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Sumping problem?

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broncosfan

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Hello. I own a 1989 FXSTS with about 40000 miles on a rebuilt engine. For about the last 3 months or so, every time I start the engine the oil dipstick plug gets blown off, and oil spits out the filler neck. This happens any time I start the engine, hot or cold. The bike runs qreat after starting and no performance loss in noticable. A mechanic told me this is caused by sumping. How would I go about repairing this problem myself? I realize I could pay a mechanic to correct this, but I would like to do it myself if possible. Any good advise will be appreciated. Thanks. RJV
 
Welcome to the forum broncosfan, that was a very common problem around your year bike, it's no biggie, what is happening is you oil bag is over filling after you start it. Suck enought oil out of the oil tank and go for a ride untill your engine is up to opperating temp, then shut it off and check the oil, make sure it is just a touch below the full mark. Sometimes a little something will get in the pump and keep the check ball from seating causing the oil to drain from the oil tank into the lower end of the engine. If it's not too bad a lot of people live with it, the important thing is to never add oil to the tank before starting and running the engine first. All those year evo's will leak some oil if left sitting all winter.
One thing you can try is to unscrew the cap #17 and use a magnet to get the steel ball #19 out, don't loose the spring, then take a pencel and and insert the eraser end down and spin it to clean the seat suface of the seat, then put it back together and see if it's any better. There are tools made for recutting the seat but they cost about $100.00. good luck

OilPump91-92.jpg
 
if you take pump body off,take a old check ball,tack weld it to old push rod and lap the seat with some lapping compound
 
Also you can use an old evo pushrod and bead blast one end. remove the check ball and use the puchrod to lap the seat while the pump is still on the bike. Then i get 2 new check balls drop one in the pump and with a small brass drift just give the ball a light tap a few times to re-seat the seat, then disguard the ball you just used and replace it with the other new one. This has worked for me numerous times.
 
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