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I thought I had a miss!!!!!!

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Old May 9, 2012 | 11:46 PM
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Default I thought I had a miss!!!!!!

Was getting the boat ready for this coming up season. Look what I found. I did have a miss and back fire this last season. Didn't know this was it. I checked the plugs the season before and they were all good. I only took the boat out twice last season. What could cause the plugs to fall apart like this? Lean ? Hot cylinder? Whats the possibility of internal damage? Please help guys. Never had a plug do this to me. Already got a trip planned and coming up soon.
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04 LS6, 243 heads, ASA cam, Vic Jr, 750 hp
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Old May 10, 2012 | 11:22 AM
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Forgot to state the plugs are autolite platinum - ap5245.
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Old May 10, 2012 | 11:54 AM
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Thats crazy. What kind of boat you got that engine in?
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Old May 10, 2012 | 12:51 PM
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Jet boat. It's in my garage.
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Old May 10, 2012 | 01:06 PM
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Looks like you detonated it, and/or leaned it. Those tips being burned entirely off, tells me it got REALLY HOT.
I'd be pulling the heads and taking a look. A leak down B4 U do that may help.
Shitty fuel from sitting? Injs clogged up?
I clean/flow injs that are in boat applications. They are, many times, so bad they have to be replaced....[Rusty].
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Old May 10, 2012 | 01:33 PM
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The plug that is totally gone and the plug with the missing tip are from the two front pass side cylinders. No injs here I'm carbed. 750 hp. Fresh gas always. I'm gonna rebuild the carb and do a leak down. Are the plugs I was using the righ ones?
Thanks for the reply.
Thanks for the reply.
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Old May 10, 2012 | 06:05 PM
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plugs are way too hot.

What rpm dose your boat sit at for an extended period of time? Stock heat ranged plugs are ment for low rpm cruising where they tend to cool off. If you're sitting at 5k all the time they never get that chance. Also try a non projected tip, they tend to run colder at rpm as well.

Edit also go with a standard copper core plug platinum holds heat as well.

Last edited by 1dirtybird; May 10, 2012 at 06:29 PM.
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Old May 10, 2012 | 06:50 PM
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It's pretty much 3500-5000 all the time. I don't know anything about plug heats. How do I tell what's what?
Thanks.
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Old May 10, 2012 | 07:46 PM
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Need more specs on your setup, how are u making 750? Power adder?
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Old May 10, 2012 | 08:55 PM
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It's a holley 750 hp carb. Not 750 horse.
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Old May 10, 2012 | 08:59 PM
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Just did the compresion test and that passed.

Blew some air in it at TDC and didn't feel anything out the intake or exhaust.
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Old May 10, 2012 | 09:07 PM
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04 ls6 stock bottom end.
243 stock heads
ASA cam, 1.8 rockers
Vic jr , holley hp 750cfm
edelbrock ign box # 4 pill
exhaust logs with over transum tips.
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Old May 10, 2012 | 09:33 PM
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I'm thinking it was just too lean. Got black soot on the carb too.
Anyone who's running carbs what jets are you running? I have 74 primary & 83 secondary.
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Old May 11, 2012 | 10:35 AM
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your plugs dont look lean.

You are running to hot a plug.

the 5 at the end dictates the heat range. in autolites the lower the number the colder the plug.

in ngk's the higher the number the colder.

I would try a NGK tr7 to start. if that seems too hot, then go with a non projected tip plug. i can get you a number if needed.
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Old May 11, 2012 | 02:14 PM
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Thanks.
I called NGK ( very helpfull by the way) and he told me go TR6 IX. What do you think 6 or 7?
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Old May 11, 2012 | 07:50 PM
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I'd error on the side of caution and run the 7's first, see how it runs
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Old May 11, 2012 | 08:25 PM
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Yeah, it's better to error towards a colder plug; pt#TR7IX,stk#2690 ($8.48) ..

If you want it in a regular V-power($2.89) here's the pt#BR7EF and stk#3346, these come gaped at .028" (0.7mm) but you can adjust the gap up to .040".

Last edited by 99Bluz28; May 11, 2012 at 08:37 PM.
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Old May 12, 2012 | 06:28 AM
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Originally Posted by Moneyshott
It's a holley 750 hp carb.
Carbs are rated in terms of airflow, Cubic Feet per Minute (cfm).

I'd say the secondary metering jets need to be upped to the next size, eg. if they're 68 now go with 70. Make a WOT blast, shutdown, and remove/read the plugs again to see how it's burning.
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Old May 12, 2012 | 12:55 PM
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Originally Posted by 99Bluz28
Yeah, it's better to error towards a colder plug; pt#TR7IX,stk#2690 ($8.48) ..

If you want it in a regular V-power($2.89) here's the pt#BR7EF and stk#3346, these come gaped at .028" (0.7mm) but you can adjust the gap up to .040".
Nice beat me to it.

Get the BR7EF Thats what i would run there as well.

I run them in my sb car when sparying. I run autolite 103's na
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Old May 15, 2012 | 01:02 PM
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So the IX is a better plug right? Maybe I'll try the v power since it's cheaper to see if it holds up. I talked to my carb guy and he said my carb looks like it's doing the job and I should look towards my ignition/timing. Any thoughts on that? I was running the #4 pill:
rpm/deg
0-15
1000-28
1700-29
6000-36
I don't get over 5000.
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