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photos from local show

K2750tracy

K2750tracy
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This year our vintage japanese swap meet and show featured the CB750 here is a couple shots of the show field line up despite the rain we had a few nice bikes show up.IMG_2163[2].jpg (312.7 KB) IMG_2164[1].jpg (312.1 KB
 

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This group is really into original machines. The second one in is a 71 in Red , was a very meticulas restore. Stunning bike. Took best in show, there were many other bikes there, i just showed the 750 line up.
 
Digger, Yea i pulled the head cause it had a oil leak. I found it has Megacycle full race cams #138-60 .413 lift 266 degree duration not sure what valves or springs but there not stock. The pistons i believe are Wiesco 68.5 mm with stock stroke Carillo rods so that makes it a 914.95cc. I have the head back on now and it fires up but i need better carbs the CV's need rebuilt and i dont want to put any $ in them as cv's suck for performance. I would rather get a set of CR's or Mikuni's, i also know where there is a set of 38mm Delorto's for a good price, just dont know where to get jets for them.
 
Yeah need to get some Keihin CR's on there, they work really well and very easy to change jets and change needle positions. You can change all 4 needles in about 5 minutes. I would skip the del ortos, at least for this bike. Can be a pain to jet just like webers.
Sounds like it has some good parts in the motor though. You gonna turn it into a streetable ride or keep it for drag racing?
 
Been thinking about selling it. I have no time for racing, I have my eye on a Santee hardtail SOHC 750 i might get if i can buy it right.
 
Big cams don't work nearly so well on the DOHC as the SOHC because the 4 valve head really doesn't flow well. Commonly the inside intake quits flowing above a certain amount due to the twist in the ports, even with serious headwork. Pretty hard to get cams bigger than around .380" lift to make more power, the engines rev higher but pull no harder. Better to short time the cams to pick up midrange so the motors last longer as they tend to blow up at anything over 10K due to several things. Rods are good there so on that one it'll be the timing gear, the chains break. This not from me but several guys who dragged the crap out of them. Honda made some big cams as well for the racebikes and the same thing, no faster, they just blew up. Some of the biggest cams were for inclusion on a super rare non-stock one-off race head that had different included valve angles from normal DOHC stuff, Honda was searching around, they knew they had a problem with the basic head. Some of the fastest draggers say the OEM 1100F cams are the best ones for an OEM head at around .370" lift..............you treat the motor more as a low rpm tractor than you do a high revver. It runs faster. The cams are greatly in demand but hard to find a good set as the hardcoat applied to them lets them commonly wear hugely even on low mileage engines. Hard to find a good set that hasn't got a lobe going away. Problem common to all of them really, just that the 750 has so little lift that the cams don't wear, the 900 they wear some with more lift but most good and the 1100 they wear like lightning due to the most lift.

There's a guy in New Zealand that has created a modded DOHC head that removes all of the kinks to then make about 20 more solid hp. over 10K and the engines then really open up to those bigger cams. That head cost around $5K though, an awesome work of art. He also makes revised cam chain guides that supposedly stop the high rpm chain breakage, he routinely runs up at 11-12K rpm. Working on dumping the primary shaft to go gear-to-gear crank drive last I heard. Head he said ran 27 and 23 mm. valves, making close to 180 hp.

The OEM head flows fine until the higher rpm then begins to choke off the one intake, then the power levels off bigtime, why it's so hard to get over 150 hp. on them. A 4V head (at least one with valves as small as the DOHC has) doesn't inertia charge at high speed anything like a bigger 2 valve can. It was leftover tech from the '60s along with the undersquare engine like the 900 had.

Hope those big cams have SOB tappets, that's shim spitting lift there.

X2, don't use CVs, it may even damage the motor.
 
Ive made a deal to trade the drag bike for this 78CB750F this Sunday, 78 is a running machine just needs tunned and cosmetics done.IMG_2166[1].JPG
 
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