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Old 11-26-2009, 08:18 PM
JLeatherman JLeatherman is offline
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383 driving me crazy, help with tuning issues (Holley Street Avenger)

Hey all. I stumbled across your message board while googling Street Avenger 670 problems. Seems like there are some knowledgable people here. I searched the old threads and haven't yet found an answer to my troubles, so I joined up and am posting my own thread.

I built a 383 for my '84 vette. The original 2-bolt block, Eagle externally balanced forged crank, reconditioned stock rods, SpeedPro hyper pistons with coated skirts. 9.8:1 compression with ported stock iron heads (462's) opened to 1.60 exhausts and stock 1.94 intakes. Basically a nice budget 383, aiming for 400 horses. Cam is a custom grind. 224/234 @ .050 .465/.488 lift with 1.5's, 112 or 113 LSA. Engine produces a good solid 15" of vac at idle. Weiand Stealth intake manifold. I think that's about it for the specifics.

Fuel supply is from the original in-tank EFI pump through a Mallory 4307 bypass-style regulator. Very steady 6psi.

So, when I dropped the engine in the first time it was sporting a Barry Grant 650 Speed Demon. That carb had some quality-control issues and hit the can after a couple long weekends of fighting with it. In retrospect, it may not have been the carb's fault, but that'll depend on what I find is causing my new troubles.

The current carb on the motor is a Holley Street Avenger 670. This was built to be a streetable engine, and I decided to run a good street carb on it. Seemed like the perfect fit, but I've had nothing but massive troubles.

At first I thought it was the typical "Street Avenger stumble" that I've read so much about. The car would idle, but would not accelerate from a stop AT ALL. I mean, it took 3k rpms and feathering like mad just to get going on level ground. But the engine ran fine at the higher ranges. From 2500-3000 and up it ran great. Broke the tires free in 3rd, etc, etc. So I set about checking all the usual suspects.

I went through the distributor first. I re-timed it entirely this week. The engine is now set to 14* initial timing. Another 20* from the centrifugal is in by 2500 rpms for 34*. The vac canister is another 16*, for a total of 50*, and ~30* at idle. Timing curve seems smooth, and is atleast a good start for an engine like this.

With that settled I went back to basics on the carb. Fuel level was next. It is right at the bottom of the sight-holes on each bowl. Check. Then I went back to trying to tune in the base-lines. Started the car, got it warmed up, and started in on the idle mixture. The car about choked me out of my garage with unburned fuel fumes. Yes, the choke kicks off entirely. I went back to the manual and it said to start out at 1-turn out on the idle screws and move them in 1/8 turn increments until max vacuum is achieved. With the gauge on the car has 15" at the baseline 1-turn. I start leaning them out and the car maintains 15" until about 5/8 of a turn at which point it stalls out entirely. So I set 'em to 3/4 and fire it back up again. The idle is pretty smooth at 800 rpms, but the car is still rolling dark smoke out the exhaust and the fumes are killing me. At this point it's atleast idling and I wanna get a roadtest with the new timing settings so I get my buddy to tail me in case of the worst and I go for a 5 or 6 mile road test.

No change. The car accelerates like crap, barely leaves a stop, atleast most of the time. Every once in a while I'll come to a stop and roll away again without too much effort. An easy 900rpm pull. Very rarely though.

So we get back to the house and my buddy who was tailing me says that the car was rolling dark exhaust the whole trip. Said the only time it eased up was when getting on it on a hill. So, it's rich at idle and I can't adjust it away, but it's also apparently rich through the whole range unless it's under hard load.

Sounds like a power valve problem to me, but this is out of the box and supposedly wet-tested at the factory. How do I set about checking the PV? And how do I get to it and remove it? With 15" the factory 6.5 PV oughta be fine right?

Can anyone else think of another cause for too much fuel across the board? I seriously doubt that the historically over-lean SA factory settings would cause my 383 to run this rich across the board. And it's definitely not fuel-pressure blowing the needles off the seat because the fuel level is fine. What else could it be?
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