Years ago while working on a KZ900 of mine for resale... I rebuilt the carbs and after two on-off tweaks.... it ran FABULOUSLY!!
What I didn't like, after sorting it out, was how ugly the float bowls and top caps looked and I wanted it to look as good as it ran.
So with only about 30-40 miles on the carbs. I popped the carbs off, removed the lids and bowls, brought them in and polished them up. Looked great.
Put the thing back together, cleaned it up and took it for a ride... it ran wonderful.
Let a "friend of a friend" drive it and he made me a solid offer so I sold it.
About two weeks later, all I heard was what a piece of crap the bike was and how it would not go over 70mph, miss and bark, sounded like it was spitting up... etc etc etc.
He pissed and moaned non stop and wanted all his money back, after he just got home from taking it on 350 mile bike trip.
I said Hell no.
The bitching was a pain and he would not let up. My real friend and I couldn't take it anymore so I told him to bring it over and leave it with me for a while and let me try it out.
Yup, ran like ass. Oh God
Nightmare running.
I tried all the normal stuff with new plugs (they were fairly sooty black), points, condenser, valve lash gaps.... float level.. etc.
Nothing made any difference... idled nicely had nice power at the front end that fell on it's face wide open .
Knowing there could be nothing wrong with the carbs, I pulled the fuel selector apart and found a little bit of crap... rinsed the tank out, cleaned the selector well and put new fuel lines on... No difference, the bike just sucked dead donkey's ass,
So I figured the coils were bad, (sooty plugs and all).
Took the ones off my KZ and used them on his... no difference.
Almost week into it, I decided he had blown something in the motor or ???
Pulled the carbs and was going to slide the head off to see if there was a cross over blown head gasket or something because my compression gauge was broken. Mistake 1
At the last second I removed one of the float bowls to see if they there was something holding the float open with the engine running or?
...
There it was laying in the bottom... a main jet!
Holy Hell... took the other three off... yup one more laying in frickin bowl and one ready to go.
Put them back in and tightened them up, installed the bowls and carbs.... fire it up and, yes, it ran like scalded monkey right up to well over 110mph.
Lesson:
I absolutely refused to accept I had a carb problem!!
But there it was...I was a dork, Finger tight main jets and forgot to tighten/torque them correctly almost 400 miles ago!
One super loose, two of them, one by one, fell off into the fuel abyss!!