83 cb750 sc troubleshooting/misc questions.

[83seebee]

Hey everybody, just wondering if anybody out there has a link for a repair manual.  I saw the 79-83 manual that is downloadable on this site but I'm not sure if that is the right manual for my bike and I tried to download it but couldn't seem to open it after it downloaded...

also, I have a manual for the 84 model and i'm wondering what changed that year aside from the shaft drive conversion.  Not sure if the electrical is any different on the 83.  I'm pretty new to this bike and any insight will be most appreciated.  I just picked it up for $900 and it sure made my day to ride it home but It's got some kinks to work out...

1: The front and rear suspension is pretty soft. I was told 200 a piece for rear shocks.  Would a bike scrapyard be a potential way around that or am i stuck with what I have until I spend the $$$$?

2: The front fork parts are all pretty spendy too for a rebuild with new parts.  what are the odds of getting good results by rebuilding with existing parts and is this a potential DIY project?

3: Throttle hangs quite a bit or just comes down slowly.  the linkage at the carbs returns fine.  Is there something sticking in the carb?

4: The bike has a really significant difference in power when you hit 3k rpm.  are these motors just weak at low rpm or could it be an ignition or carb problem?

5: Right around 7500 rpm there is a loud buzzing sound, but its only between maybe 7500 and 7600.  any ideas?

6: I need to change out the sprockets anyway and from what I hear, plugging the little sludge factory (self oiler) is easy if youre working in there.  Has anybody done this and are they glad they did?

7: I can get a K&N air filter for around the same price as oem.  Is rejetting necessary with a different filter like that?  


I'm pretty new to the motorbike world, thanks in advance to any help here.  If I get a manual I can do some troubleshooting to narrow down some issues and whatnot but thought I would just throw everything out there for now.

[TOOLS1]

Welcome to the forum. Sorry, but I can't help with the manual, but I am sure one of the other guy's will be able to.
I can answer some of your questions though.

1: The front and rear suspension is pretty soft. I was told 200 a piece for rear shocks.  Would a bike scrapyard be a potential way around that or am i stuck with what I have until I spend the $$$$?

Look at vintagecb750.com and partsandmore.com for shocks. I bought a pair of progressive shocks, for less then $90.00 from partsandmore.com

2: The front fork parts are all pretty spendy too for a rebuild with new parts.  what are the odds of getting good results by rebuilding with existing parts and is this a potential DIY project?

All, you need to rebuild the front forks are fork seals, a qt of ATF, and maybe dust boots. Cycle-X has the seals, for $7.00, vintagecb750 has the seals, for $12.00, and the dust boots. As, for instructions on how to do it, look, for "My Buddies POW/MIA Bike" in the build section. I have a step by step photo layout of it.

3: Throttle hangs quite a bit or just comes down slowly.  the linkage at the carbs returns fine.  Is there something sticking in the carb?

Does the cable need lubed, or replaced?

4: The bike has a really significant difference in power when you hit 3k rpm.  are these motors just weak at low rpm or could it be an ignition or carb problem?

The carbs might need cleaned.

5: Right around 7500 rpm there is a loud buzzing sound, but its only between maybe 7500 and 7600.  any ideas?

No.

6: I need to change out the sprockets anyway and from what I hear, plugging the little sludge factory (self oiler) is easy if youre working in there.  Has anybody done this and are they glad they did?

If the bike is self oiling, it needs a new counter shaft seal. On the contrary to what a lot of people have been led to believe. These bikes never did have an automatic chain oilier!!!!  

7: I can get a K&N air filter for around the same price as oem.  Is rejetting necessary with a different filter like that?  

Should not need to re-jet if, you just use the K&N replacement filter in the stock airbox.

TOOLS

[shinyribs]

Welcome to the forum!

I wouldn't DARE dispute anything Tools' recommends,but...

3: Throttle hangs quite a bit or just comes down slowly.  the linkage at the carbs returns fine.  Is there something sticking in the carb?

If the linkage is returning OK it should be returning the cables wit it. You could possibly have a vacuum leak.That can cause a slow return to idle,as well.

4: The bike has a really significant difference in power when you hit 3k rpm.  are these motors just weak at low rpm or could it be an ignition or carb problem?

These motors have pretty decent low-end torque,but the real power comes on in the upper rpm's.My bike really starts pulling good around 3-3500 as well

5: Right around 7500 rpm there is a loud buzzing sound, but its only between maybe 7500 and 7600.  any ideas?

Not sure about this at all,but my headlight ring used to vibrate at certain rpm's. Some strategically placed electrical taped did the trick.

Good luck on your bike

[seestheday]

Welcome to the forum.

I downloaded that manual and opened it no problem.  Try downloading it again?

I have a copy on my computer and can upload it somewhere if you're still having trouble.

Edit: Also for your issue with poor performance below 3K I'd bet your idle jet is plugged (carbs need cleaning)

[83seebee]

Well I did get that manual to download which is helpful and I'll definitely go online for the shocks.  Another question:  Theres some rattling going on in the motor and I was told it might be the cam chain.  In the manual it says you let it idle, back of the lock nut and tighten the bolt for the front and rear.  Is that all there is to it?

also, is it easy to replace the countershaft seal?  It would be nice to get rid of the sludge that coats pretty much every part on the rear half of my bike.


And with the throttle hanging I realized that it only does it once its warm. and every once in a while it will stick at 3k rpm and it will return to 3k when you are stopped and bring it down with the clutch.   but it usually drops down to idle speed when you slow down to under 15 mph or so.