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JD 620 gas in oil

E

Ed the wine farmer

Member
Before I ask for advice, I wish each and every one a very Merry Christmas. My son picked up a JD 620 a few weeks ago. Nice tractor; good paint, rubber and runs well. The oil was a little thin so we changed it. The gas line from tank to carb had a add on shut off with plastic tubing over the manifold.I changed this out with copper and a new shut off.Today I checked the oil and found gas in it again.The fuel line was off so no gas came out of the carb. We did use the tractor for about 3 Hr the day before all at low RPM. The question is, can the carb pass gas to the oil while the tractor is running? Remember, the gas line was off the carb after we stopped using it. Thanks for your help. Ed
 
Are you sure the "new" shut off, is shuting the fuel off? most of the new parts I buy anymore aren't any better than the ones I take off.
 
Does it still have the oil pressure shut off on it? If so, the diagrams are bad and allowing gas to get in the oil line.
 
I would check the float. Autos had that problem at times when their fuel pump would leak gas into the crankcase. The double action pumps were bad for it. Hal
 
Ed, was just passing thru and read your post, and yes the carb can pass fuel to the crankcase, but you say it runs good, it would have to be running very rich to do that. If it running good and putting gas into the crankcase, I would suspect a leaking fuel pump diaghram, Just my two cents. Brian
 
From your description, I would have to assume that the tractor has a mechanical fuel pump that is actuated by a rod that rides on the cam shaft (similar to some cars). If that is the case you will be time & money ahead by removing the old fuel pump and actuator rod, and capping off the hole - (Blocking plates & gasket are available at almost any auto parts store). Then put in an electric "in-line" fuel pump (Put it somewhere that it's easily accessible).
 
The 620 is gravity feed no fuel pump if it has the oil preasure shut off it can still leak fuel into the oil easy fix just get new diaphram for it. If you want the original lines are avail from deere
 
Read MSD's suggestion. You'll find your answer there. You can have the carb completely off the tractor and it'll still get gas in the oil through the pressure line to the fuel shutoff. Jim
 
I'd bet the lower diaphram had a pin hole in it. Two diaphrams A4983R $8.50ea and one washer A4978R $1.34ea

Replace them and remember or mark how it came apart. So the pieces are clocked right.
a93734.jpg
 
Ed, I recently went thru that with my 630. It's like the others said - with the engine off, and the fuel valve to the carb closed, the only way for gas to get in the oil is thru a bad diaphram in the auto fuel shut-off. I got 30 years out of the first diaphram that I changed, but only three years out of the second one. It may be the modern fuel, or mebbe the material is not as good as it used to be, but I'm done fooling with the auto shut-off. I plugged the oil lines and now I turn the fuel on and off manually. You can make a thin wedge to hold the knurled knob down on the top of the shutoff (for fuel to flow), or learn to turn the knurled knob a quarter turn left while pushing it down to make fuel flow. And to sum it up - if you DON'T have an auto shut-off, disregard all I've said, ha.

Merry Christmas,
Paul
 
There is someone out there that makes the diaprams that will work with the ethanol. When I redid my 620 I just replaced the shut off with an old stock one for a 70. No more diaprams.
 
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