Kool Yamahas

[Nathan S]

I can't imagine a production pipe from an engine with totally different bore, stroke, porting, carb, ignition and cooling system, being the best pipe you could put on YZ-A.

So I'm not sure why 'psyche out value' a clearly wrong pipe has? Maybe "Hey! Better stay away from me on the track, cause my eyesight is so bad that I put this abomination on my bike! I'll probably take out half the field in the first corner without even noticing, Mr Magoo style".
(none of which is intended to be a personal slur on Gary Jones, who is clearly a legend - just one lacking in taste, it would seem).

Surely a designed-for-YZA pipe would be the way to make it go best, and then you could make it look a lot better.

[JohnnyO]

Keep the photos coming Red, have you got any of the Legends on the track? Who gives a f#*k about what pipe Gary Jones is running, it's not in our back yard so it's not an issue. I don't like the look of it either but if it didn't work he wouldn't use it, he's smarter than the average backyard tuner. Snail pipes were around in '74 and they do use them in vmx in the US.

[jimg1au]

yes he is smarter than the average tuner.mybe it is inside yz250 2008 spec.when i used to road race there was a 125 bsa bantam with yz125 yamaha inside.back then no one cared about is elebility.this was about 1981/82.

[Marc.com]

oh I think you can make a lot of internal changes but is it cricket,

[DR]

I personally think the pipe on Gary's bike is cheating and regardless of how well it works and how much respect I have for him it borderlines insanity rather than absolute brilliance. It isn't vintage and simply does not belong and infact is detrimental to the sport. Yes, I maybe a purist but modern technology and design parts simply do not belong anywhere near a vintage bike

[Marc.com]

you could build a pipe or use late 70s YZ pipe the original position easily anyway, they were just being lazy, looks like CR pipe.

back to playing with those motors, I just ported my MX250 and added new slightly larger carb, boyesan reeds, its the same basic engine setup I used on IT250H that went like hell.

[mx250]

Sounds good Marc. Are you gonna race it?.

The MX was a very good but underrated engine of the day. Obviously had a lot of potential as well. With a 34mm carb, the back of the piston cut away and the Webco head mine use to blow away Elsies (which were the benchmark of the time) at Nepean's main straight - two bike lengths every time .  But then it might have been the rider as well .

[Marc.com]

Sounds good Marc. Are you gonna race it?.

The MX was a very good but underrated engine of the day. Obviously had a lot of potential as well. With a 34mm carb, the back of the piston cut away and the Webco head

Exactly, i see no reason why the MX250 shouldn't haul and it is easy to get parts for. I hve 34mm carb on it already, looking for Webco head, do you have details of the piston modification.

BR Marc

[jimg1au]

back to that pipe on the yz it isnt the only 1 in the usa to have it.vmx mag no 28 2006 page 50.the pipe is from 1998 yz250 noleen.also this bike has been ported to go hence the pipe quote the power that this bike puts out is amazing though it comes with a price.the power band is narrow and ther is very little power down low.
jim

[mx250]

Sounds good Marc. Are you gonna race it?.

The MX was a very good but underrated engine of the day. Obviously had a lot of potential as well. With a 34mm carb, the back of the piston cut away and the Webco head

Exactly, i see no reason why the MX250 shouldn't haul and it is easy to get parts for. I hve 34mm carb on it already, looking for Webco head, do you have details of the piston modification.

BR Marc

They were pretty staightforward 'home brew' mods. We started moding the OEM Dykes Ring MX pistons. We started by filing and opening up the original holes in the back of the skirt. After use we noted cracking. Not wanting a catastrophic failure  we thought 'why not cut away the back of the piston entirely?'. Which we did. Just hack saw the skirt away and trim up and chamfer with a file.  We timed the piston so that the port was fully opened all the time relying on the reed to keep the charge in the cases. 

We were concerned about the resulting extra tilting, thrust and accelerated wear but we countered that by frequent piston replacement. For this reason we swapped to using DT pistons. In the day they were about 1/3 the price of the 'race' MX pistons.

In this configuration the motor did MX, D/track, club road race and enduro without failure. It run the Castrol Nepean Six Hour and was second in class before my 'know better mechanic mate' took the ride and did clutchless gear changes expiring the bike with a blown third gear before it was to be handed back to me . It was fast and reliable.

Mind you, Yamaha pretty much did the same thing with the later model pistons.