1961 Corvette Advancing Problems?

[Greg Woods]

Hello all. First I want to thank you for your advice regarding the clutch spring from the other day; in less than a half an hour we had the spring on and all of the washers (spacers) out. Thanks!

Unfortunately a new problem has arisen. Starting the car is quick, and it idles quite well, but whenever we try to rev it, we run into problems.

When the pedal is pressed, the Quadra Jet carb seems to suck air profusely and it seems starved of gas. Looking with a timing light, our mark fluctuates by a couple of degrees in either direction, and it seems as though the engine isn't advancing.

When the car wasn't running well last summer (before we found the block was cracked), a mechanic put what seemed to be an alan wrench into the vacuum tube on the distributor, turning it in either direction until it seemed like it ran smoother. What exactly was he doing?

The engine block is brand new, the clutch is adjusted properly, the valves are set and the engine seems to be timed correctly, but it doesn't seem to want to go whenever the revs are up. Any suggestions? Perhaps this is a common problem or we're missing something simple?

Thanks!

[Joe L.]

Re: 1961 Corvette Advancing Problems?

Alan------

Your problem does not sound like a distributor advance problem to me, but I suppose it's possible.

Depending what distributor you have, the distributor will have a centrifugal advance system and, often, a vacuum advance system. It sounds like yours has both as most distributors do. To check the centrifugal advance system, you need to remove the cap and rotor and inspect the weights and springs to see that they are present and operating freely. If they are, then the chances are that your centrifugal advance system is operating properly. The curve may not be configured properly for the engine (you can't tell this by just looking at it), but it ought to be operating properly.

The second advance system is the vaccum advance. This is the cone shaped device seen attached at the side of the distributor. Some aftermarket versions of these are adjustable; all factory versions are non adjustable and of fixed operating characteristics. So, if the mechanic inserted an allen wrench into the vacuum nipple, then he was adjusting the vacuum advance. Most of these adjustable vacuum advance mechanisms have a "hex" shaped "snout"; I've never seen an OEM-style "round snout" that was adjustable (although some early OEM, non-adjustable vacuum advance controls also have a "hex snout").

[Greg Woods]

Re: 1961 Corvette Advancing Problems?

Thank you very much. We'll check those things, and then we're going to put another distributor into it tomorrow and see if the problem persists. If this does not remedy it, and if our first distributor has the pieces you say in working order, what then? What's our next step in getting it to work?

(As for the "snout," ours isn't hexagonal.)

Thanks again for your help!

---Greg

[Joe L.]

Re: 1961 Corvette Advancing Problems?

Greg-----

My guess would be some sort of carburetion or fuel delivery problem.

Changing the distributor should eliminate most ignition system problems except for something like a bad coil.

Are you 100% sure that the cam timing is correct (i.e. marks aligned at assembly of timing sprockets and chain) and that the valves have been pre-set correctly?

If your vacuum control "snout" is not hexagonal, then I don't know what the mechanic was doing with an allen wrench through the vacuum nipple. I've never seen a adjustable vacuum control that did not have a hexagonal "snout". Maybe there are some out there, though.

[Joe C.]

Re: 84-85 Corvette thin hard Steering Wheel

Greg,

Can you be more specific in describing your problem, for Joe's and everyone else's sake. Please be as detailed as possible, as many of these conditions can be inaccurately described.
My question is, why are you running a Rochester carb on your 1961 Corvette. What engine do you have? Any other modifications?
I am thinking that the allen key was probably being used to adjust your points gap/dwell angle, thru the distributor cap's access door.

Joe

[Greg Woods]

Re: 84-85 Corvette thin hard Steering Wheel

Yes, the engine is an unmodified 283 with a Quadra Jet carb (which was on the car when we purchased it). It is a brand new 1961 shortblock, as our last one was cracked and we're just getting this new one back together. It also has new points, one year-old plug wires, a new fuel pump, and a new coil.

It is a hydraulic lifter engine, and today we warmed the engine by idling it. After this, we removed all lash and turned one more complete turn of the locking nut (as prescribed by the auto manual). (It should be noted that when all the valves were loose, it ran well at idle, just as it does with everything tightened.) Next, when we tried to advance the RPM of the engine from idle, it began shaking and sucking air into the carb, but not giving us any power. It sounds as though it's starved for gas or air.

When shifted into gear, and when we tried to move it, at idle it moved forward, but when more throttle is applied, it stumbles as before and has no more power to pull the car.

Any help is appreciated. Thanks!

[tom444634]

Re: 1961 Corvette Advancing Problems?

Greg,

Don't forget to check all of the vacuum lines and fittings for leaks. Don't overlook the fitting at the base of the carb in the rear. I was bit by that one once........

Put a dwell meter on it and set the dwell to 30 degrees (adjusted with a hex key through the window in the distributor).

Could be an accelerator pump issue with the carb. work the throttle while looking down into the carb (with the engine off) and you should see a stream of fuel squirting as the throttle is moved.

My 2 cents........

Tom

[Greg Woods]

Re: 1961 Corvette Advancing Problems?

We'll check the lines, thanks.

As for the dwell, our manual said to place it anywhere from 28-32. We changed it around a few times and found it was running best around 29, so we've left it there.

What concerns us is the apparent fluctuation of the timing mark by two degrees every once in awhile; also, the fact that it idles well (and the fuel jet is apparently working well, as we can clearly see it before we start the car) but refuses to rev higher---intsead, sucking air, shaking, and appearing starved for gas.

Thanks again!

---Greg

[Wayne P.]

Re: 1961 Corvette Advancing Problems?

Even though you say you've checked the dwell, it sounds exactly like the dwell is way off. Make sure you have the dwell meter hooked-up correctly.

[tom444634]

Re: 1961 Corvette Advancing Problems?

and set for 8 cylinders!

[tom444634]

Re: 1961 Corvette Advancing Problems?

Another thought....

Double check the firing order

[Dave Suesz]

[Terry F.]

Re: An extremely important thing

Dave, when I get my 390/427 going again. I plan on checking the advance curve. Since it is not modified, I plan on looking at the information that describes the advance curve in the back of the overhaul manual. My question is, I assume I can just hook up my electronic tack and watch the advance with a timing light at the flywheel to determine if all is well?? It is my understanding that during part of this procedure, I will need to disable the centrifugal mechanism to only observe part of the curve. Any light that can be shown on this would be appreciated. Thanks, tErry

[Greg Woods]

New Developments

Well, the plot of the cursed Corvette thickens...

This morning we replaced the old distributor with another one. Hooking everything back together, the Corvette started and ran as smoothly as we've ever heard it, except for the fact that it was way advanced. We were even able to rev it up and get power. We tried to adjust the advance timing by turning the distributor, but the car quickly shut itself off. We tried to put it back where it was when the car ran well, but we couldn't do it.

Putting brand new points and a brand new cap inside the distributor, we tried to start it again, but got nothing except the engine spinning. Since there was no spark (after pulling the wire off of the distributor and touching it to the engine and doing the same with the wires to the plugs), we decided to put a different coil in it for a test. We were still without a spark, though.

Our thoughts now are, could it be the ballast/resistor on the firewall or something with the ignition switch or something else? The car ran so well for awhile, but now it is not sparking. Any ideas?

Thanks for all the help.

---Greg

[Timothy B.]

Re: New Developments

Greg,

There should be a procedure in the service manual to check the primary and secondary ignition circuit and this can be accomplished with a volt and ohm meter. Start taking things one at a time and follow the manual to make certain components are in working order before you move to the next. The problem can be so many things and hopefully it's not serious but there is a process of elimination to be followed to get you there.