'86 350

I've got an '86 Camaro with a 350 crate motor in it. The problem is at lower RPM's (below 3,200), the engine won't have much pick-up and it'll miss if you really mash down the gas pedal. However, at about 3,200 and above, the car has a ton of power and doesn't miss at all. I figured I had my ignition timing too advanced so I went to check it.

Now here's one of my questions, when you rev a motor, the timing generally increses right? Well mine only seems to increase about 3-5* from idle up to almost wide-open throttle. Does that sound right or is that too little of an increase? It seemed to me it was tool ittle of an increase, but I wasn't sure.

Also, wouldn't it make sense that the vacuum secondary is stuck open, since the problem only occurs at lower rpm's and not higher RPM's?

If you guys would help me answer those 2 questions then it would be greatly appreciated. Also, if you don't think it's the vacuum secondary, please let me know what you think it is.

Thanks.

P.S. Moderators, if this doesn't belong here, please feel free to move it. I was kinda confused aobut whether or not I should put it here or in the 3rd. gen section, so sorry if it doesn't belong here.

TheNovaMan

If the secondaries were stuck open, your engine wouldn't idle. There are lots of other things it could be, though...
What was the timing? Did you have the vacuum advance disconnected when you measured it?
What is the idle vacuum? What power valve is in your carb?
Have you adjusted the idle mixture?
Have you looked at your spark plugs? What spark plugs are you running?

'86 350

It seemed like it was idling fairly rough, but that could be do to the high-lift cam in it.

Well I assumed a SB 350 would have something like 10* or 12* as a base setting. I don't have a manual or anything that came with the engine so I'm not sure what the exact setting is. When we checked it, it was about 20* advanced.

Yes.

I haven't measured the idle vacuum yet. I'm not sure. How do I check which powervalve I have? It's a Holley 670cfm Street Avenger if that makes a difference.

I looked at the spark plugs. A few seemed to be fouled with oil which makes me believe I have bad valve seals since the car sat for a little while. I could understand an engine missing becasue of a fouled plug, but wouldn't that happen throughout the whole RPM range?

I'm running Accel shorty plugs. I believe the # is 576s.

Damon

It's not your secondaries staying open- you can verify that manually at idle by seeing if they're closed. Rev it up in neutral and they'll still be closed unless your secondary diaphragm spring is WAY too weak. I'll almost guarantee that is not your problem.

5* of timing advance from idle-up isn't right. That could well be the cause of (much of) your stumbling and such. You should have 4X that much, give or take. 2 things can cause this:

1. Your centrifugal advance mechanism in the distributor is gummed up or physically jammed in some way- or the springs in the centrifugal advance are just way too stiff. Try twising the rotor and letting it snap back. You should be able to twist it with only moderate pressure against the force of the centrifugal advance springs. It should be able to rotate about 10* from it's resting position to where it won't go any further. It should SNAP back when you let go of it. If not, find out why and fix it. It should never feel "sticky" or "rough". Smooth as glass. Also, VISUALLY look at the weights, centerplate and springs under the rotor. Nothing should be obviously stuck, jammed, broken or worn out. Also make sure the pins that the advance weights rotate around are not work out or worn "oval" shaped, althering the weight's geometry relative to the centerplate. This is a real common problem with old GM HEI distributors.

2. The centrifugal advance is already kicking way in even at idle speeds. Centrifugal advance shouldn't begin to kick in until about 700-800 RPMs. If the springs in it are too weak (or broken/missing) or there's a mismatch of weights and centerplate in the advance mechanism it can cause the centrifugal to advance A LOT even well below idle speed. That leaves not much advance left in the mechanism once you go above idle speed. Example: 20* of centrifugal advance built into the distributor but it's kicking in 15* by the time you're just at curb idle (say, 800 RPMs). You won't know this at the time and you'll set it at 12* BTDC at your idle speed of 800 RPMs. All seems fine until you rev it up and you only get that last 5* of advance that the mechanism is capable of supplying (20* - 15* already kicked in = 5* left to advance over idle speed). Stronger advance springs and/or a properly matched weight/centerplate set are the cure for this problem.

spinout

what is the cam that is in the engine and what is its power range
what gears do you have in the rear and stick or auto
if its geares too low or the cam is to big this could cause your problem as well

'86 350

I'm not positive on the power range becasue I bought the car used with this motor in it. I'm guessing it's around 2,500-4,500? The rear end gears are fairly low, but are being swapped out shortly. In 5th gear on the highway at about 80 mph, the car runs at about 2,200 rpms. I'm guessing 2.73 gears?

Stick shift- Doug Nash 5 speed

Damon- Thanks for the help, I'll check those things today and I"ll get back to you guys.

Zero_to_69

That stumble you feel when you mash the pedal may also be attributed to
the accelerator pump.

Probably not enough gas squirting at the proper time.

There is a pump cam, and squirter nozzle you can play with to tune the off
line acceleration.

After checking everyone's suggestions, have a look at the acclerator pump
system (transition circuit) if you are still having trouble.

If you have a Holley, I can help out quite a bit.

I would agree with the others that your secondary throttle blade is not the
issue.

Timing is certainly a problem. You should have somewhere in the area of
"mid 30" degrees of full advance timing (depending on the engine needs).