Rebuilding a DLX71 carb.

Hi all,

after letting my 52 model A sit for 6 years outside after it quit on me one day, I've decided to go about getting it running again.

The tractor has always had a problem "hunting" at idle. I could never get the idle screw to help level it out, so I figured the problem was in the circuit.

Pulled the carb off today, and drained out the varnished gas. The carb wasn't in too bad of shape, the bowl was full of rust which I buffed off with a grinder. The passages for the full load and idle circuit were clear as well as the vent. Should there be anything else that would effect the idle of the tractor?

The needle and seat look good as well. I rebuilt this carb about 15 years ago when I was just a kid.

My main question is, the big spring under the nut that holds the bowl on to the carb. What exactly is it's job? when I take off the nut all that comes out of that spot is the spring. am I missing some parts? what the heck is it there for?

While I'm thinking about it, I remember reading something once that a paper air filter element would make a good replacement for the oil bath? was off like a nissan pickup or something? Anyone remember?

Also thinking of converting this tractor over to electronic ignition since it has the delco distributor with points. I've done it to my 2520 and it's worked great.

The spring holds the main nozzle up tight in it's bore so it will seal at the top. After a few yrs it will stay there by itself from rust. You said you rebuilt it once. you should have had that brass nozzle out at that time along with ALL of the tiny brass drill plugs. If not then it is not clean. Is there a brass nozzle protruding up 1/2" into the throat of the carb about center?? If not it is either missing or put in upside down. To test for idle circuit restriction, while it is in slow idle and hunting or running rough, start to close the choke slowly. If you find a spot where it levels out and idles good then you have either a plugged idle passage or you have air leaking past your throttle blade from wear or past throttle shaft/worn bushings. My e-mail is open if you need more detail.

Yes, I have the brass nozzle protruding into the throat of the carb. I checked it for any obstructions today with light, and it's open. so is the passage that allows the idle fuel in. although I'm not sure where the idle fuel passage discharges it?

Yes, to stabilize the engine idle, I'd have to pull the choke out part way, then push it back in when I put the tractor under load.

I don't think I had a master rebuild kit then. I just had a needle/seat and some gaskets. Just a basic kit. The brass plugs I had tried to remove, they were stuck. any suggestions on how to remove them without drilling them out?

If I have to put a $100 kit in this carb, I'm seriously considering buying a rebuilt.

Check the two small holes next to the throttle plate on the left side. That's where the idle circuit gas enters. There are also two plugs on the stem that need to be removed and poked out. Ron Mn.

Forgot to say that you heat the plugs with a torch first then they will come loose easy. Ron Mn

You have to torch heat the plugs and let cool and then will come out but then you need the drill bits to clear idle passages. Hopefully the slots aren't broken out of the screws yet. A good test , also, is to open it up all the way (with throttle lever) to what is considered fast idle , and slowly close the load needle. It should stay at fast idle and not show any change in how it is running. If it stumbles then the idle circuit is plugged. I have a perfect completely rebuilt and tractor tested # 71 for sale right now if you decide to go that route. $ 350 and free shipping. Will allow you $ 50 for your old one as long as it hasn't been broken or welded anywhere and is complete. Also you get one year warr. I posted a pic but but if interested and want more info e-mail me or 989-772-0111. RB

The secret passage at the bottom of the carb stem is plugged. Take the brass plug out directly across from it and use the appropriate size dril bit and open it up.

Go to www.robertscarbrepair.com and order the DVD "How to rebuild DLTX carburetors part II". They will also have any parts and/or gaskets that you will need.

Also forgot other option, I can re-build yours for $ 150 + parts. I don't mark-up parts. Charge only what they cost me. I only use what parts it actually needs. Yours probably just needs a drill plug set , throttle shaft bushings, throttle plate and gasket set. (Right around $ 48 w/shipping)You already have new needle/seat and apparently isn't filling tractor with fuel so I assume it is a good one. So you are looking at approx. $ 200 plus $ 13 each way for shipping (USPS Priority Flat Rate Box)If you don't care to have the outside blasted/painted , knock off another $ 30. If you want to try the "do it yourself" method again , that's your choice. Life is all about choices but it's always good to know what they all are. With the right manuals , special tools and expert advise , one could rebuild his own automatic trans also, but myself, I would go re-man w/warrantee and be done with it. Each to his own tho.

(quoted from post at 19:37:23 04/19/15) You have to torch heat the plugs and let cool and then will come out but then you need the drill bits to clear idle passages. Hopefully the slots aren't broken out of the screws yet. A good test , also, is to open it up all the way (with throttle lever) to what is considered fast idle , and slowly close the load needle. It should stay at fast idle and not show any change in how it is running. If it stumbles then the idle circuit is plugged. I have a perfect completely rebuilt and tractor tested # 71 for sale right now if you decide to go that route. $ 350 and free shipping. Will allow you $ 50 for your old one as long as it hasn't been broken or welded anywhere and is complete. Also you get one year warr. I posted a pic but but if interested and want more info e-mail me or 989-772-0111. RB

Click to expand...

Is this still for sale? Very interested, looking for my dad who bought a John Deere B to restore and needs a carb, thanks

Yes it is. What year is the "B" ? The bore on this 71 is somewhat larger than the B. I run a 71 on my '50 "B" but have the gas manifold and die grinder tapered the "step" edge on manifold flange back 3 inches so no restriction ledge. They function perfect on a "B" contrary to what some will tell you. If yours is a late B gas only, it would have a 67 from factory. Older styled B , 34 and older yet would be 10. Price wise, the 67,s are running same as a 71 but you could probably get a 34 or 10 a little cheaper. I assume the tractor has no carb on it now? Not trying to sway you one way or the other, just giving you info. My e-mail is open if any questions. RB

Looks great!

I think I'm going to try and get this thing cleaned up good and give her a go.

I got all the brass plugs out this morning except for one on the stem, which I believe is part of the idle circuit. The top of the screw broke off, even with lots of heat. now I'm going to be forced to drill it out which won't be hard, but not sure what size or where to buy that replacement plug.

both ports that are inside the neck behind the choke butterfly are clear. it appears that one part of idle circuit feeds a passage back by the throttle butterfly? This is the passage that I believe is plugged down in the stem. I was able to use a drill bit to get most of it out, but still appears to be blocked when I use brake cleaner and air to test.

slowly but surely it'll get finished.

If it's a #71 it will only have the one drill plug down in the stem. Yes that is the one to remove to make sure the cross-over passage that carries fuel from where the needle lets it in. It is ,for simplicity. approx 1/16 hole in behind screw. Once you have screw out stick a piece of thin wire down the hole where idle needle would go if it were longer and thinner. Now look through where you took that screw out and you should be able to see the bottom of that wire if it's clear. If not sometimes you need a drill bit and sometimes just a good stiff pointed pick to get that rust out of there. Solvent/air won't do it . Use them both after you get it opened up. Go to Roberts Carb (J&G Regional Services) website and you can get exploaded view of all parts and they have a complete drill plug set which isn't very costly and you should get. They also have the two drill bits you need if you desire along with a brass punch for R&R throttle shaft bushings if yours are sloppy. Unless it's been replaced at some time , your throttle plate is probably worn out at bottom from it's own weight and vibration which lets it leak air around it instead of pulling a nice volume through those tiny ports by throttle plate. Check to see if the throttle plate has worn a groove in bottom of bore also. Lets the whole thing sink and leaks air at top. Punch the bushings in flush with the bore + 1/16" and then use a die grinder/rotary file to shape them perfect to the inside curvature of the bore. If you get a new throttle plate, rub the sharp (and sometimes burred) edge at an angle on some fine sandpaper to put a fine bevel on both sides as they have a tendancy to stick in bore either when closing or when all the way closed. It doesn't change the diameter at all just make it operate like it was meant to. Also, that nozzle HAS to come out of there because it has little fine holes/ports all the way down the side of it that need cleaned with torch tip cleaners. If they are plugged it won't transition from idle to wot without spittin/hesitating.Roberts has the puller for that also or you can make one. Run a tap in bottom end of it and run a bolt with washers into it to suck it out. Sometimes is best to heat it up and cool it once before starting pulling. Don't know where you got your needle/seat but if it's working good then your fine. I only use all steel needles as apposed to the cheap little rubber tipped aluminum ones which usually aren't even the right length and who knows what that black tip is really actually made of and how it holds up to alky fuel?? It doesn't center itself consistently either. For warm up open load 1 turn and idle 1 1/2 and let run half throttle for 10 min. and then open throttle lever wide open (fast idle) and slowly close load needle. It shouldn't change anything. Now very slowly close idle needle until you can just detect a little roughness/hesitation and quickly open it back a half turn. Now idle it back down low and open load needle up one turn. As quick as you can, open throttle lever wide open. It should transition to wot without hesitation and with just a couple strokes of black smoke. True working load adjustment depending on work load , shouldn't be 1/4 turn richer and maybe not any. Good luck and let us know how well it runs/idles when your done Should be a good "barking" ole A. RB

If your going to go it on your own get on Roberts carb website. He's got all the brass plugs as well as anything else you will parts wise. I'd strongly suggest buying a drill bit set from him as well, it's money well spent in my book! I bought the DVD just to make sure I was doing everything correct, again money well spent a lot of knowledge shared on the video.

Thanks for sharing your wisdom on this.

Earlier today I finally was able to get that stem plug out. it required drilling it after the head broke off. once I drilled it, I used an extractor to try and get the rest out. Then guess what happened? part of the cast iron beside the plug (bottom of stem) broke out. All that's left is a few threads at the bottom.

So, I have the correct tap to thread into the bore further. I have to be cautious not to thread in too far because I don't want to cover that vertical port that runs parallel with the stem. Epoxy may be another option for me.

While the passages seem clear. I didn't notice the passage you spoke of under/below the idle needle seat that lead into the horizontal passage that I uncovered with the plug. I'll try your wire/drill bit method tomorrow. it sure could be too rusted up to see.

When I blow air into the port below the idle needle (where it would seat ) it does blow out at a port behind the choke butterfly, but it doesn't push any air into the horizontal port behind the stem plug. I take it that the idle port feeds two separate circuits?

I'll report back tomorrow.

thanks again

DF