EDEL 1406 on a 71 360 rough cruise mode

[Bookman]

I posted this also in the FE section but this may be more appropriate. I'v been running it with a 1" riser and in the one leaner setting from the book in tne cruise mode for over a year. Recently the truck has been running rough at very light throttle positions. at idle and in the power mode it cleans up or at least gets better. When removing the Vac advance hose from the carb everything cleans up. After checking the cap and rotor there is a lot of black dust under the cap. If I suck on the vac hose the diaphram seems to be ok. Eveyone so far at the parts house and a shop say its too rich but this is some thing new and adjusting the air screw does not help the transition. What am I missing???????????

[jade79]

When you say running rough at light throttle, do you mean it feels like it's dropping a cylinder or surging? If it's more of a surge I would tend to believe it's a lean condition. If it feels like it's dropping a cylinder, a bad plug, plug wire, corroded cap and rotor could cause it. You might also check the advance weights in the distributor under the rotor to be sure they move freely and aren't sticking.
Mabey the step up springs that control the metering rods have gotten weak over time and they are "hunting" or operating erratically at that point when it tries to transition to the power mode?

[Bookman]

It's like it loads up and won't clear out , but only at light cruise. At idle or ower mode it runs normal and aggressive. That slight touch of the throttle is where this I can't run smooth area is. The magnet thing sound like a possibilty. How do I check this?

[fmc400]

What do you mean by "air screw?" There's no such thing. There are two mixture screws which should be set using a vacuum gauge, and the idle speed and fast idle speed screws.

[jade79]

What I'm referring to is'nt a magnet they are the mechanical advance weights in the distributor beneath the rotor. If you remove the distrubutor cap and rotor you will see two of them connected by two springs. Simply take your finger or a small screwdriver and gently pry them away from the shaft, then release. They should operate smoothly and snap back to their retracted position. If not, the springs may be weak or the weights may be binding due to wear on the pins, corrosion or dirt. This may cause a little roughness as they try to advance (or erraticallly advance) the timing as engine speed increases.

It could be any number of things, but this is quick, simple and easy to rule out. I have seen ignition problems effect the carb and make the carb appear to be at fault. You may also want to try removing the carb spacer and or switching the distributor advance vacuum hose between the ported vacuum and full time vacuum ports to see if it makes any difference.

[Cobra Highboy]

Edelbrock carbs is the only thing I run. The mixture screws need to be 11/2 turns out to start with, meaning screw them all the way inthen back them out 1 1/2 turns. Then you can adjust the accelerator pump which is the plunger on the front driver side of the carb. It has three positions the middle hole is the most common to use but you can play with that and see which one works best. You can also get on Edelbrock.com to find out specs and different ways to tune your carb. you can also download the complete owners manual for any of the carburetor models. The vacuum advance port os on the driver side next to the mixture screws also. the port on the other side is for an accessory vacuum. Hope this helps.

[gfw1985]

If everything works correctly without the vacuum advance then the carb is fine. I don't even run it on my 76. I would check the dizzy as stated. Sounds like something is hitting a tight spot. Clean and oil, make sure its working smoothly as vacuum is applied. A vacuum gun is really handy and should start pulling advance at about 5hg. The springs and weights only control the centrifical advance which you have proved is working properly. Has to be in the vacuum portion.

[LxMan1]

Sounds like too much advance. This can cause a part throttle miss.

[Bookman]

This is not a miss it becomes so blubbery when light throttle is applied it doesn't want to clear out until part power mode.