Bit of background, I'm building a KZ550 restomod for a friend. It had been sitting around for about 20 years (at least):
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It's had the rotten bits thrown away and replaced with more functional stuff, with revised steering geometry.
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Since then it's had a new loom, fairing, bars, carbs rebuilt and I'm currently elbow deep in the engine. Bottom end is all good but before I put the top end back together: should I drop in some ZX cams?
Has anyone else done this to a D model? Any pointers for carb jetting? I presume I need to change the ignition timing timing?
I think you can put Zx cams into a D1 engine if you use the D1 cam timing. Corey Clough recommends against using the Zx550A cam timing even on a Zx550A bike. He said the original D1 cam timing was better. It also gives more piston-to-valve clearance to be safer.
Even though the Zx550 and Kz550D/H motors have the same 10:1 compression, the pistons are shaped differently. The Zx pistons have deeper reliefs for the valves which make it possible to use the Zx timing. Presumably you won't need the deeper pockets if you use the D1 cam timing.
There was someone here who said he did it, but you will still want to try to confirm the piston-to-valve clearance somehow.
I'm not sure you would need to change the ignition timing, but you will want to make sure the advance position comes in at the right RPM. THe springs usually get a bit loose and it advances too early. You can restore the timing by tightening up one loop of one advancer spring. Usually this is enough to get the correct timing. Tightening up two springs is usaully too much and makes the motor a bit sluggish.
So just use the ZX cams to get higher lift? Seems sensible that if the mechanical timing isnt changing then the ignition timing stays the same. It's got Boyer Bransen ignition so that suits me, means that advance/retard isnt an issue too.
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Badmiker wrote: So just use the ZX cams to get higher lift?...
Any ideas on jetting?
The Zx550 gpz cams have the same lobe lift as the Kz550 gpz cams. It's the longer duration that makes the difference... more performance, but gets closer to the valve.
On the Zx cams I measured the lift was a tiny bit less than the Kz gpz cams but close enough that they are nominally the same.
I'm not sure if you've seen the page, but if you haven't I have a page on Kz/Zx cams. It's the valve-train warning page in my signature. It's a long read.
And definitely read the warning as well to prevent damage to the valve train, in case you weren't aware.
On the jetting, if you are keeping the airbox, then I'd think the stock jetting is a good starting point.
I find jetting changes using the Dynojet kit are a little less complicated since the needle is a single taper. The factory needles and the adjustable needles in the decent rebuild kits are dual-taper. That adds another layer of juggling, but will work ok as long as you are not trying to get really high fuel economy.
You can sometimes get away with a simple shimming of the stock needle and maybe a bump in the pilot jet and main jet.
I have a Tk22 site that shows how to properly shim a tk22 needle and what to look for in rebuild kits. There are some counterfeit kits which will have non-useable needles even though they look like useable needles. It also has details for the Dynojet kits and a lot of other info.