New Member - Pony problems (Help!)

It is a very simple engine. You need spark, gas and air and everthing in time. when all is correct, it starts with one or two pulls. My ponies do seem to flood easy. If you think it is flooded, open both petcocks to drain the gas and open the choke all the way when cranking.

If it ran, then it must be in time. Don't remove the mag unless you really have to and you won't have to bother with timing. You could check it though. In the simplest terms, with #1 cylinder at TDC (Left hand cylinder as you sit in the seat), the rotor should point towards the plug wire. You can remove the plug and tell by spinning the pony by hand #1 is at top dead center. I use a welding rod (or something) to 'feel' the top of the cylinder.

Good spark is a nice blue spark that will jump 3/16" or so from the plug wire to the block. I would just take out the spark plug and see if it is firing good when you turn the motor over touching the plug to the head.

I had a pony that would start cold, but not start hot. It was a bad coil in the magneto.

The jet (and passage) in the bottom of the carb bowl gets clogged. A sure sign that is clogged will be having to choke the motor to keep it running.

Due to a lot of rust in my fuel tank (even after cleaning) I removed the fitting in the bottom and soldered a small piece of copper tube to the fitting so that the sediment on the bottom wouldn't clog the fuel line. I also soldered on a brass screen. That took care of the fuel issue.

Check your float height. That is very important. Something like 1-1/8" with carb top inverted from bottom of float to edge of carb bowl. I have a carb kit at home with the measurement, but someone here will have it.

With a history of rust in the tank, and knowing how old they all are, you need to clean all the lines from tank to carburetor float needle valve with a wire and compressed air. Only way to know that you don't need to do this is to remove the drain plug in the bottom of the float bowl and see how much gasoline you get after the initial gush of what was already in the bowl. Sometimes they will run OK, but not quite get enough fuel to pull the load of the diesel under compression.

Also one thing to do is change the oil in the pony motor. It holds a quart and frequently will be diluted with gasoline from the carburetor bowl when someone forgot to shut off the gasoline valve from the tank (or it leaks a little) Anyway, good oil can be the difference in running or not, and you sure don't want to run it with any dilution because these things frequently throw a connecting rod occasionally. Sometimes when they do, you find that the cotter pins in the castellated rod nuts are missing and a nut has simply loosened, or the bearings may just be worn out (see warning about oil dilution above).

What gap did you use on your points when you worked on them? Spec for the Eiseman mag is 0.014-0.018". Plug gap should be 0.025" (might want to be a little closer if you think your mag is weak). No resister core wires, metal conductor wire only ( but I have had one with resister wires that ran fine).

Timing check, turn the flywheel around to the MAG line and the points should be barely opened and the rotor button pointing to one of the wire towers on the mag cap. Most of them will throw a 3/16" spark when you check it, so if it'll do that, start looking elesewhere for your problems.

On the carburetor clogging, I have usually been able to run one with the choke on enough to crank the main engine even with it clogged IF there was enough fuel getting into the carburetor bowl. One thing to remember is that both the idle and the high speed mixture adjustment needles on these engines are screwed IN to richen the mixture and OUT to lean it. NOT like you normal small engine. Initial mixture adjustments are high speed open 1 turn from all the way in, idle-open 1/2 turn from all way snugged in.

good luck!

Thanks for the replies. Any and all help is very much appreciated.

So, is the compression (70 pounds) okay? If everything else (carburetion and spark) are fixed, will this thing run?

I have read about the oil dilution issue, so I will definitely change the oil.

2nd question: Is the carburetor fixable, or do I need to be looking for a replacement? I broke the brass tube that goes between the float bowl and the carb body - can this piece be replaced? If not, how difficult is it to find one of these Zenith carbs?

These motors will run with as little as 35 psi. 70 is actually quite good, so I wouldn't worry about that. There are alot of these carbs out there. Zenith made them for a variety of manufacturer's. I get parts for mine from the local John Deere dealer, as they the starting motor's on the older 2 cyl diesels. Some one here should have a parts carb. Maybe post a wanted ad in the selling section. Otherwise they come up on e-bay.


Matt

Thanks Matt,

The compression information is good news. I couldn't find much info about proper compression, either searching this site or on the internet in general. Now I know to be troubleshooting the fuel and/or spark issues.

To remove the carb body, it looks as if I may have to remove the magneto to get to the inside nut on the carb flange - however, I've also read here that it's not a good idea to remove the magneto unless you have to, as it's difficult to get back in time. A socket won't work to get on the 1/2" nut - would one of those "crowfoot" type wrenches get in there? There's not much room between the carb and the magneto. Surely someone here has advice about this.

Also, to see if the magneto is throwing a hot enough spark, I've read that the spark from the wire should jump a 3/16" or 1/4" gap. Do you use some sort of a jumper wire shoved up into the spark plug wire boot to test this?

Todd

Thanks Matt,

The compression information is good news. I couldn't find much info about proper compression, either searching this site or on the internet in general. Now I know to be troubleshooting the fuel and/or spark issues.

To remove the carb body, it looks as if I may have to remove the magneto to get to the inside nut on the carb flange - however, I've also read here that it's not a good idea to remove the magneto unless you have to, as it's difficult to get back in time. A socket won't work to get on the 1/2" nut - would one of those "crowfoot" type wrenches get in there? There's not much room between the carb and the magneto. Surely someone here has advice about this.

Also, to see if the magneto is throwing a hot enough spark, I've read that the spark from the wire should jump a 3/16" or 1/4" gap. Do you use some sort of a jumper wire shoved up into the spark plug wire boot to test this?

Todd

Just use a screw driver or old spark plug to test the spark. Either wedge the screw driver in the spark plug boot and hold it about 1/4 inch away from the block and crank it over. Or take a old spark plug and open the gap up as far as possible and lay that against the block and crank it over.

To clean all the passages on the carb you'll have to remove the little bb plugs out of the bowl to clean out those passages. Then tap them to the appropriate sized plug and plug them back up. Some people just put a bb back in there and put some fingernail polish to seal it up.

Definately check the end play of the crankshaft. Mine has about 1/4 inch which is about 1/4 inch too much. The main bearings control the amount end thrust. Just grab hold of the flywheel and try to push it in and out. Maximum spec. is 0.025".

My pony is on the floor at the moment needing a rebuild before it blows up.

Good luck with yours. This Forum and www.Antiquecaterpillar.org are two great sites with exceptional friendly people who are willing to help as much as they can.

At the dealer I took a truck load of carbs off over the years and to get to that one nut I always took off the float body as you,ll be taking it off anyway if your repairing the carb and the nut is right there easy to take the complete carb off then.Also leave it off when your putting the main carb body back on and then install the float body after the carb body is bolted down.

i got a cross tube. how did you break it.