Ive done a bunch of parts comparing with the parts physically in my hands to double check and other checking into it. The first three numbers are mostly just the model that part is for or made for,( like 34l= '84xt600/motorcycle, 5lp=raptor atv,ect...) I've found that series has little to do with the actual part. It's the second series that is the specific part and design, the third 3 is any re-designs or updates ( this is where there can be some changes to the part), the fourth I'm not sure. I've probably confirmed this with about 20 parts that the first number are totally different but the 2nd series is indentical and the parts are the same .

Now this isn't fail proof or exact, but you would be surprised once you start to physically have the 2 parts in hand and make note of the numbers , how many parts are used across the model line, just the first number changes.

For instance, the oil pump on the '90 XT600 vs 2005 Raptor 660 atv
................................... 3AJ-13300-00-00 vs 5LP-13300-00-00
both of these parts are identical, I have both and measured them to confirm.


Many of these parts, like those jets, on Boats.net when you select the part number it shows a list of what models that part fits, and quite often it comes up with bikes , atv, scooter, snowmobiles , all across Yamaha's lineup ,using that part or could use it.

I'm really finding this out as I am putting the XT600 cylinder and top end on top of a 660 Raptor bottom, everything bolted right up, cam chain fits the 600 cam gear(same part #), the 600 piston fits the 660 con-rod( same stroke), many parts are the same # except the first series. Of course I haven't fired it up yet