way more than I can do justice to. It took me a while to find the rev limiter as after my experience years ago with a Husky 510 I didn't want to find out it only had a mechanical self destuct one. More flexible than I expected a high rpm tuned four stroke single to be which makes it very nice to ride at wet meetings.
Cold starting - it's a softy. Follow the drill and it's one kick.
The Hinson slipper clutch. No locking up the back wheel demon braking for hairpins.

Dislikes:

The four speed box. Not a problem at short courses (possibly even a benefit as you can do linked turns in one gear) but they are very close together. Gearing for a hill with long straights gives a pretty high first gear but I can still manage 2.2 second 64 ft times. You run out of gears pretty quickly though so rear sprocket changes of one tooth are required for optimal top speed. I'm doing my calculations based on max rpm of 11500 but max power at 10000 but seat of the pants suggests the tuning mods may have given a real rush in the 'mid range' at the expense of top end. Settling on 15/40 or 39 for most places (with 165/65 x 17 rear) which will give high 80s.

Hot starting. Well I suppose warm really. Given the slipper clutch I can't bump it down the hill as I used to with the Husky (with valve lifter) and the Norwest was obviously electric start. It's not too bad if really hot but at hills where you wait at the top for everyone else to do their runs it cools down to a temperature which makes it very fussy. The hot start lever helps a bit but it needs a very good kick to persuade it in to life. Any tips? I'm 65 and getting arthritic so this makes for a hot, bothered and very cross rider (though it keeps the other guys amused). It's become enough of an issue that I just bought a KTM 350SXF with *electric start* for my dotage.

My lad graduated from a YZ125 last season (which he came second in the NHCA 250 championship on) and has been riding our 96 YZ250 at most meetings, but he had a ride on the 450 at the first event. That was held in subzero temperatures (for humans with windchill factored in) though on dry tarmac. He put in far better times than me and pretty respectable for the 500 class but dropped it in the final 'open' run at the end of the day. Still, 10 others also did including several of the top ten championship contenders. He is looking forward to riding it again in a couple of weeks at a longer hill and hopefully in better conditions. The last few events of the season will be ones he can ride two bikes at, so he can pick up 250 points and also give the 450 an outing. If he takes to it I guess we will keep it and go 5 speed as part of next winter's preparation though I dread to think how much the parts bill will be at Yamaha spares prices in the UK. I had to repair both the bikes last month after they were damaged in a motorway crash (my trailer was rammed on the way to an event). Thank goodnes for used and pattern parts available on Ebay.

I used not to like Japanese bikes (my first love is Italian and would you believe I had a modern French road bike) but working on the YZs has generally been a good experience - not the problems with fasteners made of cheese that we brits used to complain about years ago. I've not touched the orange bike with a tool yet so I'm reserving judgment on that. ^_^

Edited by 72degrees, July 04, 2013 - 12:14 AM.


  • grayracer513

Posted July 04, 2013 - 02:32 PM

#2

The '04 was my favorite steel YZ450. Regarding the hot starting, be certain that you don't have the idle set too rich. The bike may also like the throttle tipped open very slightly when cranking.

  • 72degrees

Posted July 04, 2013 - 10:56 PM

#3

Thanks for the advice. It pops a bit on deceleration so I'm guessing the idle mixture isn't far off correct. The carb is too high tech for me to dare fiddle with much yet. I'll happily mess with old Dellortos and the Keihin PWM on the 250. If it's just a case of tweaking the idle circuit with a screwdriver I'll try it. I've found a whiff of throttle helps but it's a case of finding the sweet spot. I can kick several times without any sign of life and the next will succeed with seemingly the same technique. It won't bother my lad so much. He's a super fit rock climber and mountain biker with a kick like a mule.

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  • grayracer513

Posted July 05, 2013 - 06:36 AM

#4

Thanks for the advice. It pops a bit on deceleration so I'm guessing the idle mixture isn't far off correct.


Faulty assumption. Decel popping is also commonly caused by air leaking into the exhaust system, typically at the mid pipe joint, or the head. The pilot should be trimmed out independently of any consideration regarding popping from the exhaust.

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  • 72degrees

Posted July 05, 2013 - 01:52 PM

#5

Fair enough. It has a custom titanium pipe. I'll check for any obvious leaks. The popping isn't bad, only really showing up when riding gently back down the hill and on a closed throttle for a while.

The pilot setting procedure is similar to what I'm used to on the Morini - except that needs the two carbs balanced with a mercury u-tube manometer both at idle and on just cracking the throttle (which makes a huge difference). I'll have a fiddle at Shelsley Walsh tomorrow. Plenty of time between runs as it's primarily a car event and it's going to be hot (by UK standards).

  • grayracer513

Posted July 05, 2013 - 03:00 PM

#6

The popping isn't bad, only really showing up when riding gently back down the hill and on a closed throttle for a while.


I would call that normal.

  • 72degrees

Posted July 06, 2013 - 10:46 PM

#7

I had to spend time doing wheel swaps (to a cut slick rear) and sprocket changes (the Michelin slick is a sufficiently different diameter to affect the gearing and the wheel had a sprocket with one more tooth so I was undergeared for one run) so I left well alone. Being a hot day the only truly cold start was the first of the day but I got a bit better with my technique and found the hot start lever was doing its business. Plus you can free-wheel back down the hill at Shelsley so I coped. I managed an 86 mph through the finish speed trap which is a personal best for that hill. Quicker than the tuned 604 Gilera Nordwest. Still 12 mph and 1.5 seconds off my times on the 1000 Voxan and naturally my lad pipped me by about half a second on his YZ250 now that it has a functioning power valve governor again. I'm looking forward to Loton Park next weekend and may try pilot screw adjustment there if it gets fussy.





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