rebuilt 1971 302 wont idle below 2000 RPM

I just dropped in a newly rebuilt 1971 302 into my 66. I started it up for the break-in and it sounded a little rough to me.  When I backed off the idle screw after the break-in, it dies below 2000 RPM’s. I plugged all the ports off the Edelbrock 500, which ran fine on my 289 a month ago. I sprayed carb cleaner around the base of the carb and where the heads meet the manifold, didn’t notice and change. I’m sure I have the distributer in on the compression stroke of #1. I’m using an MSD system so no points and spark plugs are gapped at .035. I can’t check the timing because the 66 water pump cover the pionter.
I was hoping to try and get some ideas before I start tearing into the timing chain.  

did the carb get set down with the throttle blades open. .. where they could have been driven slightly off center on the shafts .. preventing them from properly closing...

does happen...

could there be any Debris holding the throttle blades open..  i have found little bits of stuff stuck in the throttle blades more than i can count..

spray a little into the secondary bores..  spray a little into the primary bores.. what happens ...

got power brakes hooked up...  the power brake booster can blow and create a large enough vacuum leak that the engine won't run..

how about the PVC valve or hose????


on edelbrock carbs... that have idle issues...   you will want to remove the idle mixture screws.. spray some carb cleaner in the opening. then follow that with a blast of compressed air..   this will usually blow out the idle air bleeds and idle feed restrictor..   put the idle mixture screws back in..   this helps a LOT of the time..

when you installed the harmonic damper... question is it one of the aftermarket versions with multiple rows of timing marks...

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this is kinda what i have seen on some aftermarket dampers..   the closest to the timing cover is like 30 or 40 degrees off the next one out.. and the third out is even farther..

you should be able to pull the number one spark plug.. and with some wire.. feel there TDC is on the first piston on the passenger side as you use a breaker bar on the big center damper bolt to rock the crank back and forth..   please use some fingernail polish to create a line for TDC from one of the options..  

After breakin if it runs fine, just will not idle down to where it should be (say 800rpm in park) I'd place my best guess on a carb issue, throttle linkage issue, or major vac leak from wrong gaskets or loose fasteners.

Is the manifold the same one from your old engine, or just the carb? Disconnect the manual throttle linkage and verify the carb closes all the way by looking down the primary bores with the engine off.

HTH...
Mark  
Mark Houlahan
Technical Editor for:
-Modified Mustangs & Fords Magazine
-Mustang Monthly Magazine

1965 FFR Roadster 427W/TKO-600 5-speed
1966 Mustang 289-4V/C4 Auto
1968 Mustang 4.6L Three-Valve/5R55S Auto
1990 Mustang 306/AOD
2001 Ranger SuperCab 4x4 3.0L V-6/5R44E Auto
2002 Explorer Sport Trac 4.0L V-6/5R55 Auto

I haven’t tried cleaning or adjusting the carb since to work fine a month ago on the 298, But I'll follow you suggestions tonight. I plugged all the vacuum ports on the carb to try and eliminate vacuum issue. The harmonic balancer is the stock unit that came with the motor. When I had the engine on the stand I used a degreeing kit and confirmed TDC on the balancer.
I'm re-using the Edelbrock carb and MSD system but installed a new Edelbrock RPM manifold.  

all that prep eliminates some of the issues..

but mark hit on something...

did this car have a 2 bbl carb.. as the 4 barrel primary linkage is farther forward than the 2 bbl..  

Well it could be timing but it really sounds like a fairly large vacuum leak. I think I would check the base of your carb for leaks as well as the port surface and be sure the pcv is hooked up correctly.  

Follow up.
I’m using an aftermarket linkage setup with my Edelbrock  that  I took off the 289.
Last night I took the idle mixture screws out and sprayed carb cleaner in them and then some compressed air; also sprayed in the card. Started the car without the fan belt and sprayed carb cleaner at the base of the carb and where the manifold meets the heads but no change to the pitch of the motor. At that point I couldn’t help myself, I had to know so I pulled the timing chain cover and the chain alignment looks good.
Is it possible to have vacuum leak on the underside of the manifold where it mates to the heads??  

I understand you're using an aftermarket linkage, but you still need to verify it is returning the carb's primary throttle plates to idle position. Disconnect the linkage from the carb and run the carb by hand to see if the idle drops any. You might have a bind in the linkage or a weak throttle return spring.

Check the carb studs to be certain they are fully seated and not propping the carb up at one corner.

Also apply a thin coating of non-hardening sealer to the carb base gaskets, sometimes that helps with small amounts of carb base warpage.

HTH...
Mark
.  
Mark Houlahan
Technical Editor for:
-Modified Mustangs & Fords Magazine
-Mustang Monthly Magazine

1965 FFR Roadster 427W/TKO-600 5-speed
1966 Mustang 289-4V/C4 Auto
1968 Mustang 4.6L Three-Valve/5R55S Auto
1990 Mustang 306/AOD
2001 Ranger SuperCab 4x4 3.0L V-6/5R44E Auto
2002 Explorer Sport Trac 4.0L V-6/5R55 Auto

Follow up
I’ll start putting it back tonight; probably take me a couple of nights before I can fire it up. I picked up a new carb gasket from Edelbrock, which is thicker than the generic off the shelf one I had on it.

Thanks  

Last EMBARASSING Follow up
After 2 ½ weeks of frustration; adjusting the valves several  times, changing plugs and gap, firing order , moving the distributor both direction, pulling the timing chain cover, replacing carb gasket , leaning the car, check compression….and so on.
It was a massive vacuum leak. On the back side of the carb, on the vertical surface of the manifold I was missing a plug. It’s a port that the Performance series doesn’t have and the RPM does.  I thought for sure I was going to pull the motor
 

First things first, you owned up to the mistake (and your buddies will never let you live it down! LOL).

Secondly, thanks for the follow up. Way too many people ask for help, fix their car, and never report back what the real issue/find was.

So, now it's on to bigger and better things. Good luck with the '66!

Mark
.  
Mark Houlahan
Technical Editor for:
-Modified Mustangs & Fords Magazine
-Mustang Monthly Magazine

1965 FFR Roadster 427W/TKO-600 5-speed
1966 Mustang 289-4V/C4 Auto
1968 Mustang 4.6L Three-Valve/5R55S Auto
1990 Mustang 306/AOD
2001 Ranger SuperCab 4x4 3.0L V-6/5R44E Auto
2002 Explorer Sport Trac 4.0L V-6/5R55 Auto