300jet

just finished the body of my project z31t, and for some reason the engine will idol but refuse to rev(backfires and stuff so i'm assuming it's too lean?).

but after the temp gauge hits half way, all of a sudden it runs like a dream.

The ecu diagnostic only pointed to the throttle position sensor(which i adjusted and fixed), but still no good.

It's got strange sparkplugs in it. (what are the best ones to chuck in?)
I'm assuming it's not the afm, or the o2 sensor since the ecu is fine with them.

any ideas? anyone else solved a problem such as this?

any help would be greatly appreciated.

Zen31ZR

You may have some VERY very cold plugs in it. The ultra cold ones WILL run like crap when cold , they shed so much heat so quickly they will foul if you spit on them. There could also may be other factors at work here , such as a bad thermostatic vacuum valve (no , not the thermoSTAT) which is pulling vacuum when it shouldn't be.

Unfortunately I'm no expert at crappy running 300s , mine has always run perfectly , and yet has never been tuned up since I bought it.

I probably jinxed it now.

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1992 Yamaha FZR 1000. 145 Hp, all stock..