I just got done rebuilding the top end on my 1997 400 sport. Bored 60 over after market pipe. My son and I got it put in today and fired it up. Ran smooth for a few min. then it coughed it really wasn't like a back fire . puffed some smoke . Keeps doing it now motor will start right up but keeps doing this . I don't want to let it run to long just incase it's something major . Any help will be greatly appreshiated .
Thanks
Wongerc

 

Did you bleed all the air out of the cooling system after you installed the coolant? 10 mm bleed bolt at rear of head.If you didn't you can blow a head gasket and over heat very quickly! Could be the cause of the smoke.Plus are you running stock jetting or have you bumped the jets up? OPT

 

I did bleed the cooling system at the top of the head . I am not sure about the jets . I bought this wheeler for $300 and was not in good shape got it for my son and I to work on together.

 

If the bottom end checked out ok(rod bearings crank bearings before the top end) and the engine head is torqued properly(head gasket on correct way,there is a cutout on the gasket that shows "up") and you bled the air from the coolant system,but it still coughs,smokes,you might check the jetting out plus check the reed cage when you pull the carb for any split or broken reed petals. OPT

 

I will. Thanks for your help will post what I find .

Thanks again,
Wongerc

 

Forgot again, gettin old Try pulling the black wire from the reverse limiter module on the circuit board and see if that might solve the problem. Could be shorting out like all the rest of em eventually do. OPT

 

Thanks will try it tomorrow

 

Sorry it took so long to get back. Works been crazy. Amy way I fond a short it took care of that problem but it seems to smoke more than I think it should and it is a white smoke?

 

Did you premix the first tank of gas? Also did you check the oil pump to see if it's operating properly and not sticking,allowing too much oil? Keep a check on the coolant level to see if it might be dropping,(seeping into the cylinder head)plus check the counter balancer fluid to make sure it's clear and not milky from coolant getting past the the water pump seals. White smoke isn't necessarily coolant burning,but could also just be a little rich on fuel,oiling too much,or even just oil in the exhaust system burning out. OPT