John Deer 304 and 390 series mower trouble

[candycar]

I'm new. Please Help! We have 2 JD mowers that have the same problem. 304 and 390. They start fine, run/mow for a while then just shut down and take a few minutes before they start again. We've replaced batteries, gas, filters, coils, fuel pumps, and cussed a lot. Even had JD service done on them. Still the same problem. I think it's some relay switch but don't know which one to look for. Our JD tractor had the same problem, and we fixed it with 2 relay switches (recommended by a mechanic, don't remember what they are called). I would take them to the JD mechanic, but they are REAL busy and we wouldn't be able to mow the yard for months.

 

[slomo]

They start fine, run/mow for a while then just shut down and take a few minutes before they start again.

Typically, this is a clogged fuel tank outlet. Trash in the tank.

Could be internally deteriorated fuel lines from tank to carb. Clogged fuel filter. Inline shutoff valve possibly not letting fuel by.

Someone using an open top spout fuel can. Passing trash from the can to the mower tank. Tank on to carb. Water, bugs, dirt dobbers, grass and so on.

Pull the fuel line AT the carb inlet. Drain into a glass jar. Should be a solid flow from tank. Look for water.

and cussed a lot.

Starting to like this guy...... LOL

Wonder if a relay is making poor contact but when bounced around the yard either makes good contact or a poor one???? Not sure of this relay you speak of.

Most of the time, safety switches are either on or off.

 

[candycar]

Thanks Slomo, I'll look into pulling the fuel lines & cleaning the block & fins. Maybe drain the fuel tank too. Yay! more busted knuckles -..- can't wait.

 

[Tiger Small Engine]

Thanks Slomo, I'll look into pulling the fuel lines & cleaning the block & fins. Maybe drain the fuel tank too. Yay! more busted knuckles -..- can't wait.

Also be sure to blow through fuel to fuel tank with cap off to remove any debris caught in the line or connections.

 

[slomo]

Also be sure to blow through fuel to fuel tank with cap off to remove any debris caught in the line or connections.

Was hoping he would replace them but sure, test what you have.

 

[Auto Doc's]

The last thing people want to deal with is the fuel tank in these. I see garbage from dirty fuel cans more often than I like. It doesn't take much to block a fuel line outlet in the tank. You can blow them clear with air, but the trash will keep repeating the problem.

Of course, the tank on these is in the worst possible area that engineers could dream up. The entire upper platform has to come off the get the tank out of one of these.

There is no easy way to clean the tank, if that is what has happened to these mowers,

 

[Tiger Small Engine]

The last thing people want to deal with is the fuel tank in these. I see garbage from dirty fuel cans more often than I like. It doesn't take much to block a fuel line outlet in the tank. You can blow them clear with air, but the trash will keep repeating the problem.

Of course, the tank on these is in the worst possible area that engineers could dream up. The entire upper platform has to come off the get the tank out of one of these.

There is no easy way to clean the tank, if that is what has happened to these mowers,

I realize that blowing back through the tank on some riding mowers and zero turns is temporary, without actually draining/siphoning and cleaning the tank.

 

[mpqualdie]

I'm new. Please Help! We have 2 JD mowers that have the same problem. 304 and 390. They start fine, run/mow for a while then just shut down and take a few minutes before they start again. We've replaced batteries, gas, filters, coils, fuel pumps, and cussed a lot. Even had JD service done on them. Still the same problem. I think it's some relay switch but don't know which one to look for. Our JD tractor had the same problem, and we fixed it with 2 relay switches (recommended by a mechanic, don't remember what they are called). I would take them to the JD mechanic, but they are REAL busy and we wouldn't be able to mow the yard for months.

My dad bought one from a dealer used last year that was doing the same thing. The guy put a new fuel pump on it, but didn't clean out the fuel lines. I had to remove the carburetor and clean it out, really good. Like a dummy i put it back together and it did it again. I had to thoroughly clean the carb bowl needle out again, but this time I flushed out the fuel line between the pump and the carb really well. Been running like a champ since. Running it with ethanol gas does this to it, it erodes the rubber lines. ALWAYS USE NON ETHANOL GAS in your mowers.

 

[smalltowntex]

Candycar, don't know if this will help but if both of your mowers have a "electronic control unit" it is possible they have gone bad. Strange though, both at once. My X324 did the same thing. Spent a boat load of money on the "sounds like" method of elimination and took it to a dealer even. They milked be for a big chunk of change and the problem was still there. I had my trusty voltmeter and got to digging around and eventually it let me to this "electronic control unit" up under the dash. Put me a new one on and I have been a happy camper ever since. I am not saying this will fix yours but ended months of doing without my mower. I know there are some pros here and I respect that but sometimes a little head scratchin and eliminating one thing after another has got to tell you that so far, none of your cures has worked.
Hope you get it going.

 

[smalltowntex]

BTW, the ECU is a sealed unit. You can't replace parts...just buy a new one and plug it in.