I just had a forced landing gear extraction due to a deadstick...the engine runs fine for 5 flights and on the last one right after takeoff its sputtered and died...you know the rest of the story!
upwind and 40' altitude at the end of runway... not much to do except pulling back to flare and hope for the best.

is there a way to know for sure if the plug is worn out or any other indication ?

my engine is a Saito fa125 with O.S ''F'' type plug, Cool power 30%

Of course there is no well defined gauge but one indicator often is a loss of rpm at idle when you remove the ignitor. Also if you have had a number of lean hot runs then that plugs future life will be suspect.

John

You can look at your plug and if it is distorted or discolored it is due for replacement.. Are you only getting 5 flights from your plugs ? If that is the case you are doing something seriously wrong like running way too lean .Maybe I am misunderstanding you.. I hope so.. On our runway that is about the worst possible spot for a dead stick..Not enough altitude to turn back and trees ahead ..It depends what you are flying of course .

I am not real sure , but to me 30% nitro is high. I don't have that large of a saito, my largest is about .90 and I run 10 to 15 % nitro. don't know if that would cause a glow plug issue.

I will be watching to see if there is any more input on the 30 % nitro, as saito is about the only 4 cycle I own.

sticks

I don't, believe the thirty percent nitro in itself is particularly a problem Of course with any fuel proper needling is a must but what in my mind is suspect is the question what 30% nitro is this car fuel ? Many car fuels have insufficient oil content for a big four stroke in my opinion.

John

I agree on the 30 percent. I fly mine on 15 percent Cool Power. I also agree with John, I don't think the fuel is the issue. As for plug life, I have some that are still going strong with hundreds of flights on them and I have had some that have crapped out after only a couple of flights. I was lucky a while back and found a modeler that had cards of K+B plugs for sale. It is hard to beat them for durability. As mentioned, the tell tale sign of a bad plug is a loss of RPM or the engine dies when you remove the glow plug igniter. Good Luck, Dave

Lose the 30%, you're just wasting money and producing more heat for the engine to have to deal with. Use 10% nitro with 18% oil, pure synthetic or a max of 5% castor. Your engine will thank you for it - and your plugs will last a lot longer.

I only run15% morgan fuel (the pink stuff) in my 4 strokes and my plugs seem to go forever ..

I also run 10% in my Saitos. I have never had a plug go bad. My Saito 72 must have 20 gallons of fuel through it and I am still using the OS F plug that I installed when it was new. I don't know if 10% is a factor or not. I'm just volunteering a data point.

I just went out and looked at the jug of fuel I am using , it is made by Morgan and it says OMEGA 15% Four Cycle Synthetic on the sticker .. I have no idea what the difference is but I have always used it in my four strokes .. I run mostly OS ..I never seem to have any problems . I use four stroke plugs in the four strokes..I always keep a few spares but seldom ever need them myself ..I did use up a few when I had an on board glow driver .

I use 15% Power Master with 18% blended oil in all my four strokes, even the YS engines but I don't think the nitro percentage is a problem. I use the rpm drop when I remove the glow driver to help me set the low ends. The rpm drops when the low end is a little fat. I don't see it as a warning that the plug is weak or ready to go bad. Plugs just happen to burn out over time, sometimes fast. If the engine is new they can short out from the metallic crud as the engine is breaking in. Pop in a new plug and see how many flights you get out of it, I get a couple years worth. I don't recall ever having a plug burn out in flight but it has probably happened to me? Most the time the plug goes when I'm starting the engine and I don't know it until the driver is removed and the engine quits. There is a glow driver that can show you the plugs condition with LED lights, a lot of pattern pilots use them but they aren't cheap.