Hope someone can help.I have a 359+21 and every third or fourth tank of fuel the glo plug goes bad.It will run fine the until you shut it off and then when you go to restart it doesn't.Tried sealing the motor with silicone,not letting it run out of gas and shutting it off by the flywheel nothing seems to work.Somebody told me to replace the con rod but there is no play what so ever.Motor was running fine then out of the blue it started doing this.I also have a JPTL3.12 that does the same thing.

How does it go bad? is the plug brown on the bottom? Does the coil get all messed up? A few more details please.

The guy was right, change the conrod, even if it doesnt have play. I would change the rod and make sure you have the correct shims on the head, if the head clearance is too low(not enough shims), the filament onthe plug will get pushed in. Also, look at you combustion chamber, if it looks sanblasted, your head clearance is too low. Remember, a conrod is $40, a whole new engine is $600

The coil is still there and it looks kind of dark when i pull it out.Im using a black novarossi 7.

Black and wet with fuel, running too rich. GP that is hot, Fuel is cold it would warp the coil of glow plug. If it blows out Running too lean. You want a clean coil a bit of ash on the coil your close. .12 engines run good with hotter GP.

In the .12 i do run a nova 5.in th .21 i run the 7.When the motor is running it runs like a bat out of hell.Temp about 250 degrees.Its just when you shut it off and let it cool down and then go to restart it won't because the glo plug went bad somehow.And i never leave the piston up.

There is your problem right there. Nova plugs used to be great but they went in the toilet about 2 years ago. I hear they have fixed them but haven't got a new batch to try yet.

Things to try:

Go to a Nova 8

Get some Sirio 7's (or Werks) amazing plug, works great in Novas.

Find some GRP 7's.

Try OD99T. Not as good as the others but dirt cheap.

As for the rod, if this thing has a couple gallons or more on it, change it NOW!

Engine Hard to restart after it cooling down. You running at 250F is running lean. When the engine cools it change a bit. Your trying to start lean. Richen you HSN by 1/2 turn and try again. Then retune for optimum performance. Cold engine richen it out and retune, like running in afternoon @ 250F, let it cool till tomorrow, 1/2 turn on HSN then retune for the day!!

250 isn't hot for that motor. Depending on conditions, they will run fine anywhere from 210 to 280. It shouldn't pop plugs unless it gets even hotter than that.

any other turbo plugs besides sirio and grp?they seem alittle hard to find.i have tried different plugs in nova's before like odonnell and os and they did not run as good its almost like the other plugs didn't seat right and caused an air leak.

I don't like OS plugs in Nova motors.

Piccos are good too.

Try a Nova ultra 8.

I agree with wingracer on this all the way and every nova plug I have ran only lasted a couple of runs and does just what you are explaning.

If other plugs do pop out as well you should check the play on the rod but also the main bearing.

When glow plug dead too quickly,

Usually because of excessive vibrations :
1. main / rear bearing need replacement
2. conrod need replacement

If the engine is relatively new :
3. nitro percentage is too high
4. engine is running too lean ( too hot ).