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Discussion Starter #1
I've got a strange one and haven't found anything on this problem. Finally got the Nova out for a spin after sitting up all summer while I worked out some problems and upgrades. I got it out on a main road and opened it up for a few seconds and when I let off the idle was at around 3000 rpm. I pulled into a parking lot, shut it off and popped the hood. I could see nothing binding or stuck such as the throttle linkage or accelerator cable. Started it back up and it drove fine without any issues, of course I didn't take a chance and open it up. I took it out about a week later and had the same issue again, just that this time it was at about 2000 - 2300 rpm. Same scenario, pulled over and turned it off, nothing binding. It fired right back up and drove normal all the way home after which was a 40 min drive.

Has anyone had this happen or know what could possibly be going on? I really don't think it's a sticking throttle cable or throttle arm on the carb. Could it be something internal with the carb sticking or out of adjustment?

The carb is a QF 680 HR series
383 Stroker
Carb is cable operated with free play

Thanks in advance!
 

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Check out your distributor. Sounds like it may not be fully returning to your set advance.
 

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Discussion Starter #5
I got a chance to open it up today and it looks like new inside. No rust or corrosion anywhere. I worked the advance mechanism back n forth several times and nothing looks to be sticking. I also took the springs off and did the same thing, everything seems to be fine so I put it all back together. Is there anything else I should look at in there? This is a MSD distributor that came with my crate 383. The engine and distributer are about 3 years old but with less than 400 miles on everything.

I did put a little (very little) high temp grease on the advance mechanism where it slides just in case there is some sticking maybe when it heats up :)confused:).
 

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Is it mechanical or vacuum advance? If it still happens check it with a timing light to rule out the advance sticking.
 

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Sounds like a carburetor issue or a vacuum leak. It would take a lot of timing advance to go from idle to 3,000 rpms.
 

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Next time it happens, don't turn off the engine. Pop the hood and look to see if the throttle has returned to the idle position. The linkage should allow the throttle to return and the idle stop screw should be in contact with the mechanism. If it isn't, push the throttle linkage manually so the mechanism is touching the idle stop and investigate why it's not doing it by itself. In my case the throttle was at the stop with engine off and engine running. Put it in gear and the engine torque would raise the driver's side of the engine as expected but it was also pushing the linkage at the same time. No problem when moving forward but at a stop the rpms increased to the point of the back wheels spinning on the pavement as I applied the brakes harder and harder. Not a fun thing to happen when your at a light with a car in front of you. Foot off the gas and the rpms increasing to around 1700.
 

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Discussion Starter #9
Is it mechanical or vacuum advance? If it still happens check it with a timing light to rule out the advance sticking.
It is vacuum advance, if I'm thinking correctly...it has the can on the side with a vacuum hose which I have connected to the timed vacuum port on the carb.

Sounds like a carburetor issue or a vacuum leak. It would take a lot of timing advance to go from idle to 3,000 rpms.
I was thinking a vacuum leak cause a high idle all the time, would that be correct?

Next time it happens, don't turn off the engine. Pop the hood and look to see if the throttle has returned to the idle position. The linkage should allow the throttle to return and the idle stop screw should be in contact with the mechanism. If it isn't, push the throttle linkage manually so the mechanism is touching the idle stop and investigate why it's not doing it by itself. In my case the throttle was at the stop with engine off and engine running. Put it in gear and the engine torque would raise the driver's side of the engine as expected but it was also pushing the linkage at the same time. No problem when moving forward but at a stop the rpms increased to the point of the back wheels spinning on the pavement as I applied the brakes harder and harder. Not a fun thing to happen when your at a light with a car in front of you. Foot off the gas and the rpms increasing to around 1700.
I did that the last time and the throttle linkage seemed to be all the way closed. My first and second thought was that it was something with the carburetor and the throttle cable binding somewhere.

Could it have something to do with the vacuum secondary, I think that's what it's called, its the adjustable thing on the passenger side of the carb with a linkage and an arm coming out with a spring and nut. it looks like it works with the back butterfly's. With the car running if I push the linkage up it causes the idle to go up. Hopefully that description wasn't too confusing.
 
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