Ball bearing in hose?

[mcditalia]

Does the car accelerate normally with a slow gradual push on accelerator pedal? But a sudden and aggressive push results in stumble. If this is case, the accelerator pump in carburetor may not be supplying enough fuel or no fuel at all.

Now back to original post asking why is the vacuum hose to distributor blocked off .
Someone(Bubba?) removed hose to set the engine idle ignition timing and didn't hook it back.
Or.
There is a problem within the distributor with vacuum advance. (1)The advance diaphragm is busted and leaking vacuum. (2)The breaker plate may be binding and not responding to vacuum properly. Someone(Bubba again?) plugged the hose as a work around.
Simple fix in one case, reconnect hose, but second case will require checkout and repair of distributor. Check of idle and advance timing should be done in any case.
Then hope Bubba didn't change anything else. :eyerole

Car accelerates normally with slow application of throttle, only with sharp aggressive push results in stumble and detonation. At this point im thinking vacuum advance or accelerator pump in carb also. Will have to check initial timing.

 

[Tom Bryant]

Uhm, will try that tomorrow when the weather clears up. Is this with car runiing or off?

Off. If the diaphragm is bad you will be able to suck air through it.

 

[Vettehead Mikey]

Car accelerates normally with slow application of throttle, only with sharp aggressive push results in stumble and detonation. At this point im thinking vacuum advance

I thought it was disconnected?

 

[Tom Bryant]

I think it is just off for the photo so we can see the ball bearing.

Tom

 

[mcditalia]

Off. If the diaphragm is bad you will be able to suck air through it.

Tried sucking through a small straw, can't suck any air at all , just getting puckered cheeks. i take it thats good?

 

[mcditalia]

Is that stumble AND detonate? Too much vacuum advance at steady cruise speeds can cause surging or detonation at throttle tip in. It would be unusual if you're seeing either/both with the vacuum advance already inhibited (?)

So with the vacuum advance taken out of the equation, as it's been for over a decade, this would not suddenly produce my current problem then. Didn't really think this through.

 

[Vettehead Mikey]

Tried sucking through a small straw, can suck any air at all , i take it thats good?

Presuming you removed the ball bearing, that's good.

Next test-

1) Check the timing at idle with the hose disconnected from the canister and plugged. Note the setting.

Reinstall the hose and check the timing again and idle speed. Note the numbers.

The timing number from test 1) should be as per GM spec. The idle speed from test 2) should be per GM spec. The difference in timing from 1 ) to 2) should be around 10-15 degrees.

 

[DGVETTE]

FYI Timing Specs,

FYI. Here are the timing specs. for 350hp 327ci L-79 engine per my 1966 Shop Manual. Two distributors are listed, breaker point and transistor(K-66 option), but timing is same for both.

Idle = 10 degrees BTDC. Idle speed 650-750RPM (check with vacuum removed and plugged).
Centrifugal Advance = 0 degrees at 900 rpm, 15 degrees at 1500 rpm, 30 degrees at 5100 rpm.
Vacuum Advance = 0 degrees at 4 inch vacuum, 16 degrees at 8 inch vacuum.

 

[haganml]

As I recall the only reason anyone put BB's in the vacuum lines on any vehicle was to eliminate the function of the piece of equipment that the vacuum line operated. It did not repair anything. When the early smog equipment came on the then new cars (late 60's early 70's) some of the people working on them thought they were eliminating the emissions related equipment. This always did more harm than good. I have a collection of BB's in a small tin that I removed from several problem cars that I worked on. After finding the BB I would be assured that who had ever done this really did not understand what the systems operations of the vehicle were. Starting fresh from square 1 and I soon found the real problem.

Someone 10 years ago eliminated your vacuum advance. Why, we will never know. I do not believe this has caused your present issue. The questions you have to ask are; has someone recently worked on your Corvette in an attempt to repair it, how often does anyone else drive your car, how close to a factory ignition do you have?

You found it (the BB) looking for something because of your present driveability issue. Remove it. DGVETTE has kindly given us the timing specifications for a stock 1966 327 engine. The timing needs to be checked at idle with the vacuum line removed and plugged (I use a golf tee) the mark on the vibration dampener should be around the 10 degree mark on the pointer on the timing chain cover.

Check the vacuum reading on the line where it plugs into the distributor at idle. Mine (1965) has a threaded chrome tube that screws into the front float bowl metering block on the passenger side of the Holley carburetor. Some replacement Holley carburetors have a tube sticking out of the metering block at that spot. That is ported vacuum, at idle there is no vacuum. As you increase the engine speed you will get more vacuum signal. If you have manifold vacuum (14-18 inHg) at idle and it decreases as the engine RPM increases that hose is installed on the wrong fitting on the carburetor, that is why the BB is in the line. Someone thought "vacuum advance, that goes to manifold vacuum". When the idle speed fluctuated because of the 16 degrees of advance at idle they removed the vacuum line from the distributor, the idle and timing settled down. Just put a BB in the line and everything is golden.

Not the problem, the line was on the manifold vacuum fitting not the ported vacuum fitting.

Now your drivability issue. IF you are using a Holley Carburetor you may have the power valve failure that is quite common in the early Holleys, late Holleys have a powervalve protection check valve in that circuit. Slow acceleration is okay, any aggressive throttle and there is a sharp hesitation on acceleration. After a second the engine will pull strongly.

Pull off the front float bowl and metering block. On the back side of the metering block is a valve about as big around as a poker chip. It unscrews and is replaceable. My car uses a 6.5 valve, it is the most common power valve. Use new gaskets on all the parts you remove. Be careful of fuel spills, there is about 3/4 of a cup fuel in that float bowl. Remove one of the lower float bowl screws and that fuel will run out of the screw hole. Catch it with a container or you could have raw fuel everywhere on your hot engine, stinky and dangerous!

Mark.

I just noticed in your picture that it looks like that line plugged into the fitting on or below the vacuum secondary canister. Look for a fitting on the front float bowl metering block. The BB may be there to block the wrong vacuum signal. My 2818 Holley doesn't have that fitting.
You do have a Holley from the picture evidence, the float bowl screws are hexagonal heads, that is a later carburetor. That fitting shown is for a later automatic transmission. Block that fitting with a plug (cut off a piece of the hose shown and leave the BB in the hose). That would only apply if your car was equipped with an automatic transmission or power assist brakes. Run that vacuum hose from the distributor vacuum canister to the ported vacuum supply located in the metering block behind the float bowl on the front of your carburetor.

 

[Ken Anderson]

If your distributor was converted to mechanical advance, then that's why the BB is there.
The person who did it was not "Bubba", he just wanted max acceleration & wasn't worried about mileage.
Leave it and search the carb for your stumble. If it's a Holley, then you could have a weak pump shot. Check & adjust the accelerator lever (1&1/2 thous. clearance). May be time for a carb rebuild-possible leaky diaphragm. Breakdown under load can also be caused by a weak ignition system( wires, plugs, coil, rotor, etc.).

 

[Vettehead Mikey]

If your distributor was converted to mechanical advance, then that's why the BB is there.
The person who did it was not "Bubba", he just wanted max acceleration & wasn't worried about mileage.

Stock distributors already have mechanical advance mechanisms, no conversion necessary. If max acceleration is the goal, disconnecting the vacuum advance will have no effect as there's insufficient vacuum at WOT to activate the canister.

For reasons unclear to me, Bubba has always had am aversion to learning how things work and why they're there and instead disconnects or removes them.

 

[Ken Anderson]

Stock distributors already have mechanical advance mechanisms, no conversion necessary. If max acceleration is the goal, disconnecting the vacuum advance will have no effect as there's insufficient vacuum at WOT to activate the canister.

For reasons unclear to me, Bubba has always had am aversion to learning how things work and why they're there and instead disconnects or removes them.

Apparently I wasn't clear enough for you. I suspect the previous owner converted the distributor to FULL time mechanical advance and chose the leave the can on for appearances. This thought is based on the OP's advance specs. Back in the day this was a common practice on HP engines with low vacuum. I also suspect that "bubba" did know how things worked as all HP Chevy engines in the late 50's had no VA, just straight dual point mechanical advance. Either way, the OP's problem is not the distributor advance curve, there are other issues such as fuel delivery and/or weak spark.

 

[haganml]

Apparently I wasn't clear enough for you. I suspect the previous owner converted the distributor to FULL time mechanical advance and chose the leave the can on for appearances. This thought is based on the OP's advance specs. Back in the day this was a common practice on HP engines with low vacuum. I also suspect that "bubba" did know how things worked as all HP Chevy engines in the late 50's had no VA, just straight dual point mechanical advance. Either way, the OP's problem is not the distributor advance curve, there are other issues such as fuel delivery and/or weak spark.

Interesting thought. You can run any gasoline engine that uses a timing advance metric for its operation with a purely mechanical timing advance. Magnetos come to mind. I can imagine someone would leave the vacuum canister in place to cover the hole in the distributor body and use a BB to plug the line for a factory appearance (the old timer "speed secret" thinking).

For the vehicle to have less than 8 inHg manifold vacuum we are talking large valve overlap that would have a severe effect on the idle speed and quality (dilution of the cylinder charge with burned exhaust gasses at low RPM). An engine with those characteristics could not use a vacuum advance

Valid point. Now on to mdcitialia's complaint.

"Car fully brought to operating temp, under light to moderate steady load and will stumble/detonate right before throttle is increased sharply, then will get going."

The photo supplied showed the line removed off of the manifold vacuum source on the throttle plate directly below the vacuum secondary canister. That source will supply full manifold vacuum (whatever it is) to the line attached at idle. The vacuum advance uses a ported vacuum signal that will be full strength at WOT, not idle. It is on the wrong source. As it is on this engine it was eliminated, it doesn't matter.

Yes the "accelerator" pump can be the sharp hesitation. The engine ran fine for 10 years. Now it has developed the complaint suddenly. The Holley carburetors use a power valve to supply fuel in low manifold vacuum situations. That is rapid throttle applications. The accelerator pump does supply fuel. Check that KOEO (Key Off Engine Off) by pulling the air cleaner assembly off, holding the choke open, open the throttle to WOT and watch the spray nozzle pattern and amount of fuel supplied. If there is a strong steady stream of fuel, no spurts or sporadic stream of fuel the accelerator pump is fine.

ANY backfire can damage the power valve. The symptom is as mdcitialia has described. I chased the accelerator pump many times. Some times it was the accelerator pump some times it was the power valve. It is easy to check the accelerator pump. The only way to test the power valve is to replace it. I had heard that if you turn the air bleed screws until they are seated on a idling engine and it keeps running the power valve is bad. That didn't work for me. There is a lot of good information on Holley.com on this. Great reading.

Mark.

 

[Vettehead Mikey]

Apparently I wasn't clear enough for you. I suspect the previous owner converted the distributor to FULL time mechanical advance and chose the leave the can on for appearances. This thought is based on the OP's advance specs. Back in the day this was a common practice on HP engines with low vacuum. I also suspect that "bubba" did know how things worked as all HP Chevy engines in the late 50's had no VA, just straight dual point mechanical advance. Either way, the OP's problem is not the distributor advance curve, there are other issues such as fuel delivery and/or weak spark.

All Chev engines have full time mechanical advance so possibly I'm misunderstanding you again.

If you're trying to suggest that the previous owner 'locked' the distributor at full mechanical advance- a practice that has some merit on the race track but is a really dumb idea on the street, we're back to it being a Bubba move again.

 

[Ken Anderson]

All Chev engines have full time mechanical advance so possibly I'm misunderstanding you again.

If you're trying to suggest that the previous owner 'locked' the distributor at full mechanical advance- a practice that has some merit on the race track but is a really dumb idea on the street, we're back to it being a Bubba move again.

Not being disrespectful, but I suggest you get a Chevy power book from the 70's and read the ignition section on how to set up a distributor. The distributor mods work very well on street cars that have had a cam change & head work. Not all Chevy engines came with vacuum advance.

 

[Vettehead Mikey]

Not being disrespectful, but I suggest you get a Chevy power book from the 70's and read the ignition section on how to set up a distributor. The distributor mods work very well on street cars that have had a cam change & head work. Not all Chevy engines came with vacuum advance.

I've read them all, in some cases when the books first came out and understand every idea they're promoting. I did my own distributors starting in the late 60s on a Sun machine when such equipment was still brand new and current technology.

I'm trying to follow what you're getting at and how you came to the conclusions you did. A distributor that has had it's mechanical advance curve optimized for performance will still benefit from having a functional vacuum advance- which in itself should also optimized in conjunction with the mechanical advance.

There's a big gap between what you're saying, the procedures for setting up a performance distributor and what the OP has told us so far.