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Old 05-21-2006, 12:51 AM
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ZZ4 tuning WOT miss

I've got a Pontiac Fiero with a ZZ4 in it; I'm using an Edelbrock 750 carb.

It idles beautifully. Part throttle acceleration is great. The motor only misses up around 3500 RPMs.

All the components are brand new with less than 10 miles on them.

Any ideas on where to start? Access to the plugs is a pain. I've got to get under the car and get them from below.

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Old 05-21-2006, 03:13 AM
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You prob. have to do this hard way, swap things to eliminate different items.

1:Make sure that your ignition is timed right.
2:Unplug the vacuum advance to rule out any items there.
3:Borrow another working carb, a Holley and how that works.
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Old 05-22-2006, 04:22 PM
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When I have issues on the high side (RPM) I like to rule out the ignition first. Is the carb new and jetted correctly, out of the box is a good starting point!
JMTCW
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Old 05-22-2006, 05:53 PM
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I decided to fix an oil leak (one of many bugs!) and put the car up on jackstands on sunday.

I'm using a transdapt remote oil filter mount (because the starter is sitting where the oil filter would!) and managed to crack the remote filter mounting boss when I tightened down one of the hoses a little too far.

What's my point? I won't be able to try anything until later this week after the summit box shows up on my doorstep.

I'm not entirely certain, but this might have been a fuel pressure problem. I had somewhere less than 1/4 tank and my fuel pressure was in the 2lb range. I put in 5 gallons and the car seem to rev ALOT better. Yes, that's right..I might have been out of gas.

We'll see! Thanks for the help so far. I'll check back later this week.
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Old 05-26-2006, 09:18 PM
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I've got my oil leak problems solved and I THINK I might have found the problem but I want to run it by you guys.

I'm running an electric fuel pump regulated down to about 5-7 PSI. The fuel pressure seems to be fluctuating quite a bit after the motor has been running awhile. I'll start out at about 7 to 8 lbs and then after the motor was warmed up--figure about 15 minutes or so to get to 180 degrees, the fuel pressure dropped down to somewhere around 2-3 lbs.

Could this cause the problem? I thought I heard a change in the the exhaust note as well. The carb is an edelbrock 750, brand new.
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Old 05-31-2006, 06:14 PM
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<shameless bump>

So I've got the fuel pressure issues sorted. It was just set too low, nothing more.

Next problem especially for the carb tuning guys.

I've got an edelbrock 750CFM carb on a ZZ4. Everything is new, less than 100 miles on it. I've got a narrow band A/F ratio gauge indicating the motor is running at the very bottom of the rich range, with an occasional flicker into the good (amber) zone.

Now. When I floor the pedal FAST I watch the A/F gauge go all the way to bottomed-out lean, and then it recovers as the secondaries start to pull open. It's hard to tell what the mixture really is, but it seems to be somewhere in the stoich area But it does seem like it's missing a little bit.

I'm finding it hard to believe that I'm actually going lean because of the size of the carb. Am I? Is this typical behavior or is there actually too much fuel going into the motor?

Help!
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