Thread: Tunnel Ram Tunning???

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Mine just started doing this.

It's a SBF with dual Holley vacuum-secondary 390's (sorry to invade Chevy-land ) and it lugs right at takeoff.

It was really bad yesterday; dying at lights and backfiring at freeway speed. I went over it this morning and couldn't find anything out of place or changed / disconnected; I narrowed it down to the fuel pump and/or filter -- the pump was the original mechanical one; the last unsullied OEM anything in the engine bay, I believe. I swapped it out with a high-peformance mechanical pump and a new filter. Ran like crap for about five minutes, then ran fine, then started hesitating again, just not as often.

The hesitation is between 1500-2000 rpm (idle in Drive is about 1000; it won't idle below 900); it nearly dies and then comes back on strong. Usually, though, it runs fine. Starts great, idles great, tons of power from 2000-up.

The kicker is, it ran KILLER until last night. Now it runs well enough but I have to baby it through the hiccup now and again.

I'm all confused. Ideas?

EDIT: Plugs are reddish, no fouling.

EDIT II: The gas tank was filled to the absolute top last weekend for the first time in the three years I've owned the car -- it sat all winter with very little gas in it so there may be water and/or some kind of schmutz in the gas. THis started when the gas got to about a half-tank. I dumped some HEET into it.