Vintage Mustang Forums banner
  • Hey everyone! Enter your ride HERE to be a part of this month's Ride of the Month Challenge!

1 - 7 of 7 Posts

·
Registered
Joined
·
28 Posts
Discussion Starter #1
I have a 351C with 2V heads in my 68 coupe and have recently replaced the intake manifold with a Edelbrock Performer 2750 model and a Summit 600CFM carb with electric choke which I have wired to a dedicated bus I connected to key-on 12V. In the process of the work this winter, I also removed the mechanical fuel pump and installed a Carter Electric pump (P4070) and a Summit 1-4psi fuel regulator (G3033B). The engine has a non-vacuum advance distributor.

Today I had the chance to fire it all up and it did fire right up! However, the idle was about 2500 RPM. I tried adjusting the curb idle screw out, but it is backed out completely and not making contact. The Summit carb manual told me how to adjust the high-idle screw, which I did to no effect. It also told me how to adjust the idle mixture screws, which I did to no effect. I tried going both more lean and more rich to see if it would change; it did not.

As I started the engine, checked RPM and made adjustments, it slowly warmed up and the choke opened to what appeared to be normal operating position. The RPM climbed as this was happening and now that things appear warmed up, it is idling at about 3000 RPM.

While I had things apart this winter, I did remove the distributor. When I hooked it all back up, I found TDC on Cyl 1, and I think I got the distributor hooked up correctly. It runs very smoothly, just really fast! I don't know if I can even set the timing with it idling so high. I connected a vacuum gauge to the carb and when it is idling at 3k, it reads about 18 inches on the gauge.

I looked down the throat of the carb with the engine off, and the throttle plates appear to be completely closed. The secondaries do not respond at all, even when I blip the throttle. I haven't given it full throttle.

I do not have the PCV hooked up yet; the valve cover PCV port is just vented to atmosphere right now. All vacuum ports on the carb are plugged (including PCV), except the full manifold port, which is connected to my vacuum gauge currently.

I live at about 4500 foot elevation. Would that cause this problem? The manual says it is jetted for sea level from the factory. I did buy a jets kit, so I can change those out if need be.

I have very little experience tuning carbs, so I'm hoping someone with more experience can give me some guidance.
 

·
Registered
Joined
·
21,340 Posts
There is a fast idle cam that keeps the idle speed high when you first start the engine. Was it still on this cam? It's located on the right side by the choke. The engine has to warm up and it'll come off the fast idle as you step on the gas. Just sitting the sencondaries are not going to open. They are only going to open as the engine needs more then the primary can supply. This is definitely not going to happen with no load on the motor.
 

·
Registered
Joined
·
3,245 Posts
Your elevation is not gonna cause this problem. Are you sure the gas pedal is not pulling on the carb? Disconnect the throttle linkage and see if it comes down. Also, and I shouldn’t have to ask this but I will, you do have a return spring, right? Haha
 
  • Like
Reactions: analog

·
Registered
Joined
·
28 Posts
Discussion Starter #6
Your elevation is not gonna cause this problem. Are you sure the gas pedal is not pulling on the carb? Disconnect the throttle linkage and see if it comes down. Also, and I shouldn’t have to ask this but I will, you do have a return spring, right? Haha
Thank you! I can't believe I didn't think to check this simple thing, but that was the problem. Disconnected it and it idles just right. Now I can keep tuning it to dial it in. Thanks everyone for your help and suggestions. Also, I do have a return spring :)
 

·
Registered
Joined
·
3,245 Posts
Thank you! I can't believe I didn't think to check this simple thing, but that was the problem. Disconnected it and it idles just right. Now I can keep tuning it to dial it in. Thanks everyone for your help and suggestions. Also, I do have a return spring :)
Glad I could help, it gives me the warm fuzzies. Good luck on the carb.
 
1 - 7 of 7 Posts
Top