Jetting question CB700SC

[Baileyman]

I apologize, if this has been covered previously.  I didn't have luck doing a search.

It looks like I've got 120 main jets in my 84 NH.  As far as I know it's all stock otherwise (pipes certainly are, and I believe air filter is too).  The manual calls for 115 mains.  Will the bike run better with 115's in it?  I don't how it runs really, because I started rebuilding the top end just after buying it, and it's not back together yet, waiting for the cylinders to get honed, rings to be replaced, and carbs to be cleaned.

Any reason to keep the 120's in there?

Thanks,
BaileyMan

[drdubb]

I've lamented about the jetting on my 750 in previous posts. The previous owner put on an aftermarket exhaust w/o changing jets. I experimented with different slow jets, but didn't touch the main jets until I put in a dynojet kit. I finally gave up and put on a stock exhaust and used the dynojet mains for stock exhaust. Jets are fairly cheap and easy to change once you get the routine of pulling the carbs. You could go to the stock jets, if there are not other mods, it should run fine. The larger jets make a richer mixture, which may not be better. You can always switch back.

[gammer]

I've got a fair bit of experience with jetting on the Nighthawk S.

If you are running stock pipes and stock air filter (with lid and snorkle) then you should run the 115 main jets. What do the needles look like? I only ask because I wonder if a PO installed a DynoJet kit. The stock needles are non adjustable and the DynoJet needles has notches for adjustment...


DynoJet left. Stock right.

[Baileyman]

I'll check the needles soon.  I just got most of the parts in that I need to get my carbs back together...

I've been waiting months to get my bike up and running.  Just about to put the top end back together too...it woul dbe a drag to have to wait another couple of weeks to get the right jets (if I need 'em).  It seems that any time I need parts, it's 2 weeks...

Thanks for the suggestion!

BaileyMan

[BlackHawk84]

After reading this thread, I started to wonder if I need to do anything about jetting my carbs.  '84 CB700SC, stock air box, aftermarket 4-in-1 Kerker exhaust.  Right now all jets are stock -115 main jet, with stock needles.  I am fairly new to riding, so I am not the best judge of the performance.  However, it feels like power delivery is very smooth at all RPMs.  The extra power kick comes up at about 7-8k.  Any thoughts?  TY.

[muttstang]

if you want to get rid of the 120 mains, I'll take em off your hands 

[Baileyman]

What do the needles look like? I only ask because I wonder if a PO installed a DynoJet kit. The stock needles are non adjustable and the DynoJet needles has notches for adjustment...

The needles appear to be stock.

if you want to get rid of the 120 mains, I'll take em off your hands 

Do you have 115 mains? Perhaps we can work a trade.  I'll PM you if I decide to get rid of the 120's.

[muttstang]

I'll have to see how it reacts when I change my cam timing!  It runs a bit lean right now but I have stock exhaust and air filter