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65 buick special, really need some mechanical advice please!!


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rebuilt the carb new plug wires new plugs, today i tried putting in a new set of points i then adjusted the gap to .016 with a feeler gauge and reassembled the distributor, after this i installed a tach so i could check the rpms, i then set the idle with the choke off, vacuum advance disconnected and plugged up to prevent vacuum leak to 550 rpms with the screw connected to the throttle, after this i put the timing gun on and adjusted the timing to 2.5 degrees on the scale with vacuum advance still disconnected and plugged, after all this i tightened the distributor down plugged the vacuum line back into the vacuum advance and took it for a spin and needless to say she still feels about the same, i haven't adjusted the mixture screws yet because it was getting dark on me but i dont think they single handedly would make it run the way it is although i could be wrong, when setting the ignition timing do i do that at the 550 rpms or lower then set it to 550 afterwords? and what should the idle speed be set at after all this is that the 550 rpms? im lost, any advice?

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What was the result of the compression test? And, by the way, can you do a bit more to describe what "Runs horrible" means to you? Are you talking about an Idle speed in Park, a miss under a load ( as when driving)? Runs horrible can mean a lot of things to others resulting in wild guesses as to a solution.

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I noticed on the other thread you posted that your number 1 plug was on the left side. I know on my 401, #1 plug is on the right side and # 2 plug is on the left side. I'm not sure about a 300 nailhead.

As we discussed on the other thread,

The 300 is closer kin to the second generation V8. Rather than the nailhead.

The original poster would do well to keep all this one thread,

For the later V8:

#1 is on the left

Nailhead #1 is on the right, as you rightly said

And of course the straight eight, the foremost cylinder is #1.

And that holds true for V motors. The foremost cylinder is #1

Edited by bhambulldog (see edit history)
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What was the result of the compression test? And, by the way, can you do a bit more to describe what "Runs horrible" means to you? Are you talking about an Idle speed in Park, a miss under a load ( as when driving)? Runs horrible can mean a lot of things to others resulting in wild guesses as to a solution.
I noticed on the other thread you posted that your number 1 plug was on the left side. I know on my 401, #1 plug is on the right side and # 2 plug is on the left side. I'm not sure about a 300 nailhead.
As we discussed on the other thread,

The 300 is closer kin to the second generation V8. Rather than the nailhead.

The original poster would do well to keep all this one thread,

For the later V8:

#1 is on the left

Nailhead #1 is on the right, as you rightly said

And of course the straight eight, the foremost cylinder is #1.

And that holds true for V motors. The foremost cylinder is #1

hey guys thankyou all for your feedback im new to the whole forum idea so i apologize for the repeated posts i wasnt to sure how to go about it, tomorrow i will be picking up a dwell meter to try an reset the point gap and dwell, the number one plug when standing infront of the car is the driverside foremost plug, ive never run a compression test on it because i do not have the right stuff, ive been reading the stockel auto mechanics fundamentals to figure out what im doing and alot of trouble shooting, as of right now the car runs good at idle but under a load it will stumble and seems to misfire, i tried putting the car into drive and putting a little strain on it and having someone spray starting fluid into the carb to see if its straining for gas but it didnt make much difference other then bogging down a little so i dont think gas is the issue, are the dwell and point gap adjusted differently or would the dwell screw in the window in control of all of this? also the car has a centrifugal advance and a vacume advance, does anyone know if that changes the way i should go about setting the points? i feel like this has to be my problem, atleast i hope so. and thankyou again, Anthony

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My experience with doing compression tests is that, as one old-line mechanic noted, it'll tell you how good the top compression ring is, plus possibly how much wear is on the cylinder bore (which the rings seal against). NO information about oil consumption, though, from a compression test. I'd be more inclined to look at the intake manifold vacuum levels at idle and "under load".

Plus, you can get variable results from compression tests. You can do them with the coil wire unplugged and the throttle blocked open, or you can leave the throttle partially closed. Altitude can affect them too! What you'll find is how well each cylinder compares to the others, but you can get similar results (especially if you're brave!) by using insulated pliers and pulling plug wires either off of the spark plug or from the distributor cap, one at a time, noting the amount of rpm drop on each cylinder. The less drop, the weaker the cylinder. The more drop, the stronger the cylinder tends to be. Do NOT stand close to the fender as you do this procedure! One thing which can be noted is how much the compression might come up when you squirt some oil into the cylinder and repeat the test, but this can be variable, too. To me, a vacuum gauge can be a more revealing test tool, plus easier to implement, less expensive than a remote starter button and flex-shaft compression gauge, etc. Your decision, though.

Just some thoughts,

NTX5467

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Willis could be spot on with the vacuum gauge. If this is a 300 V8, your problem could be in the vacuum advance unit on the distributor. I don't know how you can have both vacuum advance and centrifical advance. They easy to find and cheap to replace.

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Service manual for specs and procedures?

Dwell steady at all rpm?

Loose wires inside distributor grounding in service?

Age and condition of plugs and wires?

Some cars are timed with the vacuum advance disconnected and barely ticking over (no influence from vacuum or mechanical advance); others are timed at 1600 rpm which would have the mechanical advance all in: 5* btdc @ 300 rpm would be nearly the same as 15* btdc @1600 rpm.

After you are satisfied that the base timing is correct, observe the change in timing when the rpm are brought up first with the vacuum advance disconnected and then with it connected. You should see about 10* additional advance from the mechanical advance and then another 10* from the vacuum advance.

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Willis could be spot on with the vacuum gauge. If this is a 300 V8' date=' your problem could be in the vacuum advance unit on the distributor. I don't know how you can have both vacuum advance and centrifical advance. They easy to find and cheap to replace.[/quote']

Lots of older vehicles, trucks, and equipment had both Centrifical fly weights and a vacuum advance. Quite common from the 1930's until points disappeared... Dandy Dave!

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When the only description of the run scenario was "horrible" I immediately thought a burnt valve. A compression test would show a cylinder way out of proportion to the others, and could lead to that diagnosis. Since I now see the scenario is hesitation on take off, a compression test may not be necessary till the vacuum advance is tested and the centrifugal advance is cleaned and lubricated.

Oh, BTW, it is not true that the forward cylinder on all V8's is #1. Apparently Pontiac 400's ( at a minimum) have the forward cylinder on the passengers side, but the #1 cylinder is the one on the drivers side. Which really points out the need for a Service manual, which will also discuss potential diagnosis and repairs for the hesitation scenario.

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Most distributors have both centrifugal and vacuum advance mechanisms in them. Centrifugal is related to engine speed, vacuum advance is related to intake manifold vacuum levels. The base timing, once the point dwell is adjusted to specs, is what starts things. Mechanical advance usually starts AFTER about 1000rpm engine speed. Vacuum advance (ported vacuum) starts as soon as the throttle is opened a little bit. There can usually be a small amount of vacuum present in that vacuum supply system at base idle, but usually BELOW the minimum threshold to start the vacuum advance mechanism. Some cars use direct intake manifold vacuum to run the vacuum advance, but not your Buick, which should be "ported vacuum". If, possibly, the base timing is 5 degrees BTDC, once engine speed reaches about 2500rpm, total (base + mechanical) might be about 30 degrees BTDC together. Add vacuum advance at that no-load rpm, and the total advance could be about 55 degrees BTDC. Of course, once the throttle is floored at that rpm, the vacuum advance greatly diminishes or completely stops. That additional vacuum advance is there for fuel economy and part throttle throttle response at cruising speeds. Some vehicles (think "trucks" with large wind loads which the engine must overcome) do not use vacuum advance, just base timing and mechanical advance. Reason? The "high-engine-load" (wind resistance) would take enough throttle to get down the road that intake manifold vacuum levels would be decreased enough that vacuum advance would probably not happen. Seems like there were some '50s-era Fords which had a distributor advance system which was solely vacuum controlled? No mechanical advance, either? Several years ago, I was at a friend's service station. An elderly customer's grand-son had recently put a set of new plug wires on her car. It would not get out of its own way, until it got enough rpm up for the carb's secondaries to open. Then it took off like a jet airplane! It was a '78 Chrysler Newport with a 400 4bbl V-8. At low speed, it'd clatter and hesitate, but when it finally gained enough rpm for the secondaries to open, it "flew". The problem? #5 and #7 plug wires were backwards. In that firing order, #5 fires first and #7 fires after it. Once that was fixed, tire smoke city. As your engine is operating differently, then all of the plug wires are probably wired correctly. One other thing, probably already covered, is the fuel pump. IF the car has been sitting for a length of time, the pump's diaphragm might be failing. I'd think, though, that if it was failing, there should be gasoline in the crankcase (as smelled on the engine oil dipstick). Check out that exhaust tail pipe flow, though. Just some thoughts, NTX5467

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I stand corrected. Of course you can have both vacuum and centrifical advance within the distributor. In my defense I was thinking of the old air cooled VWS which made a distinction between a vacuum controlled advance and a mechanical advance distributor. I always considered the distributor in the 300 V8 to be a vacuum advance distributor. There is a diaphragm inside which will fail with age and not allow the the distributor to advance. A quick check with a vacuum pump or just sucking on the port will test the diaphragm.

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I've found that with today's gas, the factory timing setting is often way too retarded for a car to run well. Try running it at 5 or even 7 degrees temporarily. When it's set, plug in your vacuum advance canister. Your timing should immediately increase to anywhere from 15 to 20 or so degrees BTDC. If it doesn't, your canister is leaking and you need a new one (probably $10). Pull the mixture screws out of the carb (keep them in order, left to right) and spray some carb cleaner through the passages. Then, reinstall the mixture screws and LIGHTLY seat them (until they JUST stop--you'll ruin the carb if you crank them down). Turn them back out two turns and see how it runs. As it warms up, you can tweak those screws a quarter turn at a time for best idle.

Before you do any of this, you'll probably want to check the dwell. It should be at 30* and steady. Did you make sure the mechanical advance on top of the distributor (under the rotor) is free? If not, you'll have all kinds of trouble. Good luck...

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IF the vacuum advance is "ported vacuum", meaning the internal port for such is just above the throttle plate on the perimeter of the throttle bore, near the "transition slot" and "idle fuel port" (being cleaned out by the carb cleaner referenced), there should not be a significant amount of vacuum at base idle . . . "fast idle", yes, but not at the slower base idle speed. It usually takes about 7-10" Hg to start most vacuum advance activities, so if there's about 4" Hg present, no affect on ignition timing advance. If, for example, the engine is on "fast idle" with the vacuum advance hose unplugged (and plugged) from the distributor, then it WILL increase the idle speed when it' plugged in.

In the realm of Chevrolet, my '77 Camaro 305 used manifold vacuum to run the distributor vacuum advance activities. With the engine running at base idle, unplugging the vac advance hose would result in a markedly-decreased "hot" idle speed, like 200+ rpm or so. On a similar "ported vacuum" system, no change at all when the hose was unplugged. Not sure what your Buick might have, but I suspect it is "ported vacuum" (as most engines were in those times, except possibly some Fords which used a "vacuum bias" to run the vacuum advance).

Depending upon how much ethanol is in the fuel in your area, or not in it, the idle mixture might need to be a little "richer". The stoichiometric fuel ratio for non-eth gasoline is 14.8, yet for E10, it's 14.2, so the "2 turns out" spec (rather than the older "1.5 turns out" starting point) might be pretty close. Similarly, choke thermostatic coils can "tighten" with age, so the resultant choke thermostat setting might need to be a notch or two "leaner" than when the coil was new (back then). IN some cases, modern fuels and trying to adjust older carbs to run on them CAN result in some selective tweaking of adjustments and specs to get things to work right. Adding a few more degrees of timing might possibly help, too. Just depends, by observation, on your particular vehicle. Using the factory specs as a baseline adjustment, don't be afraid to experiment with small changes (as mentioned) to make things work the best they can (proceed at your own risk, though).

Make sure you have the vacuum lines attached to the correct ports on the carb, too. In many cases, the lines and ports can be "size specific" as to which circuit they might connect to. Please keep us posted on your progress.

Enjoy!

NTX5467

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