engine idleing too high ( questions )

[sam's 72]

I started up my new 383 yesterday. I have a 750 Holley HP series carb. NEW! MSD ING. When we started it up, it idle at around 2200 RPM's, started trying to get it down. It came down to 950 rpm's, and would not get any lower. I have mechanical advance billet distrubutor, MSD 6a box blaster two coil. Set timming at 34 total advance. Checked for vacum leaks, by spraying wd-40 around intake, and carb. No apperant leaks. only have three vacumm ports, one for brake booster, one for PVC, and one for A/C controls. All hooked up. I am running a air gap intake, with one inch spacer, spacer was drilled and taped for vacuum port for brake booster. When you go to shut it off, it wants to run on, and right before it dies, it blows out hard through top of carb. Every things seems right. The engine fired right up. What do you think this could be? I am leaning towards, carb and timming. The timming light we had was a digital light. Not sure if it is accurate with this MSD ing. Going to put my light on it today and see if the timming is correct. I am out at work today, so it will be late this evening before I can get back to it.
Sam

[franko72]

sounds like the timing is advanced too much.Check the linkage on the carb.

[sam's 72]

That is something else we did also. Linkage on carb. We disconnected the secondary's, just to see how it reacted to running on primary's. NO CHANGE. The butterflies are all the way closed.

[franko72]

try a different timing light.

[miket]

If the carb is new---did you adjust it? It sounds like it might be running lean----an untuned carb will do both of what you are talking about.

Also....what are the specs on the mech advance? Sometimes advance will start low in the RPM range and maybe back the timing down in small increments so that it is idling at an rpm before mech advance begins....then look at your timing to see where it's at. Go from there.

[67shortie]

Just something to check also, disconnecting the secondaries will do no good unless the mechanical setting for the rear butterflies are cracked open to much. It might be a pain in the butt to do, but make sure the adjustment for the rear barrels are set right. Even they look closed at idle, they still might be letting in to much air causing this.

There is a set screw in the baseplate on the pass side of the carb, and there will be a tang off of the secondary linkage with a set screw under it. you will need a small head flat blade screwdriver, and have to access it from under the baseplate but it is worth a shot. Play with this a little and see if that will bring the idle down, but only after you have turned the primary idle all the way closed and this does not lower it enough. I have run into this a couple of times over the life of my 'Holleyness' :p But found it to be somewhat common.

Other than that, your mechanical timing could be stuck open or the springs are so light that you have full advance at idle, but since you have run on and spitting through the carb when you shut it off points to to much idle air.

[sam's 72]

67 shorty
you hit it right on. Just got a call from my friend, ( my truck is in his shop ) him and another one of our friends that drag races came over and they pulled the carb off and adjusted that set screw that you were talking about. He set up the float level, and tuned the carb. Along with correct timming 34 total advance. It is running good from what they told me over the phone. I get off work today at 6, I will go check it out. And let you guys know how it goes. I am pumped over this. They let it run for a good hour, no problems, it is time for a test drive.
Sam