Vapor Lock? Not an LC problem, but maddening nonetheless...

[bassguyry]

I inherited an old John Deere riding lawnmower (a '96 LX178, if it matters... ) from my dad a few weeks back. I knew it had some issues, but figured I'd be able to replace a few parts and get it back running again. Basically, after running for about 30-40 minutes, the engine sputters and dies. It won't start up again until the engine cools down again, which makes me think vapor lock. I've replaced the fuel pump, fuel filter, took apart the carb and cleaned it, checked all the fuel lines to make sure they weren't blocked, to no avail.

The exhaust is located on the front of the engine, just below where the fuel line runs from the tank to the fuel pump, so I'm wondering if it's getting hot enough to cause the vapor lock. Maybe switching to non-ethanol fuel might help? I've also thought about wrapping the fuel lines in some sort heat shield, or even trying to build some sort of shield between the exhaust and the carb/fuel lines.

Yes, I know this isn't a Toyota-specific issue, but I'm running out of ideas and about ready to set fire to the damn thing.

 

[60wag]

Any chance its a vacuum leak on the intake manifold between the carb and the head? Look for loose bolts and deteriorated gaskets. I've chased a couple of these on small engines.

 

[bassguyry]

Any chance its a vacuum leak on the intake manifold between the carb and the head? Look for loose bolts and deteriorated gaskets. I've chased a couple of these on small engines.

Probably not. When I disassembled the carb, all the gaskets looked to be pretty darn fresh - my dad rebuilt it a few years ago and hasn't really used the mower since, so everything looks to be in good condition. Bolts are tight, etc.

 

[rover67]

is it starving for fuel because the float bowl is slow to fill or something?

 

[bassguyry]

is it starving for fuel because the float bowl is slow to fill or something?

I don't think so, because the problem only happens after it's been running for quite a while (30-40) minutes, which makes me think it's something heat-related. Oil and coolant levels are perfectly fine, so I'm stumped.

 

[rover67]

sometimes coils fail when they get real hot, another thought. does it have spark when it wont start?

 

[RicardoJM]

When it dies, check that the fuel is still getting from the tank past the pump. This is a short video of how to check.

If there is no fuel, it would indicate; the pulse signal to the pump is weak or the pump is on it's way out. If there is fuel, leaving the pump it is likely getting into the carb and the suspect area would be air and spark as Marco mentioned.

Spark can be checked with spark checker. Just google spark checker and the results should have pictures of them at the top. I have one if you need it, but there is likely someone in the club closer to you with it as well.

The fact that it happens after it has been running a while doesn't seem to be consistent with an air issue but don't rule that possibility out.

If it is fuel not getting out of the pump. It is possible there is a vacuum leak it would affect the pulse signal and it may be the vacuum leak is there all the time but it gets more pronounced as the engine temperature increases.

 

[AlpineAccess]

Check your ignition coil. I had an issue last year with my ski boat and was chasing fuel all day. On a whim I figured I'd swap the original coil out. Sure enough it was getting hot and building lots of resistance.

Very similar symptoms to vapor lock when it starts going.

 

[bassguyry]

Thanks guys, super helpful info. It's definitely not the fuel pump - I've replaced it already and checked to make sure it's working correctly. I'll check to see if it's getting spark. Also ordered a new ignition coil, since they're $18 on Amazon. Hell, a new carb is only $40.

I grabbed 5gal of non-ethanol gas over lunch, so I'm going to try that first and see if it helps. Hell, if it's just enough to keep the damn thing running long enough so I can mow my entire lawn, I'll take it.

 

[SteveH]

When it seems to be vapor locked or out of fuel, loosen the carb bowl drain screw (if it has one) and see if gas runs out. You might re-route the OEM fuel line to a cooler place, too. Is the gas cap vented and the vent open/working?

 

[bassguyry]

When it seems to be vapor locked or out of fuel, loosen the carb bowl drain screw (if it has one) and see if gas runs out. You might re-route the OEM fuel line to a cooler place, too. Is the gas cap vented and the vent open/working?

Yep, gas cap is vented and the vent works just fine. That was the first thing I checked, actually.

 

[rover67]

When it seems to be vapor locked or out of fuel, loosen the carb bowl drain screw (if it has one) and see if gas runs out. You might re-route the OEM fuel line to a cooler place, too. Is the gas cap vented and the vent open/working?

good idea to check for fuel in the float bowl when it quits!

 

[Stuckinthe80s]

Here’s a good way to check for spark:
1. Remove spark plug wire.
2. Remove spark plug.
3. Reconnect spark plug wire to spark plug.
4. Ask wife to hold spark plug while you crank the engine.

If she jumps, screams, and starts beating you, then you know you have spark.

 

[ccslider]

Can you run a fuel line to a temporary gas tank?

 

[Rzeppa]

4. Ask wife to hold spark plug while you crank the engine.

If she jumps, screams, and starts beating you, then you know you have spark.

🤣🤣🤣

 

[bassguyry]

So far, the non-ethanol gas has done the trick! Managed to mow the entire lawn without issue on Saturday. Even took a few victory laps around the street with my son, with no issues. Granted, it was quite a bit cooler on Saturday, so we'll see if the issue persists, but so far, so good!

 

[rover67]

 

[AlpineAccess]

Did you end up swapping the coil?

 

[bassguyry]

Did you end up swapping the coil?

Nope. Bought one. Guess I'll keep it as a spare.