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Old 06-19-2011, 10:38 AM
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454 bad misfire around 4500 rpm

Hey guys, I just built a 454 for a jet boat, around 4500 rpm I get a bad misfire, the engine shakes like crazy, any rpm below is fine and has big power up till, I'm running an hei, 10.50 to one compression and super cold plugs to avoid detonation, 8 degrees initial timing, I put in a hei module with a rev limiter which is 6 grand, thinking maybee a issue with that, any ideas?

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Old 06-19-2011, 11:24 AM
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Wouldn't have a regular HEI module laying around you could try just to eliminate the posibility of a miss-adjustment or bad rev-limiter would you?
A quick and easy test.
ssmonty
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Old 06-19-2011, 11:55 AM
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Yeah that's my next move, I'm thinking I'm exceeding the capability of it
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Old 06-19-2011, 01:25 PM
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misfiring chevy

check your valve springs !!! #1
#2 ignition timing 32-34 total -forget the at idle crap!!
#3 fuel supply and jetting
#4 maybe ignition box problem -throw a points job into it.
hopefully your running good fuel !!!
route your ignition wires to combat cross firing .
check quality of ignition wires. ect ect
id make sure your valve springs are up to the task first !!! maybe u have
a weak or broken one?
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Old 06-19-2011, 01:27 PM
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ignition problems

we all try to make our ignitions so exotic nowadays !!!
put a points unit in good shape and wouldnt suprize me if problem goes away
big heavy ignition system - maybe 10 hp ??????
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Old 06-19-2011, 08:07 PM
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Yeah I thought of valve springs too but I got the matched ones to my cam and set the installed hight myself, the engine is capable of 500 HP and is strong as a mf up to it, it won't do it all the time either, its possible I'm not getting a nuff juice to my coil too , I know it ain't valves cause when it misses the cranks pressure goes up and a little oil will come out the dipstick, so I have good compression. It's like I got 1 or 2 cyls missing, no back fire whatsoever
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