DLTX carb overflow....NOT needle / seat/float..check this !

[RandyB(MI)]

DLTX 67 carb on JD late "B". Complete rebuild inc new float, steel needle / seat. Float level set on bench first with fluid and sealed perfectly. Mounted loose on test tractor, turn fuel on fills up and runs full stream out front of carb. (this is why I mount loose first) After hour of re-checking everything I took complete bowl off a perfect 71 that i knew was right and put it on. Same thing! Switched back and with fuel level check tube on, turned on fuel, way over top edge of bowl. Over filling but eliminated whole bottom of carb. What , in the body of the carb, would cause the fuel to overflow and run out ends of carb? Well I found out what caused it . Have never seen it before and have never seen it on any how-to vids or even on here. It was plugged , in and just above the two baffles in the bowl vent port (top or roof of bowl) The way I found it was I threaded the load needle out all the way (which will vent the bowl) and re-checked the fluid level tube and opened up the fuel and it set right there at 5/8" right where it belonged. What was happening was the bowl wasn't actually filling up over full. It was filling up to correct level but it was pressurizing the air above it and forcing fuel through the tiny idle needle port and the tiny load needle port (about 1" off bowl floor) and up through the load nozzle into throat and up through idle passages and out through throttle plate idle ports into throat leading one to believe the float bowl was full and overflowing. When using the level setting tube, it showed way over full also because the pressure,not volume, was what was pushing the fuel up the tube. You have approx. 12 psi air pressure and the pull of gravity compressing the air / fuel in the bowl and once above the ports, the air can't escape so fuel is forced out since you don't have the 12psi coming in from the vent to neutralize the incoming pressure. So all those posters on here complaining about their "new" needle/seat float not shutting fuel off and filling crankcase, may NOT be the "junk " needle/seats in every case. Who would think just a little vent port plugged would overflow your carb and fill your crankcase ? Drove me nuts for a while.

 

[Cliff Nelson]

I ran into a similar problem last year on a Deere lawn tractor. When running it would smoke and run rough like it was flooding. Took carb apart and cleaned, nothing obvious. Ran great for about 30 seconds then same thing again. Ended up calling a friend that is in the l&g business and figured it out. They have an external bowl vent with a vinyl tube that goes through the frame to vent away from the muffler. Bottom of the tube gets plugged and, as with your experience, pumps gas directly into the engine.

 

[RandyB(MI)]

We never stop learning do we ? Usually one thinks of a plugged vent causing starvation as apposed to flooding.

 

[Moonlite37]

I had a similar problem with a Zenith carburetor in a B Farmall, I fought this thing several months, It would leak after running but would not leak after reassembly. I discovered that the new bowl gasket did not have one of the holes. It looked like the gasket was die cot and the slug did not fall out,

 

[Mike M]

BTDT, Had one give me fits years ago from a plugged vent.

 

[PopinJohn]

Actually, this problem applies to ALL DLTX 67-71 carbs as used on late A's and B's.
John Deere knew about this back in the 1950's and issued Service Bulletin 216, (206?) showing a mickey mouse fix.
Their fix involved fabricating a brass jumper tube from the rear of the vent passage over to the other side of the body, thus creating an atmospheric vent for the bowl. I always make sure the vent passage is clear from the choke end, and from the throttle end. Takes 2 different size
drill bits to clear the entire passage. .150" from the front; .180" from the rear.
Most common cause of plugging is dirt by-passing the air cleaner.
M.

 

[rustyfarmall]

Sometimes we have to learn the hard way that a carburetor, any carburetor, is not ready for a rebuild until it is thoroughly clean. Soaking it in carb cleaner overnight is NEVER good enough. You have to KNOW where all those passages are, and make sure they are clean.

 

[RandyB(MI)]

Yea, I hear ya. I've done a ton of these and always drill everything. I don't soak anything, I blast and drill Then I spray brake clean in the big port (drill plug hole) on throttle end (air vent passage) and watch to see if it cones out the bowl vent where the little brass baffles are. Have never found a plugged one yet. Just saves ripping out and replacing two brass baffles if free. This carb was super clean to begin with and the only one I didn't do that to,and guess it taught me well not to take anything for granted. Also learned a physics lesson on how fluid can flow up into carb bore when the float bowl is only half full and as long as it has a way "out" it will never fill up and needle valve will not shut off as long as there is an air "bubble" in the top half of the float bowl. This is also why the "tractor test" is something one never omits. That test doesn't have any mercy on you and will humble you in no time if anything is not right on. I have no problem admitting I,m human and I don't mind "airing" my mistakes if it even helps one person in the future. By the way, it was just that, a mistake, as taking something for granted usually is. Thanks all. RB

 

[Mike M]

That's part of the reasons I quit doing carbs. for others. I want the whole machine here because 1/2 of carb. problems are something else entirely.