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My Nova doesn't accelerate as quickly anymore.


SuperNova75
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I own a 1975 Chevy Nova that has not been accelerating as quickly as I think it should, could be a vacuum leak, granted it is Carbureted. I'm changing spark plugs tomorrow and just got an oil change yesterday. The engine is a 350. What could cause the engine's power to be suppressed like this? Unless all the problems are with my carb. (I've ordered service manual, arrives tmrrw.)

20200407_205709.jpg

Edited by SuperNova75 (see edit history)
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A couple of items.  What is the timing? How clean is the air cleaner? It has been a long time, but is that a 2 barrel carb? How old is the fuel in the car? How old is the fuel filter and has it been changed recently?  What is the fuel pressure at the carb?  These are just a few of the things to start with.

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That's a 2GC carb. Smogged 2bbl V8s were common in the 70s. Three is better but a manifold and a QJ are cheap

 

That said you did not mention the milage. If 100kish then a stretched timing chain can retard the can and kill power. Have had just a new chain feel like a new engine. Also the rest mentioned (retarded timing, low(er) compression, secondary ignition, or clogged catalyst (drained they make good mufflers) can all be factors but retarded timing or cam with still run and star smoothly while feeling down on power.

 

Need more info (timing, compression, miles,...)

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Mileage isn't correct but it says 76K miles. Idk timing right now, doing compression test today now. I feel with what you've all said that it may be the catalytic converter but idk how to test that. Don't have the experience. My old mechanic friend can't work right now buy says that the compression last he checked was good.

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Back in the day there were CC "test pipes". Many became permanent. Those early GM ones had a hex plug in the bottom that allowed draining all of the pellets and were very restrictive.. Today I'd just replace the whole thing with a modern free flowing catalyst and discard the muffler.

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There is no electric fuel pump and therefore no fuel pump fuse on a 1975 Nova. Are you using a generic fix-it manual?

 

You will, however, want to at least disconnect the coil wire from the distributor.

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17 minutes ago, mike6024 said:

 

maybe the vacuum advance on the distributor is another possibility? can see the small tube in this picture.

 

Do you mean the vacuum advance looks bad and needs replaced maybe ?? The round saucer/bowl to the left of the distributor? 

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No it looks fine. You should check the tube anyway. Is it cracked, or leaking, or loose? I had a similar type problem on a different car and it turned out to be one of the small vacuum tubes. When they get old they can crack, or come loose, due to the rubber getting old, hard.

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Guys ! This is that same MODIFIED car that was posted on April 7  with the topic; 1975 Nova Carb help. Engine sputter.

   at which time I said;

 

In the first picture I see the ATC air cleaner is inoperative, I also see the TVS switch vacuum hoses missing. On the last picture with the air cleaner is off there is a vacuum hose ( To Auto Trans Vacuum modulator? )  bent over to 90 degrees and appears there might be a vacuum leak there. The intake manifold is suspect, is it the original manifold/where is the EGR valve? I see a vacuum hose to the distributor, Where is the distributor getting it's vacuum signal?. It's supposed to get it from the TVS switch and not straight intake manifold vacuum. The TVS switch gets it's vacuum from the carburetor's ported vacuum and then if the coolant temp.  is at operating temp goes through the TVS sw. to the distributor. 

1975 Nova, Ventura- Phoenix ,Omega, Skylark-

1975 Buick Skylark "Beloved Skinflint" magazine ad - VG | eBay

 

 

 

 

= all X bodies also have a Idle solenoid because those cars have a relatively high warm Idle when it engine is on the solenoid is working and when the engine is shut down the solenoid is off dropping the idle to a so low a level the engine will not diesel or run on after the ignition is shut off. On some cars we call this the anti dieseling solenoid.

 Someone has tampered with this vehicles emission system which by the way is a federal offense called emission tampering. I applies to every vehicle with Exhaust emission controls.   

 

Chasing this down a rabbit hole is a waste of time

Edited by Pfeil (see edit history)
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a) "Nova, Phoenix ,Omega, Skylark" Nyet tovarich, Is Nova, Omega, Ventua, Apollo. Phoenix is a year or two off and Skylark was an A-body.

b) the compliant is about performance. Many of the things (GM called ATC a Thermac, TCS (TVS ?), vaccuum, EGR, advance,...) may affect cold start,  MPG, and "smoothness", not performance. OTOH centrifical advance, timing chain stretch, retarded spark, clogged CC will affect "performance" (accelleration).

c) If concerned about go then I know how to slide a breaker bar on the crank snout and feel the timing chain slack. Doubt that this is taught any more. Can also use a timing light to check the advance curve (dial back light is good, Snap-On is great). Can also pop the EGR and detect back pressure (clogged CC). I do have an HEI adapter for my Heath ignition scope but most common HEI problems wil cause a bad misfire.

 

75 SBC is a transition engine between many kludges for emissions (first year of CC) and computer controls/diagnostics ('81). I'd be surprised if one was stock any more.

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The kid is coming here for help.  I hope our knowledge is helpful to him, just like others were to us at one time.  My first thought was maybe the transmission is slipping but no one else mentioned it so maybe not?

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Great, can walk you through the basics. Unfortunately is pre-O2 sensor because the bung makes an easy place to check exhast back prssure. EGR is a lille harder (may need a gasket) but another place to check.

Are you familiar with the breaker bar method to check a timing chain? Have seen replacement on a tired engine feel like another 20 hp.

Unfortunately I no longer have a mid-70s SBC resident but can promise the carb is very limited particularly for a 350, may even be a 1 1/4" venturi unit (cant see bolt pattern. Were some 1 3/8" venturi 2GCs but a QJ will wake any 350 up. Good cam (easy when doing timing chain) even moreso.

All depends on what you want to do and what is meant by "performance". Does Indiana still have annual emissions testing ?

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I am going to make a correction that I missed on looking on the first picture.  This car has electronic ignition.   

 

Electronic ignition was required for cars that had catalytic converters.  There is always a possibility that when the module gets hot the vehicle will start acting up.

 

NOW THAT SAID, a personal experience with a '76 Chevy that MIGHT BE your problem.  On that era of cars there is a piece below the distributor called  a pole piece.  This part move with the vacuum advance and over time the wires that are attached to it can eventually break.  Pictures below.  

 

To fix this possible problem, you will need to remove the distributor.  Remove the gear at the bottom of the distributor and take the shaft out of the distributor body.  Replace the pole piece and reassemble everything.  

 

MARK the location of the distributor to the motor and the location of the distributor shaft & rotor to the distributor body to make sure that you get it back in the correct location. Note that when you remove the distributor the shaft will rotate.  When installing you will need to start the rotor ahead of where you want it to end up as it will rotate as you put the distributor assembly back in. 

 

A new pole piece will be in about the $60.00 range. 

 

You might be able to check the integrity of the wire by pulling the wires.  If they break, you found the problem, but I would still consider replacing the part if the rest of the checks are good.  It is possible that the "wire" is really just a connection of one or two strands of a maybe 12 strand wire.(I don't know the wire count, just guessing as an example)  The vacuum advance rod goes through the hole on the 4:00 position of the illustration below.

 

30357 - 82-91 Distributor Pole Piece. With Plate

30357-2T.jpg?v-cache=1495527359

Edited by Larry Schramm (see edit history)
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Yup like I said an HEI (high energy ignition). BTW the '62 Delcotronic ignition used the same sort of pole piece. The larger HEI type was used by some Pontiacs in '72, other lines in 1974 and became standard  at GM in 75.. Major issues where carbon tracking and literally arcing a hole through the cap. Ignition scopes of the period had a special adapter for the HEI.

 

Delcotronic distributor from '60s.

 

60sdelcotronic.jpg

 
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45 minutes ago, SuperNova75 said:

My mechanic friend says my car doesn't have a catalytic converter and its pre-emissions so doesn't need an egr valve too apparently. And the red wire is the electric choke.

 

I would look at replacing the pole piece then.  On my car and this would happen, I would be accelerating and the car would seem to die.  Replaced the part and all is well.

 

No EGR??  I believe it is supposed to have an EGR.  There is really no downside to having an EGR on the engine under normal driving as long as it is working properly.  I would be sure to have a working EGR. Plus with no EGR, you will increase emissions.

 

Vehicles were/are designed by smart engineers.  Everything that is on and engine is designed to work together.  If you remove one thing it can have an affect on another item and maybe performance.  Engine and vehicle design is like a musical song.  If you remove a bunch of notes in the middle of song it will not sound right. 

 

Edited by Larry Schramm (see edit history)
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2 hours ago, SuperNova75 said:

My mechanic friend says my car doesn't have a catalytic converter and its pre-emissions so doesn't need an egr valve too apparently. And the red wire is the electric choke.

Your car is not Pre-emissions and came with a catalytic converter I mentioned before some of the things that are missing ( emission wise) on your car. Again I said below:

n the first picture I see the ATC air cleaner is inoperative, I also see the TVS switch vacuum hoses missing. On the last picture with the air cleaner is off there is a vacuum hose ( To Auto Trans Vacuum modulator? )  bent over to 90 degrees and appears there might be a vacuum leak there. The intake manifold is suspect, is it the original manifold/where is the EGR valve? I see a vacuum hose to the distributor, Where is the distributor getting it's vacuum signal?. It's supposed to get it from the TVS switch and not straight intake manifold vacuum. The TVS switch gets it's vacuum from the carburetor's ported vacuum and then if the coolant temp.  is at operating temp goes through the TVS sw. to the distributor. 

 

 

I suggest you get a factory service manual and then attempt a fix and only after you re- equip your engine back to factory standards and emission standards for 1975.

If your mechanic friend says your 1975 Nova is pre emissions I suggest you find a mechanic that knows the vehicle and the law pertaining to your vehicle. 

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2 hours ago, Pfeil said:

Your car is not Pre-emissions and came with a catalytic converter I mentioned before some of the things that are missing ( emission wise) on your car. Again I said below:

n the first picture I see the ATC air cleaner is inoperative, I also see the TVS switch vacuum hoses missing. On the last picture with the air cleaner is off there is a vacuum hose ( To Auto Trans Vacuum modulator? )  bent over to 90 degrees and appears there might be a vacuum leak there. The intake manifold is suspect, is it the original manifold/where is the EGR valve? I see a vacuum hose to the distributor, Where is the distributor getting it's vacuum signal?. It's supposed to get it from the TVS switch and not straight intake manifold vacuum. The TVS switch gets it's vacuum from the carburetor's ported vacuum and then if the coolant temp.  is at operating temp goes through the TVS sw. to the distributor. 

 

 

I suggest you get a factory service manual and then attempt a fix and only after you re- equip your engine back to factory standards and emission standards for 1975.

If your mechanic friend says your 1975 Nova is pre emissions I suggest you find a mechanic that knows the vehicle and the law pertaining to your vehicle. 

The engine is from 1974 there is no place for an egr valve, its a non egr manifold and my friend has proven a lot of people wrong. I'm not trying to be disrespectful but he has worked with my car and I for awhile and recently hasn't had time, he says it's pre-emissions and that's what I am also getting from research but I can't argue or agree or disagree with most car crap because I don't know anything because I haven't been taught it. Still, I am grateful for everyone's responses. Thank you.

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+1 on what Pfiel said. Regardless of the current engine, the CAR came with a EGR (GM since 1973) and Catalyst (75 was first year). I had a very similar 2bbl 305 for many years (wound up with dual quads but another story).

 

Bottom line: we have not a clue what you have now. 350 but which heads, which cam, which  carb (GM 2GCs came in many kinds from 178cfm to 435 cfm, 17056114 sounds like a 75 Calif emissions carb body but what that needs is hard to determine). all make a difference. Age is also a factor. Collapsed lifters and thoroughly-ex cam lobes are common and will kill power as will a stretched timing chain.

 

Frankly I have doubts about anyone who says it is not an emissions car.

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2 hours ago, SuperNova75 said:

The engine is from 1974 there is no place for an egr valve, its a non egr manifold and my friend has proven a lot of people wrong. I'm not trying to be disrespectful but he has worked with my car and I for awhile and recently hasn't had time, he says it's pre-emissions and that's what I am also getting from research but I can't argue or agree or disagree with most car crap because I don't know anything because I haven't been taught it. Still, I am grateful for everyone's responses. Thank you.

The first cars with exhaust emissions came in 1966! The way the law works is you can install a newer engine in a older car, but it must remain emission compliant to the year of engine, and in the opposite direction it is technically illegal ( Federal Emission laws) to install a old engine into a newer vehicle using the old cars emission systems.

As Padgett says; EGR goes back to the 1973 model year for your car.

Like I said before, get a service manual to see what your car needs and when that's done repair it properly. 

Edited by Pfeil (see edit history)
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Unlike the A.I.R. the SBC EGR was wentirely in the intake manifold (not for Cosworth Vegas) and fed from the exhaust crossover (used for carb heating) to the intake. So all you needed to delete the EGR was a non-egr intake manifold. (also there were block off plates for EGRs).

Thing was the engine was designed for EGR dilution at cruise and MPG would head into the toilet if just removed the EGR without making other changes.

Guess few are left who were there. Could make a pellet remover from a long mag 3/4" lug nut.

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I agree that the first year for vehicle emissions was 1968 when PVC Valves(positive crankcase valves) were installed.  These valves sucked the crankcase vapor from crankcase and and put it below the carb to burn the vapors.   

 

Before the PVC valve, cars had a "road draft tube" that allowed the crankcase vapors to vent to the atmosphere.  Here is a road draft tube on a SBC engine. The black tube on the back of the engine.

 

image.jpeg.15f60585b500ef19b2638c4111675abe.jpeg 

Edited by Larry Schramm (see edit history)
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6 hours ago, Larry Schramm said:

I agree that the first year for vehicle emissions was 1968 when PVC Valves(positive crankcase valves) were installed.  These valves sucked the crankcase vapor from crankcase and and put it below the carb to burn the vapors.   

 

Before the PVC valve, cars had a "road draft tube" that allowed the crankcase vapors to vent to the atmosphere.  Here is a road draft tube on a SBC engine. The black tube on the back of the engine.

 

image.jpeg.15f60585b500ef19b2638c4111675abe.jpeg 

NO, the first PCV was 1961 in California and 1962 for Federal cars. The first cars with exhaust emission control was 1966 in Ca. and 1967 for Federal cars. The first year for Catalytic converters was 1975 although some foreign cars could pass with Thermal reactors like BMW and Honda but soon standards were too strict and they went to catalyst.

Edited by Pfeil (see edit history)
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Just a minor quibble, fed law was in 67 for the 68 model year. Same time side markers became mandatory. Often the year of the law and the model year it applied to were different. Coulda swored my 63 split window had a draft tube but they say the memory is the second thing to go and I forget.

 

And then there was the '74 seat belt interlock...

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45 minutes ago, Pfeil said:

NO, the first PCV was 1961 in California and 1962 for Federal cars. The first cars with exhaust emission control was 1966 in Ca. and 1967 for Federal cars. The first year for Catalytic converters was 1975 although some foreign cars could pass with Thermal reactors like BMW but soon standards were too strict and they went to catalyst.

 

I will agree with you as I thought '62 was the first PCV year but a quick search showed up '68, that is why I said '68.

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