john deere A backfire issue

[gary in neb.]

bout 4 months ago was using my A for fertilizing and the longer it ran the more popping and banging it did. no power, but ran pretty well at idle. got done, parked in shed and forgot about it. last weekend went to use it and would not start. dropped bowl off carb, full of water and rusty gunk. took carb off, took apart, cleaned what i could, put in my "sonic" parts cleaner. ran for 10 hrs. put it back together, same damn thing. backfires, pops and bangs, coughs. so, took mag cap off, found rotor really loose on shaft. got a new one. seemed to help some but not much. when it does run, at idle aint bad, go slow to high throttle, coughs, bangs, runs good, cough bangs a while, then smoothes out. dont seem to make much difference if i adjust the screws in or out. checked float level(bowl off) seems good (top of float to bowl edge bout 1/4 inch. checked fuel flow to carb, runs good. when it coughs and backfires, blows some black smoke. am i looking in the wrong place here?

 

[Husker44A]

Carb is plugged tight. Take it apart including brass drill plugs and main jet inside Carb body. Get the correct drill bits from robertscarb and hand drive the bits in ALL passages . Any amount of soaking will not remove rust. Don't forget the secret passage at the bottom side of Carb body stem. There is a good diagram on robertscarb for the passages. Good luck. Also check or replace points and wires with solid core wires and run Autolite 3116 plugs.

 

[greenmech]

On those carbs all the brass plugs need to be removed and the passages need to be cleaned out with the proper sized drills. Nothing else will do the trick. Ron Mn.

 

[gary in neb.]

i was afraid of that. gonna replace cap rotor and points as well.

 

[Greenday]

Sounds like a ignition problem to me

 

[gary in neb.]

i'm gonna replace rotor, points and condensor tonight. also thought about spraying carb cleaner in intake and see if it gets better. could eliminate spark that way and point more at carb.

 

[David G]

I would see if you have good spark BEFORE replacing more components.

 

[Anonymous-0]

I agree with Dave & Greenday. The load fuel passageway in these carbs is pretty much huge & pretty tough to plug up. NOTE.... I didn't say it was impossible and that is especially true if the bowl has had water standing in it!

On the other hand the IDLE passageways are noted for corrosion and are the ones absolutely requiring attention via removal of the drill plugs.

But there's a rub..... You say it idles pretty well which is the key to making me agree with Dave & Greenday. If the idle passages were closed it would be more likely to idle poorly. In many carbs the load and idle fuel flows through some of the same passages but NOT SO in the DLTX series carbs. In these (beyond the float bowl) idle and load are completely separate and if it idles well.... your grief is not so likely to be behind all those pesky drill plugs. It MAY be but I doubt it.

When you "overhaul" your mag, do yourself a favor and make sure you have plug wires with real copper in 'em. Don't just look for copper in the ends, measure with an ohm meter or a continuity test lamp! Then put in a new set of plugs. Most seem to prefer Autolites and some won't use free Champions for gravel. I use only the Champion D21 and D23 and I have no grief with them.

Adjust your mixtures as lean as you can without compromizing performance. My tractors ALL require some choke for a few minutes after a cold start or they will flat out die if I'm not there to grab a hand full of dhoke lever. You didn't tell your tractor's age but I find unstyled and early styled (more so than the later styled) like be up to temp.

Sometimes sticking, burned, maladjusted or ill seating intake valves can cause considerable grief very much like you describe. Not so bad at idle but won't pull the hat off yer head under load.

Do a good ingition tune up first and remember good clean properly working points with an accurate gap is even more critical in a mag than it is in a distributor! Battery ignition is most always more forgiving of minor points trouble than a mag.

Hope that helps.

 

[RandyB(MI)]

Don't know if you checked it or not but sounds like you have a "flake" of rust scale in the small orafice in the top of the sediment bulb housing. It will flop back and forth like a valve and causes an intermittent fuel starvation/backfiring problem. May have had good fuel flow when you checked at carb but things change when tractor moves or fuel flow catches the rust flake. Blow everything from carb up out with high pressure air and also clean out the tank. That's wehere the flakes come from. My '37 A did the same a couple yrs ago before I rebuilt it all. Blew air up the fuel line and had a freind hold his hand over the fuel filler hole to see if air was comming out. When it let go it stung his hand like a bee. Cured the problem. Intermittent problems are the hardest to find , but usually mean somethings dirty. Clean it ALL. Let us know what you find.RB

 

[Engineut2]

While you are at it, remove the Air-Filter oil cup and run a cut-off end of a garden hose up it..(all the way up, Past the Dog-Leg, into the upper inlet tube), with the water on fairly slow...
NO water will get into the engine..
You will be amazed at how much mud will wash out..which may, possibly be part of your problems..(Mud-Dauber Nests)...

Ron..

 

[Engineut2]

If the tractor may have plenty Moisture inside the crankcase, from setting outside, you could be having a problem with Moisture accumulating inside the Mag cap..
It does not even need to be enough to SEE, to cause a problem..
I know how many times we have had to deal with this, but I don't see it being mentioned on here at all...
I think it should ALWAYS be a consideration, on a JD with a MAG...
Just opening up the Mag and letting the Morning SUN shine on it for 20 Minutes usually can be all it needs...

Ron..

 

[[email protected]]

I think the thing that many miss is the obvious. You say its lost power and its popping and a backfire issue. The thing to remember is that the timing doesn't magically change. The lean condition will make a backfire. Lack of fuel "pops". It seems everyone is gung ho to change the timing when its actually a lean fuel issue. Properly clean your carb with the drill bits required and you will solve your problem. No doubt in my mind.

 

[Dave in SV]

Is the problem resolved? If so, what was the fix?