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My 1982 cb750SC

c3powil

'82 Nighthawk 750sc
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Metro Atlanta
Hi guys!
I recently purchased a Nighthawk 750Sc. It's got ~35,000 miles, and aside from the MAC looking 4-1 exhaust, it looks pretty stock. The PO told me he had rebuilt the front brakes, cleaned the carbs, and changed the oil and filter. After that it sat for two years. The owner before him bought the bike in 2002 and put 2,000 miles on it in the 10-11 years he owned it. It was the original owner that put the brunt of the miles on this hawk, then it basically sat for 13 years.

After I picked it up I took it to my local vintage mechanics shop. I was told that it sounded and felt as if it's only running on three cylinders and has a little front brake drag.

I was quoted 750 to have the carbs rebuilt with dynojets and synced.

That is steep money for me, so I just opted to go with a general checkup to make sure all cylinders have compression, stator and charging system is working, and other General things. I should get the bike back in a few days.

Now I'm fairly confident in my ability to rebuild carbs and front brakes, so I'm planning to do that myself if there are no other drastic needs. My plans for the bike are nothing special. Get it running well, make it safe and reliable, and ride the heck out of it.

Is there anything I should know about this model before I continue?



The only "modifications" I have planed are dynojets and some lower bars (superbike or similar). Would love to add a rear rack, too. I just want a reliable bike that will be a good daily driver and fun for weekend trips.

Pic:

nighthawk.jpg
 
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RUN THE VALVE CLEARANCES, they are 8 out of 10 times why people that are unlearned go for the carbs first. The valves tend to CLOSE UP rather than the norm of getting looser and then a valve somewhere in there begins to hang open to leak compression then motor runs like crap.

IGNORE the OEM clearance of .003" nominal, get them no less than .005" and they go MUCH longer. The cams are so loose even with new engine that the valve clearances are not what you think you see with engine stopped, the cams get pushed around in the head clearances to give fake valve readings. .003" can be close to zero running and for sure .002" IS zero. Why you loosen them a bit to get a guarantee of proper compression.

There are those who make a habit of buying those bikes running like crap and then fixing valves to then get $1000 more dollars when they resell it weeks later. They usually have to straighten out the carbs when somebody screwed them up thinking he was 'fixing it' as well.

The Dynojet kit is often a waste of cash, you can easily get the carbs to work fine without them.
 
Thanks for the info. I've had an experienced mechanic (runs a shop focused on vintage japanese bikes) take a look at the bike, and he's the one who told me the carbs needed a cleaning. He is also the one who told me to do the dynojet upgrade. With the carbs working well, valves in spec (.005 as you mentioned), and charging system gone through (it was giving weak readings), I should have a good running bike.
 
Okay, so update on my bike...

I have a broken valve cover bolt. Yes, it's broken in the thread. No, it is not sticking out of the thread. Also, to make my day just that much more awesome, it's the middle upper right one. It looks impossible to even try to drill out without removing the coils or taking the engine out.
 
How people manage to do this stuff???

Do you have the other half of bolt? If looking at it and broken clean enough the other piece may be possibly just screwed in there. Seen it more than once and like a sharp sewing needle used competently will unscrew it right out...............after that you are history. The end of the upper half of bolt will tell whether you can do it or not.
 
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