I had my own farm fuel tank at the county airport for many years. Filled up with the auto fuel at home airport and with 100LL on trips , I was burning about 50/50 and the Cont-0-300 liked that. No lead problems.
DT is right! When I ran one mag and one EI in my 360 Long EZ I would get an occasionally fouled mag plug. After going to the REM37BY's I never fouled a plug.... never. I finally installed a second EI and now run eight $6.00 car spark plugs instead of four.An engine like that should use the UREM37BY plugs, and I think they're approved for the O-300. They have extended electrodes that are really resistant to fouling.
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Champion REM37BY at the top. UREM37BY is Tempest's version, and a better plug. I used those Tempests in all our engines that were approved for them, with great success, especially in the O-235 in the Citabria 7ECA. Those engines are famous for running cool and fouling sparkplugs. No lost flights due to fouling with the UREM37BYs, though.
Besides that, the O-200 and O-300 have cylinder heads that have the bottom plugs really low in the head so that oil in the cylinder runs into the bottom plugs. Idling when cold will let plenty of oil past the rings in those engines, sometimes even when hot. It's ridiculous. Such leaky rings. It's the low manifold pressure that sucks the oil past the rings at idle.
And yes, a stuck valve is a possibility.
The issue was interesting too.:Do the plugs happen to be older Champions? They are known junk. Champion finally admitted same and redesigned the internal resistor. Check resistance value for all the plugs. I forget what value range is acceptable but I think anything over 5K ohms is no good.
you probably should just pull that engine and use the jugs to make 3 O-100 engines
Put a little food coloring in the water so you can detect the interface. You'll end up with lower octane gasoline though, as ethanol boosts octane. There are YouTube videos on how to do this.had friends would scrub the alcohol out by putting the mogas in a tank with 10% water shake it up and decant the gas so you do not get the water/alcohol or drain the water alcohol/water first. somewhat a PTA.
VB there is a shop near KVNY that will clean the lead off the plugs for a cheap price. Mine came back looking brand new and same day turnaround if I dropped off in the morningI have seen shiny round lead balls in spark plugs, but I never saw the elongated tan colored mouse turds. Is this a different problem, or a different material, than the round balls? Is this the Marvel Oil burned into a turd, or is this some other issue?
I want to relate one potential issue with the -300,-200 series engines once you go messing around with the pushrods:So the stuck valve is one issue that can be solved easily, either take off the cylinder and have it top overhauled, or try the old "rope trick" and see if it can be fixed in place.
depends on how well you sleep at night..... as long as the engine will fulfill your mission it gets complicated.......all of your options have risks .... obviously if you can not taxi and take off without a fouled plug you will need to do something....probably starting with the least complicated fix and working up from there.Second question... at what point do you just remove and repair just the bad or weak cylinder(s)... and at what point do you say "well, jeez, it's kinda worth it to just take them all off and top them... and at what point do you start thinking it's worth it to put six new replacement jugs on it???