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Discussion Starter #1
Have 65 nova with 283 cu.in.It has an aluminum intake and Summit carb with a mild cam. It starts great and idles at 1000 rpm. Timing is at 4 degrees btdc with no vacuum advance.As soon as you get stopped at a traffic light or stop sign the idle drops to 350-400 rpm and engine dies. It will then start right up.It has new plug wires,plugs with HEI distributor. Not sure where to look next. Any ideas will help.
 

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Is 1,000 rpm the high idle? Or is that after kick-down?

I suspect that the idle is set too low, and the carb is sitting at high idle longer than it should, fooling you into believing that the idle is set properly (or close to it).

What transmission is in the car?
 

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Discussion Starter #3
1000 rpm is cold start up. Has electric choke but not hooked up. It has the powerglide trans.
 

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power brakes?

could a vacuum leak that occurs only when you stop using the brakes be the cause?

try pressing the brake in park and see what happens.

If you don't have power brakes I am clueless:

If an Automatic is your TC staying engaged?? I think you would have notice if that's the problem.

GL
 

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Discussion Starter #5
It has power brakes. Disconnected the vacuum hose and plugged it and still the same results.A friend of mine who used to build race motors is baffled to.Thanks for the response.
 

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Mike - 74 Nova Baltimore, MD
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Do you know what your total mechanical advance is?

I would recommend increasing your initial timing to about 10°-12° BTDC. Then... reset your idle speed when the engine is warm.

I also recommend connecting your distributor's vacuum advance canister to a full time vacuum source and also install an HEI vacuum advance limiter plate set to limit the vacuum advance to about 11°-12°. This step will significantly help your idle characteristics and engine vacuum.
MSD 84281
https://www.summitracing.com/parts/msd-84281
 

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Do you know what your total mechanical advance is?

I would recommend increasing your initial timing to about 10°-12° BTDC. Then... reset your idle speed when the engine is warm.

I also recommend connecting your distributor's vacuum advance canister to a full time vacuum source and also install an HEI vacuum advance limiter plate set to limit the vacuum advance to about 11°-12°. This step will significantly help your idle characteristics and engine vacuum.
MSD 84281
https://www.summitracing.com/parts/msd-84281
Rif,

Original post says no vacuum advance. I was thinking of that too.

Sounds like the idle speed and/or mixture needs to be reset.
 

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There are some other good suggestions, including power brake vacuum and advance problems.

If the car will start and idle OK in place, and this problem only occurs as you come up to a stop, I'm going to say that the float level might be a problem. Float level too high or too low as you come up to a stop could be an issue with flooding or starvation of the carb. Typically, it's a flood problem, especially if it starts right back up.

Let us know what the culprit is when you find it.
 

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Mike - 74 Nova Baltimore, MD
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One other question... how old is the fuel in your Nova's gas tank?

Winter blends of gas contain ethanol and I believe that the ethanol starts to break down after about 6 months.
I had the rough idle problem with my Nova on it's first Spring drive of this year. I had winter fuel in the tank and my car ran like crap. I took my Nova on a couple of long drives to use the old fuel and refilled with 93 octane. My Nova ran great after the fill up with new fuel.
I also use Stabil Fuel Treatment.
 

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Discussion Starter #11
Thanks for all the responses. I will be going to try all and see how things go. Will let you guys know. Thanks again.
 

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I was having this issue as well I just turned up my idle mixture screws 1/4 turn in on all 4 corners it’s perfectly fine now
 

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Rasf53,

Not sure where you are, climate wise, I hope you have backed your choke off seeing as it is not hooked up. Could be many things, but I suspect idle and mixture as suggested. I also do not like your timing. Would think it would be more 8-12, but I do not know your set up and this may be N/A.

Electronics could be giving fits, like the module or coil. Also, did you cut your power wire near the fire wall and put non resister wire in? The pre 74 cars had a white cloth wire that reduced voltage as it heats up, HEIs in particular do not like low voltage.

Strangest thing I ever had happen was after a TPI install. My engine would randomly shimmy or die (minutes to days). I had bought a napa plug wire kit for the new dist., but it didn't have a coil wire; so I had to buy a random coil wire (for some reason they out). I chased it for months and changed a lot of parts, but seemed to change the pattern after moving my external coil location again. So on a hunch, I got another new but higher quality coil wire and cut the former one open. Turned out it was 3 pieces of wire inside, and I am talking about a 4 inch wire! The dang thing was moving and maybe expanding inside, losing contact.
 

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It's weird so many of us are having this problem. My 302 Ford started doing this same thing last week. It runs down the road fine but suddenly developed a very slow laboring idle. I double checked my timing which is still at 10*.
This weekend I'm going to pull the carb and remove the idle screws and clean the idle ports and idle air bleeds.
I also have a multi-layer heat insulating base gasket which I have heard can deteriorate and may cause a vacuum leak through the various layers.
Might be worth while checking these out on your car too.
 

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Discussion Starter #15
Yesterday I adjusted the timing to 10 degrees BTDC.The idle increased a bit and then turned out the mixture screws a quarter turn. Checked the vacuum at 8 lbs.of vacuum at idle. Took it for a spin and idled at 800 rpm and didn't stall. Seems to be fine. Thanks again for all the help.
 

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Yesterday I adjusted the timing to 10 degrees BTDC.The idle increased a bit and then turned out the mixture screws a quarter turn. Checked the vacuum at 8 lbs.of vacuum at idle. Took it for a spin and idled at 800 rpm and didn't stall. Seems to be fine. Thanks again for all the help.
8" of vacuum at idle seems pretty low if your engine is close to stock. I know you said "mild cam" which makes me think you have some more work to do.
 

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Mike - 74 Nova Baltimore, MD
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OP should be using a vacuum gauge when adjusting the carb's idle mixture screws. Turn them both equally (and just a little bit at a time) in... or out until you see the highest vacuum level.
8" of vacuum at idle seems pretty low if your engine is close to stock. I know you said "mild cam" which makes me think you have some more work to do.
I agree with the above statement.
I had also recommended the OP to connect their distributor's vacuum advance canister to a full time vacuum source and also install an HEI vacuum advance limiter plate set to limit the vacuum advance to about 11°-12°. I beleive this step would significantly help the OP's idle characteristics and engine vacuum.
MSD 84281

Quick test for OP to determine if connecting distributor's vacuum advance canister to a full time vacuum source (with vacuum advance limiter plate) would help. Vacuum advance canister is disconnected for both tests below.
1 - Set idle to 850 and turn the idle mixture screws in... or out as described above to achieve the highest vacuum level.
2 - Adjust your distributor to give you 21°-22° BTDC initial timing @ 850 RPM and note your vacuum level (readjust idle mixture screws as needed).

If your vacuum increased with the initial timing set to 21°-22° BTDC, that is an indication the use of the distributor's vacuum advance (connected and limited as described above) would help improve the idle quality... and the throttle response of this engine.
NOTE: After this test, readjust your timing back to 10° before driving your car.
 

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Discussion Starter #18
I will be purchasing the limiter advance plate and trying your suggestion. Will get back to you and let you know how things go. Thanks for the help.
 

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Just an update on how things went with my low idle problem, in case it may help someone in the future. I replaced the multi-layer gasket (didn't look too bad) with a thinner base gasket and did a through cleaning / rebuild of the carb. One idle air bleed was blocked and float height and drop were off. Now she idles smoother than when the carb was new at a nice and steady 700 rpm. The throttle response seems much snappier too.
 
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