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Discussion Starter #1
Hey guys slight problem with my nova. Upon it starting up it seems to idle fine for a second or two then immediately starts increasing idle speed. Seems to get pretty high (not sure of rpm because there is no rpm gauge.) I usually turn the car off after a couple seconds because it doesnt seem right to me and I honestly get nervous that something catastrophic might happen.
Any idea what could be causing this??
 

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Is the engine just cold on start up and the choke kicks in? Is it a carb or fuel injection?

Not much info on what you have. Yes...check all your hoses and the little plugs on the vacuum sides of the carb...IF you have a carb. They break down in a few years...not as good as the older rubber hose ends.



Dave
 

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Discussion Starter #4
305 engine
Edelbrock carb 1405 manual choke.

I still have to set the idle mixture screws and make it idle perfect but it seems to wanna increase rpm only when I start to shut the choke. When the choke is on it seems to idle fine is what I'm trying to say.
 

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If the RPM increases when you partially close the choke it indicates a lean condition. When the choke is engaged there is also a fast idle cam on the carb linkage designed to increase the idle speed. From what your saying it seems to be a lean mixture issue. Vacuum leak?
 

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Discussion Starter #6
If the RPM increases when you partially close the choke it indicates a lean condition. When the choke is engaged there is also a fast idle cam on the carb linkage designed to increase the idle speed. From what your saying it seems to be a lean mixture issue. Vacuum leak?
Okay should I be adjusting that when the car is idling? How would I go about adjusting the lean mixture?

Is there an easy way to check for vacuum leaks?
 

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Mike - 74 Nova Baltimore, MD
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Upon it starting up it seems to idle fine for a second or two then immediately starts increasing idle speed. Seems to get pretty high.
I'm not sure I am clear on what is happening....
You first state that the engine RPMs increase on their own after starting.

305 engine / Edelbrock carb 1405 / manual choke.
... it seems to wanna increase rpm only when I start to shut the choke. When the choke is on it seems to idle fine is what I'm trying to say.
Then you state that the engine RPMs increase when you shut the manual choke.
Can you explain exactly what you are doing.

My next question is "Do you have a manual choke cable attached to the carburetor's manual choke linkage that you are able to physically control the closing and opening of your carb's manual choke?"

To help us understand your situation, it would help if we were all using the same references regarding your manual choke.
Closing the choke = Pulling out on the manual choke cable to move the choke blade (that is located at the top of the carb) towards a closed position - restricts airflow into carb.
Opening the choke = Pushing in on the manual choke cable to move the choke blade (that is located at the top of the carb) towards an open position - unrestricted airflow into carb.

Note that when the manual choke is moved towards a closed position, the engines idle will increase as there is a fast idle screw that contacts a fast idle cam.
When you open the manual choke, your engine's idle should go down.
 

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Discussion Starter #8
Upon it starting up it seems to idle fine for a second or two then immediately starts increasing idle speed. Seems to get pretty high.
I'm not sure I am clear on what is happening....
You first state that the engine RPMs increase on their own after starting.

305 engine / Edelbrock carb 1405 / manual choke.
... it seems to wanna increase rpm only when I start to shut the choke. When the choke is on it seems to idle fine is what I'm trying to say.
Then you state that the engine RPMs increase when you shut the manual choke.
Can you explain exactly what you are doing.

My next question is "Do you have a manual choke cable attached to the carburetor's manual choke linkage that you are able to physically control the closing and opening of your carb's manual choke?"

To help us understand your situation, it would help if we were all using the same references regarding your manual choke.
Closing the choke = Pulling out on the manual choke cable to move the choke blade (that is located at the top of the carb) towards a closed position - restricts airflow into carb.
Opening the choke = Pushing in on the manual choke cable to move the choke blade (that is located at the top of the carb) towards an open position - unrestricted airflow into carb.

Note that when the manual choke is moved towards a closed position, the engines idle will increase as there is a fast idle screw that contacts a fast idle cam.
When you open the manual choke, your engine's idle should go down.
Sorry about that I wasn't sure on correct terms.

It is a manual choke with a cable

Let me try it again. When it starts it would idle poorly (shaking engine, idle would go down then come back up) when it is first started the choke is in the closed position with restricted air flow once I started opening the choke it would start increasing the rpm almost immediately.
 

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Discussion Starter #9
I did check 2 of my spark plugs number 1 and the one right behind it and they were Black. Not sure if that helps any!
 

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Mike - 74 Nova Baltimore, MD
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A manual choke is going to operate a little differently than an electric choke.
You do not want to fully close your manual choke, as this will significantly restrict the air flow to your engine causing the rough/inconsistent idle conditions you are experiencing.

I also have a manual choke on my carb, and below is how I start my engine.
Before starting, give the accelerator pedal a couple quick taps to prime the carb. With the choke completely open, attempt to start the car.
NOTE: If the engine starts and is idling too fast with the choke open, you need to adjust your primary idle speed screw to lower your RPM's.

Once you have your primary idle set to the correct RPM... with the engine still running, slowly pull on the choke cable to partially close your choke. As you are closing your choke, the RPMs should increase. You only need to close the choke enough so that when you start a cold engine, you increase the idle enough so the engine won't stall.

Once your engine is warmed up, the choke should be moved to the "completely open" position.
 

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Discussion Starter #11
A manual choke is going to operate a little differently than an electric choke.
You do not want to fully close your manual choke, as this will significantly restrict the air flow to your engine causing the rough/inconsistent idle conditions you are experiencing.

I also have a manual choke on my carb, and below is how I start my engine.
Before starting, give the accelerator pedal a couple quick taps to prime the carb. With the choke completely open, attempt to start the car.
NOTE: If the engine starts and is idling too fast with the choke open, you need to adjust your primary idle speed screw to lower your RPM's.

Once you have your primary idle set to the correct RPM... with the engine still running, slowly pull on the choke cable to partially close your choke. As you are closing your choke, the RPMs should increase. You only need to close the choke enough so that when you start a cold engine, you increase the idle enough so the engine won't stall.

Once your engine is warmed up, the choke should be moved to the "completely open" position.
I think that's where my problem lies when I bought the car he said to close the choke so its restricted then after a couple mins go half way then another couple mins open it fully.

When you push on the accelerator pump on your carb do you immediately see fuel shooting out? Everytime I push the accelerator before I even think about starting the car nothing comes out. It's almost like a delay. Then after trying to start it or pumping it a few times it looks like it comes through.

When the car starts should I immediately open the choke halfway or even all the way then start adjusting the idle speed screw? It should eventually stop increasing rpm right? I'm only worried since it keeps increasing its idle that it could redline and I would have to start shopping for a bigger engine lol.
 

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Mike - 74 Nova Baltimore, MD
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I have a Holley carburetor.
Yes... You should instantly see fuel shooting out of the carb's squirters when you push the accelerator/open the throttle. There should be no delay. If there is a delay, something is out of adjustment... or your accelerator pump diaphragm/plunger could be ruptured or leaking.

As you open the choke, your RPMs should drop... not increase. Something seems wrong with the way your idle speed screws are adjusted.
If your think your engine's RPMs are too high with the choke completely open, you can turn the carb's primary idle adjustment screw counter-clockwise to lower the RPM's.

It would also be advisable for you to research some additional information on how to troubleshoot, adjust, and tune your Edelbrock 1405 carb.
 

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Discussion Starter #13
I have a Holley carburetor.
Yes... You should instantly see fuel shooting out of the carb's squirters when you push the accelerator/open the throttle. There should be no delay. If there is a delay, something is out of adjustment... or your accelerator pump diaphragm/plunger could be ruptured or leaking.

As you open the choke, your RPMs should drop... not increase. Something seems wrong with the way your idle speed screws are adjusted.
If your think your engine's RPMs are too high with the choke completely open, you can turn the carb's primary idle adjustment screw counter-clockwise to lower the RPM's.

It would also be advisable for you to research some additional information on how to troubleshoot, adjust, and tune your Edelbrock 1405 carb.
Okay I guess I'm gonna have to take it apart and recheck everything. I did replace the accelerator pump with a brass one and a new diagram so maybe I'll put the old one back on and see if that helps.

I definitely am gonna have to research my carb.
On the idle speed screw and carb idle screw It seems that your right those screws are severely out of whack. Is there a good starting point for those screws?
 

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Is there a good starting point for those screws?

I would gently seat each idle mixture screw and then back it out 2 turns, that will be in the pall park. As far as the Base idle screw goes, make sure the choke is wide open "off" then back the screw out until there is clearance between the screw and throttle arm. Screw the base idle screw in until it just touches the throttle arm and then 1 and 1/2 turn more. Let the engine reach operating temperature (with or without using the choke) then with choke open adjust the base idle speed first. You can fine tune the mixture screws and base idle from there.
 

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Discussion Starter #15
Is there a good starting point for those screws?

I would gently seat each idle mixture screw and then back it out 2 turns, that will be in the pall park. As far as the Base idle screw goes, make sure the choke is wide open "off" then back the screw out until there is clearance between the screw and throttle arm. Screw the base idle screw in until it just touches the throttle arm and then 1 and 1/2 turn more. Let the engine reach operating temperature (with or without using the choke) then with choke open adjust the base idle speed first. You can fine tune the mixture screws and base idle from there.
Okay perfect I'll definitely start with that baseline and hope for the best. I bought new spark plugs since the ones In the car now are black.
 

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Discussion Starter #17
Just because your spark plugs are black does not mean they need replacement. Unless the electrodes are brned off and/or eroded.
Reading a Spark Plugs
Thanks for the video I'll definitely check it out but the reason I changed them out was for the fact that is was fairly easy to do except for a couple and I couldnt remember the last time it was done
 
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