Topic: 1982 CB650SC Winter Project

[Alldatjazz]

Hello, Everyone!

During the summer I helped my buddy fix up his 74 cb550. I realized how much I enjoyed fixing it up, and was debating starting my own project. I've never worked on motorcycles much, but have a good amount of experience fixing up my cars, etc.

Well, one day another friend of mine shows up and sees my buddies bike in my garage. We start talking about it, and he offers to sell me his 82 cb650sc.

I thought about it a bit, and decided that I have both the time and funds this winter to go all out on this project. I hope to make it into a hardtail bobber. Hopefully you'll join me on this journey of my first motorcycle.

So here's the details:

1982 CB650SC
7353 Miles

It runs, shifts, and the price was right... It has bad tires and needs some work, but given the scope of the project, it seems to be a solid base.

I got to work this weekend and drained the tank, changed the oil/filter, plugs, and am in the middle of cleaning out the carb (was surprisingly clean already).

I plan on putting it back together and running it this week to get a baseline of it's health, and may end up doing a compression test for my own peace of mind. My buddy offered to take it back off me if it doesn't pass, so I figure I may as well do it.

I have been trying to learn as much as I can about these machines, but there's honestly not a ton of resources for these in particular. If you have any pertinent links along the way, please feel free to drop them in here for future reference.

Well, enough with the rambling. Here's a few pics.

[Alldatjazz]

So for some reason the forum won't let me attach more than two pictures at a time. Not sure why? Oh well. Here's a few more pics of the progress

[Alldatjazz]

The carbs were already pretty clean, but i still decided to get them a bit cleaner. However, when I went to flip the carb over, I found a few very small washers. I can't tell where they're from, so if anyone can chime in and let me know, that'd be great. I put a dime for scale.

[RAFster122s]

Do not even think about running pods on the CV carbs, they do very poorly on stock motors trying to run pods. Most cannot tune them to run well on pods.
Welcome to the SOHC4 forums and a project...

[Alldatjazz]

Do not even think about running pods on the CV carbs, they do very poorly on stock motors trying to run pods. Most cannot tune them to run well on pods.
Welcome to the SOHC4 forums and a project...

Thanks for the welcome, and the insight!

I have read m alot about pods for these. Switching jets, making air dams etc. I know it's a P.I.T.A  it's still tempting to try, though. But that's wayyy down the road for this.

You mention "not running well on a stock motor" I have not heard anything about internals etc relating to the pods. Care to explain/drop a link? Would love to read about what you're referencing.

[Alldatjazz]

So- as most know the screws on this thing are a pain in the a**. I ended up having to extract a few of them. No biggie. It gave me a reason to swap them out with stainless steel hexes. If anyone needs this info- they're m4 16mm. Stock is 15mm but couldn't find em so 16 should do.

Idle mixture screws are set to 2.25 turns out for this carb. Float height is non adjustable for these carbs (vb44c)

I found that the "tees" in between 1&2, and 3&4 are cracked and exposed. Im trying to find replacements but it seems to be a dead end. I've read some posts but they also died out. Anybody have any ideas?

I figure since thats gonna take a bit, I'm gonna start on something else. The carb insulators are freakin STIFF. Theyre just shy of 39mm ID. Does anyone have a suggestion as to which brand they prefer? Honda genuine is 21/ea and while I'm not strictly OPPOSED to it, I'd like to see if there's other good options out there.

Sorry for the bad pics on the carbs... My camera on my phone is super finnicky.

[kerryb]

Do not even think about running pods on the CV carbs, they do very poorly on stock motors trying to run pods. Most cannot tune them to run well on pods.
Welcome to the SOHC4 forums and a project...

Thanks for the welcome, and the insight!

I have read m alot about pods for these. Switching jets, making air dams etc. I know it's a P.I.T.A  it's still tempting to try, though. But that's wayyy down the road for this.

You mention "not running well on a stock motor" I have not heard anything about internals etc relating to the pods. Care to explain/drop a link? Would love to read about what you're referencing.

Here's my attempt at an anti-pod setup.  Tried pods on this engine before, not worth it, maybe this stock size filter and fiberglass snorkel tube will make the carbs happy. (82 cb650sc )

[fizzlebottom]

If you are 100% in favor of going with pods, then get different carbs. The engine is not the problem: the CV carbs are. They need to pull from the exact same, non-turbulent source of air which is what an airbox provides.

Consider contacting Murrays Carbs regarding their CB650 bank of Mikuni VM34s.

Aside from this, it hurts my soul to see another CB650 potentially chopped up. They're weird an unique and parts are becoming more impossible to come by.

Good luck on your project.

[pangloss]

My take on alternate air filter for the CB650 motor. Dual Flange Oval Universal Air filter x 2. By K &N.....fit straight on...Motor is fitted into cb500 frame and has cb500 exhaust system which complicated the jetting somewhat....

[fizzlebottom]

My take on alternate air filter for the CB650 motor. Dual Flange Oval Universal Air filter x 2. By K &N.....fit straight on...Motor is fitted into cb500 frame and has cb500 exhaust system which complicated the jetting somewhat....

How does it run across the entire RPM range? The K&N filters would probably do a good job equalizing the air delivery between 1&2 and 2&3, but I'd be really interested in seeing if there is trouble equalizing between the two banks.

[Hutch]

I did this...  The K&N filter is very similar in size to stock, I can find the filter number if anyone needs it.

[pangloss]

My take on alternate air filter for the CB650 motor. Dual Flange Oval Universal Air filter x 2. By K &N.....fit straight on...Motor is fitted into cb500 frame and has cb500 exhaust system which complicated the jetting somewhat....

How does it run across the entire RPM range? The K&N filters would probably do a good job equalizing the air delivery between 1&2 and 2&3, but I'd be really interested in seeing if there is trouble equalizing between the two banks.

So far seems pretty good across the range BUT  my exhaust system is very restrictive compared to standard cb650...... idle screws are out to 3 1/2 turns so now option is to upsize pilot jet....which is a so called non adjustable ie press in jet ... and maybe lift needles with shim....
Both the above available from  jets r us.. https://www.jetsrus.com/a_jet_kit_street/honda_650_CB650_1981-1982.htm⁷⁶

[rb550four]

pangloss , what did you use to seal those itty biitty 550 pipes in the 650 openings, just wondering.

[Alldatjazz]

Alright so a little update:

First I'd like to thank all of you for your input for the air situation. I'm leaning away from pods at the moment, but I may fiddle with some alternative situations down the line. They're plenty of work to be done before that becomes a decision.

I performed a Leakdown test on all cylinders, and everything came back groovy. 8-10% loss per cyl on a cold motor, so I'm pretty happy with it.

I started stripping things down and pulling off parts I don't really want (gauges, fuses, front fender, chain guard etc).

After going through the entire electrical system, I've noted that the relay is toast, the regulator is original, the turn signal switch is sloppy, and there's been some sloppy electrical work in the past. I also dislike that the bars are solid so I can't hide wiring. I've decided to go with completely rewiring the bike with a motogadget m unit blue. That way I don't need to replace the relay, buy gauges, etc. The functionality of the system will pay off, considering I was also intending to do self cancelling turn signals. It's also a much slimmer package with absurdly good functionality.

I have toyed with the idea of this becoming a hardtail bobber, but unfortunately no weld on kits work for it, and I simply am not equipped to make my own conversion. Therefore I'm going to make this into a cafe/scrambler restomod. I'm currently looking into changing out the triple/forks to a more modern set. I've been doing exhaustive amounts of reading on motorcycle geometry lately.

Any recommendations for the above?

Next up is stripping the paint off the motor and starting to prep it for a fresh coat.

[Alldatjazz]

Aside from this, it hurts my soul to see another CB650 potentially chopped up. They're weird an unique and parts are becoming more impossible to come by.

Good luck on your project.

Don't worry bud, it's not getting chopped up. The Nighthawk gods apparently agree with your sentiment lol.

[Alldatjazz]

So- I'm gonna ramble here for a little bit about alternate airflows and cv carbs, although I've been trying my best to not let this become another pods discussion. Simple pods are out of the equation for me, personally.

They look great but functionality is typically garbage somewhere along the rpm range. This is a huge factor to me.

On a fundamental level, the cv carbs work differently from the carbs I've been accustomed to on cars, especially since each cylinder gets it's own.

They require stale air that they can pull a laminar flow from. They require even distribution, without external turbulence (crosswinds etc).
 
While studying the airbox and blowing a bunch of smoke through it (while it was off of course)I noticed a few things worth noting.  for people that want to attempt to build their own:

The air inlet is SMALL compared to the filter.
The air inlet faces the rear of the bike, in order to avoid excess intake at speed.
The filter is extremely free flowing.
The passageway from the filter to the carbs have a few key design elements: First, it has a sharp upsweep that helps to act as a dam, and disrupt any potential external turbulence.
Once the air passes that upsweep, it has an almost triangular/oval shape that has a twist to it. This aids in quickly replacing air at high rpms, considering the shape is pretty good at creating a vortex for fast flowing air.
Once it gets past there it opens up... BUT the isolators aren't just flush mounted into the carbs. The air would be too turbulent. So they actually protrude into the chamber. It slows airspeed down dramatically and equalizes pressures inside the box. From that point it's pretty easy for them to pull consistent vacuum. It's like a baffled velocity stack.

I've been toying with the idea of filling the intake with water to get a correct internal CC capacity, measuring the stock air inlet surface area, and stock filter resistance, then 3d printing something up for fun. That's 90 percent of the battle. The rest is just making sure there's proper baffling in the box, with even air availability.

But that's for way down the road. I have other battles to fight first... Like motorcycle geometry, which is a new topic for me.

Sorry for the rant! I must be feeling the effects of the smoke test lmfao