TOPIC:

I like the look of your bike .
FYI   a set of 1015 cc pistond will not drop in a 900 hole
Just raising the compression on a 900 would help performance  vs a overboring  but you still need to check the bores to see condition and actual  size of the holes 
before making a final decision 
Dave

you can bore a stock 903 cylinder "block" to 1015 cc's.  

Oh, and when I said in my first post a ‘chunk’ of the cam chain guide, I meant pretty much the whole thing. No choice in having to pull the head.

It looks great. Normally I’m not a fan of anything but black frames but the blue looks right. The pistons I posted are 10:25 to 1 compression on a .5mm overbore of the 1015. You can bore out your block 4.5mm or find a block from a 1000 up to 1980, and bore it .5mm. You won’t get much performance bump with bigger cams on the stock compression. If you want to do only one (Pistons vs cams) your better performance is pistons with higher compression. Later you can install bigger cams and then see a better performance. The 26mm carbs you have now will be ok. They will give you good response on the bottom but limit the power on the upper end. Finding a stock airbox is going to be expensive, around $400-$500. Just stick with the K&N pods. zed1015 sells corrector Jets that will improve idle and pilot circuit performance. Most of the spit back is from a larger pilot jet that people install to compensate for the higher air volume from the K&N’s. If you install the corrector jets then you can go back to stock pilots, 17.5’s and a lot of the spit back will stop. To get the most out of the electronic ignition, you need to test battery voltage at the coils, also make sure the advancer is moving freely.

Real good to know. I was led to believe by a tech support guy at Schnitz racing that I could do up to 1015cc without any boring. Maybe I read him wrong. So to do anything over stock pistons I’ll need to bore regardless. At 10:25.1 compression 91 octane ethanol free fuel will be ok? If so I’m all over it but I simply don’t want to have to run race fuel.

”Finding a stock airbox is going to be expensive, around $400-$500“

Fortunately I have all the stock parts that came from the factory on this bike, including these:
 

He might have been saying you can go to a 1000 (1015) block and pistons. That would be just buying a used set and installing them on your cases/crankshaft. The performance between the 900 and 1000 are similar so no real big gains. Wiseco sells 70mm pistons for a 4mm bore on a 900 block. I’m not sure if they would drop into a 1000 block without boring correctly though. Your next option beyond the 70.5mm that I posted is to go to 71mm which would be a 1045 kit. 

900 liners will easily bore out to the stock max oversize of 70mm (1015cc) and then over bore to 1030cc and 1045cc.
1015 block will fit 900 cases.
Some 900 cases will accept the 1015 liner spigots with no mods but others need slight easing of the case mouths for them to clear..
Very little material needs removing from the case mouths and  does not require machine boring or milling but just some short work with a file or rotary burr.
 

A slight groove as can be seen in the pic. 2nd from the right. I can feel it with a dental pick. Replace all?

I wouldn’t. NOS are about $180.00 a set. Aftermarkets are hit and miss. What does the cam journal look like?

I would running a Z1 (re-pro) air box, much easier to handle the carb in/out install and sounds/perform a lot better than stock or pot filter.

Sweet. The journals are perfect and the cams ALL measure exactly .983 &1/2. Haven’t measured cam lobe height but I don’t think I need to. This top end is pretty clean. I’ve organized every bushing and lifter bucket to it’s proper place in an egg crate.

On to the head. Sure enough the chain guide is broken right at the top screw. Didn’t know I’d have to pull the cylinder to change that but now that I see I have to, I think I’ll go with the 1015 pistons and bore the sleeves. Haven’t got to the valves yet but I have a feeling I’ll be doing at least a cleanup and lapping, maybe more. I checked all my lifter clearances before I pulled the motor they were all around .002-.0025. Good news. I’ll post a pic of the valves, pistons.