carb. problem help- Oliver 1650

anyone ever have a carb. (updraft marvel-schebler 807 ) that the idle screw is turned in all the way to idle engine properly ? shouldn't that kill engine ? cant get idle down to 500 like it should only about 750 or it will stall out like it runs out of fuel but if you turn idle screw out it is to rich and wont idle either , also if you idle it down from wide open it sometimes stall right out & if it dont it will stumb till it catchs up again , carb is fresh rebuild & engine is 100% with no intake leaks ( have presure test it carb to head on engine ) anyone have this happen to them or ideas to fix it?

Well my best guess is several things are going on here . First you have a passage in the carb that is plugged , second you need to scync the carb to the gov. nest make sure your intake and exhaust manifold is tight and your not sucking any extra air in after the carb. Now if it was me i would pull the valve cover and run the valves and make sure they are set correctly then put a timing light to her and check timing . Last year i had and oliver carb that about drove me nuts and i never have a problem doing a carb rebuild , that one was a whole lot of other problems to deal with once i got them all worked out it ran like a Swiss watch. Farmer said it has never run that good in the twenty years he had it.

You sure you're turning the idle air screw and not the load needle??? Idle air screw shouldn't change the mixture enough to make it run rich. If it stumbles try opening the load needle a little or check timing and point gap.

some more info on this engine , head was just rebuilt , valves adjusted , new distributor , set timing , went though govener , set to spec. per original shop manuel & works great , no intake leaks as i put pressure into carb. on engine & used soapy water to look for leaks anywhere , the only leak is at throtal shaft but thats very little , over 50 psi & no engine will ever have that much vacume 15 psi is about std. & as far as odstruction inside carb. i soak in new carb. cleaner the good stuff that eats you skin off, blew every little hole out & ran a small wire throw them. one question i do have is can the main nossel jet cause this problem , it wasnt replaced because i think it will brake off from being so tight , i already had to drill out the valve seat in this carb. also to add engine holds 175 lbs of compression consitent acros all 6 cyls. & runs great 800 - 2200 rpm , its just at idle there a problem

I can turn the idle mixture screw all the way in to nearly falling out and it doesn't affect the idle. Don't know why but it runs good so I leave it alone. I disassembled and cleaned it out once because the float stuck open but it wasn't bad inside. This is a TSX 610, not the 903 it's supposed to have. Replaced by PO.

There may be an idle circuit problem, but...

The idle mixture screw (the small screw in the side of the casting just under the bolt flange) is actually an air bleed adjustment.

Turning it IN restricts the air bleed to the idle circuit, which enriches the mix.

Turning it OUT leans the mix.

Start with the screw about 1/2 to 1 turn off the seat, fine tune it from there.

It is not like a modern carb that the screw adjusts the fuel flow. That said, it is near impossible for the idle circuit to be so rich it won't run. If it is blubbering black smoke at idle, chances are the float level is too high, the float is sunk or bent, or there is a problem with the needle/seat, loose, bad seal, trash holding the valve open.

But, you need to get the engine speed down in the idle circuit range for the idle circuit to be in use. Once the throttle is partially open, the idle circuit stops drawing and it's trying to idle on the main circuit, which won't work very well.

Be sure when the dash lever is in the idle position, the throttle stop screw is held firmly against the stop. If there is slack in the governor link, the idle will be erratic, never return to the same speed.

Other causes of carb idle problems can be a worn throttle shaft, throttle plate loose, bent, installed backward, or not properly centered in the bore.

Another common problem, warped housing where the bowl screws to the upper housing. There is a small hole in the gasket that aligns with a passage from the bowl to the upper housing. That is the fuel supply for the idle circuit. If the upper housing is warped (tightened down with the venturi installed upside down or not seated), or the hole in the gasket is in the wrong place, or the passage is blocked down by the main well, it will not draw up fuel for the idle circuit.

But...

Many times an innocent carb takes the blame for a multitude of problems!

A sick engine will not idle well. Have you checked the compression, set the lifters, checked the distributor for side play in the shaft, checked the centrifugal advance and timing, adjusted/replaced the points, checked/replaced the plugs, wires, checked the air cleaner for free flow (mouse, bird, mud dobber nests)?

Let us know...
Idle Circuit

If you put 50 PSI in the the carb, chances are the float is crushed.

Well since you said you DRILLED and DRILLING on a carb is a NO NO i havve no idea what all you have done . Now as to youir carb cleaner the same as mine i doubt it and even when i soak the carbs i am working on at a 180 degrees i still have to go in with the number drills to clean out passages and even i miss somethings once in a while . Had the carb off my S/MTA four times before i got that blockage out . BUT since you can not get it to ideal down and run on the ideal circuit your problem is in the ideal side as you are drawing off the main jet above a cub ideal . But you could have stated what all work was done before hand as it help . I gave you a run down of where to look beside just the carb . Now here is the kicker i am not there with hands on and to recheck your work . I am at the end of a wire god only knows how far from the tractor . I have made a good living fixen stuff that others can't and fixen what others have screwed up.

i didnt put air in the fuel line just the air intake. but yes ive learned the hard way in the past & crushed a float befor , but not this way , and as far a drilling in a carb. ya its a NO NO but it had to be that way & turned out fine it was just the needle seat & its not my first time around the block , ive worked as a machinest / rebuilder for 20 + years , i can understand anything you all throw at me , ive done the same, fixed things that people said couldnt be fixed , but im scratching my head on this one , i will do some double checking of new parts & open carb again check all holes ect.. thanks for all the input sometime other people can think up stuff i am overlooking.