Topic: First Motorcylce 1978 CB750K. Cafe Build

[TommyT]

OK new to this forum and have been checking out the cafe racers and wanting to build one for the last 3-4 years.  Finally got myself an old CB750K off craigslist about a month ago for $550.00  it's running great and drives perfect.  So naturally I'll cut it up and make it my own.

Here's a little background into my past and current projects. I've been building and racing offroad prerunner race trucks for the last 5 years.  Having my own 1450 sq ft fabrication shop building and prepping a few vehicles at a time.  here's a couple pics of my truck and ongoing project.





Back to the motorcylce.

Here it is the day I brought it home.







First to go was the king/queen seat and the rear fender section.  l.  I pulled the motor since the previous owner had heli coiled one of the spark plugs back in the head and was kind of suspicious of the job he had done.  Overall it was done very nice and professionally like he said.  Motor will stay sealed up, just with new paint and polish up the side covers and such.
I then turned to the look of the bike.  Didn't want that cruiser feel but more cafe racer styling.
Decided to build my own rear fender and modify the rear frame to match the shape of the new fender as well.









With that roughed in moved onto the giant tank.  It looks straight as can be but stripped off old paint and found bondo and dents all over.  So I figured why not practice making some knee dents on this tank.  Worse case I'll get a new tank anyways.  I think it turned out decent and definitely improved comfort when sitting on the seat. 











Still not sure what to do with the front of the tank since I want to run a drag bar or something lower profile but I'm sure they will hit the wide K8 tank.

Other minor upgrades I've done or are doing is replacing rear shocks, front progressive springs, new headlight bucket, new bars, relocate ign switch, switch to a 530 chain/sprocket, and paint.

[TommyT]

Got a few more things done.  Frame is painted, just gotta get the engine all cleaned up and put back in then I can get this thing going.







Pulled covers off engine and inside was spotless.  That's good news compared to the outside of the engine.

[Really?]

Kewl so far.  Looking forward to the rest!

Welcome to the forum!

[hapakev]

Nice work man, your momentum is inspiring!

[78whiteorbs]

that tank came out great ! I like the dent lines mixed with the stock ones~ How long prepping that tank?

[TommyT]

Well  after making the templates and marking out where I wanted them to be it took about 45 min to get the dents knocked in.  THEN i cut the back edge and re welded that a few times till it held pressure.  Then another 15 hours or so into all the body work to get it into primer.  Just gotta sand it again and then it'll be ready for paint. 

[TommyT]

Getting closer.  Still have little things to finish up like linkage for rear sets,  exhaust brackets and modifying pipe a bit to clear rearsets and such more.  Finish air cleaner I am building and paint tank and seat. Also going to ditch the gauges once I get it going for a single speedo/tach unit to clean up bars a bit and bob/paint the front fender as well.  Turning out just like I had hoped.

[TommyT]

OK so I have a few clearance issues,  First the kickstand comes into contact with the rearsets.  Have you guys ever bent the kickstands in towards the frame to clear rearsets or what you guys doing.

Next is the rear brake lever.  The way I have it mocked up now it seems like it would want to apply the brake as the rear suspension cycles.  Are you running the linkage forward towards pivot then back to get rid of this or is it not noticeable like I think it would be

[78whiteorbs]

Tommy, seems like you are gonna have to relocate that kickstand. Might as well get rid of that centerstand while you are at it.

[Gixxerusa]

Great progress so far.
Never thought a golden frame would look good on a cafe. You proved me wrong. Keep up the good work....

[TommyT]

OK centerstand is just slipped on so I can work on it easier.  Comes right off when I go to ride.

I think I figured out the kickstand and I'll post up if it works out.

[MCRider]

Its not often talked about but the rear brake will engage itself partially as the wheel goes up. I think the stock geometry is about as best your going to get unless you convert to a cable.

So your rearset linkage would have to go forward to the stock pivot point and activate the stock spindle. I notice it barely on a stocker. Any change would have to be well thought out.

I had rearsets many years ago and that's how they worked.

[TommyT]

I would love to go to the factory mount but I already removed that I am machining a bellcrank type pivot now that will mount to the backside of the lower rearset mounting bolt to  which can change the forward push to a rearward motion and hopefully make the pivots closer to in line to reduce brake engagement as wheel cycles.
 
If that doesn't work I'll have to make a bracket and run a cable.  Any ideas on what cable type or size would be needed to make stretch and risk of breakage a minimum.

[MCRider]

Many bikes of days gone by had a cable rear brake. I'm thinking of my 1968 CB77 305cc Superhawk. The rear brake on it was a double leading shoe, more powerful than our CB750 brake. Wouldn't hesitate to use that cable. Its a pretty hefty piece. Certainly there is one like that you could use.

I think the Daytona CR750s used a cable brake. It may have been a double leading shoe as well, I think it was. Don't know if they got it from the 305 or not. The last Cb77 was made in 1968, the Daytona CR750 was a 1969, so...

There is a CR750 thread that's full of all that stuff.

Yours doesn't need to be a DLS, that was just talk.  I think I've seen a stocker converted to a cable here by welding a cable lug onto the brake plate.

[TommyT]

One more question.  I was looking at the pivot to arm length to see what ratio they are stock to what I have now and it appears my rearset arms need to be about 1" longer and the arm on the drum about 1.5" shorter to get similar ratio's so I don't have to push down on the brake 2-3 inches to get full engagement.  Does this sound right to you guys.  How much downward travel does your rear brake have before it's fully applied stock?

[MCRider]

One more question.  I was looking at the pivot to arm length to see what ratio they are stock to what I have now and it appears my rearset arms need to be about 1" longer and the arm on the drum about 1.5" shorter to get similar ratio's so I don't have to push down on the brake 2-3 inches to get full engagement.  Does this sound right to you guys.  How much downward travel does your rear brake have before it's fully applied stock?

If you adjust the rear brake on a stocker to where its touchy feely with weight on the bike, like 1/2 to 3/4 inch full on, when you go into a dip and push the rear wheel way up, you can actually feel the brake engage and slow the bike down. If you adjust it so that never happens, you have a pretty sloppy feel in regular circumstances, like 1.5" or more. So its a compromise.

This is part of the same geometry lesson I've spoken about re: chain adjustment. With the chain it starts loose with the wheel/shocks at full extension, gets tighter at mid-arc, then gets loose again as the wheel/shocks nears bottoming out.

With the brake it gets progressively tighter as the wheel raises.

[TommyT]

OK got exhaust all on and mounted now, brake linkage figured out, just need to weld a longer tab onto the lever to get the ratio closer to where I want it. 

Now I got another question.  I got new from brake pads  with the piston 100% compressed and the caliper mounted back onto the bike that pads are so tight onto the rotor I cannot push the motorcycle.  I did notice the old pads are worm at a 10 to 15 degree angle as well.  Any ideas on how to fix this and make these new pads work.  They are EBC.

[TommyT]

Getting Closer, Gonna try and get it fired up today if I can get the wiring finished up.  Got a few unlabeled plugs I gotta track down on the wiring diagram.

[d1000rr]

wow great job!

[TommyT]

Thanks,. tried to fire this afternoon and as soon as the fuel was turned on the bowls started leaking.  Gotta order some new gaskets.  Anyone know a place on the west coast preferably California or close that has some for the 78 in stock?

[lucky]

Of coarse a gold frame can look good on a cafe.

[lucky]

If the float bowls are leaking is it the overflow hoses or the bowl to carb body junction?

It the overflow is leaking, you just have to install four new float needles.
Thats it. Not the seats too, just the needles.

[TommyT]

With the carbs off and on the bench when I hook up the fuel it's leaking on the #2 carb between the body and the bowl.  I cleaned off all the silicone #$%* the PO had put on there and cleaned it all out but still leaking a bit.  Floats/needle and seats all look good. Float levels are spot on and everything was running great when tore down.  Just sitting for the last 3 months without fuel i think the carb gasket dried out a bit letting it leak out.

[TommyT]

WEll got the carbs back together and it doesn't seem to be leaking anymore.  Got it fired up and it sounds great.  Will get a video clip tomorrow for you guys.  Just gotta finish up a few things and get the tank and fender paint, seat upholstered.  Then i'll be off enjoying it just in time to park it again for winter. 

[wannabridin]

looks GOOD Tommy!  that's almost like a green-gold huh?  graphite/gunmetal tins would look the part with that color frame!!

do you have the exact color you used for the frame?