Weird Surge After 1985 Capri Warms Up

As the title states, I have a 1985 Mercury Capri and it is a really fun car to drive, The only issue is, after about 10 minutes of normal driving, the car starts to surge when in low RPMs through 1-3 gear, still does it in the later gears but its really unnoticable. What I mean by surge, is that the car bucks back and forth, as if I'm hitting the gas and letting off over and over, yet my foot is steadily slightly depressing the gas pedal. This ONLY happens after the car has time to warm up a bit. Not even necessarily at full operating temps.

The ONLY thing that isn't stock is 1406 edelbrock carb. Any ideas?

If there are any questions please ask! This is a big issue when it comes to driving to and from classes and I would love if anyone could point me in the right direction.

90sickfox said:

Can't be too complicated...

I had the same exact carb for years. I'm sure someone will bash edelbrock... but it worked for me.

How old is the carb ? Does it have an electronic or a mechanical choke ? Is it hooked up ?

The only problem i ever had was with a Mr.Gasket fuel pressure regulator. The ethanol in the gas would eat the diaphragm and cause the regulator to surge. It would stop keeping a steady pressure. It would actually start vibrating and the fuel gauge would go crazy.

Sounds like it is a fuel or air problem.... meaning possibly a vacuum leak.

Do you have any type of O2 sensor or air fuel ratio gauge in the car ? I had a cheap sunpro one that lit up red, yellow, or green. It was hooked up to a factory o2 sensor. It worked for what it was. Now I use a LC1 innovate wide band and it is a lot more accurate.

Click to expand...

First off, thank you for the speedy reply. And yeah I embrace edelbrock despite all the hate.

The carb is about a year old, and it has an electric choke. I hooked it up but didn't really adjust it too much from factory. I failed to mention that although I love foxbodies and I am very intrigued and have a general to higher understanding with how engines work, I don't have too much time under the hood. I received this car as a gift and have been working on it little by little ever since.

funny you mentioned the diaphragm, is it possible that sitting for a while could cause the diaphragm to begin to "decay?" The car was sitting for 18 years and after changing fluids, taking out the old gas, and changing the spark plugs and wires it started up and ran completely fine. The engine only had 51k on the odo. (completely fine meaning it starts and runs fine, but at the time I did not do any extensive driving so I am unsure if this issue has been there from the start or not)

okay, vacuum leak... I installed the carb myself and since an edelbrock is a different design than the factory holley, to be completely honest I wasn't 100 percent sure I hooked all of the vacuum lines up correctly. Not to mention I noticed vacuum lines sitting completely open even before my installation, so trying to trace to vacuum lines and see what the previous owner messed around with is very challenging. And if I find open vacuum lines, I'm unsure if I should plug them up or hook them to something..

Lastly, I do not have a air/fuel gauge in the car. The car didn't come factory with o2 sensors and neither I nor the previous owner installed one. But that is something I hope to change in the near future.