motor looses spark when cold

Hey guys, I have a 89 B2200 5spd, I just replaced the motor and it starts and runs good until you kick it down, then after a few seconds it just dies (no stumbles, or anything, just straight up dies). It has been checked and found out that I am completely losing spark when this happens, if I hold the idle higher till the temp gauge hit a quarter or so it runs fine, no problems. I never had it running on the old motor so I don't know if this is a new problem or not.

hope someone knows what is going on, this one has me stumped

Rich

rich it seems normal for a mazda b to run high idle til it warms up a bit - but for it to totally kick off with out studdering, ( like almost shutting down) is weird . But this motor is new ? or new to the truck (transplant)?

junkyard block, everything else is from the truck originally

How do you know that it is losing spark?

What tests have you done?

with a timing light hooked up as the motor is spinning down (stalled but still decelerating) it looses signal to the light

as well as running with a spark gauge in place it acts the same way

Let me see if I understand this correctly. . .

If you start the engine when cold, and keep it at a fast idle, it worms up, and never stumbles, misses, shuts off. Continues to run fine from that point. No problems whatsoever.

If you start the engie when cold, and do anything to take the engine off the fast idle (choke circuit), the engine shuts off and then you have no spark.

Is this a fuel injected motor, or a carbureted motor.

It might make a little difference in diagnostic proceedure if that detail is included.

sorry, it is carbed,

when kicked down it will run for afew seconds, and then die. most times about ten seconds or so after kicking it down

Youneed to guy buy the distributor igniter its inside the distributor has two wires plugged in it looks like a horse shoe shape.. good luck

thanks, I will try that

i heard from someone that detonation can cause spark plugs to loosen.