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Discussion Starter #1
John Deere X320 was running perfectly fine. I suppose this is a perfect example of not fixing something that ain't broke. Did complete maintenance kit with filters, sparkplugs, & all this time, rather than just oil change & deep cleaning, as technically it was past due. Engine is now backfiring a lot & does not seem to have the same power as before. Any ideas as to what the cause could be? John Deere said spark plugs are pre-gapped.
 

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I don't know much about your X320, but I use my general engine knowledge and duh moments.

Did your air filter change somehow jam the choke shut or partially shut? Check the linkage and make sure it's free.

Assuming it is a twin, does switching spark plug leads do anything?

Even though your spark plugs come "pre-gapped" did you verify that they weren't bent shut "by accident"?.

That's all I got so far. (my 2 cents).
 
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When is it backfiring? On acceleration, when it gets loaded up, at idle? Or sometime else?
 

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Even though your spark plugs come "pre-gapped" did you verify that they weren't bent shut "by accident"?.
good place to start and are the tops of plugs tight?
 
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Discussion Starter #5
TomFive, N, & Herminator, Thank you for your suggestions. Yes, it is a twin, but not close enough to switch plug wires conveniently. Yes, I did look at the gaps & electrodes before I installed them & all looked well. They were brand new plugs & matched what was there before. Not to say I have not ever had any problem with brand new parts from them as I have had enough. I do not even know what the gap is supposed to be so I could check it, but there seemed to be a reasonable gap. I don't know how I would have jammed the choke, but I suppose anything is possible. On the other hand, the choke works normally & as it should. I will take the filter back off & check down there. It is hard to get to on this one & not wide out in the open. Initially it started up fine, then after about 30 seconds or so of running it started backfiring regularly as it is running & did not seem to have the same "power" as it did before I changed everything. I did not specifically check the tops of the plugs per se', but they seemed fine. I will pull the wires again & double check.
Thank you again. Dave
 

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It's possible that its just one of the ignition wires isn't properly seated on the plug or the plug connector is broken. The unburnt fuel will cause a backfire when the exhaust valve opens and gas hits the hot exhaust. It would also explain your loss of power.
 

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A quick google search should glean you the plug gap. Verify that first, then check the actual plug wire ends and make sure they’re not corroded and have good connectivity. Both ends. Take a close look at those plugs and check for debris stuck in there.
 
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Did you happen to install the fuel filter backwards? There should be a direction of flow arrow on it. It needs to flow towards the engine
 

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Does the X320 require periodic valve adjustment? You might have some junk in the carb, run some seafoam through it and see what happens.
 

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Did you happen to install the fuel filter backwards? There should be a direction of flow arrow on it. It needs to flow towards the engine
I always do that but thought it had more to do with dirt holding capacity rather than flow.
 

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By deep cleaning did you hose down the engine?

You didn’t gap the plugs, but just looked to see if it was reasonable? I would pull them and set the gap. Yes new plugs have 90% consistent gaps from the factory, I rarely find them to actually be what the engine calls for.
 

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If it ran fine before you did the maintenance service, it's most likely caused by a bad part or a wire(s) that got disturbed, which it sounds like you are leaning towards. Another common problem, at least with the FS651V engine, is the coils.

Depending on the year of your X320, it came with either a FH661V or a FS651V engine. I have a 2014 X360 with the FS651V engine so I'm a little familiar with that engine. The quick, easy way to tell which engine you have is the air filter element stands up and down on the FH661V, or lays flat on the FS651V.

It looks like both engines use the same spark plug. The tech manual for my FS651V calls for the spark plug gap to be 0.028"-0.031". I'm sure yours is also. I think I set mine closer to 0.030" when I changed mine last year.

Inspect the spark plug boot and lead to make sure they didn't separate or have a poor connection. Did you make sure the spark plug boot is fully seated? Have you tried putting the old plugs back in, and seeing if that makes the backfiring go away? If it does, most likely one of the plugs are bad. If the backfiring continues, I'd be looking at the coils.

One thing I found out about these coils is the importance of have the proper gap at the flywheel. I was having 'no start when hot' issues. New plugs didn't fix the issue, but resetting the coil gap did. With yours running for ~30 seconds before it started acting up, it may be the problem. The manual calls for a gap of 0.008"-0.016" between the coil and the flywheel. I set mine at 0.010" and it's been running great since.

What I've found is the coils seem to act up when warm/hot and not as much when they are cold. Some people have reported that they had to change the coils to fix their problem. I only had to adjust the gap. I removed the coil and cleaned it with emery cloth as well as the flywheel, to remove any rust. Reinstalled, adjusted the gap and it's been doing well.

It's important to set the coil gap with the flywheel in the proper position. You can also check the coil with an ohm-meter. See the 2 pictures posted below.

Let us know how your repair is going/went. We all would like to know (y)

732100


732101
 
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Another thought came to mind, but a much more obscure cause. I have seen (and done this) where the high tension spark plug lead was damaged when removing the boot from the sparkplug. Sometimes when removing by either tugging on the wire instead of the boot, or when the internal connector is tight, the connection between the wire and internal connector gets damaged. Sometimes you can check with an ohmmeter and the wire shows very high resistance, and sometimes when tugging/pulling the wire and boot will show a change in resistance. The ignition coil inspection resistance tests posted by kylew may show this issue.

I also read about the case where a break like this opens when the wire heats up and temporarily heals itself when it cools (and vice versa).

Good luck, and let us know how you make out.
 
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Discussion Starter #14
Thank All You All for all your suggestions & thoughts, I really appreciate it. I honestly thought the most likely thing was perhaps I did not put the plug wires back on securely, but here is the whole deal. It is really weird, but this is it. First I checked everything mentioned here except the plug gap, because I still did not know it. Everything looked perfectly fine, nothing loose, nothing out of place. Everything looked good.
Then I fired it up today & ran it for a few minutes. It never back fired once, period. However, it seemed like the motor was throttling, (high/Lo). Then, when I went to back it out of the garage, it stalled. It kept stalling, & I would re-start it right up. I did this maybe four to five times before I figured I had better have another look. I pulled the air filter off again, looked at the fuel filter (I had always installed that correctly & made certain from the get go), etc. No problems. Then, I fired it back up & it started running like it had never ran before, even when new. Then I mowed & it ran for three hours mowing & maybe only tried to stall twice towards the beginning of the mow. It ran perfectly fine & then I shut it of just as smooth as ever. By the way it also cut better than ever. It was strange as in dong the major maintenance, I could not believe the levelness was so far off from the dealer. It is strange because I had purchased all sort of parts from the dealer, at their recommendation, to try & resolve a gouging issue. It cuts beautifully now & was way off level from the dealer. I have to believe they never adjusted the deck before selling it to me, probably just took it right out of the box. I could probably go on & on, but I will not. Anyways, it seemed to resolve its problem on its own. Maybe when I changed the filter the other night some gunk or even excessive air got into the fuel line & it all had to run itself out. That is strange though as I fired it up right after changing the fuel & oil filter & it was fine. The problems did not start until after the plugs & air filter were changed, last. I know it is all a strange story, but that is my story & I am sticking to it.
Thank you all again for all your tips & suggestions. I learned something from them, even if they did not seem to be the solution. Thank you.
 

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That makes sense if there was a slug of air in the fuel line due to the empty new fuel filter you installed.

Thanks for following up.
 
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