1948 John Deere A Carb problems

I have posted on here about my carburetor before and I'm still trying to figure it out. It is still running rough at idle and it is still puffing out black smoke when idling. When you turn the gas off or it runs out of gas, for about a good 20 to 30 seconds prior to it dying it starts purring and stops smoking and runs perfect. I checked the float level which is set at 3/8 inch, I have put a new float in it I have also put a new fuel nozzle in it new idle screws and load screws, also pulled out the baffle vents also installing two new vents also put in a new needle and seat assembly viton tip. I have the two aircraft drill bits and cleaned out all the recommended passages throughly with them amd also let the entire carb soak in berrymans carb cleaner for several days just to make sure !!!! Also all new gaskets all and all the above mentiomed parts from Roberts Carb Repair I have also checked for Mud Daubers nest in the air cleaner and habe ran it without the air cleaner still same results also put new points and condenser and changed out the spark plug wires and spark plugs!!!! So that being said, it is still running rough at idle and is still smoking at the exhaust amd every time I turn of the gas it purrs for for about 20-30 seconda before shutting off..I now officially have NO IDEA what to do?? .I just got in the mail the fuel level test tube to check the fuel level in the carburetor but after checking this I will officially be lost!!!! It almost seems like it isnrunning way to rich hence the reason it starts running smooth right before it does so Im pretty sure the problem is still in the carb, but am I missing anything???..... Please anyone I need help and advice...yearly tractor is show next weekend and I dont want it puffing smoke the entire time runnning.....thanks in advance.

I would set the float level at 1/2" and adjust your idle needle on the carb until it smoothes out.

I had one that run like that and the needle and seat was not shutting the fuel flow off.

Based on the black smoke and the fact that it runs good as its running out of fuel, it's running too rich. You should be able to lean it out with the idle adjust screw. If you can't there's either a plugged passage still or more likely the tip of the adjustment needle is broken or damage to the carb where the needle goes into.

I am with Mark, I think your gas level may be going high. Ron Mn

Your problem can also be caused by the throttle disc being excessively worn.
It lets too much air pass at low RPM causing fuel to be drawn from the main nozzle,
therefore carb is not running on the idle circuit.
Try turning the load screw off or almost off and see if it makes a difference.
If it does, replace the throttle disc, and re-set load needle.

How many turns out is your idle adjustment? How about the load adjustment? Do the needles bottom out?

From your description it is running rich and when you shut off the gas you reach point where the mixture is correct. Before I would go through the effort of working on the float, I would make sure that I ruled out the adjustment of the idle and load needles. I start out with about a turn and a quarter out on each and then go from there. The load setting doesn't come into play until higher rpm and even then you really don't know if it is right until you actually get some load on the motor. On my 44 A it was running fine up and down the road but when I put it on a cultivator I had to open up the load needle another quarter turn.

A couple of things you could try. Set the idle and load adjustments as I said and start the tractor. Set the throttle to idle and if it is running rich, start turning in the idle needle. If it doesn't clean up back it out to the starting position and turn the load adjustment all the way in. Then turn in the idle needle all the way, this should starve the tractor for gas and kill the motor. If it soes not, you have an issue with your needles or possibly then the float.

Hey,
I had an A that did exactly the same thing. It turned out to be the bowl vent was plugged. Punched it out and was full of curd.I didn't have a new one so I tried it without one. It ran like a charm. I ordered a kit that had the vent in it. A son of gun to install without wrecking it, but finally got it. Give it try. It might be your problem. Good Luck!
John

For one thing the fuel level needs to be 5/8" , not 3/8" , on a #71 which is what you should have. That tractor should idle perfectly with load needle completely closed. Try it as a test. If it doesn't then you have a plugged idle circuit OR like Popin John said you are sucking air around throttle shaft bushings or the blade is worn out letting it suck air. I just built one that someone had shaved off 1'8" off top and bottom of throttle plate and that tractor ran like crap, backfiring etc.Probably some tractor puller secret gone wrong. Since they fire on exhaust stroke also , any raw fuel dumped into exhaust from over choking and sucking off the load circuit, will set off "the exhaust bomb". After you get the float set correctly at 5/8" do this test. Open load and idle needles two turns. Now get it started and run for a couple minutes. Now open throttle up to at least 3/4. Now shut down load needle little at a time. You should be able to close it tight and engine rpm should NOT change as it should still be using JUST the idle circuit at this point. If it quits you either have plugged idle fuel circuit and/or you are sucking so much air through worn shaft bushings or worn blade that it won't suck the fuel up the idle passage. The reason this is important in your "flooding" case is that when it won't suck idle fuel the gov will open up blade and it will now take a gulp from load nozzle and be rich. Personally I think your 3/8 level is causing your problem. Most DLTX single throat carbs are 3/4. It is only the late A and late B that went to 5/8 and that is why they had to put bowl vent baffles in them to keep the higher fuel from splashing up into vent. Now you are raising it 1/8" more yet. You also didn't mention replacing the rotor. Most have the little clip inside them broken letting them wobble on shaft and potentially only firing once in a while or only on one.

I agree its running too rich. Check the fuel level by removing the drain valve on the bottom of the bowl and installing a fitting with a clear plastic tube attached. Hold the tube up along side of the bowl. The level of fuel in the tube will be the same as in the bowl.

So here is an update from today. I tested the fuel level in the bowl with the clear tube attached to the drain plug in the bowl. Fuel was at 1/4 inch or less from the top of the bowl. I adjusted the float and rechecked the fuel level and it is at 3/4inch from the top. Fired up the tractor and still doing the same thing....I am almost 99 percent sure the idle circuit is not clogged becuase I do have the two aircraft drill bits and I cleaned out all the passages thoroughly that were recommended to clean with them. I messed with the shut off at the sediment bowl and got it to a point where it idled perfectly without dying just to see what happens becuase at that time I couldn't think of anything else. I took it for a spin and when going up a hill it died out....just fyi...so I ordered a throttle disk today since that seems like the next logical step....from some of the other responses, I did take of the baffle.vents and cleaned them out and replaced them with new ones. So that being said any other ideas until I get the nrw throttle disk?? Not going to lie starting to get a little frustrated!!!! Thanks again.

Is the "secret" passage at the bottom of the stem open?

...so you didn't say whether it will run at 3/4 throttle as you close the load needle ? This will identify the problem.

should have read "shaved 1/8" off top & bottom. and should have read " now you are raising it 1/4" more yet". It was late.

OK _ No insult intended here but How does a throttle disk wear out???? Only way I can see anything ever happening to a throttle disk would be wear from being installed improperly or bent from some obstruction.
How does this happen? Is some gasoline or fuel additives so corrosive as to eat away at a metal disk!!!???

The throttle disc wears out from the weight of it and the throttle shaft vibrating vertically in the cast iron bore of the carb. The blade is soft brass and wears at the bottom which then lets there be an open crack (ever widening) at the top that will leak air and lessen the suction signal to the idle ports and not pull up enough fuel and cause a lean condition or no idle at all and then governor opens to help out and lets it gulp a big dose from the load nozzle and very eratic operation. Throttle bushings wear out causing even more leakage.I found a blade the other day that someone had perfectly ground 1/8" off top and bottom. No idea why but tractor won't operate correctly like that unless wide open all the time in which case wouldn't even need a blade , a situation that will never happen without blowing it up once load was removed.

Also , on the same note , the brass blade will eventually wear a groove in the floor of the carb bore which will also let even a new blade sit too low and cause leakage at top. I blast and use JB Weld to fill these. Beats throwing them away. If people would press the new bushings in and grind flush with circumference of carb inside carb throat, then the blade would ride on the bronze edge of the bushing as apposed to just the rough cast iron bore surface. Also seals up the bore better and even better idle.

Thank you Randy - I can see how that would effect the running ability! Thanks for the education!

Randy. So I messed with it today. I turned thue load screw down and was at 3/4 throttle and it didnt affect it. I also installed a new throttle rod. The old one had some play in it. When the throttle disk is all the way closed should i see.any light at all? At a certain angle I can see the tiniest but if day light, but it isnt anything measurable at all. Just a very very tiny sliver of light. Would that affect it?

Also i meant I replaced the throttle shaft.

Also anyone going to the Nippha tractor show this weekend? It's in Valparaiso Indiana at Sunset Hill Park right off Rt. 6. I will be there with it trying to get some help/advice.