The quad riding hill Billy's must have been on the moonshine....ha..
I have had deluded ideas about pressing a 2 stroke twin crank apart and rebuilding so both cylinders fire together,wouldn't be a problem on any of the Yamahas that have a wasted spark..I don't think it would vibrate any worse than a Maico or yz 490 etc?....if it gives you pins and needles so bad you can't shut the throttle it could be an issue?...

Yeah, they call that a "TWINGLE"

Twin cyl 2 stroke with both pistons rising and falling together. Goes like the clappers.

There a bike called the "Yankee Boss" sold in the USA in the late sixties, it used a modified Ossa twin engine.
500cc two stroke.

More info............
http://www.yankeetwin.com/

Potentially that could give a crf 450 a run for its money,with the right ingredients in it....not sure about the suspension and brakes though.....although I've seen a few riders on older bikes that it doesn't seem to bother in the the least..

marcm wrote: I have had deluded ideas about pressing a 2 stroke twin crank apart and rebuilding so both cylinders fire together,wouldn't be a problem on any of the Yamahas that have a wasted spark..I don't think it would vibrate any worse than a Maico or yz 490 etc?....if it gives you pins and needles so bad you can't shut the throttle it could be an issue?...

I've never ridden a big single 2stroke, what do you see as the pros & cons of a 360 degree twin over a single

Rick

First bike I ever rode was a Jawa with that "twingle with shared combustion chamber" configuration. My brother swapped it with a friend for doing some work on his car. I never could figure out whether it was a 175, a 250 or a 350. It was pretty horrible. I've never been able to figure out the benefits of that sort of engine configuration.

It is a very good layout if you are seeking a kickback capable of launching a person into low earth orbit. That thing had a kickback like a mule. The only other bike I experienced that had close to that much ankle-breaking power was a Yammie RT1.

I have a theory that when the Russians launched Yuri Gargarin into space for man's first ever orbit, they used a Jawa, not a rocket. They already had the technology, see. Same as how the Americans spent a gazillion developing a pen that would write in zero G, upside down, sideways, whatever - while the Russians just used a pencil.

I also had my first crash on that Jawa - straight into the clothes line when the front end washed out during a torrid lap of the 7 Ballance Avenue grand prix course. The clothesline, compost bin and our two dogs were constant hazards.

Doing the usual on the net looking at modified 660s & came across HV (high velocity) tuning on a raptor forum.
Which lead me to

Mototuneusa

Lots to read on porting & using that "shit to a blanket" stuff so you can undo what you've done if you don't like it

Not sure if this site's been mentioned before Too much in my yoof

Rick

Mototune has good stuff there.
A god-awful web site but good info.

I wanted to velocity port my xr250 but the intakes were too small to work with...

I ran it in hard though and each lap, I could feel it getting stronger. 6 years later, it's starting to lose some compression.

NordieBoy wrote:Mototune has good stuff there.
A god-awful web site but good info.

Agreed, that's why I loaded that page to start from, easiest to find articles from & go back to to find the next installment
It'd be easier if he just explained his ideas instead of trying to get readers to think for themselves all the time

I've been thinking of raising my port floors for while. Always known gas velocity is important & the right hand port on the 660s is massive compared to the carb that feeds it, slowing gas down right where you want it to accelerate even using standard porting practices.

J. B. weld tomorrow I think & give it a try.

Rick

Is that guy welding his ports shut? or JB weld?

Mezo.

Mezo wrote:Is that guy welding his ports shut? or JB weld?

Mezo.

JB weld on the inlets, I think it's alley weld on the exhausts to get the "D" shape, no idea how they manage that.

Rick