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Author Topic:   End of spark plug burnt off
posted April 14, 2004 03:53 PM
Sounds like you were on the lean side and burnt a hole in the piston. Being lean and maybe having too much timing for the fuel you used all contributed to it. The plugs should have shown some color so if they were white or glazed over then yes it was too lean. I dont know what autolite heat ranges compare but we run NGK -9s on a mod motor. Also could be timing marks off on your balancer and what you thought was 38 is really more than that. Id check everything but I think you were prob lean more than anything.

Earl Parker II
posted April 14, 2004 05:29 PM
An Autolite 303 corresponds to a Champion RJ6C (the only numbering system I'm familiar with) so I doubt that heat range in and of itself was a factor (I'm assuming a track of 1/2 mile or less). If the plugs had any 'pepper' specks on the core noses, greenish ground electrodes or both then timing may have been a factor but, as dirtbuster said, it sounds like it was simply too lean (38 degress of timing may have aggravated the situation somewhat).

You didn't say what carburetor you have, what the jet size(s) are or if it was stock or not, so I can't comment there. You also need to check your fuel pressure at idle (you should have no more than 6 psi assuming the use of a Holley) and WOT (it shouldn't drop much if any). Also, are you sure you had a complete fill when you put water in it, i.e., no air pockets? Also, as dirtbuster said, are you absolutely sure you had 38 degrees of timing? These are just some of the factors that can come into play here.

Earl Parker II

[This message has been edited by Earl Parker II (edited April 14, 2004).]

[This message has been edited by Earl Parker II (edited April 14, 2004).]

[This message has been edited by Earl Parker II (edited April 14, 2004).]

[This message has been edited by Earl Parker II (edited April 14, 2004).]

posted April 14, 2004 06:36 PM
Very lean is my guess. I think you need to identify what fuel your running. The flashpoint I take was too high. Pump gas is only good to about 10.2 (at best), Your local tracks 107 112 (cam 2) often times doesn't work well past 11. 115 should take you to 14:1 with everything (timing, header configuration, plug range ect. Do you know what compression ratio you have? i

posted April 15, 2004 09:56 AM
juliaferrell could be on to something. High compression + low octane = bad.

posted April 15, 2004 10:06 AM
That carb would not have been on the lean side at all. Honestly, it was just about right unless the compression ratio was a LOT higher than we were told, or timing was advanced too far (I agree, 38 is a bit much).
But just 38 degrees timing alone may not have been the entire culprit here.
The combination of low octane fuel, higher compression, AND 38 degrees timing can add up to what happened.
It's really hard to pinpoint unless we were to see the piston, and engine damage and examine it closely.
As for timing, it never hurts to double check ignition timing with more than one timing light, too.

Hope we can help you diagnose problem/cause and make sure it gets corrected.


posted April 15, 2004 11:27 AM
Based on KP response then I would look into the fuel you used and also what the actual compression ratio is. Sounds like you might have too low octane fuel.

posted April 15, 2004 12:04 PM
I ran AR72's in my 461s with a 355, flat top 10:1 and 100-104 octane fuel with no troubles. The plugs came out looking just a little white-brown.

A 303 is a 'standard' type plug equal to a 74 or AR74.

I'm with the mulitple causes of the meltdown. Timing should be in the 34-36 degree range (2-4 less with KB pistons), fuel? and 303's are a little on the hot side. Add them all up and you get the nice new bench racing piece (piston).

posted April 16, 2004 10:26 AM
I had an experience like yours and it turned out to be a bad seal between the heads and block. I burnt 2 plugs that way.The heads weren't machined right on mine.It's enough to **** you off.

posted April 22, 2004 04:49 PM
I had a motor do this to me also. and i thought i had my timing set at 36 advance. but come to find out i really had the timing at 76 adavnce.

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