Farmall 706 Carburetor - Tractor Vet? Anybody?

I have a 1967 Farmall 706 gas and am having problems with black smoke at idle speed. I have had the tractor for 6 years now and have always read Tractor Vet's postings on these tractors. I run IH 30 wt. low ash oil in it and 92 octane gas. Locally our premium gas is 92 octane. The tractor runs great and starts instantly however it has black smoke at idle speed. The carburetor still has the solenoid shut off. I read the manual and it shows that the original solenoid had a fuel adjustment screw on it but the current solenoid has no adjustment. The carburetor was rebuilt approx. 4 years ago. Is there any way that I can adjust the fuel to get rid of the smoke? Would replacing the solenoid with the needle and seat give me adjustment for this? Any suggestions? Thanks.

Well first off When was the last tune up and timing check done on her ?? When was the last time the valves were adjusted . Then i would try and adjust the idle screw and the bleed screw and make sure that the idle RPM is correct. As for the main fuel load screw they did away with them many years a go because people would try and lean them back and melt them down When you lean a gas engine out tomuch she gets really hot in there and when worked hard ya get the same think today with the 87 octane in a C263-301 . And now we are starting to see the same thing on the old M's and 450 gassers in our area trying to run the 87 , you start to put her to work and like pulling a loaded silage wagon out of the far end of the field in soft ground once my buddy's 400 with a 450 kit in it starts to work in about a 100 feet she starts to loose power Ping and knock and just up and die . HE argued with me about this for two days and he went and got 40 gallon of 93 and put in it and she was back up and pulling like she was suppose to . Also so i have noticed that there has been a bit more hazzing at idle and also when you first nail the throttle The gassers are Puffing a little like a diesel It just could be the fine gas that we get today .

You might want to take the carb apart and see what else is going on inside. The float may have developed a leak and is now no longer floating, or it may just be out of adjustment. You might also inspect the float valve and seat. It could be worn or maybe a small piece of foriegn material is preventing it from fully shutting off the flow of fuel.

Yes, that solenoid CAN be replaced with the adjustment screw set-up.

Yea ya can but i recommend that ya don't , Like i said lean is mean and when you get that tractor warmed up she will diesel on shut down that is WHY THEY PUT THAT IN THERE . And to keep guys from trying to lean them down .

The solenoid controls the LOAD or high speed circuit in the carburetor. Smoking at idle should be cured by backing out the idle mixture screw. On this carburetor counter clockwise is leaner on the IDLE screw. Another possibility is a needle and seat that is intermittently leaking fuel. Another possibility is the idle air bleed or the air supply for the idle air mixture screw being plugged. Still another is a plugged air cleaner. An M Farmall does not need high octane fuel, that is just nonsense.
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(quoted from post at 12:35:18 10/27/09) The solenoid controls the LOAD or high speed circuit in the carburetor. Smoking at idle should be cured by backing out the idle mixture screw. On this carburetor counter clockwise is leaner on the IDLE screw. Another possibility is a needle and seat that is intermittently leaking fuel. Another possibility is the idle air bleed or the air supply for the idle air mixture screw being plugged. Still another is a plugged air cleaner. An M Farmall does not need high octane fuel, that is just nonsense.
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The idle air bleed screw went away with the M carburetor. The idle mixture screw on the 706 is a fuel adjust screw, not air adjust.

Turning the screw clockwise will go lean, counterclockwise will screw it out and allow a richer mixture. This is just the opposite of the way the adjustment works on the M and H models.

Ya know TOM when you have spent as much time as i have working on tractors and a bunch of them Gas tractors . Then you just might know somethiing . Also if the OLD M has flat tops and distliate head maybe it just might run sop so Bt when ya start putting step head pistons in them and god only knows how many times .020 has been shaved off the head the 87 just don't cut it . And if 40 buck more per 200 gallon is going to send you into bankruptcy Then ya might want to start selling off a few . Or put your old lady to work .as we have been having problems since last year with the Four S/MTA's that are still earning a living everyday and one 400 with a 450 kit in it , When they start to work they will do the same as the 6 cylinders do . They will start to loose power knock back fire and die , put the 93 in them and they will work all day and never miss a lick . So don't go trying to tell me what works and that ya don't need this or that . IF the tractor is going to just drive on and off the trailer at the shows then on run what ever ya want but for the guys that want to try and make them do what they were made for then a littel better gas sure will held them do it . Also keep in mind her that the rebuild kits ya get today do not have the FROGED pistons that use to come in a rebuild kit and the cheap cast pistons can not dissipate the heat to the skirts as fast and they will swell a bunch . Also when was the last time that you had a long talk with a chem. eng. about the fuels of today and what should be run in a working engine ?? We have the Paper work from said chat that shows the BURN curve between the 87 and the 93 . And the difference in the heat made by the 87 compared to the 93 . The 87 is a HOT short burn and the 93 is a longer cooler burn and gives a broader power curve .

Thank you everybody for the information and suggestions. I plan on working on it over the weekend. I took the tractor to an ex-IH mechanic 5 years ago and let him do a complete tune up on the tractor.