69volunteer 84 Report post Posted August 1, 2023 I have a fastback that I restored 10 years ago. Unfortunately it does not get driven often any more—I’m a terrible owner. I have made a list of a few upgrades and will be posting more often. I moved the car over to my shop 6 months ago and noticed that at idle it is surging. It will drop to 500 rpm and nearly stall to maybe 1100 (going off memory). I adjusted the idle to about 1100 where it stayed steady and then sprayed carb cleaner all around the intake and carb thinking it was a vacuum leak. No change to idle. Now I think it may be the carb— new Edelbrock back in 2013. Tried using non-ethanol gas but that went by the wayside a few years ago. EFI is possibly on my list of upgrades. I don’t mind rebuilding the carb so I can start fresh with the EFI conversion but want to eliminate any other issues first. C4 auto with Pertronix ignition upgrade. thoughts? Quote Share this post Link to post Share on other sites
jmlay 80 Report post Posted August 1, 2023 After setting for 10 years with little to no use * would expect all seals & rubber to dried up. At a minimum I would disassemble, clean & inspect to see if it needs to be rebuilt. A basic rebuild kit is fairly inexpensive.: https://www.amazon.com/iFJF-Carburetor-Rebuild-Edelbrock-Gasket/dp/B07S8FHCTQ/ref=asc_df_B07S8FHCTQ/?tag=hyprod-20&linkCode=df0&hvadid=362768105905&hvpos=&hvnetw=g&hvrand=17447957952955106925&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1026836&hvtargid=pla-785655582198&psc=1&tag=&ref=&adgrpid=75266506039&hvpone=&hvptwo=&hvadid=362768105905&hvpos=&hvnetw=g&hvrand=17447957952955106925&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1026836&hvtargid=pla-785655582198 Quote Share this post Link to post Share on other sites
Midlife 814 Report post Posted August 1, 2023 Sounds very much like a vacuum leak to me! Quote Share this post Link to post Share on other sites
RPM 1,190 Report post Posted August 1, 2023 Does the C4 have any vacuum lines to it like the FMX? Quote Share this post Link to post Share on other sites
Ridge Runner 1,113 Report post Posted August 2, 2023 C4 has a vacuum line to the vacuum modulator valve at the bottom side of the C4 ,it has a short rubber elbow to the modulator ,they rot and split 1 RPM reacted to this Quote Share this post Link to post Share on other sites
69volunteer 84 Report post Posted August 2, 2023 It does get driven just sits for quite a while. I thought vacuum leak as well but didn’t find anything at first glance spraying carb cleaner. I’ll investigate this further before pulling the carb. Quote Share this post Link to post Share on other sites
nymustang1969 22 Report post Posted August 4, 2023 The idle circuit on the Edelbrock carbs tend to get gummed up. Unscrew the two idle mixture screws and spray in some carb cleaner. Blow out with some compressed air if you can. Then put idle mixture screws back in, adjusting to 2-2 1/2 turns out. Good chance this will solve your problem. Quote Share this post Link to post Share on other sites
