Can't get my 302 to idle in gear.

[RagTop]

I've got a 69 302 with a 625 cfm Road Demon, Edelbrock Performer, a 351W cam (single profile, .224 duration, .500 lift), GT40P heads and Motorsport roller rockers. The darn thing doesn't want to idle in gear. It's got a pretty bumpy idle, which I love, and it will idle normally in neutral, but as soon as I put it into drive it starts to lope harder and then just dies. I've tried raising the idle to no avail. I took the car to a guy who did wonders with my 69 Vette's 750 cfm Rochester Quadrajet and he actually made the problem worse. He said he didn't like Demons and I should have listened and gone somewhere else. He left the front float level screw so loose that it was flooding my intake manifold. I tightened it down after adjusting both float levels to midway on the large sight glasses on the Demon. The strange thing is that the problem comes and goes. It'll start fine, but by the time I get to the stop sign about a quarter mile from the house, it will stumble and die if I don't slip it into neutral. After it's been running for a while it will idle fine in gear at stoplights. It's still bumpy but that's part of the joy of having a performance cam. If I stop and let it set for a half hour or more, it will be hard to start and will start dying under any load like the power steering to turn out of a parking place. It'll die several times before I can get it going again. I've noticed that, if I drive with two feet at those times and feed it more fuel, it will keep running, but that is a dangerous practice. It makes hitting something or someone a little more possible. Any ideas what might be wrong with this thing? It never used to be a problem.

 

[AzPete]

Sounds like it is running lean after warm up. If it dies as you say, just a short drive away, it sounds like the choke is coming off and then it is lean, causing it to die.

The hard starting after warm also indicates you need to dial the carb in better. Go back to the basics and check everything, adjusting as you go.

 

[cmayna]

Ken,
I have a couple Carb gurus over here when you are interested.

 

[buening]

It could very well be a vacuum leak as well. A vacuum leak will cause it to run lean at idle, and by giving it some gas it kicks it out of the idle circuit and provides more vacuum and fuel for it to run better.

 

[johnpro]

It could very well be a vacuum leak as well. A vacuum leak will cause it to run lean at idle, and by giving it some gas it kicks it out of the idle circuit and provides more vacuum and fuel for it to run better.

:wstup

Put a vacuum gauge on it. That sounds like a classic vacuum leak problem.

BTW, the floats should be set so the fuel is at the BOTTOM of the sites, not the middle. You could be starting to flood, and the increased idle helps overcome this.

If there's no vacuum leak, and you get your floats set correctly, it may just be time for a rebuild. The Demon carbs, while I've never had one, I have heard they can be extremely finicky.