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UF's cb750k

10K views 125 replies 23 participants last post by  scottyp 
#1 ·
Dad and wife got me a cool bike for christmas (best.gift.ever)

Its a 1972 cb750k supposedly with high comp 836cc
Its running rough oil fouling plugs and i think the timing needs advanced a hair

Future plans are
-electronic ignition
-retune carbs (piss poor low end/ off idle)
-re gear (way too tall)
-raise up the suspension
-replace the hard strut ("monoshock") with some progessive twin shocks
- tlr swingarm
-replace side covers and tail and possibly change color?

-need to investigate the big bore claim (i have a feeling thats not true) as it also needs a head gasket and valves adjusted maybe seals too.

Trying to take baby steps so i dont de-commission it for too long. Should be fun:fu:


http://s1379.photobucket.com/user/J...15_zpsnea6nawb.jpg.html?src=pb&fb_ref=Default
 
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#10 ·
GS tanks have a neat little flange at the front that allows you to effectively scoot the tank back, while still hiding the neck. They're also pretty wide. Exactly the same width as the engine. That's what I put on my 76F and the GSXR forks cleared well with minimal steering travel loss. But I don't recommend them on these particular chassis'. I can elaborate if you want, but I know you know what's up, so I won't derail too much. Just wanted to mention that about the tank. Carry on...
 
#12 ·
What about a F tank off of a DOHC? It's about the same size but as a narrower profile up front that should clear your USDs. I don't have any issues with clearance on mine


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#14 ·
got the cable on and started it cold. Has some valve adjustment needed and some hotter plugs, also need to adjust the idle air screws a bit. Otherwise i'm pleased... for now. Still doesn't seem to have the power on the low end. I've heard the .370 Valve Lift and 282° Duration cam from web works well with the 836 kit but i'm still not convinced this is an overbored engine yet.

http://vid1379.photobucket.com/albums/ah144/Justin_Clements/IMG_00941_zpsujm0kcak.mp4
 
#16 ·
Have you done a compression check on it....?
That might tell you if you need to go deeper into it...or give an idea if it does have bigger/higher comp pistons
 
#17 ·
ive only had a few 1/2 hour blocks to work on it. I wanted to see if the digital ignition and new advancer helped. It did a little. But its in need of a new head gasket and studs anyway. Im not discounting the cases havent been split it looks like a fresh bead of hondabond, but its not half as fast as i got my Kz650

Ive seen other cb836 and they can break the rear tire easy. Almost certain the valves are adjusted wrong as well but i cant seem to find my offset wrench to fit
 
#18 ·
#21 ·
well, it was in the oil bucket along with a screw driver and a few loose screws/bolts. Someone has been busy....

Went ahead and adjusted the valves, most were way out on the intake side, exhaust was within .002"


Still some issues


floats were all different levels, the float needles decided to start sticking all o'asudden, and the sync adjuster were outta whack too
new carb kits and fuel lines on the way
 
#25 ·
I have a spare 750 engine all though i had a tough time getting those off too
A beaut! Them USDs really drop tha front on older bikes fer sure,does it need some extender tubes? ( need some for a set I got here and am looking forra source) . Twin shocks woud fill out that long rear end and beef up tha look ,what arm isist Justin?
I had some new shock bosses turned up on a lathe and bought some Progressive cb700sc

Not sure what brand the arm is. I think im going to keep it but i might put a tube under brace on it
 
#26 ·
got the shocks but haven't got the needle valves yet. Got the fuel lines on and tried to get it to fire but 2 carbs are sticking shut.

I hope to have it running before to long. Build a brace for the swingarm and mount the shocks and bosses up. Ready for some smokey burnouts on that old rear tire!
 
#27 ·
Went ahead and ordered all new floats/ needle valves and seats. Installed and it fired up. Synced the carbs and this fucker rips when you twist the throttle. It pulls like my fj1100 did. Smooth idle, hangs a bit when its cold but im glad its nothing major.
Ill probably be bending up the brace soon and putting on the shocks.. Then to punish the old rear tire:CK187:
 
#28 ·



did 20 miles in between yard projects. Runs strong. Needs a new rear tire and probably some stiffer clutch springs. It pulls hard then starts to overpower the springs. But it will spin all the way thru 2nd :CK187:
 
#30 ·


Ended up being totally carb related. One needle was wrong, one float was from a different kehin carb set so it wouldn't open when the bowl was installed. A cross over in between carb 1 and 2 was got plugged with gunk (possibly from the old fuel line)after i cleaned them the first time. And also the slide adjuster threads for carb syncing didn't have any lock nuts so they would vibrate out and come out of sync.

Also the 97 octane with a 110 octane boost additive was playing havoc with pinging so i did strait 110 torco and it runs smoother and cleaner.

Still need to play with the timing. Gearing is too low. At 55 the rpms are too high.
 
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