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Slight Surge In 67 Camaro 383

1614 Views 10 Replies 7 Participants Last post by  Deangelo66
I had a 383 built last month and it was running great. The shop had to fix a few leaks. They removed the intake manifold to fix one leak. After completion, it now has a slight surge. The idle RPM is about 700 but it used to be 800 before the leak repair. It idles like this: bum, bum, bum, bum, BUM, bum, bum, bum, BUM, bum...Hope that explains how it sounds. :) It has a kinda lumpy cam but I can tell the difference from before. The surge is noticeable even with the fairly rough idle. It is very minor but it is driving me crazy. It wasn't like that before. When it is in drive and idling, if I keep my foot lightly on the brake, I can feel this slight surge of power. Is it caused by idling too low or is it a fuel mixture problem, etc.? I don't see how they could have touched anything on the carb when reinstalling the intake. I hate to take it back to them for the 6th time. They may think that I am crying wolf because I keep going back to them. I paid a ton so it should be right! I am just tired of dealing with this speed shop in VA. I am going to increase the idle speed tomorrow when I am free. I just want to get a heads up in case that does not solve the problem. I have no idea how to adjust fuel mixture properly on my 770 Holley Avenger carb if that is the problem. How does one accurately do that without a machine or analyzer? I hope this is the right forum for this question. Or should it be in the "Engines" forum? Thanks, DeAngelo
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A couple of things come to mind. When they did the intake manifold, they might not have gotten a good seal and there might be a vacuum leak. That will cause a surge. Or, when they put the distributor back in they may have set the timing a little retarded from where it was before. Again, that will cause a surge. As for setting the mixture, when the motor is warm and ideling, turn out the mixture screws one at a time until you have the highest RPM possible, then turn in, a quarter of a turn at a time, until you hear the RPM's drop, then turn the screw back out just until you get the lost RPM back, no further. Now do the same thing to the screw on the other side. I usually go back and forth a few time to get it just right. There are lots of reasons a motor might have a surge, but I am trying to think of ones that might have come from changing an intake gasket. Hope this helps.
Wonder how many guys have hovered over this thread trying to decide if they want to type anything, like I'm doing right now?
Ya know Deangelo, the guys who can help the most probably need to stand next to your car and 'feel it' or take it out for a spin. I would do both. This is not an economy hobby if you aren't 'mechanical'.
Try this; Open the hood and look at the air filter and see how to take it off. (I'm really taking a chance that I'm talking 'down' to you) Remove it. Have someone inside the car step on the gas pedal slowly so you can see how it works. You will then note the location of the idle set-screw. Turn it to raise the idle and then replace the air cleaner and go for a ride. I suspect that nothing much is going to change but at least you tried. (Oops, I see that you're going to do this tomorrow.) But while you're under the hood, do so with the engine running. A surge is caused by a lean condition. Either the carb is jetted too lean or, as I suspect, someone left a vacuum line off/unplugged. Listen for a whistling sound under the hood. Good luck.
P.S. And do what Eric said too!:yes:
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Thanks, Eric and Fred. I know a few things but not as much as you guys. :) I know how to increase the idle speed and even a little about the air/fuel mixture routine but didn't think that it was an accurate enough technique. I thought there was a special analyzer to use. :) I appreciate your help! I hope it's not a vacuum leak!! Thanks, guys! DeAngelo
sometimes when you do in intake, you clean the intake ports off with a cleaner spray(like carb cleaner on a rag)...if you get gasket material or coolant, or any foreign material into a cylinder, you could crap up a plug...intermittant spark in 1 cyl will also cause a surge...pull the plugs to see if one has a bunch of schmegma on it...(techincal term for
As Fred said, it's hard to troubleshoot this kinda of stuff from a keyboard a thousand miles away. While I have no doubt I€ could tune your car as good as it can be tuned in a few minutes, or determine there is a problem beyond tuning, that only really works when I can hear it, feel it, and touch it.

And then we get into you bringing it to a professional and proceeding to tell him what a bunch of guys on the internet told you is wrong with it. Please don't do that, it won't get you the best results from them.

If you want to do this yourself, you need 2 tools, a vacaum gauge and a timing light. If you have them, I'll let you know what to do with them.
Thx, Jim and Mike. And you are right, one should never tell the performance shop they are wrong even though these guys are half of the time. :) I have a great timing light but no vacuum gauge. How much is one? I can go buy one. It is a good thing to have. What do I do once I have the vacuum gauge? And it seems a little more noticeable. Sounds like it could a spark "miss". I am going to take it back to them AGAIN if I can't figure it out. I hate to do that but I should get what I paid for. Thanks! P.S. Jim, I wished you lived in Va Beach!! :)
I have a hand pump vacuum gauge. I like it because it not only will read vacuum, but it will pump a vacuum as well for checking things like vacuum advance canisters and a/c servos (or RS headlamp doors). I got mine at an auto parts store for about $9. I saw sears had one for $30 that contained a brake bleeding bottle and other gizmos -- kind of a rip off in my opinion.

a basic vacuum guage should be pretty cheap - less than $20. Check your local auto parts store.
Thanks, Dave. I believe that I have found the culprit! I hate to even admit it but it was the timing! You would think that the shop would have ensured the timing was correct after they reinstalled the intake manifold. I noticed that the surging also accompanied a "unevenness". The tach was bouncing back and forth between 750 and 850. It didn't do that before they worked on it. I advanced the timing a bit and it smoothed out. Thanks to everyone who pointed me in the right direction. I kept thinking it was a fuel mixture issue but it wasn't. THANKS! DeAngelo
Glad to read the car is running. Speed shop in VA, Where is your location?
Northern VA.
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