'82 cb650. Best purpose for this motor?

Well, I am in the process of acquiring a cb450, but my first build will be a cb650 that I picked up for free from my friend's dad, who wants to see it put to good use. I know that the 650 is kind of the bastard child of the cb line, but I'm going to make this one my winter project. It needs a TON of work, but all of the parts are there. My question is this:

Having never ridden an 82 650, I have no idea how quick or slow they are, so I'm not sure whether to do a tracker or a cafe racer. Either way, I'm going to weld a flat seat pan and hoop (I hate the slanted frame in the 80's cb's). If It's kind of a dog, I'll make it into a tracker, as I don't want to build a cafe racer that isn't fast.

So are these worth cafe'-ing for speed, or would this powerplant serve me better as a tracker/adventure bike?

What model? C or standard?

The cb650 engine is a damned fine engine.

I suppose "fast" is a relative term. Is it fast for it's displacement? No. Is it fast compared to a CB350? Yes.

I'm not a huge fan of the 650 frames, but the 650 engines are still SOHC. This means they have a nice kind of vintage look to them, but they're still second place to a CB750.

mlinder said:

What model? C or standard?

The cb650 engine is a damned fine engine.

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It's a standard, and I have spokes instead of ComStars - which I prefer.

Sonreir said:

I suppose "fast" is a relative term. Is it fast for it's displacement? No. Is it fast compared to a CB350? Yes.

I'm not a huge fan of the 650 frames, but the 650 engines are still SOHC. This means they have a nice kind of vintage look to them, but they're still second place to a CB750.

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I guess I'm thinking of low-end get up and go around the twisties. I love the look of the motor, and I agree - the 650 frame is ugly, but nothing a little mig welding can't fix, right? ;D

Joshing_Machine said:

I guess I'm thinking of low-end get up and go around the twisties. I love the look of the motor, and I agree - the 650 frame is ugly, but nothing a little mig welding can't fix, right? ;D

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Its a 4 banger, you don't need any low end, because you should have it revved out at all times ;D

Joshing_Machine said:

I guess I'm thinking of low-end get up and go around the twisties. I love the look of the motor, and I agree - the 650 frame is ugly, but nothing a little mig welding can't fix, right? ;D

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As SONIC said, it's a small 4 banger, a SOHC4. It's made to rev. Dropping below 6.5 grand in the twisties is dumb.

Get a big twin for low end grunt.

Sonreir said:

I suppose "fast" is a relative term. Is it fast for it's displacement? No. Is it fast compared to a CB350? Yes.

I'm not a huge fan of the 650 frames, but the 650 engines are still SOHC. This means they have a nice kind of vintage look to them, but they're still second place to a CB750.

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A hell of a lot more powerful than a cb500 or cb550. Also faster than cb750k's from 73 to 76.

mlinder said:

A hell of a lot more powerful than a cb500 or cb550. Also faster than cb750k's from 73 to 76.

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Yeah. You're right. For some reason I had it in my head that because it was still a SOHC, it would have less power than a 750. I just looked up the numbers and it seems that the two engines are only a couple of ponies apart (with the nod still going to the 750).

I retract my previous statement.

mlinder said:

A hell of a lot more powerful than a cb500 or cb550. Also faster than cb750k's from 73 to 76.

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I'll race ya from 73-76 an we'll see who's faster

SONIC. said:

I'll race ya from 73-76 an we'll see who's faster

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1973 to 1976.

While Honda still claimed 72HP or whatever, real dynos generally showed less than than 50, down to less than 45 for the k5 and k6.

mlinder said:

As SONIC said, it's a small 4 banger, a SOHC4. It's made to rev. Dropping below 6.5 grand in the twisties is dumb.

Get a big twin for low end grunt.

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I'm not really going for low-end grunt. I have a harley softail for the useless sound and bark, haha. I just meant that I wanted to make sure
that it wouldn't be a dog as far as acceleration, having never ridden a 650. My first bike was an r6, and after having the Harley, I miss being able to
corner at high speeds and have that quick pull. But from what everyone is saying here, it would be a good bike to build for speed. If I do this cafe' style,
I plan on doing a half fairing and using it for track days. I've heard once you do track, you never go back.

I like the CB650's. Good engine, good performance.

If you want that baby to really shit & git, put a set of Murray carbs on there and it'll go like Hell.

If you don't want to spend the money, just a little rejetting helps them quite a bit. The are on the lean side from the factory. It's easy to make them breathe more by installing a better filter, and opening up the snorkel on the airbox. About six jet sizes larger after opening up the air flow, and they run great.

AlphaDogChoppers said:

I like the CB650's. Good engine, good performance.

If you want that baby to really shit & git, put a set of Murray carbs on there and it'll go like Hell.

If you don't want to spend the money, just a little rejetting helps them quite a bit. The are on the lean side from the factory. It's easy to make them breathe more by installing a better filter, and opening up the snorkel on the airbox. About six jet sizes larger after opening up the air flow, and they run great.

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I dunno much about "Murray Carbs", but every reference points to cx500's. How would this help a cb650?

Murray has carb kits for many different bikes, including the CB650.

mlinder said:

I dunno much about "Murray Carbs", but every reference points to cx500's. How would this help a cb650?

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He has tuned Mikunis for a lot of different bikes, CB, CX, GL etc. He builds manifolds and brackets and tunes them for each bike. I do not yet have a set but I am very likely to bite the bullet and order a set from him soon.

AlphaDogChoppers said:

I like the CB650's. Good engine, good performance.

If you want that baby to really shit & git, put a set of Murray carbs on there and it'll go like Hell.

If you don't want to spend the money, just a little rejetting helps them quite a bit. The are on the lean side from the factory. It's easy to make them breathe more by installing a better filter, and opening up the snorkel on the airbox. About six jet sizes larger after opening up the air flow, and they run great.

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I've read that with a 750, anything but the stock airbox is a no-no, but with the 650, can I run velocity stacks? Or if I go with a better filter, what brand would you recommend?

That's for the DOHC 750s. SOHC is a lot more forgiving of pods and such.

Sonreir said:

That's for the DOHC 750s. SOHC is a lot more forgiving of pods and such.

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Thanks for the advice, sir. I'm assuming that whatever I go with, I'll just have to keep testing and checking to see what combination works best. I'm getting carb rebuild kits, and am not going to go with the Murrays for this build. This is going to be a budget build for now...
...at least, that's what I told my wife.

the CB650 engine is honestly the culmination of a LOT of research and is widely thought to be honda's BEST single-cam motor efficiency-wise. The head flows quite well for a stock piece, and the best tech from the 750 was put into cases based on the 550 and this motor is what came of it......making nearly the same power as a cb750, but placed in a lighter smaller frame based on the 550.....they are great bikes and only considered a "bastard child" because they didn't get to selling them much before the market shifted into DOHC bikes being the way of the future. the CB650 was the last SOHC effort by honda.

that said, there is an awful lot you can do with these motors to make them even better.

- certain years of GSXR rods fit without modification
- cb750 liners can be modified, along with the cb650 cases being modified....and can be pressed in and then opens up a WORLD of overbore options.
- aftermarket 550 cams fit
- early cb750 carbs fit (to ditch the crappy carbs they were equipped with)
- there's a lot of how-to's on making the electrics system perform lightyears better for minimal investments


(I'm myself using 836cc kit pistons with 750 liners and GSXR rods to build a 741cc cb650 lump to put in my cb550 cafe racer...have 750 carbs but recently bought cbr600 throttle bodies to convert to EFI)