520 gas 'overflow' tube and backfiring

Coyotefred

New User
Hi everyone,

Newbie question here. I have a 520 gas that has run pretty reliably for several years. I hadn't been able to run it since Nov 2013 and today I finally got around to starting it. It wouldn't start and wouldn't start so I pulled and cleaned the plugs, but still no luck. Eventually I shot a little gas into one cylinder to prime things (something the previous owner suggested) and I eventually got it to catch and run. But when I throttled it up several ounces of gas squirted out of a tube on the underside of the tractor, and the tractor had several loud backfires. This happened a few more tires as I throttled it up and down. I let it run for awhile and eventually only a few drips of gas were coming out of that 'overflow' (?) tube and there was only one backfire in about 5 minutes. I'm attaching a picture of this tube/pipe on the underside that the gas came out of.

I've never had this gas discharge/overflow happen before...what is the explanation?

Thanks for your time,

mvphoto9843.jpg
 
That pipe is your crankcase breather tube. If gas is coming out there you may have a bad diaphram in your sediment bowl letting gas pass into the crankcase. Drain the crankcase oil to see if gas has flowed into your crankcase. Do this 1st before trying to start it again. Gas vapor in the crankcase can be a dangerous thing!!
 
Does your tractor have an automatic fuel shutoff? I agree with Randy G. Both 60's I've owned eventually needed a diaphragm kit installed.
 
Pull the crankcase oil level dipstick and check for
a gas smell on it. The crankcase may show a level of
oil above what you filled it to-this is also a sign
of bad diaphragms. If there is a gas smell, replace
the sediment bowl diaphragms and the oil-do not run
the engine with the old oil/gas mixture or it may
seize the crankshaft.
 
I appreciate the explanation and the advice; I'll do as has been suggested...

(quoted from post at 07:32:22 08/05/14) Pull the crankcase oil level dipstick and check for
a gas smell on it. The crankcase may show a level of
oil above what you filled it to-this is also a sign
of bad diaphragms. If there is a gas smell, replace
the sediment bowl diaphragms and the oil-do not run
the engine with the old oil/gas mixture or it may
seize the crankshaft.
 
Is the backfire a sudden one or does it miss a few beats and then make a big bang? If it misses a few beats and then makes an ear splitting bang the condenser might be the culprit. My 630's oval muffler is a little more round after the condenser started acting up, cutting out the spark for a few beats and then lighting up again with the gas built up in the muffler. I've replaced two more condensers on this tractor, with a Wico distributor. I've also put a condenser in another 630 with a Delco distributor, to cure a weak spark problem.

If it's a random backfire with just a little stumble my instinct tells me you have a lean fuel mixture.

The gas in the crankcase has already been covered. Jim
 
Well we drained the crankcase and there was almost 4 gallons of gas in there :shock:

I ordered the standard sediment bowl diaphragm kit and will replace that.

It's shocking to think of that much gas entering the system...is the faulty diaphragm the only thing I should be checking/looking at?

Thanks for the help
 

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