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Anyoneknow the difference between 900 twin cylinders from year to year. Seems that 03 has there own part number for the cylinder as well as for the power valve. 04 and up seem no different. Also, any compatibility issues between diff year parts like cdi or ecu, stator, valves cables. I looking to put 900 stuff on my 02 800efi motor. It needs to be absolutly trail safe!!! I may stick with the efi, not sure yet. could go carb, I have 800 carb stator and cdi- Iwas told you can use them as long as you change the needles.

Best ecu for efi and best cdi for carb. I might put a speedwerx pipe on that I have.
 

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The '03 didn't have decompression holes that the later 900s did. That's most likely the part number difference.

All carb stuff will interchange from year to year, the only difference that I know of is the ZRs have less timing on the top end than the Mountain sleds do. The power valve cable adjustment is different for the '03s, but I'm not exactly sure which part is different to cause this.

If you're going to mod more than just the top end, I'd personally go for carbs, but that's just me. If you do that, you'll have to build a mount for the timing sensor, as the EFI case is different and mounts the sensor in a different location than the carb motors. The crank is also different, so that may make it more feasible to keep the EFI, and swap to all 900 parts. The ECUs are different, and I believe they will not just plug-and-play. You'll need the 900 stator also.

If I think of anything else, I'll let you know.
 

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The 02.5 and the 03 900 had the decompression hole on the left side of the the bore that exits in the left side smaller triple exhaust port at a angle.
The 2004 and newer had the decompression hole in the center of the bore that exits into the
exhaust valve.
 

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The power valve cable adjustment is different for the '03s, but I'm not exactly sure which part is different to cause this.
Sorry to revive an old thread. But I just put a 900 top end on my 02 ZR 800 and had to figure some of this stuff out.

The 02.5 and 03 900's used a longer power valve. The 04's and up used a shorter power valve, and as snow800 mentions, the 04 and up power valves have hole in them which coincides with the decompression hole on the 04 and up cylinders. This would explain the difference in cables and cable measurements.

Thanks to user Twatermelon, we were able to sort out power valve parts between us so I could get my new 900 top end put together. He has 03 900 cyls with 04 power valves, and I had 04 cylinders with 03 power valves, you cant use 03 valves in 04 and up cyls and vice versa.

See the attached pic, 03 power vavles on top, 04 and up power valves on bottom. You can see the 03's are longer (from base to the tips). When I put the 03's in my 04 cyl, they protruded into the bore and would have prevented the piston from moving in the bore. When I got the 04 valves from Twatermelon and put them in my 04 cyl, they fit perfectly with proper clearance in the cyl bore (I also installed shims too, for insurance).

While I was playing with APV parts, I measured everything else and other than the cables and valves themselves, all other parts are identical between all years 800 and 900.
361925
 

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I am running a set of 04 zr 900 efi power valves in mine . The power valves have a hole in each one of them and using the 04 cables on my 02 zr 800/900. You telling me now this won’t work???


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04 zr valves and 2.5 zr valves
great more things to worry about


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I believe they are 88J2 ?
I will try to zoom in on the pics, I didn’t no I couldn’t run the 04 zr 900 valves. I thought if I used the 04 cables and adjusted them right I would be ok. If there shorter then the 03 valves then I don’t have to shim them then ?


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It looks like from your pics, those are the 03 900 cyls, based on the decompression hole not being on the middle exhaust port. I would need to see pics of the bore with the exhaust ports to be sure though. When you install the valves, they should be just about flush with the bore. If they are receded from the bore, then they are not the right valves. As well, the 04 valves have the hole in them that lines up with the decompression that is on the middle exhaust port on the 04 and up cylinders. So if yours doesn't have the decompression hole on the middle exhaust port, then your 04 valves are not the right one's for you cylinder.
 

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Was afraid of that. I bought a guys 04 zr 900 efi motor and a bunch of parts last year. I can’t remember who had told me that I could run the 04 valves in mine. I asked about the hole in the power valve and I remember they said the hole was for oil lubrication. So that sounds totally wrong. Good thing you sent me that post so I can change them. That thing. Would of blown up for sure.



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