New Member - 1983 Nighthawk CB650SC - first bike - brake and sync question???

[rotomotor]

Hi everyone, great forum!
I've been reading it for awhile and I finally bought my first bike last week, a 1983 Nighthawk CB650sc. It is from another forum member and has 19,500 miles on it. I have driven it 100-150 miles over the last week and I have a couple questions. A strange thing happened today with the front brake.

The brake handle was half broken off when I bought it and I ordered a replacement handle. The bike had been knocked over in a parking lot the day before I bought it. Bummer. I replaced the handle yesterday, went for a short test ride and everything seemed fine. This afternoon, I went to take it for a ride and the front brake seemed somewhat locked up. I could move the bike but just barely. I was able to move it around enough to get it into 1st gear and out of the garage. It didn't seem safe so I put it back in the garage.

Trouble shooting note: I noticed that when I eased the clutch out, the front fork would drop.

So, I decided to remove the new handle and see if that made any difference. It did, and freed up the front wheel, now the bike moved normally. I put the handle back on and it still worked just fine. Against my better judgment, I took the Nighthawk out and rode for 20-30 miles with no issues.

What is going on here? A coincidence that I replaced the handle and the brake locked up because it needs servicing? The handle caused it? If so, why did it work in the test ride and all afternoon today after being removed and reinstalled.
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Second Issue: The previous owner installed rebuilt carbs and believes that the carbs should be sync'd. I have been reading about the DIY carb sync tools and some posts on this forum. Can someone please answer these questions?

Will I need to remove the seat and fuel tank? I read that on Nighthawks, someone has sync'd the carbs without removing the tank.

Is there a graphic posted somewhere that shows which screw to turn on the carb when I hook it up?

This is a 1983 CB650sc, is one of the carbs the reference carb or do they all get balanced?
 
What is the order in the procedure?
Warm up bike, attach vacuum hoses, start bike, etc. Is there a way to really mess this up??

Thanks in advance for any help given, I really appreciate it!!
Scott

[detdrbuzzard]

hello and welcome to nighthawk forums rotomotor. when you tightened up the brake lever it got pinched in the housing and would not fully release. when you reinstalled it, well its obvious what happened

[Zugzug]

The #2 carb is the ref carb. #1 will adjust by itself in relation to #2. The adjustment on #3 carb ajusts 3and 4 together and then #4 adjusts by itself in relation to #3. I hope this made since for ya.

[gammer]

The 700s/750s does not need to have the tank removed to preform a carb sync. I have sync'd my 750s several times without removing the tank. I also sync's another members 700s with the tank on as seen in the pic below. Not sure if the 650 is the same way? But I suspect it is.



The syncing process is really easy. Please refer to your manual for exact instructions.

I recommend this exact carb sync tool:
http://www.carbtune.com/

Its a tad on the expensive side...buts its the "Bee's Knee's" when it comes to carb syncing. 

[rotomotor]

Thanks detdrbuzzard, Zugzug, and gammer.
Those are the answers I needed to know. Thanks again!

[wingman]

Welcome to the forum.

Even if you do have to remove the tank. It is quite easy to do. Take off the seat. Turn petcock (gas switch) to off position. wiggle off gas supply lines and unbolt tank. Will take you about 2 min and it gives you a little more room to work. There should be plenty of gas left in the carbs to complete the sync.

Not to be picky but it is CB650SC (Sport Cruiser) not cs.

[happycommuter]

Rebuilt carbs should be balanced upon installation, but they are likely very close out of the box and a minimal tweaking would be needed.  Probably acceptable as is, just not optimum.  If there is poor mileage, idling or some other symptom then it is more recommended.  It's nice to check every couple thousand miles but it can be overlooked for a long time as the imbalance gradually grows.

Some sort of balance gage and a (preferably stubby) screwdriver is all you need.  Do a search, there are some good previous posts on the topic.  I mention the Twinmax in most of them.

[rotomotor]

Welcome to the forum.
Not to be picky but it is CB650SC (Sport Cruiser) not cs.

THANK YOU! not being picky at all, I'm a detail guy. I have not seen the letters SC defined anywhere yet and I was wondering what the designations were. It's funny how some of the simple stuff is so elusive.

Thanks happycommuter and wingman. I really appreciate your input.