• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

mako1001

CB750 Member
Messages
11
Reaction score
0
Points
1
Location
illinois
Ok I will get straight to it. I have an 82 cb750sc nighthawk I've been bringing back to life after a 20 year hibernation. One setback after another. Anyway I was rebuilding the carbs and discovered I can't remove one of the main nozzles which is damaged. I'm sure I will find a way to get it out but after I do I will need a new one. Are any other cb750 carbs compatible with the 82 cb750sc? Thanks for any help you may have.
 
OK I have to respond to my own I was able to remove it using an old timers technique still trying do get the beast running but at least this problem has been solved
 
Hey know this is a little old but did you fix all your carb issues I've come to know these cv carbs quite well...thanks
 
Not yet, I got them all put back together back on the bike and no go. One would flood and the rest seemed like they aren't getting enough fuel. I know it's a carb or vacuum issue because I can spray starter fluid in them and it fires right up. They are just sitting on my work bench in the basement waiting for me to tear them down again and figure this mess out.
 
Your probably right. The cv carbs are a b×#!× when you said rebuild did you cleasn all fuel jets and air jets? how are you trying to run them pods or stock air box? Do you have the vacuum valve on top of carbs? Can you run Me through it real fast what upgrades and things you've done to fix?
 
You must absolutely guarantee that the pilot jet is open and the air cross passages in the top above the metering hole are open too. They clog super easy and then the idle is lean but as soon as you raise throttle any at all then goes super rich because of the seesaw action the pilot and primary systems have on each other. The pilot fuel feed hole becomes an air bleed as soon as the primary strikes up operation.

As well, the bowl under the small fuel progression holes that feed as soon as the butterfly moves open any at all causes trouble if clogged, the holes all or part can then work or not work depending on how clogged. So idle and off-idle will be plenty messed up. You'll be amazed at how much % of driving goes on at those lower open throttle amounts.

Everybody cusses the CV action but it's pretty simple and reliable, people just don't get that the different cylinders will open the carbs different amounts based on how well each cylinder sucks. Meaning any missing compression (common on these) makes people go for carb work when often none is needed. You need solid compression or these will run like utter crap even if you've been through carbs umpteen times. I won't even think about carbs until the motor is well sealed. A waste of time otherwise.

Ethanol if used in your fuel causes issue with flooding when the superfine rust from it gets in needle/seat to mess with you over and over.
 
Reliable yes, simple yea if your good with a wrench. He is right clean and clean again. More hands on and learning the carbs and tweaking to the bikes liking will take several hours maybe a couple weekends of work but you look on this site and their is plenty of info on forums about how "simple" the cv carbs are with people that have had your same problem probably as we speak with no luck yet. But don't give up on them just yet. just ask questions you'll get it. Any mods on the bike? Pods? Exhaust?
 
As far as cleaning the first time I had to soak them in simple green for 24 hrs that's how bad they were and then three additional cleanings but I'm no expert at these carbs so the cleaning is fairly basic fuel holes air holes just really the basics as far as upgrades I have a mac 4-1 cannister style and using the stock air box I bought pods but everyone has told me not to use them so now they are ornaments for my garage someone was telling me to make sure the coke circuits are clean but I haven't gotten back into them yet maybe late tonight I will
 
New member, does anybody know the answer to the original question? Rebuilding a '82 CB750SC and the whole carb set is missing. Thanks!
 
If looking for the entire bank grab a good set off any '79-83 750 DOHC, much better '81 and later though as they have screw in pilots, the earlier ones are pressed in. Other than that almost exactly the same other than very small main jet differences that are small enough that if stock bike they pretty much all interchange.
 
Awesome, I found one that's off of an '82 CB750 (11/8 Keihin VB 42A B UA), and one with no year but it said from a CB700(?) (Keihin VE65A A). Trying to restore as close to factory as possible, manual says carb is VE65A, but that one doesn't look like the one I've seen on a '82 CB750SC. Haven't done much carb work before so any recommendations or thoughts are helpful. Push comes to shove I can always wait to find a parts bike. Thanks!
 
CB700 is a totally different engine and carbs will not fit.

The VB carb series is DOHC that year range and some others (CX series, CB400), the correct ones according to service manual is VB42A for '82 Nighthawk CB750SC model. Then there is still the '83 model. Sure you got the correct manual? CB700 was '84 model Nighthawk, they then popped the 550 and 650 ones too. That engine is the next gen after 1st DOHC, a more upright cylinder motor.
 
Last edited:
Wow, you guys don't miss anything. Looked at the manual again (it was off of motodataproject) and it had said the manual was 82-84 but the first page of the manual says 84. That was an oversight on my part. Looks like I'll be picking up the VB42A then!
 
Yah, the '84 uses rubber diaphragm type CV carbs, the 1st gen uses solid piston CVs like the old CB450s did. A lot more research went into how to make those suckers work with the heavier leaky type slide. Why that type hates individual pod type filters, the carbs open too slow because the slides leak and by design. Among about 50 other reasons.
 
Back
Top