Hey everyone,

So i am new to this forum but have been working on skis forever.I have to say I am stumped and need some help. Heres my issue.
I have a 97 gp 1200 non pv. Last season my ski would backfire only on startup. After that it would run fine.I ran it like that for about a year.Then i fried my # 1 piston.Long story short I decided to replace the motor because after said and done I would of been into it for around $1000.
So i replaced the motor,all new gaskets,new reeds,plugs,fuel filter,fuel lines,battery.The carbs were rebuilt and rejetted about 2 years ago from Oside Bill.So i know the carbs are good.I did to be safe check the filters inside the carbs.All is good right?

After the motor install I started her up and its still backfiring.I am stumped and I really dont want to take a chance of running it until it is fixed.
Ski is premixed 40:1,aftermarket reeds,k&n filters,other than that it is stock.Plugs are gapped where they should be.
Only thing I am not sure of is the water box.I did pull out the water box to check but I am not sure how to tell if it is bad.Water does come out.
Any help on this guys will be great.Thanks