1943 JD D needs a little choke

Been working on this D for a while, rebuilt carb, and mag, all new valves in the head. It cranks good with hand start but seems to run its best with just a little choke. I have the idle and load set to specs. and it runs ok but give it about 10% choke and it smooths out and runs better. What am I missing?
 
It sounds like the carb has a plugged or partially plugged passage. I don't know if you had it apart or someone else, but they're easy to miss. Usually takes a drill bit of the proper size to fix it, blowing or running a wire usually can't clear it enough.

Brandon
 
I have no investment or personal connection with Roberts Carbs, however, these VIDEOS are GREAT.


Watch them and learn.


Bob.....
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That's what I was thinking too. It might be that simple ?

If "set to specs" those are only initial settings and fine tuning is always needed.
 
Even if all the passages are drilled and open to size, there are some things some will miss. One is the throttle blade being worn on bottom from sitting in there and vibrating, lets unmetered air slip past top of blade. Assuming the throttle shaft and it's bushings have been evaluated and either replaced or are tight , the one thing people miss is they don't press those bushings on in to the bore of carb, they leave them a 1/4" back. Another place for un-metered air to slip past. One other wear area to leak air is where the throttle blade wears a groove in bottom of bore. Once you have new , properly installed bushings and blade installed, now the blade will sit back to normal and there will be those grooves left under it to pass un-metered air. So what is this "un-metered air" issue you say? If the tractor can suck air at random...it will not suck fuel up through those little passages and through those tiny pin ports in side of bore so it will idle. Simply put, it will run lean..doesn't mater where you set the idle needle,it will not pull the fuel. What you are doing by applying choke is increasing the vacuum and negating the for-mentioned air loss. This is only for idle issues as most any carb will haul the goods under load on load circuit. They've got to be "right & tight" in these wear areas. Most have never heard of a worn out throttle blade...70% of ones I build are worn out. 99% of bushings are improperly installed. 20% have bore wear. Doing this makes them idle even better than new because even Deere didn't push their bushings all the way in. It's the "stacking affect" , no one of these alone will be the problem...but when one is worn, usually they all need attention. You should also spray some solvent around your manifold to make sure it isn't cracked and/or gasket leaking. Will cause you to use choke also.
 
Thanks for all your replys and suggestions. I have rebuilt several of these carbs in the past and have all the drill bits for cleaning but must have missed something.throttle shaft is in great shape with no wear that I can see. I will take it back off and go through it again. I installed all new brass plugs so it will be easy this time. This tractor has not ran in about 12 years, I cleaned the tank good before putting gas in. May have gotten some debris in the carb after I put it back together from a small portable tank that I used to run the tractor before putting the tank back on. I'll check everything again, thanks.
 
Sand blast and fill with Quick JB Weld. After 24 hrs, sand with coarse to fine paper wrapped around a large socket. They're usually not very deep so very little JB and it will "flow" itself level before it sets up. Never should sit in fuel so no worry there. Only sees air/fuel mixture. Never had a problem.
 
Only hole in this theory is I have seen several tractors with VERY sloppy throttle shafts/bushings and worn out plates run and idle pretty darned good. Too tight of a shaft and bushings seems to get one into more trouble if they stick.
 
...and I have not. I've had people send me theirs that they've done everything but the air leaks because they weren't aware of it. Sent back and they posted before & after vids on JD FB group. night and day diff. GTX Jewiston on here , used to claim you could throw a cat through his throttle slop and ran & idles great. To that I say BS. I've proved otherwise plenty of times. yes, they will run and load great and with a little choke and / or high float level or a partially plugged bowl vent....they would probably even idle since any of these conditions would cause an over rich idle mixture just as choke will. By my experience on 100,s of carbs..and many happy customers, my opinion stands. One in particular...who frequents this site in JD and Pulling forums..."AllColorPuller"...'37 US "A"..he knows now. Had a JD dealership and privateer both go through his carb...couldn't fix problem. Give him a holler on here.
 
Sorry it comes across that way. I'm retired and have been doing these for a while. I have chosen to do only JD horizontal 2 cyl carbs and learn all I can about them. By tractor testing them, I can put one on and see just what it does before and after with a certain problem/complaint from customer. The customer I mentioned in my above post to "Mike" actually brought his whole tractor over an hour to me because two other "builders" failed to solve his problem. Sloppy idle and occasional loud backfire through muffler etc. He was embarrassed to even parade it. One guess what they missed. They've probably also been told the air leaks don't make any diff. Not a "genius" ...still and always learning. I don't mind sharing what I've learned...I don't , however, choose to argue with others about it. I seem to get some of that over on JD facebook group. There's always that one carb that runs/idles perfect with a lead float....I have just not seen it I guess. Thanks for your posts.
 

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