Jawa Flat Twin

[Barry]

Here a 500cc flat twin I'd never seen before.  It was a prototype made in small numbers and never made it to the market. Looks to me like they put the gearbox under the engine which pushes the engine higher up. Look at where they tucked the bings away !

From the real Classic web site.

[Luca]

And look at that, Bing carburetors!

[montmil]

Jawa built some solid, dependable motorcycles in their time.

That's a clean looking and very interesting design. At least your feet are not banging Bings. On my R100S, I have to move my foot up n' under the right side 40mm Bing just to reach the foot brake pedal.

[nhmaf]

Same basic layout as the Honda GL1000 goldWing, though with less cylinders.   And, it is also the same layout that BMW is using on the new Waterboxer with the intakes on top, exhaust on the bottom..

Everything old is new again... eventually the bell bottom slacks, afros, and miniskirts will be in vogue again too!

[Barry]

No chance of just popping the float chambers off on those carbs. Perhaps not a great design from the maintenance point of view.

On the other hand most bikes (airheads excepted) have poor access to the carbs. Same goes for spark plugs. Access on airheads is brilliant where as on some other bikes with V twin engines it takes half an hour to change the rear plug.  

I guess we are spoilt.

[steve hawkins]

The do seem to be making things unnecessarily difficult....I wonder if they were just trying to differentiate themselves from BMW?

.....Can't imagine there would be a good technical reason for it.

 I would like to have heard the salesman's 'blurb' !  By that I mean the bollocks he/she would be spouting to explain themselves.

Rev. Light

[montmil]

Jawa produced some strong 2-stroke MXers back in the day. Been whupped by a few. Then there's the vintage CZ models still showing up at AHRMA races.

Old'scool [smiley=thumbsup.gif]

[Barry]

Some more info on that Jawa flat twin.  It had over head cams and 4 valve heads. Bike was built in 1984 so if it looks a little like an oil head it wasn't a copy.

[Luca]

.....Can't imagine there would be a good technical reason for it.

Probably because it's a DOHC engine.  If you want separate intake and exhaust cams, that is the way to set it up.  It also keeps the intake or exhaust from having to run through the cam chain...  come to think of it, I've never seen the intake/exhaust flow move parallel to the axis of cam rotation.

Honestly, it looks like with the gas tank off the carbs would be easy to remove.

[Luca]

move parallel to the axis of cam rotation.

on an ohc engine

[nhmaf]

I'm sure it all made perfect sense to the design team at the time..  Don't think that I'd want to own one, but I would enjoy taking one for a little ride

[clonmore1]

"eventually the bell bottom slacks, afros, and miniskirts will be in vogue again too"!

Great, I'm glad I kept mine (er...not the minishirt of course... )

[balibeemer]

How do you adjust the air mixture screw which is on the bottom of the carb?

[Tony Smith]

How do you adjust the air mixture screw which is on the bottom of the carb?

It was a prototype - get it up and running, then fix the fine detail later.

[balibeemer]

Must have been designed by an Italian!