Topic: Direct Swap? 1982 CB650 Nighthawk / 1979 CB650

[LampyB]

Hey guys, first time posting here but I could use some advice.

I’ve got a 1979 CB650 frame and I found a 1982 CB650 Nighthawk for a parts bike.

Is the 1982 nighthawk engine, carbs, and tank a direct swap onto the ‘79 frame without modification?

I’m an experienced VW guy, but bikes are new to me. I’d love to pick the nighthawk up, but it’s prob not worth the trouble if I’m going to run into a number of unforeseen compatibility issues.

Is the ‘82 basically a direct swap onto a the ‘79 frame?

TIA!!!

[Alan F.]

I'm a 750 guy but I think your answer is yes.
Take a look at the parts diagrams to verify same or interchangeable parts like engine cases and mounting bolts for instance.

https://www.partzilla.com/catalog/honda/motorcycle

[bryanj]

If they are both sohc probably, if the 82 is twin cam probably not, have to ask as nighthawk never came to UK so no idea what it is

[grcamna2]

The last year the sohc 650 Nighthawk was sold here was 1982'.

[Scott S]

 Didn't the '79 have that slightly chopper-esque tank, bars and stepped seat?
 Whereas the Nighthawk had the more sporty, cafe tail type look?

 We're there changes in the mounting points for the tanks (front and rear mounts), seat mounting and side covers?
 I'd be surprised if all of that is a direct swap, even if the main frame is substantially the same.

 **EDIT: it looks like the '80 model was the "chopper" style. The '79 650Z was more similar to the Nighthawk **

[Kelly E]

As far as I know the only frame change was lowering the 2 horizontal bars under the seat to lower the seat height. The 79' was a standard bike like a K and from 80' to 82' it was a Custom. The differences are longer fork tubes, stepped seat, 16" rear wheel, 4 into 4 exhaust, custom style gas tank and pull back handlebars. In 82' it got dual discs and twin piston calipers.

[fizzlebottom]

'82 engine and carbs will go with the '79 frame just fine. The '82 tank will not. It will require some form of modification. The only similarities between the two years are engine & carbs. Just about every other part, aside from some fasteners, is different. And I mean just about everything.

[scunny]

79 and 80 had PD carbs, 81 82 83 had CV carbs and different head.

[Hutch]

Do you happen to know if the 79/80 PD carbs fit 81/82 motor and heads?  I'd like to replace the CV carbs on my 82 CB650 with mechanical.

[scunny]

Anything is possible, but that would be a lot of work. I would get the 79/89 head to go with the PD carbs.

[fizzlebottom]

Do you happen to know if the 79/80 PD carbs fit 81/82 motor and heads?  I'd like to replace the CV carbs on my 82 CB650 with mechanical.

Won't work unless you have some custom insulators. The intake spacing changed between 80 & 81. You'd be better off paying for a set from Murray's Carbs unless you can find some insulator set that both fits the diameter of the carbs and have the correct offsets to mate carbs to the head.

Curious why you want to replace the CV carbs with PD carbs? The VB44 carbs work great if you take the time to make sure they're setup correctly. They're honestly dead simple to work on, minus that pesky choke spring.

[RAFster122s]

Do you happen to know if the 79/80 PD carbs fit 81/82 motor and heads?  I'd like to replace the CV carbs on my 82 CB650 with mechanical.

Won't work unless you have some custom insulators. The intake spacing changed between 80 & 81. You'd be better off paying for a set from Murray's Carbs unless you can find some insulator set that both fits the diameter of the carbs and have the correct offsets to mate carbs to the head.

Curious why you want to replace the CV carbs with PD carbs? The VB44 carbs work great if you take the time to make sure they're setup correctly. They're honestly dead simple to work on, minus that pesky choke spring.

And you use the stock airbox…
VB/CV design carbs are very picky about back pressure and the air flow feeding them… really tough to jet CV carbs for pods unless just looking to optimize for a narrow throttle range…

[Hutch]

Thanks all.  I don't have a big issue with my CV carbs, and they are super easy to break down and clean, just wanting to simplify to mechs.  I was mainly concerned about the spacing.  I love the Murrays, but just not worth it to me at this time.

[fizzlebottom]

And you use the stock airbox…
VB/CV design carbs are very picky about back pressure and the air flow feeding them… really tough to jet CV carbs for pods unless just looking to optimize for a narrow throttle range…

Weirdly enough, the VB44 carbs really do not care about what you're doing with exhaust. No jetting changes are typically necessary if going from stock 4-into-4 to 4-2-1, for example. Just gotta adjust the pilots and it'll be good to go.

Intake, on the other hand, is said to be an actual nightmare. They are so incredibly sensitive to intake changes, which is why everyone who attempts pods tends to give up and sell the bike, give up and revert back to the stock airbox, or falsely claim that garbage midrange performance is "how the bike is supposed to run".

[RAFster122s]

And you use the stock airbox…
VB/CV design carbs are very picky about back pressure and the air flow feeding them… really tough to jet CV carbs for pods unless just looking to optimize for a narrow throttle range…

Weirdly enough, the VB44 carbs really do not care about what you're doing with exhaust. No jetting changes are typically necessary if going from stock 4-into-4 to 4-2-1, for example. Just gotta adjust the pilots and it'll be good to go.

Intake, on the other hand, is said to be an actual nightmare. They are so incredibly sensitive to intake changes, which is why everyone who attempts pods tends to give up and sell the bike, give up and revert back to the stock airbox, or falsely claim that garbage midrange performance is "how the bike is supposed to run".

I guess I used the wrong term...
Back pressure or restriction of the intake charge was what I failed to convey... The carbs are really really picky about the filters of pressures or lack of pressures to breathe...
The other CB bike carbs are a cakewalk compared to CV model carbs if you try to use pods on a stock or near stock motor. The Honda engineers did their jobs on the intake designs...

[kerryb]

I should know soon if the hidden air filter and snorkel works near enough to stock.  Tried pods on this when it was stock, not worth the trouble at my "tuning" ability.  But I still didn't want the stock airbox on my 82 cb650sc (sport cafe)
I got lucky, the petcock on a k8 750 tank falls into a good spot for cv carbs!

[Scott S]

 That's a really interesting set up. I like it. Where are all the electronics, since that's where most people hide them on Cafe bike?

[kerryb]

That's a really interesting set up. I like it. Where are all the electronics, since that's where most people hide them on Cafe bike?

The k8 cb750 tank has a generous tunnel for some components (connectors, igniters), the battery is stock size behind the tranny.  The seat hump got the reg/rec, fusebox (removed from h-bars), flasher relay, and the embedded LED tail light.  Oh, starter solenoid hangs off the side of the new battery box.  I'm still working on shortening the wiring harness (almost stock), it's like trying to stuff 5 lbs of sausage into a 2 lb bag. (Headlight bucket)  sorry for the threadjack, but maybe LampyB will see stuff he wants to avoid on his bike.  Here is the link to my thread.  http://forums.sohc4.net/index.php/topic,174985.0.html

[Bankerdanny]

Didn't the '79 have that slightly chopper-esque tank, bars and stepped seat?
 Whereas the Nighthawk had the more sporty, cafe tail type look?

 We're there changes in the mounting points for the tanks (front and rear mounts), seat mounting and side covers?
 I'd be surprised if all of that is a direct swap, even if the main frame is substantially the same.

 **EDIT: it looks like the '80 model was the "chopper" style. The '79 650Z was more similar to the Nighthawk **

The '79 650 was basically a '78 550 with a 650 motor and some minor styling changes. In 1980 they further modified the styling and changed the frame.

A SOHC650 Nighthawk engine should plug right in to a '79 650 frame or even an earlier 500/550 frame with minimal mods.

[grcamna2]

I should know soon if the hidden air filter and snorkel works near enough to stock.  Tried pods on this when it was stock, not worth the trouble at my "tuning" ability.  But I still didn't want the stock airbox on my 82 cb650sc (sport cafe)
I got lucky, the petcock on a k8 750 tank falls into a good spot for cv carbs!

Great work on your custom airbox 

[kerryb]

[quote

Great work on your custom airbox 
[/quote]

Thanks, fingers crossed.

[Hutch]

And you use the stock airbox…
VB/CV design carbs are very picky about back pressure and the air flow feeding them… really tough to jet CV carbs for pods unless just looking to optimize for a narrow throttle range…

Weirdly enough, the VB44 carbs really do not care about what you're doing with exhaust. No jetting changes are typically necessary if going from stock 4-into-4 to 4-2-1, for example. Just gotta adjust the pilots and it'll be good to go.

Intake, on the other hand, is said to be an actual nightmare. They are so incredibly sensitive to intake changes, which is why everyone who attempts pods tends to give up and sell the bike, give up and revert back to the stock airbox, or falsely claim that garbage midrange performance is "how the bike is supposed to run".

I kept the plenum, but eliminated the stock air filter box in favor of one large pod style filter.  It works great since airflow is consistent. 

[kerryb]

I kept the plenum, but eliminated the stock air filter box in favor of one large pod style filter.  It works great since airflow is consistent.

This was the concept I was chasing with the flat filter hidden under the seat.  There is an area at the rear of the space that can be used to limit air intake if it proves neccesary.

[fizzlebottom]

I kept the plenum, but eliminated the stock air filter box in favor of one large pod style filter.  It works great since airflow is consistent.

Oh yeah, look at that. I think it seems like a great compromise. Did you have to fab up the adapter between the filter and the intake chamber?