Motor stumbling at full throttle and low oil pressure

Went racing for the first time in two years this past weekend. All was going well until about 5 laps to go in the feature. At full throttle the motor was stumbling. I could let out of the gas and get back on it and it was fine until you get to full throttle. I pulled off not wanting to damage the motor any further and when i did i noticed the oil pressure was down to about 20 and the oil pressure light came on. No obvious leaks or damage to exterior of motor. It does have a minor leak coming from the rear main seal, but only a few drops. Any ideas where to start looking first?

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Originally Posted by modified11

Went racing for the first time in two years this past weekend. All was going well until about 5 laps to go in the feature. At full throttle the motor was stumbling. I could let out of the gas and get back on it and it was fine until you get to full throttle. I pulled off not wanting to damage the motor any further and when i did i noticed the oil pressure was down to about 20 and the oil pressure light came on. No obvious leaks or damage to exterior of motor. It does have a minor leak coming from the rear main seal, but only a few drops. Any ideas where to start looking first?

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Make sure the oil hasnt gotten full of fuel. If it was stumbling from fuel spilling over, it could have thinned up your oil, which would cause it to loose oil pressure,

Okay thanks! I plan on changing the oil tonight so i should be able to tell then. What would cause fuel to get in with the oil?

If it is dumping raw fuel into the cylinder, it will get down into the oil.

far as the stumbling, sounds like fuel pressure or a stuck float or something

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Originally Posted by modified11

Went racing for the first time in two years this past weekend. All was going well until about 5 laps to go in the feature. At full throttle the motor was stumbling. I could let out of the gas and get back on it and it was fine until you get to full throttle. I pulled off not wanting to damage the motor any further and when i did i noticed the oil pressure was down to about 20 and the oil pressure light came on. No obvious leaks or damage to exterior of motor. It does have a minor leak coming from the rear main seal, but only a few drops. Any ideas where to start looking first?

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you probably just have fuel issues ; filter stopped up , carb running out of fuel, low fuel pressure.. etc...

The oil pressure issue sounds real normal......I didn't have very many motors in 25 yrs of racing that didn't drop down to around 20 and the light flicker on and off idling around after a race...Hot oil, big clearances... sounds normal to me....

Start at the fuel cell and work forward, for fuel problem. Agree with Johnny v on oil pressure problem. JMO.

My oil pressure problems went away when I changed to Brad Penn. Are you running Valvoline? Always had that same issue with valvoline as well as milking. Not with the Brad Penn.

Every engine I ever had had that same oil pressure problem, except this one I have now. I have had it for 4 years and freshened it every year. It runs 60 pounds after a race constantly.

If a float stuck it will flood over and possibly thin out the oil. One way to tell if it's too much or too little fuel is to smell the filter and see if it smells like methanol or gas whatever you are running.

Thanks for all the advice guys. I drained the oil and there did not appear to be any fuel in it. I pulled the plugs and they had quite a bit of oil/fuel on them. I then moved to the carb and the back float was stuck. I'm sure this was probably the issue. I do use Valvoline VR1 Racing Oil, and it sounds like low oil pressure towards the end of a race is normal. Thanks for all the responses! Hopefully this fixed the problem.

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Originally Posted by modified11

Thanks for all the advice guys. I drained the oil and there did not appear to be any fuel in it. I pulled the plugs and they had quite a bit of oil/fuel on them. I then moved to the carb and the back float was stuck. I'm sure this was probably the issue. I do use Valvoline VR1 Racing Oil, and it sounds like low oil pressure towards the end of a race is normal. Thanks for all the responses! Hopefully this fixed the problem.

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If you are using VR1 be sure to add a zinc additive. VR1 changed it's formula a few years back and it has very little zinc.