Topic: Got a new bike...

[Dunk]

Well I bought a bike today. Absolutely gorgeous '71 CB750. Needs a bunch of little things but nothing major. Didn't run when I looked at it yesterday. Told the guy I'd pick it up in the morning. When I showed up he had it running, barely. Took it home and put the Dyna ignition from my '72 on it. I would ru but wouldn't idle nice. Sprayed carb cleaner in each of the carbs and it idles great now.

Took it out for a ride and... What came to mind was HOLY S**T. It's the fastest bike I've ever rode. Way faster than my buddys 1100 Shadow, which my '72 CB 750 could just about keep up with from a dead stop. This '71 engine breaks the tire loose like nobody's business, powerband doesn't come on 'till 5000 or so and then once it hits 8000 it takes off like a bat outta hell and goes past 11000 that the tach goes to. Once it past the end of the tach I let off, didn't wanna blow it up but it was still pulling strong.

I figure there's no way it's still a 750cc engine. Gotta have a big bore kit or something. Crazy fast.

Needs a few things, like bars (currently have dirt bike bars), brake shoes, left side panel repair/replace, and a few otehr things that would be nice. Most of the stuff I can take off my '72. Also, anyone have a picture of a correct '71 CB750 seat? I don't think the seat on this bike is original and amy use the one on my '72.

Anyhow, not bad for $700.

[Tim.]

Well, the 16" rear wheel and FUNKY exhaust are clues someone did something to that thing.  I've never seen a header like that.  Bobbed front fender, missing rear fender/grab rail - someone was on their way to something.

Might have a different cam in it.  I don't think just a big bore kit alone would explain the changed powerband.  And revving beyond 9-10K sounds like lighter rods etc.

Guess you'll have to take it apart to find out   Wonder if there's a way to measure cc's - guess you could pour fuel into a cylinder through the sparkplug hole at bottom dead centre from a graduated cylinder to find out how much it holds.  Be a rough guess and you'd have a mess to clean up

[.RJ]

Anyhow, not bad for $700.

Damn, where are you guys finding these deals

Nice bike

[andy750]

Nice bike and agree about the headers - very cool!  More photos please!!!

Great find!
cheers
Andy

[Roach Carver]

i think the 71 seat and 72 seat are different. the 71 looks almost exactly like the later versions--- no ducktail, but I think the brackets are different from 72 on.

[andy750]

The 71 and 72 seats are different - I have both. The patten on top is different and the 72 is slightly thicker.

cheers
Andy

[PxTx]

Did you start lookng the bike over for clues?  That Sidewinder equal lenth header is the obvious clue.  Got any closer pics of the engine?  I know on some vintage prepped bikes, I have seen mods tot he valve cover to keep more tention on the cam caps.  My biddies Russ Collins engine has an RC and something else stamped where the 836cc pad is cast.  Looks like a real unique bike!

[754]

Now THAT is the Gnarly header I been talking about that a buddy ran on his 71 when I rode with him in the 70's!! Those and my pipes are the coolest I have seen!!


Easy check, get a cylinder light, pull a plug and you will get an idea of bore size and compression ratio.. just be careful setting valve clearances on an unknown cam. Check your clearances now and record..before you set the valves.

Pic of the front taken from left of the front wheel please

[Dunk]

Just rode out to a bar and grille about 20 mins ride away to have dinner and a brew witha  buddy of mine. This bike is totally awesome. Take off from a red light and twist the throttle just a tad and you're already slowing down for the next red light while all the cars behind me are jsut taking off from where I started. I'm so amazed at how fast it is, and I still haven't gone wide open! Feels like if I give it much more throttle it'll throw me off the back!

The thing revs so quick. I want to verify tach and speedo are accurate, though I don't see why tach wouldn't be. What can I do to verify/calculate speedometer accuracy? What is stock front tire size? That's all that would affect speedo accuracy right?Twisting the throttle a bit from a stop in first gear only I'm at 50-60 MPH in no time at all, assuming speedo is accurate. On the way home I was romping it from lights not quite winding first all the way out, then quickly shifting to 5th and letting it slow down to a normal cruising speed for that road (45 MPH or so)

After that ride back home my left arm hurts... Clutch is rather hard to pull. Not sure if it's springs or the cable. Cable is longer than it should be. I think I'll swap cables off my '72 when I swap the bars. Probably have the bars chromed before putting them on as the chrome isn't perfect. Would I be correct in assuming '71/'72 bars are the same?

Also, bike it set to idle at about 1700-1800 RPM and engine feels a little rough (rumpity-rump cam I assume) until about 2500+ RPM when it starts to smooth out and pull harder.

I'm gonna go out and put the bike back in the garage for the night. I'll take some more pictures and post them in a little while.

[fuzzybutt]

great deal on the 750, however you really dont want to use that header, i'd be willing to take it off your hands. juts kidding, sweet bike, wish i had it

[Roach Carver]

if the motor is built, it may have hp clutch springs causing stiffer pull on the clutch.

[KB02]

Or it could be a bad cable...

Pop the cable off and check it out for smoothness. If it's good, than it's probably a HP Clutch like 71cb750 said.

[Dunk]

Cable went out last night so here are a few pics...

[andy750]

Great photos! Those have to be most interesting and cool headers I have seen on a CB750!

I can also see why your clutch might have been a bit stiff - the clutch cable looks a tad long....interesting bike for sure with some later 750 parts (tank, sidecovers look to be from a `75).

cheers
Andy

[Roach Carver]

i wonder if that header is off of a wrecked bike.