Canadian Carbs vs US Carbs on XJ/M/Seca 650's

Hey friends, bought '82 Hitachi carbs online and they came from Canada. Broke them open and found that CAN carbs were OEM #43 pilot jets and #112 main jets compared to the US which has #40 pilot jets and #110 mains.

When reading the "where to start when removing an airbox and rejetting for pods/pipes upgrades" the general formula (and I know it's simply "a place to start") says for every 2 bumps in the main (going from 110 to 114) the pilot should generally be bumped up once (40 to 41). I was curious to see that on the tuned oem CAN carbs (with airbox of course) the jets do not fit that general formula. Anybody know why (besides that's what the factory determined would be best)? And is that a common mod for US bikes? Is it a significant change in the running and power of the bike?

It's a fairly moot point for me as I'm putting the XJ Hitachi's on my CB750A (Hondamatic) but I was curious as there could be some overlap with how I'll be trying to tune the carbs for my bike. I'm most likely going to be using pods (doesn't look like anyway to get them to work with the airbox) and will either try to add a couple inches of pipe between the air intakes and the filters to try and smooth out some airflow or will see if there's a way to fit an XJ/Maxim aribox in my CB750 frame...

Anybody got an XJ/Maxim airbox laying around they'd like to send me to see if I could make it work??

Toran

 

My best guess based on some light google searching this AM (had some free time):

Canada's emissions requirements were not aligned with the US until 1988 therefore each county had established their own requirements and manufacturers released products to meet those requirements based on when it was exported to.

I think we also saw some changes in the US in 1982 because in 1981, the EPA changed its SEA policy to place greater reliance on manufacturer testing programs and less on EPA-mandated audits. The audits were expensive and producing few failures. THis seems to line up with the jetting changes between countries pre 82 and 82 and later.

I don't think this is a manufacturer suggestion but more of some guidance based on people tinkering with XJ bikes in the past, there is a lot of knowledge on this forum and in Len's catalog. In my experience with jetting, this rule has not applied but I have no experience jetting in this application.

 

carb specs
http://xjbikes.wikidot.com/carb-specs

the US bikes tend to run a little lean so Canadain specs would cure that but likely reduce gas mileage.
Canadain bikes also use resistor spark plugs along with resistor caps

in wiki specs you will see different jets on cylinder 2 and 3 the euro 84 xj550L