Can't get idle speed down

[yamadog]

Hey Guys- I am trying to help a friend tune his new motor. It's a 302 bored and stroked to 331. The specs i know are this: flat top pistons, Roller cam, gt40p heads, chinese made intake, demon 650 carb, shorty headers, msd ignition. He built it and it is his first motor ever. First real experience with a car actually. He asked me for help when he could not get it started. I have found that he had no idea where the timing was (he actually had no timing pointer on the motor). I used a dergree wheel and a piston stop to find tdc. And then made a pointer from a coat hanger cause he was not able to buy one. We got the motor to fire and it went to 2500rpm! Then i found that he left a 3/8 plug out of the intake just under the back of the carb. Of course a massive vacuum leak. Fixed that. Now, with the idle speed screw backed out, i have adjusted the idle mixture screws (all 4) and it still idles at almost 1200 rpm. Again, idle speed screw all the way out. Not even touching the linkage. If i got the timing right, its set at 12 btdc. That was done with a cheap timig light and a coat hanger pointer. Any ideas? And thanks for making it through such a long read. jason

[68Formula]

Sorry, but there is still a vacuum leak somewhere. Check all the carb ports, and intake/carb gaskets.

[ZZ430]

The secondary throttle blades could be opened too far.

There is an adjustment for that, the carb will have to be removed and turned upside down, There is a small screw that works as a stop for the secondaries. Ballpark adjustment is 1 turn from closed.

[MrQuick]

Agree with all above.

One trick is to put a rag in the secondaries and see if the curb idle drops.Same trick for finding a Vac leak...rag in all bores.

Another is to disconnect the vac advance hose to the distributer and see if the idle drops...but I gotta ask...the choke cam and lever is down right?

[oestek]

Have you timed it with a vacuum gauge?

[HILROD]

Your problem sounds like it's from the demon carb. I've dealt with 2 that were sold to people on their reccomendations that did this, and other bad stuff. First I had to take the carbs apart, clean all the junk out of them, then change the idle air bleeds, then the power valves and jets. One carb was O.K. after this, one was still junk. After a new demon, with hours and hours of tuning, and parts repacement, was replaced with a holley it ran great, out of the box.

[yamadog]

Have you timed it with a vacuum gauge?

Heading over later today to try some more. I have never heard this method... Could you explain it? And, yes, choke is completly open. I will definatly try a rag in the secondaries. Thanks guys, keep the advice coming, very helpful. Jason

[Shawn MacAnanny]

cover carb with hand/rags. It should stall out. If it doesnt, you have a vac leak somewhere. If it does, tak off carb and look at throttle blades. Make sure they are all sealing. I had to loosen mine and force the throttle closed then tighten them back up. They were slightly off centered which was causing one side of the blade to bottom out while leaving the other side unsealed.

There is an adjustment for the secondaries you have to hold the carb upside down and use and electronics flatblade screwdrive to reach it. It's on the choke linkage side of the car. There is also an adjustment for the primaries on the same side with the choke. Atleast there is on my holley.

[Shaker455]

Break the whole carb down, clean and inspect.

I recently found one carb displaying the same problems and the well plugs in the metering blocks were not installed properly.