First of all, I recently installed a 350 in my Camaro. I'm using the relatively mild XE262 cam in my car from off of my 305 and I have headers on the way. I have underdrive pulleys on the car. I've since bought new wires, changed the coil and purchased a new module for the distributor, however...

I'm looking for some help with tuning my carb. I have correctly tuned the q-jet three separate times now, setting the timing at 0 (as it says to do on my hood sticker, I know, most are 6), and setting the idle screws so that they max vacuum with the computer unhooked. I've also fixed the A/V tension, although I know that that will not have any affect on idle.

My problem is this - when I'm not stepping on it, the car is not running very well. It isn't at all hesitant, rather, it's as though it's "lurching", like perhaps the car isn't receiving enough fuel. I'm hoping that you can help me somehow, I know that this isn't very specific, but, I don't want to have to take this to a mechanic, I like to do things myself (Perhaps it has something to do with the float...?)

Thanks

 

You don't have the engine that the sticker was made for, so ignore what it says the timing should be set to. The engine will want whatever timing it wants, and does not look out around itself at the sheet metal and say "hmmmm..... this car is red, I think I'll work best at 2 degrees" or any similar foolishness. Set it to where the car runs the best. A good starting point would be to advance it until it pings when hot and under a heavy load, then back it off a few degrees past where it quits pinging.

The "idle mixture screws" have essentially no effect whatsoever on idle. Most of the time they make no difference at all to idle quality. I never bother with them. They are an extremely fine pitch thread. Set them at 7 turns out and leave them there.

It is altogether meaningless to set anything "with the computer unhooked". Don't unhook anything when making idle mixture adjustments; depending on what you unhook, the carb may be going to full rich mode, then when you hook it back up, it will be somewhat leaner. A better way to adjust it is to look for the mixture control solenoid to be around 50%, i.e. the middle of its range, which is what the computer will be able to do when the mechanical settings are within its range of control.

The thing that has the greatest effect on idle and off-idle tip-in fuel metering is the idle air bleed valve. This is a large thing in the very top of the air horn, inside the air cleaner, at the top front of the choke blade tower. It comes from the factory with a sheet metal cover pressed in over it. Remove the cover and look down in there, you will see a screw. Adjust it inward slowly, like 1/8 turn at a time, and see if it helps. Write down how far you've moved it so you don't lose track.

Use a dwell meter on the bright green connector to measure duty cycle. Shoot for 30 degrees on the 6-cyl scale or 22 degrees on the 8-cyl scale.

 

I'll give that a shot. Sorry, I'm not very familiar with the effects of the computer on the engine. I've definitely noticed that it seems to advance the timing on its own, so I assumed that this meant that it would optimize timing if it was set on what the factory recommended. Thanks for all of the info, I'll mess around with it when I get back from work

 

The ECM advances the timing based on a "curve" using throttle position, engine speed, and vacuum data. It has no clue where the timing actually is, though. So, the total actual timing is a combination of the "base" timing - where you set it - and the "advance curve". If you set the base timing at 6 degrees advance, for instance, timing at any given throttle position/engine speed/vacuum will be 6 degrees more than if the base timing was set at zero degrees under the same conditions.

The only exception to that would be if the knock sensor retards the timing because it sensed pinging/knocking.

 

Just to let you guys know, I think that I've discovered what the problem is with my car. The 1981 350 that was installed in my car appears to have had a "2:00" timing tab, thus, the timing mark on my balancer and the "12:00" timing tab on my lg4 timing cover seem not to match. Last night I messed with my timing and ultimately came to this conclusion when I set up my dad's gas analyzer and found that my hydrocarbon levels dropped almost 1000 points while my CO2 levels optimized to around 14.9 as I backed my timing into the "2:00" position.

Any thoughts?

 

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