I've spent the last week slowly but surely working over my D6 9U. Many thanks to CCJersey. His advice was very helpful.

So I mostly have it back together, and I went to fire up the pony motor and the cylinders are flooding. I'm assuming that the float is stuck. It's very frustrating, as it had been fine earlier this week.

Here's my basic question: Is there a way to fix this without tearing apart the carburetor?

Looking at my parts book there is a nice little thumb wheel on the needle assembly. Quite frankly, I'm scared to fiddle with the screws and knobs on the carburetor. I'd hate to mess with something and mess it up worse than it already is.

Any and all help would be much appreciated. Thanks!

On a related note, I'm getting a fair amount of leakage out of one of the stop cocks on the pony cylinder. Any tips on fixing this, or do I need to just get a replacement valve?

The cover on top the carb. bowl is where the float is so no you don,t have to take the carb. apart to get to it but just remove that cover with 4 screws holding it on. It isn,t a big problem to adjust the high and low screws on it so don,t let it scare you.I have set a truck load of them but been a long time ago so probably start out by screwing them in and back out a turn or a little more and then start it up and fine adjust one at a time from there till it runs correctly.

Just finished the pony on my D2, which I think is the same or at least close. SJ is correct. The four screws will get the float out. I found mine to be full of crud, so had to remove the whole thing. The entire carb will come off the side veturi with the two screws, one on each side of the low speed ajustment. There is a needle which goes through the venturi into the carb so be carefull not to break it off. The first time I pulled apart, I took the whole card and veturi out to clean first, after that just the carb. Good luck Tim

initial adjustment on the mixture is 1 turn out on the high speed needle on top the bowl and 1/2 turn out on the idle mixture.

adjust high speed needle OUT to richen mixture, adjust idle mixture IN to richen mixture.

The properly adjusted carburetor will allow the engine to be started at near idle (throttle control pulled out) with the choke on fully (knob pulled out all the way). When it starts, the some of the later choke plates will spring open enough to keep it running until you can manually adjust the choke some.

If you haven't already, go back upstream and eliminate the trash that is making the needle stick in the seat of the float valve. Also check the float for gasoline inside of a brass one (sink it in hot water and watch for bubbles from any leaks) or heavy from gas eating into the black coating of the "cork" type.

The petcock leakage isn't usually a biggie, probably would be simpler to just buy a new one. Other than that you could use some lapping compound and work the valve to make the two pieces fit better.

Thank you all! My pony motor is indeed running as it should . . . mostly. I was able to take the top off, clean things out and put it back together. The only issue I'm running into with the fuel is that a previous repair to the fuel tank means that it needs to be pretty full or there isn't quite enough fuel pressure for everything to run right.

However, I still have a problem. The governor is running the pony motor too slow to start the diesel. If I pull the throttle arm by hand, the engine will rev sufficiently high enough to start, but the governor fight against me trying to slow things back down.

If I let the governor spin things it will turn the diesel, but the fuel pressure never makes it to "caution" (green), much less "normal" (white). It just hangs out at "out" (red). If I override it, I can happily get the fuel pressure up.

Thoughts? Is there a way to adjust the behavior of the governor? Is there something wrong with mine that it is keeping the speed to low? For that matter, what is the correct RPM for the pony motor? Could I measure it with a contact tachometer push onto the shaft of the main pulley?

In the computer industry we sometimes say, RTFM -- Read The Fine Manual. Which I went and did. I found a lovely section in the Servicemen's Reference Book for Caterpillar Diesel Engines talking about how to adjust the governor. Seems pretty straight forward. (Page 104)

I have two questions though that aren't addressed by the manual.

(1) As I asked above, can I read the RPM with a contact tachometer off the main shaft, or is there some other way I do it?

(2) The manual talks about the high idle speed and the low idle speed. What causes the pony motor to shift from one to the other? I haven't put a tachometer on it yet, but it sure seems like it's only operating at the low speed. Can somebody explain this to me?

High idle is maximum UNLOADED rpm. should be 3350 for the D318 pony As it assumes the load the engine will slow down a bit (this is called droop) and rated rpm is 3000 As the diesel overspeeds the pony motor, the pinion latches should kick out a little over normal high idle rpm.

Low idle is the slowest rpm it will attain (no load-throttle control pulled all the way out to keep the idle speed screw against the stop) should be about 800 rpm.

Either a contact tach or a photo tach can be used on the pony motor quite easily.

Sometimes you only have one cylinder firing and if you can get the other to kick in, then away she goes! It could be a bad wire, bad plug, sometimes it's just weak spark and adjusting the choke a bit can change the mixture enough to allow it to run on both cylinders.

I would tend to check spark and compression more than mixture/fuel if it will run at all, but it could be the common problem with fuel flow through the main circuit in the carburetor that 's limiting power. Try leaving some choke on and see if you can make it run full speed like that.

Thanks all. My pony motor was running around 2300 rpm. It appears that my tension spring really needs to be replaced, as it was already stretched about as far as it would go. I made some modifications to the spring, adjusted the tension using the nuts, and I now have it running around 3180 RPM. I think I'll need to get a new spring, or make further modifications to the existing one, to get up to 3350, but 3180 seems to be enough to get it started, so I'm pretty happy.