70D Pony Motor Problems

I just recently acquired a 1955 70 diesel. The tractor runs great, but the pony motor is another story. Sometimes you can get it to start, but it will only idle. When you move the lever to "Run" it dies. The guy I bought the tractor from had the carb off twice and cleaned it, put new coils in it, etc. You get great blue spark in the points, but the motor just will not wind up. He had it running great at first, but then it started acting up like this. And yes, we are keeping the gas tank completely full. Any ideas would be greatly appreciated.

Thanks
Matt

Even if you are on the choke, it will not wind up..??

Sounds like it is not getting fuel..

Ron.

A lot of times folks think that they are cleaning the pony carburetor, but they don't go far enough. The main jet is in the very bottom of the bowl, and by now, it could stuck tight, so much so that the cleaner is reluctant to try to get it out for fear of harming it. I bet the jet needs to come out, and that that passage has some debris in it. Also, all of the ponies I have worked on seem to be very cold blooded, liking their choke even on a warmer day. If you give them a richer mixture for easier starting, then they try to flood once warmed up. If you adjust them to start hot with no chocke, then you really have to feed the choke to them when they are cold.

As to cranking speed....is the linkage from the governor arm to the pony carb adjusted correctly by the book? I have seen those missing before. There is a small angle iron bracket that connects the governor spring to the carb pivot, and where this angle iron is positioned determines the high speed of the engine. If you start the pony and manually operate the long, vertical governor arm, will it make speed that way? If so, you just need to slode that angle bracket to where it needs to go.

The old flex line between the gasoline tank and the gas valve can internally fail with age and aggressive fuel.
I located and installed a new weenie little sediment bowl under the gas tank on my 70D. And a new fuel injection rated line to the gasoline valve.
Amazing what collects in a sediment bowl.
I have no clue why but the 720D and 80's starting engines will run on anything. The 70D's is snarly unless it' fueled with 100LL.
100LL costs within a few cents of 94octane pump gas. And doesn't gum,varnish or deteriorate. Problems with small engines ended here when 100LL started to be used.

My pony is doing the exact thing. some times it will do ok then other times it wont do well at all. IT is tough to start then will run bad for 10 seconds then die out. I have taken my carb apart twice and cleaned all passages I think. Put new fule line, a in line filter,made sure it is flowing fuel to carb. Still not fixed. But when I did the carb I neglected to clean the air filter element. I think I will try that next. Probably not today though it's 100' outside. Not fun. My motto, if its not fun, don't do it. If you get your pony running right let us know what you found.

It has the new line on it purchased from Deere. Thanks for the suggestion, though.

Matt

They will act as though they are fouling if you have low voltage to the distributor also. The newer off-shore replacement coils must have a few extra wingings in the primary, because to get the spark voltage up to where they do not foul, I had to remove the dropping resistor. Been running the same coils for 8 years now with no problem. I started out by trimming in less and less resistance until I got to almost nil, and the difference was impressive. You can use a quickie alligator clip lead to send power direct to the distributor post and see if that improves anything. That is, unless you are using the original coils. Then I would not without some careful experimentation.

After that be CERTAIN that you have removed the jet in the bowl of the carb and cleaned that passage. It's a one bbl carb and it has to flow freely in every passage.

Also, you can remove the mesh in the air cleaner and substitute an upside down dry conical paper filter such as was used on the Tecumseh vertical engines on lawn mowers. Just get one that would fit a JD '68' lawn mower. It will stuff up in there and stick, though I also placed two layers of furnace filter material in there to hold it in place and to serve as a precleaner. No oil dripping off of the air cleaner now when I operate on a slope.

Long post but.....

I'd like to second all that FIT has said. I'd also like to add regarding some of my recent trials with a rather cantankerous 70D cranking engine. The short of it... they're quite sensitive to the fuel level in the bowl. Below is my saga and what has convinced me.

I've been all through the ignition system new coils, resistor experiments much as Frank described. Has almost scary lightning like spark but it still ran terrible requiring constant choke fiddling. And the smoke... how that little engine makes so much smoke is simply amazing! I never understood why it didn't foul plugs but it never has done so though I use those dreaded Champion brand plugs!

Last fall I tore into the carb.

Internally it was immaculately clean and the jets all came out with little trouble. I don't know when it was last apart but I've owned it since '81 & had never opened it up.

All I found wrong in there was a cork float that was so shriveled and wasted away (one crack was so big I could see light clear through it) that it could only just barely float enough to shut off the fuel. Someone had apparently deliberately set the fuel level VERY LOW to compensate for this tired float condition. As a result it also had almost NO FLOAT DROP. This engine would NOT run with settings by the book but was usable if load adjustment was more like 4 turns. I obtained a set of gaskets and a new float, installed same as per the shop manual and put it together!

That cranking engine performed like I'd never before experienced. It was wonderful. The next start however was quite a different story. In fact the cranking engine would not roll over. Rats.... time to do some starter service. New brushes & some time later the starter worked fine though it didn't appear that bad to begin with. Hmmmm? Put it back on, checked the gas... Hmmm. Empty. I though I'd just filled that? Filled it again. Still no cranking. Turned off the ignition, removed the plugs.... gas everywhere & the starter works fine. I had a float problem ands decided it was time for an oil change too.

Removed the carb & found the brand new float was swelled up quite large, was soft, spongy and would only float if provided with a life jacket! Actually it sank like a rock! Called my parts provider who agreed this was not unheard of and I was now their third customer to experience this problem with cranking engine floats. They're in the business of rebuilding carbs specializing in JD carbs and they had NO suggestions. They assured me this is a JD exclusive part. They were working with a supplier to try to make a brass one but they were not even to the prototype stage yet.

What to do?

My wife (an avid and expert shopper) found me a bag of assorted corks at her local Wal-Mart. Using the worst looking of three wine bottle corks, I set about making my float that was a bit larger than the original cork float. I reasoned if the original was about 1.5 mm shy of being tight on the rivets that the cork had overall shrunken that much rather than the brass rivets having grown. I made a new one that much larger in all dimensions. It fit in the bowl perfectly though it was mighty ugly. Ya know.... cork is a pain to cut with even the sharpest knife! For "the next" round, I used a nicer looking cork and found it a lot easier to use coarse sand paper to shape the cork although when almost done, I dropped it and stepped on it breaking it. Grrrr. I set about trying the third one with the nicest looking cork, no gaps, cracks, holes etc.

Deciding this one looked like a keeper, I set about adjusting the fuel level. Try as I might I never found any recommended fuel level settings. For you "manual pushers" that includes my inch or so thick JD brand 70D shop manual, this and other sites as well. Thinking it not to be rocket science, measured the levels of the fuel passageways to the gasket sruface and and tried a setting of about 1 mm below the main horizontal passageway going from the bowl assembly to the main body of the carb. I never found a hose barb to fit the threads of the plug in the bowl so I removed the main needle and started a siphon with some tiny vinyl tubing, stopped the siphon and let the fuel level settle in the tubing like a "U" tube manometer. This worked great because for testing I could open the drain to make fuel flow and stop. After several tries we settled on a level that is right between the N and the I in the word ZENITH cast on the outside of the bowl. This may not be teh same height in all carbs so I'm NOT recommending it as any good measure! It's just where mine wound up.

I set all the adjustments as my manual says, installed it and it had never run better. I did not have time then to tinker with it that night (does anybody ever reach a mile stone in a project during normal hours?) but the next round proved to me the load was a bit lean and it runs beautifully at 3/4 turn open. At that setting the idle can be set from a lean roll to smoky rich. The cranking engine (after a few minutes warm up) will crank under full compression until the gas runs out! Constant choke manipulation is no longer required and the smoke... well it's very little as compared to before. Since it no longer needs to be choked to do his job I'm guessing the smoke problem to be valve stem/guide related.

Maybe next I can figure out how to post a picture of him at work knifing 28% in corn so you can see him in his work clothes.