bradley23150

iTrader: (10)

Without knowing my engine problems, I would like to know the answer to these questions to help narrow the problem down.

1. What are the symptoms of running a lower octane fuel in a motor that has a high compression?

2. Why would an engine be BOTH hard to start while hot, and have small backfires through the exhaust as it runs, no matter where the timing is at?

3. If the carburetors' idle adjustment screws are set to have an engine run (idle and drive) in the wrong timing, would that motor shut off when the timing was set PROPERLY (2-4*PTDC)?

Thanks.

Atilla the Fun

too low of octane results in detonation. not always audible, but hurts parts and power just the same.
Typically, this calls for retarding the spark.
Anytime you adjust the carb, you need to re-adjust the dizzy. And vice versa. The goal is always highest idle vacuum with the vacuum advance connected to manifold vacuum.
Keep doing both until you find no more improvements.
Also, each time you do something helpful, you'll have to reset the idle speed screw to keep a constant idle rpm. No point in even trying to tune if you don't keep resetting the idle speed to whatever rpm you started tuning at. And have the engine fully warmed up before starting on the tuning.
So, to clarify: [1] drive car until engine is hot [2] set idle speed as low as possible, note tach reading. [3] adjust idle mixture for highest vacuum [4] reset idle rpm [5] adjust dizzy for highest idle vacuum [6] reset idle speed [7] adjust idle mixture [8] reset idle speed, and so on.

bradley23150

iTrader: (10)

1 more

What is the approximate CR of this:
906 Vortecs
.044 head gasket thickness
87+ 350 bored .040

Atilla the Fun

flat tops or dished?
zero decked or not?
if zero decked and flat tops, could be as high as 10.5:1. If not decked but dished, could be awfully low, depending on the dish volume

bradley23150

iTrader: (10)

Cant believe I forgot that!

They are flat tops with 4 valve reliefs
I will assume not decked

Atilla the Fun

I'd say 9.80:1-9.95:1 depending on the VRs and the gasket bore. This is fine on premium unleaded, try for about 32 degrees total centrifugal advance, which includes the initial.

bradley23150

iTrader: (10)

Hm, than it isnt as high compression as I thought.

I run 93 Octane.

I am unsure how to set "total timing advance", I set the timing, with the advance vacuum line unhooked, and put it at ~2*BTDC, and then readjusted the idle screws on the car the best I could, the constant small backfires through the exhaust seemed to stop, but I still think I can feel them while driving, and the car bogs HEAVILY under acceleration, still.

I am only going to try to many more times before I give up.

Thanks for your continued help, I really appreciate it.

New2Chevy

iTrader: (11)

Sounds like your carburetor, if it's bogging heavily. Either that or you have some type of malfunctioning mechanical or electrical switch that prevents the vacuum timing advance from giving you the spark you need, OR your vacuum line is leaking or not connected properly.

Of course, it could also be a weak part in your ignition system.

How do your plug wires look? Are they burnt anywhere or touching something hot/metal or both?

Just trying to help narrow down the problem.

bradley23150

iTrader: (10)

The wires are brand new, and have 1 or 2 small burns on them, but I added some of those wire boots to protect them from the headers.

I think the carb is too small.

Roller 350 bored out .040
Vortec heads with 2.02/1.6 valves
Performer intake
MSD distributor
Shorty headers
600cfm carb

New2Chevy

iTrader: (11)

Try setting your timing to 10 btdc, just for shiznitches and giggles. Your carb could be bigger, but that's not going to cause it to bog down like crazy. I'd still get one of these http://www.barrygrant.com/demon/default.aspx?page=10.

It could be a problem with your carburetor, internally, though. I'd get a Demon carb, if I were going to dish out cash for a carburetor.

bradley23150

iTrader: (10)

Im not ready to drop cash on a carb like that! Haha.

But, pepboys sucks, trying to return the carb, I believe it has something internal wrong with it but they wont take it back until I contact Edelbrock, and then edelbrock has to give my "permission" to return it as a faulty unit. Of course Edelbrock never answers, I just sit on hold for 30 minutes. Absolutely ridiculous. I am going to get a Holley 670 or similar if I can get this carb returned, I truly believe I need a larger carburetor.

New2Chevy

iTrader: (11)

Edelbrock eh....there's your problem. The only thing they're good at is making manifolds.

bradley23150

iTrader: (10)

Yeah my buddy keeps telling me that.

lol!

New2Chevy

iTrader: (11)

I think Edelbrock used to be a pretty good company back in the old school days, but then that changed. They still make great manifolds, though.

If you're going with Holley, get a Street Avenger 670. That'll be a nice carburetor for your 350. Shop around, and you'll find a pretty good price, as far as new carburetors are concerned. I would say that the Street Avenger is a great carburetor, for the money.

bradley23150

iTrader: (10)

The more I think about this problem and drive this car, the more I blame the spark plugs and wires. They are all new, but they have been through hell with me trying to get the initial startup of this motor going, and a couple of the wire boots that plug into the plugs, are significantly burned.

The car stumbles through ALL RPM's and bogs hard when given moderate to heavy throttle, and there are occaisonal backfires.

I am tired of looking like an idiot with this car jumping, bogging, and backfiring. I am supposed to ENJOY my IROC convertible, not loath it!!

Anyway, what plugs are recommended for Vortec heads, and what should I gap them to?

Thanks.

bradley23150

iTrader: (10)

Car is missing like crazy.

What plugs and what gaps are recommended?

Anyone?

game1939

wow,,, ok where do i start, if your running that low of compression a bigger carb is not the answer, and to all edelbrock haters read my car specs, i first had a holley 600cfm on my 383, hated it if it rained hell brakes loose........... so broke down bought me a 600cfm edelbrock 1406 bolted it on and instanly ran better than that holley ever did, i get better gas milage and a whole lot of torque and hps without the headaches, point is people do and have every right to put whatever carb they want on there ride, no need to bash though...lol, my motor has a compression ratio of 11:1 i run on 93octane, with air conditioning. 450+horse...... i agree with you on wires and plugs, im running the q power ngks, i will post #'s and gap later, cant remember. so try the wires and plugs then holler back.........

game1939

goin to work, i will get plug #'s and gaps today

david chambers

ummm, forgive me but exactly what is a dizzy?????

bradley23150

iTrader: (10)

Distributor.