RFVC, another Honda better idea that no one asked for.  It was an engineering solution to a problem that didn't really exist.  With conventional 4-v heads it required the valves to be set in parallel layouts and there was surface area in the head that was basically unused.  This was the area on the sides of the combustion chamber.  By spreading the valve placement and setting the valves roughly equidistant around the chamber. This allows a basically Hemi shaped chamber that is fairly good for flow, but carries its own problems.  One of which is that both the intake ports and the exhaust ports are now splayed apart.  Running dual carbs and dual pipes help with the design because they can allow the ports to be fairly straight adn flow well.  Muzzy did some GREAT port work and engine building with the early 250 and 600 engines.  The dual carbs also allow good tuning of the flow and bigger carb area between the two carbs without losing the bottom end power of the engine.  Honda used a progressive carb linkage, while the Yamaha used  a vacuum secondary carb. 

The Europeans that ran hemi chambers in their custom designed race Thumper engines in the late '80s and early '90s generally uses tapered lobes on the cams, which allowed splayed rocker arms with out the sub-rockers that Honda had to use.  They were much cleaner designs and did well in the unlimited Thumper race classes.

Yes, the single shocks are better suspended and handling.  The 600s aren't hard to start.  At least not if you know how to start a Thumper.  It is not a small displacement 2-stroke and you don't "fan" the kick starter.

Ride them before you buy them.  The newer 650 will have far superior suspension than the '80s bikes.

Swiss

My buddy has an 83 XR500 (an RFVC?).  He wants to make is street legal which I think in California means having a headlight and tail/brake light.  Anyone know of a kit he can buy to do the conversion?  Or is there a lights, brake light switch, and a battery box, combination off say a comparable vintage XL that would work; if so how would he do the electrical connection i.e. is there a wire out of the magneto that would work, would he need a voltage regulator or diode like the early XLs?

hey Jee, sorry for the delayed responce, Ive been offline for a while.. and thanks for the complments.

before the Honda XL there was SL and before that CL, yeah they go WAY back! now were down to one XR, kinda sad really...

yes Honda still produces the RFVC engine, that should tell you something. this valve arrangement increases flow and rpm. combined with the dual-carbs its a tuners dream!


my XR250L is a real wimp compared to my XL250R when both were bone stock, except for the suspension and disc brakes. the dual-carbs give tremendous mid range grunt compared to the single carb and revs much quicker too. both would hit 85mph in stock form but the dual carbed 250R got there in half the time and wheelies with much less effort. now (after many mods) it really gets it and I have to keep the brake pedal covered when riding wheelies! the 600R is definately a wheelie monster but its a work out off-road and on-road all that weight is really noticable when stopping fast or when cornering hard. needless to say I dont ride it much for fun, but its better for the longer road trips because it doesnt have to buzz as much at speed.

the dual carbs are a bit harder to remove/install than a single and jetting can be tricky. I use an o2 sensor in the pipe coupled to a rich-lean indicator for re-jetting, not really nesasary if you keep the engine stock though.

the 600R isnt too hard to start if everything is right but (3 kicks max when cold)but if its not right it will literally break your ankle! that how I got this one, the guy I got it from broke his ankle trying to start it when it kicked back. its only got me once hard but that was because I stalled it and tried to kick it on the fly but it only brused my ankle real good, next time that happens I'll stop to restart it.

Ive been looking for a dual-carbed 350R to restore next but they are not easy to find either..

Id seriously consider the older XR250L over the 650 if most your riding is off-road unless you are over 200lbs. the 250L is gonna be harder and harder to find since all honda offers now is the 650 for a dual-sport. Honda really dropped the ball in the dual-sport catagory! they should have made an XR400L but if they will give US the CRF450R dual-sport like Italy and Belgium gets I will forgive them. I'll give them one more year... then its KTM time for me.

have a good one!

 Just a note that in 1985 the Honda XL350R RFVC was Cycle Worlds Dual Sport Motorcycle of the Year.
 That means it beat them all, KTM, BMW ETC.

 Oh, and I bought one this Summer after selling my XL500R, FT500 and XL500s this Spring.