Topic: CB650 Cylinder Head Swap

[papi_sosaa]

Would the cylinder head from a 79-80 CB650 work with the block for a 81-82 CB650?

So far from what I've read online, the heads are identical except for the intake spacing (PD carbs vs CV carbs). Does that mean all of the oil passages and such would be the same as well? Has anybody done this swap before and can document their experience with it?

[fizzlebottom]

You got it. Just the intake spacing is different, which means you'd need carbs to match the head. Everything is bolt-on.

[bryanj]

Will only fit with all the inlet stuff that goes with i

[fizzlebottom]

Actually now I'm looking and you might need to change out the air cleaner chamber as well. I don't know if PD carbs have the same spacing on that side as the CV carbs.

What's your goal anyways? Are you looking to make the change because you NEED to swap heads due to availability, NEED to change carbs, or just because you just severely dislike your CV carbs and think PD carbs will be easier to work with?

[papi_sosaa]

I was only asking because it seems like there are more carb options available for the 79-80 heads than for the 81-82 heads. This is more so me being picky and wanting to go all out with the bike.

My goal was to eventually go with Keihin CR29 Special carbs. Dynoman Performance used to sell a V2 kit for the 81-82 CB650's but it looks like they stopped selling them and only make the V1 kit for the 79-80 model years.

Murray Carbs also sells the Mikuni VM34 kits for both cylinder head types. This was my alternative option but if the 79-80 head will fit then maybe I'll revisit the CR29 idea again.

[pangloss]

CR carb banks are adjustable spacing .. I had cr28 on my 82  650. 

[papi_sosaa]

CR carb banks are adjustable spacing .. I had cr28 on my 82  650.

Oh, they have a slotted bracket that you can use to slide the carbs side to side. Clever.

I guess I can just order the V1 set off Dynoman Performance and just slide them into the correct orientation.

[fizzlebottom]

Oh man, I'll love to hear about the CR swap if that's the route you go. The idea of having modern carbs with easily replaceable parts (when needed) is very alluring. I feel like I've done a good job making sure my VB44C carbs working well, but I'm not looking forward to having to replace floats for $80 a pop, float valves for $32 each, and whatever myriad of 40+ year old parts might wear out in the coming years.

I've heard both good and bad things about Murray's carbs, but Dynoman's CR banks seem like another beast altogether.

[willbird]

Oh man, I'll love to hear about the CR swap if that's the route you go. The idea of having modern carbs with easily replaceable parts (when needed) is very alluring. I feel like I've done a good job making sure my VB44C carbs working well, but I'm not looking forward to having to replace floats for $80 a pop, float valves for $32 each, and whatever myriad of 40+ year old parts might wear out in the coming years.

I've heard both good and bad things about Murray's carbs, but Dynoman's CR banks seem like another beast altogether.

Every video I have seen about the Murrays 2:1 carb setup the dues rides it up and it sounds like total crap and he is gushing about how GREAT it runs with them LOL.

Bll

[ROB26-DETT]

CR carb banks are adjustable spacing .. I had cr28 on my 82  650.

Oh, they have a slotted bracket that you can use to slide the carbs side to side. Clever.

I guess I can just order the V1 set off Dynoman Performance and just slide them into the correct orientation.

Hey, sorry to butt in. I am in the same boat! I emailed Dynoman and they said, “All of the CR carbs that we sell are custom built by us to for the customers requirements, however we do not have the parts required to build them for you and they sometimes hit the petcock and cam chain tentioner as well.” - Dynoman GM

(I hope it’s alright to share that.)

Have you tried mounting a set yet?

[papi_sosaa]

Have you tried mounting a set yet?

Hey, I haven't done anything yet. I think I'm going to use the stock CV carbs for now and then eventually do CR carbs in the future.

I emailed Dynoman and they said, “All of the CR carbs that we sell are custom built by us to for the customers requirements, however we do not have the parts required to build them for you and they sometimes hit the petcock and cam chain tentioner as well.”

I emailed Dynoman as well and they essentially said the same thing to me too. They stopped making the V2 kit for the CB650's that had CV carbs because there were multiple '82 model year CB650s that used CV carbs.

multiple versions = multiple problems

Petcock hitting the carbs, carbs hitting the frame, carbs hitting the chain tensioner, etc.

I'm curious to see where the carbs are colliding but I'll figure that out when I eventually come to do the upgrade.

[ROB26-DETT]

That makes total sense, but hey you’re a gem for trying lol.

I just got my CV carbs dialed in with velocity stacks, but I am tired of playing with that.

I would like to move on to other areas of maintenance or get to the cosmetic stuff, but I’m holding out for a reliable tune first.

I hate to rush out and buy Murray’s if Keihin makes a proper set (adjustable V1 set that is).

[papi_sosaa]

I just got my CV carbs dialed in with velocity stacks, but I am tired of playing with that.

I would like to move on to other areas of maintenance or get to the cosmetic stuff, but I’m holding out for a reliable tune first.

I just got my engine back from the machine shop so I'm getting ready to put it back together and slap it into my donor so I can get some ride time in.

I'm still going to try experimenting with the CV carbs when it's time move the engine to my project bike. One guy I know used the Dynojet Jet Kit and has had positive results.

I hate to rush out and buy Murray’s if Keihin makes a proper set (adjustable V1 set that is).

Might be easier to buy a set of CR29's off eBay from a guy who installed them on a 750 or something and get the spigots from Keihin that will fit the CB650.

Even if you buy the V1 kit from Dynoman, you'll have to re-jet it anyway, especially if you're running an aftermarket exhaust.

[ROB26-DETT]

That’s not a half-bad idea I’ll look into that.

Thanks for the tip, you’ve been super helpful.

Keep me posted on your progress, would you?