PLease Help asap

[Foxrage]

I just got done rebuilding my 400ex with a hotcam and 416 piston.....It started for like 5 seconds then every time after that it backfired. I was thinking i messed up the time like the exhaust valves are open when it fires? Thanks

[woprs50]

did you make sure your tensioner is tightening the the timing chain ? sounds to me like it jumped time

[cals400ex]

you could be lean on the jetting if it is backfiring when trying to start it.

[Foxrage]

what should it be jetted at with open air box and a slipon with a 416 kit? Thanks

[04'400ex'er]

probably your jetting.

[Foxrage]

well i worked on it today and i clean the plug(not fouled or anything) then it will start for a max of 30 seconds then stall then everytime after that it backfires??? Thanks

[cals400ex]

what pilot jet you running and where is the fuel skrew set at?

[EXDUNER127]

Are you sure that you put thetiming right, if you believe you did then it has got to be the jetting. what did you change in jetting after you had finished building your motor?

[foleyit]

The backfiring would indicate that you are possibly a little lean. But I check the timing again. I had a similar problem with mine and darn it if the damn thing wasn't 180 out on timing. I checked my timing a 3rd time and it fired right up no problems.