John Deere 1520 Misfire

[ChrisGS]

Hi everyone, I have a 1520 that just started misfiring. While running it is constantly missing. I filled it with new gas but haven't inspected the spark plugs yet nor
have I adjusted the carb. I also noticed the tractor has a difficult time starting with less than half a tank of gas. Hopefully someone chimes in and can guide me in
the right direction.

 

[JD Dave]

Time for a tune-up. Replace the ignition parts. Then move on to the fuel supply, clean the fuel tank, fuel filter and carb. It's probably not a serious engine problem. Just some thorough service of the fuel and ignition systems should solve the problem.

 

[used red MN]

Hello Chris welcome to YT. I am wondering a little from my normal hangout on the IH page it is a little slow over there. No offense to his methods but JD Dave must have a lot of time on his hands. It takes much more than a misfire to get me to clean a fuel system including the tank but his approach and time investment and nothing to me. I like to troubleshoot and pin point a problem first then form the plan of attack. I would probably open the distributor and take a quick look at the points just to make sure they are not completely burnt up and are opening on the high point of the lobe to near the proper gap of about a dime thickness. If that looks good close it back up. Then pull the plug wires out of the cap and just set them back in their hole. Then start it up and grab each wire about an inch above the boot and momentarily pull it away from the cap to cut out that cylinder. If it makes a change in the engine sound that plug is firing. If when you cut out a cylinder and there is no change you have found the one that is not firing. I always have a good spark plug laying around for test purposes. Take that plug maybe you can use the one out of you lawnmower and plug the spark plug wire on that and make sure it is grounded to the engine, then start it to see if it fires your test plug. If that is good your spark plug is fouled. Pull it out to confirm, put in a new set. Now if the test plug did not fire you would have known the wire is bad. To rewind, so even if the points were okay it may be time to change them if it has been 2 or 3 years. If you describe a misfire to mean the same as most folks, the fuel system can usually take no blame for that type of an issue.

 

[ss55]

I also noticed the tractor has a difficult time starting with less than half a tank of gas.

- Check if the fuel lift pump is working.

 

[calf]

Used red has some good points.

If you really think it gets worse when the gas tank is low, can you check the fuel flow when the tank is full and then again when it gets lower? Check as close to the carb as possible.

Are all the plug wires on good and tight? Both ends?