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Discussion Starter #1
Hey everyone!

My Dad and I recently picked up a 1950 A propane version that had been sitting in someone's yard as an ornament for years. After completely tearing it apart and rebuilding it we decided to switch it back to gasoline. The carburetor that was on the tractor was a gasoline carb that had been converted to work with propane so we just switched it back to run on gasoline. (replaced the tank and sheet metal of course to the original gasoline version's look). The tractor ran fine for a little bit, even though it never sounded perfect. As we were driving it one time the pin on the carb that prevents the throttle butterfly from closing too far and thereby reopening broke and so when the governor tried pushing the throttle to idle, it overturned the plate and ended up revving the engine very high. We fixed the little pin so that this cannot happen again, however now we cannot get the tractor to run properly. I'm thinking it is a carb issue but since I don't know enough about these tractors I was hoping someone could give me some useful input. It also seems to only want to run when it is its mixture set very rich. The Manual we have says that the adjustment is 1.25 turns out on both adjustment screws however this one only wants to stay idling at about 3.5 turns out. I live at a high elevation (4000 ft.) so it should even be leaned out more not richened.

Any advice would be greatly appreciated!!!
Thanks!!!

IMG_1587.jpg
 

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:wgtt:

That's a great looking tractor! Hopefully someone can help you soon.
 

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I'm still learning about two cylinders myself. My question might be like trying to tinkle and aim in the dark:laugh:, but did you reuse the old pistons? Reason I ask, is that was the first thing that came to mind.

I bought a model 70 that was converted to propane and am still working on getting it going. It's the one in my avatar. The motor was seized when I got it,but was just sitting in a barn for 20 years unused. I'm wondering just what all was swapped on it.


But, on the other hand it almost sounds like something on yours is obstructing an area of the carb.
 

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Discussion Starter #4
but did you reuse the old pistons?
Yes, we reused the old pistons. this one was sitting in a barn too and was seized too. Cylinder 1 was rusted because it sat with a valve open. we were able to loosen up the piston and hone the cylinder really well and luckily were able to save it. We have about 100psi of compression in both cylinders so thats fine. ours didn't even have a real propane carb, it looked more like a gasoline carb was converted to propane because it still had the float on it. We were able to convert it back to gasoline and it ran alright on it for a couple of months. The intake/exhaust manifold says LP GAS on the top of it but thats the only difference we can see. I assumed it was an obstruction in the carb too but even with a different carb we can't get it running right. :(

Another thing I noticed was that right where the carb and intake meet, when it is running there is condensation on the outside of the intake manifold. I have never seen this on a gasoline-powered vehicle and I can't figure out what it could be. It also makes no sense that the condensation appears there instead of elsewhere by the carb.

Thanks
 

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Welcome to GTT!

Another thing I noticed was that right where the carb and intake meet, when it is running there is condensation on the outside of the intake manifold. I have never seen this on a gasoline-powered vehicle and I can't figure out what it could be. It also makes no sense that the condensation appears there instead of elsewhere by the carb.
That condensation is caused by the cooling effect that evaporating gasoline downstream of the carb. Most engines the intake manifold has enough heat in it from the engine that it wouldn't be cool enough for moisture to condense on it.

You stated that you have 100 psi compression. Is that after the over-speed incident? If you have (or have access to) a cylinder leak down tester, you could perform a much more informative test. It'll tell you if you have any mechanical issues within either cylinder. The head and valve train on these twins are very robust, but I think the possibility of a bent valve exists. Can you tell if it's running on both cylinders? Disconnect a plug before starting it to verify. The other possibility I was thinking of was the magneto/ignition system. Not sure what you have due to so many being upgraded. You'll want to verify timing and the integrity of the ignition system. Some of these won't stand up to over revving very well.
 

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You stated that you have 100 psi compression. Is that after the over-speed incident? If you have (or have access to) a cylinder leak down tester, you could perform a much more informative test. It'll tell you if you have any mechanical issues within either cylinder. The head and valve train on these twins are very robust, but I think the possibility of a bent valve exists. Can you tell if it's running on both cylinders? Disconnect a plug before starting it to verify. The other possibility I was thinking of was the magneto/ignition system. Not sure what you have due to so many being upgraded. You'll want to verify timing and the integrity of the ignition system. Some of these won't stand up to over revving very well.

The 100 psi compression is after the over-speed incident, we checked that. As far as I can tell it is firing on both cylinders but I will check it to verify. I don't have a cylinder leak down tester but I can see if I can get my hands on one.

We assumed it could be the magneto/ignition system too so we verified spark,checked the timing and all of that seems to be in order. We have a strong spark and its still sparking at the right time. I have the magneto turned all the way counter-clockwise as this is where it runs best...I have no more room for adjustment which I think is a bit odd but it isn't the biggest problem right now. I'm really leaning into it being a carburetor issue.

The fact that the manifold says "LP GAS" on it can't have any negative impacts on the operation of the motor on regular gasoline can it?
 

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Does your magneto have an impulse coupling? It's a device that springs the magneto forward during slow RPMs during starting to provide a spark. Magnetos don't perform very well at low RPMs without one. If has malfunctioned, it can cause many issues like the ones you are experiencing. The lack of adjustment left in the timing is a red flag.
 

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When I first read about the engine revving up, I did picture the possibility of a bent valve. It's just not always easy to diagnose an engine problem without having the luxury of seeing and checking things in person. A friend of mine has one like yours, but he had a totally different problem. He couldn't get fuel to flow.

Hope you locate the problem soon and without having to spend much $$$$ to fix it.
 

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It's just not always easy to diagnose an engine problem without having the luxury of seeing and checking things in person.
Well said. :good2: It can make one hesitant to answer a question here on the forum. People just have to remember we're all here to help each other and have some fun doing it. :thumbup1gif:
 

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The 100 psi compression is after the over-speed incident, we checked that. As far as I can tell it is firing on both cylinders but I will check it to verify. I don't have a cylinder leak down tester but I can see if I can get my hands on one.

We assumed it could be the magneto/ignition system too so we verified spark,checked the timing and all of that seems to be in order. We have a strong spark and its still sparking at the right time. I have the magneto turned all the way counter-clockwise as this is where it runs best...I have no more room for adjustment which I think is a bit odd but it isn't the biggest problem right now. I'm really leaning into it being a carburetor issue.

The fact that the manifold says "LP GAS" on it can't have any negative impacts on the operation of the motor on regular gasoline can it?
IMHO, Yes, it could have some negative impact. What I do not know.
 

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Discussion Starter #11
Thanks for all of the quick and helpful responses!!! I'm glad I finally found a JD forum thats useful! haha

We're having a friend of a friend of a friend come out to look at it and diagnose whats wrong with it. He is somewhat of a 2 cylinder expert so we'll see what comes up. Before he comes though I'm going to take the magneto off and see if the spring action still works properly.

Thanks again for all the help!!
 

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alright so our mechanic friend wasn't able to come out. We took the magneto off and tried it on a friend's tractor and it worked fine so thats not the problem. The sprocket that turns the magneto shaft was off by 1 tooth on the cam shaft sprocket when I know for a fact that when we put the tractor back together we had aligned them. How can this be off by one tooth? needless to say i realigned it but the tractor still won't run. we get one fire every now and then but nothing that even hints that it is close to running.
 

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I've thought about this for a long time. This is one those instances where it becomes very difficult to troubleshoot without seeing or hearing the tractor.

One question. Is the grounding lead to the magneto disconnected while trying to start your tractor? If not, try disconnecting it. Maybe it has a short to ground somewhere. The only other thing I can think of is still timing.


Wish I could help further....
 

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Yeah, Thats what I'm thinking too...We took off the cover over the sprocket that powers the magneto and noticed that it was a tooth off, I'm sure I lined it up properly when I put it together...We fixed it and it seems worse off than before...I'm on a trip right now but when I get back i'll retake it apart and check it all piece by piece. Thanks for all the help!!
 

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Are the ignition leads going through the steel tubes? If they are, try using different spark plug wires outside of the tubes.

Just another thought...


Sent using Tapatalk.
 

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When I can get through with all the stuff I'm having to work on now, I'll get back to work on my own two cylinders and see if I can come up with anything helpful towards finding a solution to your problem.

Haven't even fixed the poppin johnnies and here I am trying to buy more stuff to fix up.:empathy:
 

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Alright, I tried the leads idea and it made no difference. I swear they have a very weak spark! my neighbor has the same tractor but he's a finicky person so I have to catch him in the right moment to ask if I can try his magneto on my tractor. We tried ours on his and his ran fine but I swear its a spark thing....Tried new plugs too (still not running)...as a shadetree mechanic i'm definitely out of ideas on this tractor...I guess we'll see what the other magneto does...I'll keep y'all updated. Thanks again for all the help!
 

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Turns out it was the Magneto...now I'm on the hunt for anew magneto...It ran great with my neighbors....the little spring that pops the magneto forward is no longer working...it pops apart because it is bent....strange that it ran a while ago on my neighbor's tractor but oh well...at least I found out what the problem was
 

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Turns out it was the Magneto...now I'm on the hunt for anew magneto...It ran great with my neighbors....the little spring that pops the magneto forward is no longer working...it pops apart because it is bent....strange that it ran a while ago on my neighbor's tractor but oh well...at least I found out what the problem was
That's called an impulse coupling. It springs the magneto forward at low speeds to generate a spark for starting. It is replaceable. Small airplanes are still manufactured with this same technology to this day. Without the coupling working correctly, the magneto will not generate a charge hot enough to jump the gap on the spark plug.

Glad you found the issue.:good2: Maybe you can post a video of your tractor when you get it running. We'd love to see it. Ok, I'd love to see it.:lol::lol::lol:
 
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