GS550 --> GS 650 SWAP --> KZ 700 jugs and pistons fitment???

[Guest]

Hello from France
I'm working on getting parts to upgrade my GS 550 motor. I already get a GS 650 top head (8 valves, with GS 650 cams and sprockets), I'm going to get VM24 carbs from a KZ 650 and a 750 gsxr full exhaust....
I find it very hard to get 650 jugs and pistons from US to France, because of shipping costs. Moreover, I learned that Kawasaki made a upgrade for their KZ 650, there was the KZ 700 which was just a KZ 650 upgrade....
I would like if it was possible to fit a KZ 650 (or 700) jug / cylinder block and pistons on a GS motor (here GS 550)? Parts seem to be the same but maybe any similar experience here?

thanks!

[GregT]

I suspect you're on your own with this swap, Boris...There's a world of maybes involved. Bore spacings ? Cylinder block stud spacing ? Suzuki rods, kawasaki pistons, are the piston pins the same diameter ? Piston crown shape - enough valve to piston clearance ?
I'd find the money to ship the GS650 barrel as it's a known swap.
And just to add to the misery, the Z650 VM24's are a poor choice of upgrade carb. I've adapted a set to a big Honda CB350/4 and with no alternative needles, it's an uphill struggle. Small CR's or RS's are a much better choice - albeit more expensive.

[Rensdw]

I suspect you're on your own with this swap, Boris...There's a world of maybes involved. Bore spacings ? Cylinder block stud spacing ? Suzuki rods, kawasaki pistons, are the piston pins the same diameter ? Piston crown shape - enough valve to piston clearance ?
I'd find the money to ship the GS650 barrel as it's a known swap.
And just to add to the misery, the Z650 VM24's are a poor choice of upgrade carb. I've adapted a set to a big Honda CB350/4 and with no alternative needles, it's an uphill struggle. Small CR's or RS's are a much better choice - albeit more expensive.

You have to read this as a friendly question, but how is your experience with VM carbs relative to his problem? it's a completely different bike, In other words I disagree with your point of view on this, just because you had one bad experience doesn't mean they are a poor choice.
VM's are simple carbs en thus easy to adjust, CR, FCR etc are more complicated, better but harder to adjust and properly tune, I would say the VM is an excellent choice if your not looking for that extra 1 or 2 HP.

And buy and AFR gauge with logger, that will help too.

[boris.h]

ok, ok, thanks! That's the aim of the discussion! I want to keep the same look on my bike and I don't care of extra 1 or 2 hp, so the VM carbs will be a good choice I think..
I understand that it is important to go to GS 650 stuffs, starting on a 550. I just received the gs 650 top end with cams. I have a lot of work on it (broken plug on it). I just have to be patient for the gs 650 bottom end with pistons... discussing with someone on the forum who's going to be able to bring me jugs and pistons...

[GregT]

You have to read this as a friendly question, but how is your experience with VM carbs relative to his problem? it's a completely different bike, In other words I disagree with your point of view on this, just because you had one bad experience doesn't mean they are a poor choice.
VM's are simple carbs en thus easy to adjust, CR, FCR etc are more complicated, better but harder to adjust and properly tune, I would say the VM is an excellent choice if your not looking for that extra 1 or 2 HP.

And buy and AFR gauge with logger, that will help too.

My point of view is based on forty plus years of building race bikes. One of the first things I learned was that if you couldn't source alternative needles for a set of carbs, you were in for a lot of problems adapting them to alternative motors. The VM's in sets of four, particularly early ones as are being discussed, are application specific. What this means is that unless you get lucky and find different markets used a different needle, you're stuck with what they came with.There's only so much you can do with different needle jets, the slope of the fuelling curve is set by the needle taper.
CR's and RS's are made to be an aftermarket carb, hence there are a lot of alternative needles available.

But by all means try to make them work, i've got lucky more than once.

[Rensdw]

My point of view is based on forty plus years of building race bikes. One of the first things I learned was that if you couldn't source alternative needles for a set of carbs, you were in for a lot of problems adapting them to alternative motors. The VM's in sets of four, particularly early ones as are being discussed, are application specific. What this means is that unless you get lucky and find different markets used a different needle, you're stuck with what they came with.There's only so much you can do with different needle jets, the slope of the fuelling curve is set by the needle taper.
CR's and RS's are made to be an aftermarket carb, hence there are a lot of alternative needles available.

But by all means try to make them work, I've got lucky more than once.

Ok, I got you know, finding the right needle is indeed the biggest issue but not impossible
I usually buy my Mikuni stuff here, never had to buy a needle because I have plenty laying around but I'm sure they have lots of needles for sale.

I see what you are saying though, there are only so much different needles for sale, but you were building race-bikes, always looking for the highest performance.
He is just looking for a "cheap" set of reasonable performing carburettors, as long as the engine runs smooth and has a reasonable AFR, he will be fine right?

[IanW]

Hi Boris,

As far as I understand it, if you are staying with the 550 bottom end (which is quite a good idea due to the excellent needle roller bearings on the crankshaft), you also have to stay with the 550 cams, as the number of teeth on the drive sprocket matches the teeth on the 550 crankshaft. I think the 650 cams and crankshaft have a bigger sprocket. At least I would check this out!

[boris.h]

Thanks for your answers, everyone. The aim of the subject is an "international" discussion about this kind of swap...
so, I'm (re) centering my choice in a gs 550 bottom, all above of gs 650 excepted cams and sprockets... I love the original 550 behaviour, "all above 6000". I use to prepare all top ends I work on. It's not a big gain, but nice parts, maybe 1/2 hp... hum interesting. I just started to remove cams valves on my gs 650 top end, which is going to be prepared and totally new... I will watch about 750 or 1000 valves diameters....
About the carbs, they will be vm 26 ones....