300U still wont fire

Good news is, I am 100% planted and we got a little rain. Bad news, the 300U won't start this Spring and I need it to pull the sprayer in a couple weeks here. So, to update, I had a bad battery isolation switch and I have a replacement but currently I am just bypassing the switch to make life easier. The starter has been tested by a good guy and is working fine, no drag. I replaced the solenoid as it went bad. I have a brand new charged battery because the old one was questionable. So I have moved over to the other side of the engine and am testing the ignition. My handy dandy probe tester flashes when put on the distributor side of the coil. I pulled the plugs and they are old, so I replaced them all on spec. When I lay them against a ground and crank the engine I get a yellowish spark...not the hot blue spark I would hope for. I gave it a breath of starter fluid and it sounded like maybe it fired on one cylinder one time, but no more than that. I am wondering if my coil is weak? How would I know? This tractor was running last fall when I drove it into the shed. Any suggestions welcome, I am only an amateur mechanic. I get it done, just takes me a long time and a lot of head scratching.

Thanks!

Check that your point gap is correct at if I remember right 0.020. Then pull the center wire from the distributor cap and make sure you have a good blue/white spark there that will jump a 1/4 inch gap or more. Also make sure you have the firing order right as in 1,3,4,2. Then check that you have the same spark at all the plug wires. If you have that then

Pull the carb drain plug and make sure you have a good steady flow of gas that will fill a pint jar in under 3 minutes

Stupid question, how do I know which wire is 1 to four?

cylinders are numbered front to rear. # 1 is nearest radiator.
uh, take some fine sandpaper, open the points and clean the points. wipe them with a clean rag and then spray them clean with ether.
there is probably some kind of a drain plug on the bottom of the carb., remove and let some gas run out.
good luck

#1 if the plug closes to the radiator and #4 the one closes to the seat then you get the #1 cylinder at TDC and and see where the rotor is pointing and also as your getting it to TDC watch which way the rotor turns

Ok, Rich. Thanks for the shove. Maybe get me going in the right direction!

To bad your not a whole lot closer to me I am sure I would have it running in just a short time

Dave, also check where the wires go into the cap. Pop them out one by one, including the coil wire and look in the cap at the termine in the cap. The newer caps have aluminum contacts in there, not brass like the better old ones. Anyway, I have had quite a few instances where I have had poor spark on one cylinder due to the cap being corroded down in the terminal tower, and I've had them cause a no start or poor spark to all cylinders when the coil contact in the cap gets corroded. Also pull the coil wire out of the cap and hold it to the block when cranking, see what you have there, it should have quite a crack and be nice and blue. Don't get your fingers too close to the end of the wire. Just something to check out. Oh, and you may want to check your valve adjustment, it has nothing to do with poor spark, but certainly won't help it start any if it's way out of whack.

Has this tractor been converted to 12 volt? You could have a bad connection. The solinoid for a conversion should have two terminals. One goes to the key and the other to the coil to give it a kick in the butt to start. We are still going to need a little more information.

I'm not a mechanic but upon reading your post I noticed you replaced spark plugs. Are you sure you got the right plug wire from the distributor to the spark plug. On my 450 the dist. order is top outside 1, top inside 2, bottom outside 3, bottom inside 4. Working with my brother I saw many cases of wires in wrong order. Jr finally started marking them with masking tape.

I would clean the points with a dollar bill, and see how pitted they look. I was amazed how quick a set of BW points wore out on Charlene.