70 ford 4000 gas idle problem

[swattley]

since i got this tractor it has two idle, when running perfect it will idle throttle full closed run at 800 rpm, and run so smooth. then something gets in idle port i guess and when close throttle the governer kicks in idle goes up nd down back fires air jet screw makes no diff when you turn.
so i did full rebild kit of carb and then it ran perfect, back to nice smooth idle full throttle with nice responce.
next the fuel pump need replace on front of engine (what a night mare) all back this time with correct oritation fuel pump but i did notice some dirt getting down in supply line and tried to flush it out turn gas on best i could. tractor ran great no more leak gas it ran for two days and someting got stuck in idle port and now back to the SAME horible idle, if you give little choke it helps ?
i hope some one can help what part i can blow out or find with our total carb removal. this carm is not the holly by the way. but i forget name. and i will note the fuel tank has been cleaned and looks spotless inside.
anyone have this idle issue with a 3 cyl gas

 

[Gabi]

I am not a mechanic! My work has been done by 1 mechanic over 4 years. If carb is not the Holley then it is most likely a Zenith
replacement which I have. If you have found debris in the fuel system, you may have more or needle valve is damaged. There are likely 4 screens in the total
gas line. One at the fuel tap fitted to the bottom of the tank, 1 at the sediment bowl, 1 at the fuel pump, and perhaps 1 at the
fuel inlet to the carb. Governor controls engine speed and not the throttle.
When engine not warmed up it is somewhat normal for it to stutter when advancing throttle, but should disappear shortly after
startup. If idle screw has no affect on idle rpm then governor control rod back to carb is not adjusted correctly.
Original distributor had vacuum advance (mine is disabled) as well as mechanical advance and needs a little lube from time to time.
As a personal choice, I do not run ethanol gas in mine. Hope some of this helps.