87 CC hard start when cold, backfires

[s2real]

I replaced the engine in my 87 with one from a 85. The only difference I saw was that the 85 had no place for the vacuum fuel pump, so I set up the electric pump on the 87 the same as it was on the 85. The problem is it is very slow to start, especially when cold after sitting for the week at the campground. Last weekend it backfred on me while trying to start and had backfired once before when off the gas going down a hill. Once I get it started it runs good and usually starts faster after the initial start up. I've replaced the plug, air and fuel filters. Any ideas?

[crash12888]

Usually a sign of leaking air box assy since the choke is the last thing in line.
After a week of sitting, before you try to start it remove the air box tube from the carb and hold your hand or rag over the carb opening, try to start it.
If it starts right up you have an air leak somewhere in the air box assy or the actual choke assy is not working.
If still hard to start, pull the carb and give it a good cleaning.

Backfire means the throttle is not closing all of the way when foot is off of the pedal and motor is turning over, usually after coasting down an incline.
replace the plug.

[s2real]

Thanks, I'm heading to the lake this weekend and I'll give it a shot.