Xj650 head swap with Yics

Hello everyone, I recently bought a 84 xj650 and a 84 xj650 YICS. (Years might be incorrect) The standard 650 had destroyed exhaust studs and holes for them in the block. I took it apon myself to swap the top end of a YICS version, cylinders to valves section of the block. (The YICS had shredded gears) Got the bike running and it seemed to run alright but it sounds like there's a timing issue. Wondering if anyone knows of different timing on the two types of engine

 

So you included the YICS cylinder jugs with the head swap, right?

I don't think there's any difference in timing - basically the same cams.

 

Yeah basically the whole top end was switched. Are the pistons different? Could that be causing different compression? That shouldn't effect back firing

 

No. Should be same 63mm bore.

I think it would be really obvious if pistons were wrong size

 

Did you check the valve clearances when you fitted the replacement head and cylinders?

 

I haven't gotten around to it ask I work away from home but, it'll be my next step for sure

 

If you have to change shims do a carburettor sync afterwards.