I have a 67 chevelle with a 72 LT-1 350. and turbo 350 trans. w/ 411 gears. The wide open throttle performance is excellent, but throttle response around town is terrible. I've got to push the throttle down half way to get a decent acceleration. It just fells like it has no power until I get my foot into it. I don't have any detail on the cam, but judging from the "lumpy" idle, it's pretty agressive. What can I look at to improve part throttle response assuming everything is in tune?

How big is your carburetor?
Too big of a carb with a good overlap in the cam will loose a bunch of vacume at lower rpms. that translates into poor throttle response to anything but wide open throttle.
Also, check the ignition timing and squirter timing. If you are not advanced enough and have a late accelerator shot, it will bog.

The carb is a edelbrock 650. Does't seem to be a bog, but rather a general lack of power at part throttle.

Do you have a stall convertor?

Yes, but the previous owner could not tell me what the stall rating was. I would guess it's around 2500.

How's your gas mileage? Sounds like you car may be running too rich except under full throttle. A simple check to lean it out & take it for a drive.

Don't know about mileage as I just bought the car. I'll try the mixture and see what happens. With 411 gears, I'm sure the mileage will be terrible no matter how it's tuned..

What kind of intake manifold?

Edelbrock Performer Intake

Here's some suggestions you might want to try. First of all do a compression test to see what kind of cranking pressure this thing produces. Compression in the 150 to 200 range is what you should get if the engine isn't overcammed, has good ring seal and valve seal. Generally engines with 150-170psi will run OK on low octane, over 170 you'll need premium or better. If the compression test checks out OK then start tuning. Check your spark advance curve, should total at about 36-40 by 3000rpm with initial at 10-15BTDC. Tuning the curve may take awhile to see what the engine likes. How does it idle? Usually cleaning up a rich idle condition will help the midrange big time. If the idle mixture adjustment screws are not at or about 1&1/4 to 1&1/2 turns out then the idle mixture is probably out of wack and may require some tuning. Powervalve or metering rod selection is also important, it richens up the mixture when the engine is under load and at wot. Hope you figure it out graemlins/thumbsup.gif

OK, checked evrything out and here is what I found. Compression is at 160 to 170 PSI. Idle mixture is fine and the timing was at 10 and I bumped up to 15 degrees and no real difference to speak of. The idle is very erratic. I measured the vacume at idle and get a fairly steady reading between 8 and 9 PSI. This seems low to me. I'm guessing the roller cam is the cause of my problem. I think the grind is really sacrificing low to mid range torque for top end performance. My next step is to order a streetable cam to see if this is the problem. I hate to tear into the motor but I'm out of ideas?

Your idle mixture is meant only for your idle - it does not affect your lean/richness during cruisiing or WOT. If you are too rich in your primaries, it is one possible reason for what you describe. I don't know too much about edelbrock carbs, but I would first eliminate the possibility that you are running too rich in your primaries. Change your jetting to a leaner setting (you would go down 2 sizes at a time for a Holley) and check out the performance.

If that's the problem, it should improve part-throttle performance, but you would then run the risk of being too lean at WOT and might need to adjust that also.

Your type of carb is usually very lean at part throttle. Try getting some pri. rods that are smaller on the low speed steps if it's lean like I think. If it's rich advancing the timing will usually make it run better.

Timeless,8-9 inches vac @ idle is normal for a 350 ci motor if it has a hot cam with a lot of overlap. But if your running a very mild to stock cam something is wrong.

I see you bumped up the intial timing from 10 to 15 deg btdc. Most perf cams nee at least 16-18 deg btdc intial advance to try 17-18 deg btdc with vacuum plugged and idl low at approx 500 rpm idle to keep mech advance disengaged.

Also,with you fairly low idle vacuum it may improve a little at 18 deg btdc but still check your power valve to ensure it's rated at least 2.5 lower than your lowest idle vacuum (if it's a holley) in gear to ensure it's not opening at idle creating an over rich idle mixture.

Check your plugs to ensure they are not black/fuel fouled at this point.

Maybe you could also try running your vacuum advance hose to a full on/continuious vauum source to aid in your idle/low end perf if advancing your intial timing to 18 deg btdc does not do the trick.

With 411 gear even a 350 with a hot cam should feel fairly snappy.

Happy tuning.

Scott