300U not firing...here is how it went...

Dave H (MI)

Well-known Member
Thanks for the many replies below, I keep my tablet handy in the shop so was able to access all of those. So I started out with the points today, loosened the screw and regapped. I then checked the spark from the coil and then each plug. The wires are correct, I never undo more than one at a time unless I mark them with tape. Getting a little frustrated because I really don't have the experience to recognize a good spark. It jumps a quarter inch, but blue??? Are we talking blue/white? Cause I got a yellowish with some blue in it. Pretty lively though. Took a walk. Decided to pull the drain on the carb and get some gas out of it. This is where I had my OOPS moment. The thing I pulled was not a drain, it is some kind of needle. Most of the older Farmall tractors seem to have a drain on the end opposite the air intake but this fool thing has a needle for what I assume is one of the jets...but I dunno. Anyhow, it was out and the flow was pretty good but the gas was murky and had water in it. I took out about a quart of gas. I put that needle back in but had no idea how far so just until it snugged down. Told my wife I was screwed because it would never start with the carb out of adjustment. Turned the key and it fired to life. Ran pretty good too. I think my chin hit the floor I was so surprised. Sooooo....can someone tell me what this needle is that I unscrewed at the end of the carb opposite the air intake right at the bottom?
 
That would be the power jet.

Sounds like it was good to drain carburetor, there is a pipe plug for the real drain.
 
With out going out and looking at the 300U I have here I can only take an educated guess but I bet it is the main jet adjustment screw and it should be around 4 turns out form bottom to be set close to correct. Sounds like your main problem was water in the gas and maybe a clogged up main jet so when you pulled that adjustment off you also cleared rust/dirt/water out of the carb so it could then get good gas to run on
 
I have done that to clear out the main jet on more then one tractor and yes it does help when yo udo that
 
Like others said, that's the main jet. How about this, when it ran before, could you snap it from idle to wide open without any hesitation? Then could you bring it from wide open to an idle without it dying? Just trying to get an idea of how your settings were before. The main jet adjustment is what allows your throttle to be able to go from idle to wide open without hesitation. Keep turning it out until you get to that point if it doesn't.

Ross
 
The color of the spark is very dependent on what it is jumping to. A good clean spot will show a better blue spark whereas a greasy, or painted spot may show more yellow.
 
My memory is that it had a bit of a stumble moving up before. It certainly had none today. The idle was rough before, you throttled down and it would sound like it was shutting off, then it would come to an idle. After idling for a minute or so it would start to want to stall.
 

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