help please

[modock84]

just got our 50 running son went and rode today--heres what happened

he rode for about 20 min went off a jump had slight backfire(just enough to hear it) the next corner it bogged down and wouldnt hardly pull.......when i took the spark plug out ( its a iridium) plug the center above the porcelain was burnt down to the porcelain.

malossi cylinder
hetrick pipe
stage 6 pvl set at .126 before TDC
brand new crank bearings
brand new crank seals
20 carb with 125 main 48 pilot

any ideas could the new crank seals be bad

thanks in advance...........

brian

[mmsoup]

Will it run with new plug?

[EthansDad]

oh no!

there is a real good chance you have a matching hole in your piston head. must have been running too lean due to jetting or air leak. with all the $$ you have in the motor, I'd personally take the cylinder head off and have a look-see before I put a new plug in and tried to run it again.

If that is a gen 3 pipe, they like to run rich. I want to say when I started out on that 20m carb with a similar setup to yours, I had a 135-145 main jet in it.

-EA

[machwon]

I think .126 is too much timing advance, and a little too lean on the main as EA said might have lead to some detonation. Check compression or pull the head. You could also pull the exhaust and look at that side of the piston as well. Hopefully its nothing serious.

[bb49]

I run my stage 6 ignition with a malossi cylinder. set the timing on it at 141. but i have a 85mm rod crank.

[jerkyboy]

Pull the head like they said above and check the crank seals. Ive seen them backfire and push the seal on the stator side out.
Just somthing else to check if everything else looks ok.

[modock84]

i pulled the cylinder off and the piston out and everything looks good.

forgot to mention we are running the u4.4 gas

the .126 timing came from g-force.

i checked the seals and they still look good

should i jet up on the main and put new crankseals in it.....

the pipe is a gen 2

thanks

brian

[EthansDad]

Just looking at some articles, looks like you might have pre-ignition more so than detonation - especially if your piston is still OK.

Check this out for a picture reference - is this your plug (pre-ignition one):
http://www.gnttype.org/techarea/engine/plugs.html

Also found a good article on more info about pre-ignition - basically fuel burning before its time.
http://www.clubwrx.net/forums/tuning-electronic-engine-management/14426-engine-basics-detonation-pre-ignition.html

The take away I get from pre-ignition is your fuel is burning due to something glowing / very hot in cylinder on off firing cycles. I'd double check the heat range of my plug, and if nothing else is found assume my jetting was so lean, it got things very hot to the point of glowing and caused pre-ignition.

As for how the ignition timing plays a role, I don't know.

-EA

[modock84]

ya mine looks like the pre-ignition one

[EthansDad]

yea, here is a dumb Q for you - did you pre-mix the gas with oil, or are you sure your oil injector is working properly if you have one? lack of lube might have also caused the overheat condition, but after 20 min of riding with no lube, I'd expect to see more damage than just the plug.

-EA

[modock84]

Ya pre mix 32:1

[Logan #34's Dad]

The fuel (U4.4) will cause you to need to go even more rich on your jetting than what these guys are recommending. Whatever you would run with regular race gas - You'll need to go up another 4 or 5 points with this fuel.

[modock84]

On the stage 6 pvl do you run the green wire grounded or unhooked


Thanks
Brian

[Logan #34's Dad]

I run mine grounded.

[EthansDad]

we've seen modest, yea measurable performance increases with it grounded, but it will run just happy either way.

-EA

[modock84]

How much does the different heat range on spark plugs affect the motors. Enough to make one pre ignite.